Adding a filament winding to a toroid power transformer

[K9MB]

I am starting this topic because I figure someone here has experience in this area of expertise.
I am building up a pair of 4-1000As or 3-1000z tubes in an amplifier that will serve as a SSB linear and an AM linear amp.

I am wanting to put the RF deck in a simgle 15 x17 x 6 chassis.
I have a beautiful pair of Raytheon 7.5volt at 21Amp filament transformers, but they are bulky at 4x5x5 and weigh 12 lbs each.

They take a lot of precious real estate under my chassis, however, and I realize that the total power for both tube filaments 7.5 x21 x2 = 315 watts.

I happen to have a 400VA  Surplus toroid transformer, and it is only 5.25 inches across and a bit over 2 inches thick. I figure to mount it on one of the 6 inch interior walls of my 6 inch deep chassis across from my tube sockets and run the filament chokes across to the sockets.
I have both, #9 and #10 magnet wire for a pair of center tapped windings.
Two windings allow separate cathode current meters and separate cathode bias diode stacks so the tubes can be balanced.

My questions are:

1-Has anyone on here wound a filament winding on a toroid?

2- Is it possible to wind each filament winding as a bifilar winding?
I have wound RF transformers this way and it works great to achieve perfect phase balance, so why not a filament power transformer wound over existing windings?
Has anyone done this?

I know that I can just calculate turns by winding 10 test turns to calculate turns per volt and to design for a bit over 8 volts so it will be right under load and after IR losses and core losses. Any insight on how much more is helpful, too 8.5volts unloaded??

The technique proposed is to pair two wires together and wind them like a bifilar rf transformer. The ends that are together (or a single wire doubled and a loop at the beginning will be the center tap of the winding.
Unlike a linear winding tapped at the center, the center tap will be at one end rather than in the center.

Figure to save time and expensive copper wire by, asking  and hoping for expert advice.

Finally, awg 10 theoretically is rated at 21 amps in transformers, so it should work.
The #10 is easier to wind than the #9 though the #9 is rated at 25 amps.

Advice? Thank you in advance.
73, Mike

[w8khk]

I have done something similar to what you propose.  I needed a good deal of voltage isolation for the filament winding of my 3CX3000A to use it as a series modulator for a final running a pair of Eimac 304-TLs.  We are talking about 7.5 volts at just over 40 amperes, which is similar to your load of a pair of either 3-1000A or 4-1000A bottles.  Instead of an existing toroidal transformer, I chose to use a 120 volt, 10 amp GR Variac.  This is probably overkill, so I ran it using the entire 135 volt primary on the 120 volt supply.  (I removed the rotary secondary tap assembly and shaft.)

I do not recall how many turns I used, but I wound the secondary with #6 stranded, insulated electrical wire.  I provided more than 7.5 volts with 120 in, such that I could add a series resistor to the primary circuit, allowing adjustment of filament voltage, and controlling inrush current surge.  

In order to perform the load test, I connected the original 7.5 volt, 50 ampere filament transformer backwards, feeding the secondary from the Variac secondary.  I loaded the primary of the original filament transformer with several light bulbs, totaling around 300 watts.  This gave me information as to the required secondary turns on the Variac, and allowed me to load test for a period of time to determine heating effects.  You could perform the same test with one, then both 7.5 volt 21 amp transformers, giving an indication of the voltage drop when going from one to two tube loads.

If you use a bifilar secondary winding, the center tap would not be at one end, rather, the tap would consist of one end of one winding wire, and the other end of the second wire, such that the two windings add in-phase.

I see no reason why your method would not work, so long as the toroidal transformer has the VA capacity needed for the intended load, and this may be determined by load testing for a period of several minutes to an hour, monitoring temperature rise.  Since my Variac is rated at 1200 VA, it was barely warm to the touch after an hour-long load test.

If your toroid transformer is not quite up to the task, you might consider a 120 volt 5 ampere Variac, which would still be small enough to fit into your available space.

[K9MB]

I have done something similar to what you propose.  I needed a good deal of voltage isolation for the filament winding of my 3CX3000A to use it as a series modulator for a final running a pair of Eimac 304-TLs.  We are talking about 7.5 volts at just over 40 amperes, which is similar to your load of a pair of either 3-1000A or 4-1000A bottles.  Instead of an existing toroidal transformer, I chose to use a 120 volt, 10 amp GR Variac.  This is probably overkill, so I ran it using the entire 135 volt primary on the 120 volt supply.  (I removed the rotary secondary tap assembly and shaft.)

I do not recall how many turns I used, but I wound the secondary with #6 stranded, insulated electrical wire.  I provided more than 7.5 volts with 120 in, such that I could add a series resistor to the primary circuit, allowing adjustment of filament voltage, and controlling inrush current surge.  

In order to perform the load test, I connected the original 7.5 volt, 50 ampere filament transformer backwards, feeding the secondary from the Variac secondary.  I loaded the primary of the original filament transformer with several light bulbs, totaling around 300 watts.  This gave me information as to the required secondary turns on the Variac, and allowed me to load test for a period of time to determine heating effects.  You could perform the same test with one, then both 7.5 volt 21 amp transformers, giving an indication of the voltage drop when going from one to two tube loads.

If you use a bifilar secondary winding, the center tap would not be at one end, rather, the tap would consist of one end of one winding wire, and the other end of the second wire, such that the two windings add in-phase.

I see no reason why your method would not work, so long as the toroical transformer has the VA capacity needed for the intended load, and this may be determined by load testing for a period of several minutes to an hour, monitoring temperature rise.  Since my Variac is rated at 1200 VA, it was barely warm to the touch after an hour-long load test.

If your toroid transformer is not quite up to the task, you might consider a 120 volt 5 ampere Variac, which would still be small enough to fit into your available space.

Thanks for the detailed and very helpful post OM.

It is funny about the bifilar winding idea.
When I woke up this morning, I realized what a chuckle headed notion it was because I had forgotten the part about one winding crossing over and being tied to the other on the other winding. Phasing is everything.
I appreciate your not laughing at my idiocy…😉

I have heard of using a rewound variac for the purpose but I think that I will try the adding windings to my toroid first.
The toroid has a 21 volt winding that I can use to power 24-28volt relays. I need less than an amp of 24 vdc so it will only use a bit of the excess capacity.
I am going to use the variac anyway, though to fine tune the voltage at the sockets under load. That is why I am thinking of a 8.5-9.0 volt winding unloaded.
I also like your method of testing it using 7.5 volt transformers in reverse and illuminating light bulbs.
Incandescent bulbs are more rare now, but I think they are available. I remember that as a novice a 100 watt bulb was a great dummy load. Those wide range pinets on those little CW transmitters did fine on that inductive load…

Good stuff based on experience- the best kind of advice. Many thanks.

73, Mike

[K1JJ]

Mike,

I have wound at least three filament transformers using Variac cores. They work FB. A couple were HV insulated for PDM tube rigs.

T

[KB2WIG]

Yah can always try auto junk yards for some 12  V headlamps.  200W  lamps are still available.

https://www.walmart.com/ip/GE-Cyrstal-Clear-Incandescent-Light-Bulb-200-Watt-1pk/16911775?fulfillmentIntent=Pickup&athbdg=L1600


KLC

[K9MB]

Mike,

I have wound at least three filament transformers using Variac cores. They work FB. A couple were HV insulated for PDM tube rigs.

T

Thanks Tom.
I do have a 5 amp variac. If my scheme falls through, will ask for mor particulars from you and Richard, who also suggested it. 73, Mike

PS: a guy gave me a 5 volt “low capacity “ 5 volt at 30 amp filament transformer. It was HV
And open frame like a commercial plate tranny.
Lucky for me, my application will be no more than a few hundred volts.

[K9MB]

Yah can always try auto junk yards for some 12  V headlamps.  200W  lamps are still available.

https://www.walmart.com/ip/GE-Cyrstal-Clear-Incandescent-Light-Bulb-200-Watt-1pk/16911775?fulfillmentIntent=Pickup&athbdg=L1600


KLC

Thanks. Yes, those heat lamps are still popular. One of those and an old school 100 watt
Bulb will give me a 300 watt load.

[w8khk]

Thanks for the detailed and very helpful post OM.

It is funny about the bifilar winding idea.
When I woke up this morning, I realized what a chuckle headed notion it was because I had forgotten the part about one winding crossing over and being tied to the other on the other winding. Phasing is everything.
I appreciate your not laughing at my idiocy…😉

I have heard of using a rewound variac for the purpose but I think that I will try the adding windings to my toroid first.
The toroid has a 21 volt winding that I can use to power 24-28volt relays. I need less than an amp of 24 vdc so it will only use a bit of the excess capacity.
I am going to use the variac anyway, though to fine tune the voltage at the sockets under load. That is why I am thinking of a 8.5-9.0 volt winding unloaded.
I also like your method of testing it using 7.5 volt transformers in reverse and illuminating light bulbs.
Incandescent bulbs are more rare now, but I think they are available. I remember that as a novice a 100 watt bulb was a great dummy load. Those wide range pinets on those little CW transmitters did fine on that inductive load…

Good stuff based on experience- the best kind of advice. Many thanks.

73, Mike

You're Welcome, Mike.  If your toroidal transformer holds up with the load of two 4-1000 heaters, you should be good to go.

In one of my earlier restorations (1937 P-P Eimac 250-THs modulated by P-P RCA 810s) I used separate 5 ampere Variacs to adjust the filament voltage on the final and modulator tubes, respectively.  They allow accurate voltage adjustment, and the ability to bring the voltage up slowly, sparing the massive inrush current when the tubes are cold.  It also makes it possible to bring the voltage down slowly when turning the rig off, eliminating the massive transition from full current to none.  I am not sure the latter is of any true value.  But it is necessary to remember to always bring the Variacs down before turning the rig on next time.  The nice thing about the series resistor is that it allows voltage adjustment and inrush current reduction, without any manual steps by the op.  So my later rigs all used the less expensive series variable resistor.

No concerns regarding the center tap wiring.  I know that you knew how to do that already, but I added the comment to benefit other folks reading the thread.  Even at 75, I am not too old to learn new things from folks with different experience than mine.  No laughter needed in situations like these.

73, OM
Rick

[K9MB]

Thanks for the detailed and very helpful post OM.

It is funny about the bifilar winding idea.
When I woke up this morning, I realized what a chuckle headed notion it was because I had forgotten the part about one winding crossing over and being tied to the other on the other winding. Phasing is everything.
I appreciate your not laughing at my idiocy…😉

I have heard of using a rewound variac for the purpose but I think that I will try the adding windings to my toroid first.
The toroid has a 21 volt winding that I can use to power 24-28volt relays. I need less than an amp of 24 vdc so it will only use a bit of the excess capacity.
I am going to use the variac anyway, though to fine tune the voltage at the sockets under load. That is why I am thinking of a 8.5-9.0 volt winding unloaded.
I also like your method of testing it using 7.5 volt transformers in reverse and illuminating light bulbs.
Incandescent bulbs are more rare now, but I think they are available. I remember that as a novice a 100 watt bulb was a great dummy load. Those wide range pinets on those little CW transmitters did fine on that inductive load…

Good stuff based on experience- the best kind of advice. Many thanks.

73, Mike

You're Welcome, Mike.  If your toroidal transformer holds up with the load of two 4-1000 heaters, you should be good to go.

In one of my earlier restorations (1937 P-P Eimac 250-THs modulated by P-P RCA 810s) I used separate 5 ampere Variacs to adjust the filament voltage on the final and modulator tubes, respectively.  They allow accurate voltage adjustment, and the ability to bring the voltage up slowly, sparing the massive inrush current when the tubes are cold.  It also makes it possible to bring the voltage down slowly when turning the rig off, eliminating the massive transition from full current to none.  I am not sure the latter is of any true value.  But it is necessary to remember to always bring the Variacs down before turning the rig on next time.  The nice thing about the series resistor is that it allows voltage adjustment and inrush current reduction, without any manual steps by the op.  So my later rigs all used the less expensive series variable resistor.

No concerns regarding the center tap wiring.  I know that you knew how to do that already, but I added the comment to benefit other folks reading the thread.  Even at 75, I am not too old to learn new things from folks with different experience than mine.  No laughter needed in situations like these.

73, OM
Rick

Hi Rick,
I had not thought about the benefit of a slow on filament voltage rise. I actually will adjust my home made transformer with a 5 amp variac, so I will be sure to add that protocol to my routine. I will have a dedicated ac voltmeter on my panel, somjust need to establish a set point and go back every time.

My Father-in-law Pete Sawyer W9UWL got his license in the 30s
(“Old 160meters days”) and he had a pair of 250th triodes by 250th tubes I think. I loved those old Tantalum plates. They were white hot when he was transmitted.
It is amazing how tough they were.
His mentor was Bob Riseling who told me that he had a kilowatt rotary spark gap transmitter in 1924. It was a real privilege to meet and get to know real radio pioneers.
Rick, you are right, I knew better, but I wrote my request late at night when my old brain was transitioning into dream land where everything works…😉
I am 74 and unlike that proverbial naked Emperor, I deeply appreciate it when a friend points out that I am an ass, if not- like the emperor exhibiting one.…😉😂

This is ehen this forum shows it’s worth. There are centuries of radio art experience in the members here and any time one can benefit from that wisdom, then it becomes a no brainer.
I often worry that so much of this art may perish by not being passed on as those guys did for me. They are gone now, but the art lives in the guys who like us have 5 or 6 decades of building and learning from mistakes… when I was designing receivers and transmitters every day for 34 years, I lost interest, but the passion returned after I retired.
Thanks again. It is great fun to learn new things, even if they are old art.
73, Mike

[w8khk]

Mike, I did just that for metering filament voltage.  I am sharing a few pics of my grandfather's (W8YNG) rig that I restored.  In the late 60s, my dad, W2DU disabled the modulator, and used it as shoes for his HW-100.  The 250-THs did marvelous service as a linear amplifier. 

When dad retired and moved to FL in 1980, it was disassembled, and many parts were saved, some were scrapped.  Luckily the final deck, and the Thordarson CHT mod and driver transformers were preserved.  I, with the help of a couple younger local hams, restored it, or should I say resurrected it.  Previously, when my grandfather built it in 1935, it had no fuses, circuit breakers, overload detection, no protection at all.  It used a battery for the modulator bias, and just grid leak for the final. 

I added lots of fuses and circuit breakers, and where the 100-TH driver used to live, I added a bias and control deck.  It has a bias supply for the final, and another for the modulator.  The bias on each mod tube is individually adjustable from the front panel, and plate current on each modulator is independently metered.  I added overload shutdown relays on the final and modulator HV supplies.  Most important, I added interlocks which will not allow the high voltage to be on unless the back door is securely locked in place.  At 75, I am too forgetful, and thus I typically run it as a single-bander, even though I have coil sets for 75 and 40.

Back to the metering, If you look at the row of four meters, the left meter is calibrated to display filament voltage, and a switch under the meter selects either mod or final filament circuit.  The other three meters are mod plate voltage, final plate voltage, and line voltage, with a switch to select either incoming line voltage, or plate transformer primary voltage, after the big variac at the bottom center.  The filament variacs are controlled by the knobs to either side of the bank of four 866A tubes.  It used to use eight, but the final supply is solid state, capacitor input, while the mod is mercury vapor, choke input.

Dad used to adjust the swinging link with a wooden stick.  I added linkage to adjust it from the side of the cabinet, next to the plate tuning control.  The plate capacitor was oriented sideways to maximize symmetry.  I run the plates much cooler than the old timers, but beat some of the newer tubes a bit harder.  2KV at about 175 mA loads up very nicely.  Modulator, at lower plate voltage, still provides plenty of headroom.  I would never be able to find another Thordarson CHT TM1178 500 watt mod tranny, so I baby this one very carefully!

If you would like to see the restoration story, search this site for W8YNG, I am sure you will find it.

[K9MB]

Rick, That is a beautiful rig. Those 250ths on display like midget suns and the blue glow of mercury rectifiers are sights that caught my imagination and admiration as a young teenager.
That classic rig looks amazing.
The 810s do not shine like the 100th or the 250th, but those carbon anodes give them a lot of dissipation and their high perveance curves allows them to perform at high peaks at lower voltages.
They are super cool too with the tall envelopes and grid caps on the side. Perfect modulators…
Those CHT trannys were pretty good iron. I have not seen a 78 for sale, though I have seen 77s and 76s.
If it did go out, theoretically, you could melt out the potting and rewind, but that is a big job. BC1 iron is around, but you would need a reactor to use the mod tranny.
Your strategy of running it gently, therefore is wise and pushing it would result in unmeasurably different signal strength anyway.
That great old transmitter is a time machine and the fact that W2DU ran it makes it even greater.
I have read a lot of articles by your Dad. He was quite amazing. His Reflections volumes are an essential part of my library to understand transmission lines and antennas.
 I downloaded a number of handbooks from the 20s and 30s and it is amazing how quickly thar AM transmitter design and antennas were developed to excellent performance levels.
As I got older, and had time to reflect, I realized just how much I owed to these Old Timers. Preserving one of those old transmitters allows a new generation to look backward to see what they gave us. 73, MB

[w8khk]

Mike, thank you for the compliments.  Yes, I still study Reflections now and then when a question comes up.  I am lucky to have learned so much from my grandfather and father.  My grandfather taught me to solder with an American Beauty when i was four, and gave me a Wen gun (a little Weller) when I was five.  Dad taught met to build amplifiers when I was five and six.  He gave me an oscilloscope when I was eight. 

It is truly amazing how much the old timers accomplished in so little time.  Loy Barton showed the world how it should be done!  We are blessed with lots of inexpensive test equipment, unavailable to the innovators of the day.  My grandfather built several receivers, speech amplifiers, and complete transmitters.  He never had a VTVM or scope, just an old Hickok VOM.  He passed from cancer in 1958, and had a converted BC-375 with four glowing VT-4C bottles at his bedside.  He had a BC-654 running mobile in his '55 Plymouth, with the dynamotor in the trunk.

I am nervous about pushing that plate iron because I could not rewind it properly, and my broadcast iron, or my Stancor A-3899 just would not fit in the space available, without major rework to the 250-TH rig. 

Most of the older handbooks, etc. are available on WorldRadioHistory.com, formerly AmericanRadioHistory.com.  I find reading the older handbooks and mags very interesting, but it can be quite a time sink if allowed!

[W3SLK]

Mike, prior to your father passing away I was fortunate to strike up a conversation with him. He was kind enough to send me a signed copy of 'Reflections III' gratis. I love reference books for that simple reason when you need information you can refer to them. To him I am forever grateful! The fact that your transmitter is now in its '3rd generation' is quite an accomplishment. The craftsmanship from devices from generations past is a testament to the word 'quality!' That being said, I have a transmitter that is not quite as old as yours but it deserves some attention. I like how you 'adorned' it with white-background meters for easier viewing. I have EMCO's in mine which are a 'iron-vane' style as opposed to D'Arsonval style. They are plastic and moisture seeped in and now the background is flaking off. The plate transformer was 'home-brewed' and works quite well. Seeing yours just placed a greater importance on wanting to restore it properly. Adding inrush to the filaments was not considered, however I will consider it now. What a neat looking rig! The only thing that is missing is 'black krinkle'!

[K9MB]

Mike, prior to your father passing away I was fortunate to strike up a conversation with him. He was kind enough to send me a signed copy of 'Reflections III' gratis. I love reference books for that simple reason when you need information you can refer to them. To him I am forever grateful! The fact that your transmitter is now in its '3rd generation' is quite an accomplishment. The craftsmanship from devices from generations past is a testament to the word 'quality!' That being said, I have a transmitter that is not quite as old as yours but it deserves some attention. I like how you 'adorned' it with white-background meters for easier viewing. I have EMCO's in mine which are a 'iron-vane' style as opposed to D'Arsonval style. They are plastic and moisture seeped in and now the background is flaking off. The plate transformer was 'home-brewed' and works quite well. Seeing yours just placed a greater importance on wanting to restore it properly. Adding inrush to the filaments was not considered, however I will consider it now. What a neat looking rig! The only thing that is missing is 'black krinkle'!

I think you mean to address Rick who is the son of Walter Maxwell W2DU and a Maxwell in his Father and Grandfather’s tradition, apparently. What a heritage in the radio art!
Reflections 1,2 and 3 would serve many who do not understand feedlines and matching to antennas.

[K9MB]

Mike, thank you for the compliments.  Yes, I still study Reflections now and then when a question comes up.  I am lucky to have learned so much from my grandfather and father.  My grandfather taught me to solder with an American Beauty when i was four, and gave me a Wen gun (a little Weller) when I was five.  Dad taught met to build amplifiers when I was five and six.  He gave me an oscilloscope when I was eight.  

It is truly amazing how much the old timers accomplished in so little time.  Loy Barton showed the world how it should be done!  We are blessed with lots of inexpensive test equipment, unavailable to the innovators of the day.  My grandfather built several receivers, speech amplifiers, and complete transmitters.  He never had a VTVM or scope, just an old Hickok VOM.  He passed from cancer in 1958, and had a converted BC-375 with four glowing VT-4C bottles at his bedside.  He had a BC-654 running mobile in his '55 Plymouth, with the dynamotor in the trunk.

I am nervous about pushing that plate iron because I could not rewind it properly, and my broadcast iron, or my Stancor A-3899 just would not fit in the space available, without major rework to the 250-TH rig.  

Most of the older handbooks, etc. are available on WorldRadioHistory.com, formerly AmericanRadioHistory.com.  I find reading the older handbooks and mags very interesting, but it can be quite a time sink if allowed!

Hi Rick,
I downloaded several old ARRL handbooks from the 20s and 30s from World radio History. I agree that it can eat a lot of time, but also yield a lot of wonder and pleasure.
The oldest Old Timer I knew was W9BJE Bob Riseling. He told me that he had a KW rotary Gap spark transmitter in 1924and he is listed as having a Kilowatt that year in a log I found of stations. Bob was 9BJE in 1924. They added the Ws layer and then Ks. WAs, WBs, and then I lost track. I a;ways wanted a 1x2 call and W9MB was taken, so I got K9MB, which actually was better for CW and phone operation.

 The thing is that two years later, he had a 100 watt station snd no doubt, it was a coherent oscillator rather than a damped wave spark gap generator. Those things were pretty wide I guess, but the rotor interrupter gave them a kind of tone modulation. In those days, neighbors did not all have even a battery radio about here, sp complaints must have been rare……
I confess my first experimental transmitter used a model T ignition coil which gave about 40kv and I used an aluminum foild and window glass to make a tining capacitor and a ground rod and a long wire completed my pirate station. I transmitted code to a friend one mile away with good signals. Unfortunately, my neighbor also received me on channel 2 on his TV. He was nice about it, but I stopped transmitting and went to work on my novice while listening to K4KYV and other Hams on 75 meter phone on my same regen receiver. I got. Superhet after I got my Novice in 1964 and built a Knight T60. It was a great time and I have never lost the love of building and testing and learning from great Old Timers and hearing their stories…

[Opcom]

Those tubes are expensive. It might be worthwhile to also use a ferroresonant transformer for the filaments. The rheostat or pot would then be pretty much set-and-forget.

I had to use one for the 3CX3000 filament transformer the summer mains voltage intermittently drops and rises, seen it as low as 109 when both HVAC are on. Hooked up the rectifiers fil xfmr to it too.

[K9MB]

Those tubes are expensive. It might be worthwhile to also use a ferroresonant transformer for the filaments. The rheostat or pot would then be pretty much set-and-forget.

I had to use one for the 3CX3000 filament transformer the summer mains voltage intermittently drops and rises, seen it as low as 109 when both HVAC are on. Hooked up the rectifiers fil xfmr to it too.

Hi Patrick,
Thanks for the heads up. I had not thought of line variations being an issue though our local power grid voltage varies from 240 to 255 at times and it os mafe worse by my 20K Grid Tied Solar Array in the middle of the day in Summer when loads are  up and down.
I have a few questions on the effects this will have on my tube filament voltages.

1- Is the concern about transient voltage spikes or just a gradual variable rise and fall in voltage?
2- The specs for 4-1000a and 3-1000z tubes is 7.5 volts +- 0.37 volts
In my setup, that corresponds to a variation of 120-131vac input to the filament transformer, give. The 16:1 stepdown ratio and the variac I will use to set voltage to 120vac at 0.96 of the 125vac average grid voltage.

My protocol will be to constantly monitor filament voltage on the front panel and begin at zero voltage on startup to prevent a surge to s cold filament. The variac will be adjustable on the same front panel.
If a surge would not cause immediate failure, I could just watch it and keep,the voltage close to 7.5vac.

2- A constant voltage (ferroresonant) transformer is heavy and expensive, so how about just hooking a cheaper 1kva UPS to a cheap surplus isolation transformer and get a regulated 120vac that will be immune to variations? I have some 1kva UPS and a couple of 2kva isolation transformers in stock. Will assume a 0.7 power factor but only need 300vA for filaments anyway.

Comments please. Thanks fir your help on this.
73, Mike

[w8khk]

Mike, prior to your father passing away I was fortunate to strike up a conversation with him. He was kind enough to send me a signed copy of 'Reflections III' gratis. I love reference books for that simple reason when you need information you can refer to them. To him I am forever grateful! The fact that your transmitter is now in its '3rd generation' is quite an accomplishment. The craftsmanship from devices from generations past is a testament to the word 'quality!' That being said, I have a transmitter that is not quite as old as yours but it deserves some attention. I like how you 'adorned' it with white-background meters for easier viewing. I have EMCO's in mine which are a 'iron-vane' style as opposed to D'Arsonval style. They are plastic and moisture seeped in and now the background is flaking off. The plate transformer was 'home-brewed' and works quite well. Seeing yours just placed a greater importance on wanting to restore it properly. Adding inrush to the filaments was not considered, however I will consider it now. What a neat looking rig! The only thing that is missing is 'black krinkle'!

Hello Mike, Sorry for the delay in responding, I have been away. And thanks so much for the complments!  I am glad that you got to meet dad and received a copy of Reflections III.  I remember being there in Dayton when he was signing copies upon the unveiling of the third edition.  He purchased the first 100 copies off the press, he said he wanted to pass them on to friends and acquaintances at future hamfests.

It is great that you are the custodian of another vintage rig.  Do everything you can to preserve it for future generations.  AM, the oldest and finest voice mode, should live on forever.  It does not require any proprietary codecs to receive, just a Quaker Oats box, a hunk of wire, and a crystal.  Your EMCO meters add to the vintage quality!

I realize the 250-TH rig lacks the black wrinkle, with the hammartone gray wrinkle cabinet and aluminum panels, but I attached a photo of my grandfather's shack from 1956, and you can see to the left of the restored rig is another pair of racks, black wrinkle matching that of most of the equipment on the operating table.  The two racks have exciters and finals, but rely on the power supply of the one on the right.  The far left had a pair of 450-TH finals, and the middle one a pair of 813s.  I still have the chassis of the 450 final, and may get around to restoring it someday.  It had a novel split stator (butterfly) plate tuning cap, with the neutralizing caps mounted on the back, utilizing the main stator as one of the terminals.  I don't know what was used for plate transformers in the old rig, so I used a pole pig that provides around 2400 volts with 240 on the primary.  I never thought I would use 866A rectifiers again, but I just couldn't bring myself to load this relic up with a lot of silicon.

Good luck on your restoration, and please share photos as you progress through the journey.  You will have many fond memories of that project!

[w8khk]

Hi Rick,
I downloaded several old ARRL handbooks from the 20s and 30s from World radio History. I agree that it can eat a lot of time, but also yield a lot of wonder and pleasure.
The oldest Old Timer I knew was W9BJE Bob Riseling. He told me that he had a KW rotary Gap spark transmitter in 1924and he is listed as having a Kilowatt that year in a log I found of stations. Bob was 9BJE in 1924. They added the Ws layer and then Ks. WAs, WBs, and then I lost track. I a;ways wanted a 1x2 call and W9MB was taken, so I got K9MB, which actually was better for CW and phone operation.

 The thing is that two years later, he had a 100 watt station snd no doubt, it was a coherent oscillator rather than a damped wave spark gap generator. Those things were pretty wide I guess, but the rotor interrupter gave them a kind of tone modulation. In those days, neighbors did not all have even a battery radio about here, sp complaints must have been rare……
I confess my first experimental transmitter used a model T ignition coil which gave about 40kv and I used an aluminum foild and window glass to make a tining capacitor and a ground rod and a long wire completed my pirate station. I transmitted code to a friend one mile away with good signals. Unfortunately, my neighbor also received me on channel 2 on his TV. He was nice about it, but I stopped transmitting and went to work on my novice while listening to K4KYV and other Hams on 75 meter phone on my same regen receiver. I got. Superhet after I got my Novice in 1964 and built a Knight T60. It was a great time and I have never lost the love of building and testing and learning from great Old Timers and hearing their stories…

Mike, sorry for the delayed response, I have been away.

Interesting that you met and enjoyed time with folks that worked spark.  I met many old timers, most of them worked  with dad at one RCA facility or another.  There were many in the NY and NJ area.  I learned a great deal from them, snd realized the pleasure and satisfaction of building, rather than buying everything for the station.  I build several of my earlier receivers and transmitters, but ended up using an HRO and SB-101 most of the time I was in the US Air Force.  I built a dual 4-400A linear in my barracks room in Tucson. 

My dad gave my older brother Bill and me each a Model-T spark coil, with the agreement that we would never attach an antenna.  Interesting little device in the wooden box, I still have mine.  But I went one better with a science experiment detailed in a Markus and Horton elementary text, using a pair of 6L6s and a three-turn link of 1/4 inch tubing, and split stator capacitor, a little oscillator running straight off the mains raw AC.  Along with it, a matching coil for a wavemeter.  It could light up a 40 watt fluorescent a couple feet away.  When dad discovered what was tearing up the color picture one evening, I was given explicit instructions to "disassemble that thing".

The progression of your call sign is interesting.  Dad never had a vanity call, as W8KHK and W2DU, along with all the others, were sequentially assigned.  He was proud that the CW sequences for KHK and DU had bilateral symmetry.  My older brother William Maxwell now has W2WM, and younger brother John Robert Maxwell has K4JRM, but I am just as happy with dad's original call.  He gave me two cast aluminum call plates, one for the transmitter, and one  to attach to a license plate, both made in the '30s.

Yes, those old magazines and handbooks provide a lot more interesting ideas than the current publications do.  Enjoy reading them!

[K9MB]

Hi Rick,
I downloaded several old ARRL handbooks from the 20s and 30s from World radio History. I agree that it can eat a lot of time, but also yield a lot of wonder and pleasure.
The oldest Old Timer I knew was W9BJE Bob Riseling. He told me that he had a KW rotary Gap spark transmitter in 1924and he is listed as having a Kilowatt that year in a log I found of stations. Bob was 9BJE in 1924. They added the Ws layer and then Ks. WAs, WBs, and then I lost track. I a;ways wanted a 1x2 call and W9MB was taken, so I got K9MB, which actually was better for CW and phone operation.

 The thing is that two years later, he had a 100 watt station snd no doubt, it was a coherent oscillator rather than a damped wave spark gap generator. Those things were pretty wide I guess, but the rotor interrupter gave them a kind of tone modulation. In those days, neighbors did not all have even a battery radio about here, sp complaints must have been rare……
I confess my first experimental transmitter used a model T ignition coil which gave about 40kv and I used an aluminum foild and window glass to make a tining capacitor and a ground rod and a long wire completed my pirate station. I transmitted code to a friend one mile away with good signals. Unfortunately, my neighbor also received me on channel 2 on his TV. He was nice about it, but I stopped transmitting and went to work on my novice while listening to K4KYV and other Hams on 75 meter phone on my same regen receiver. I got. Superhet after I got my Novice in 1964 and built a Knight T60. It was a great time and I have never lost the love of building and testing and learning from great Old Timers and hearing their stories…

Mike, sorry for the delayed response, I have been away.

Interesting that you met and enjoyed time with folks that worked spark.  I met many old timers, most of them worked  with dad at one RCA facility or another.  There were many in the NY and NJ area.  I learned a great deal from them, snd realized the pleasure and satisfaction of building, rather than buying everything for the station.  I build several of my earlier receivers and transmitters, but ended up using an HRO and SB-101 most of the time I was in the US Air Force.  I built a dual 4-400A linear in my barracks room in Tucson. 

My dad gave my older brother Bill and me each a Model-T spark coil, with the agreement that we would never attach an antenna.  Interesting little device in the wooden box, I still have mine.  But I went one better with a science experiment detailed in a Markus and Horton elementary text, using a pair of 6L6s and a three-turn link of 1/4 inch tubing, and split stator capacitor, a little oscillator running straight off the mains raw AC.  Along with it, a matching coil for a wavemeter.  It could light up a 40 watt fluorescent a couple feet away.  When dad discovered what was tearing up the color picture one evening, I was given explicit instructions to "disassemble that thing".

The progression of your call sign is interesting.  Dad never had a vanity call, as W8KHK and W2DU, along with all the others, were sequentially assigned.  He was proud that the CW sequences for KHK and DU had bilateral symmetry.  My older brother William Maxwell now has W2WM, and younger brother John Robert Maxwell has K4JRM, but I am just as happy with dad's original call.  He gave me two cast aluminum call plates, one for the transmitter, and one  to attach to a license plate, both made in the '30s.

Yes, those old magazines and handbooks provide a lot more interesting ideas than the current publications do.  Enjoy reading them!

Hi Rick,
😂😂😂…
You were obviously better supervised than I. I do not know what happened to that model T coil in that neat litle wooden box.
I actually knew so little that I ran my spark gap pirate abomination by hooking a Lionel Train transformer to it. Those things had a built in variac and you could turn the lever to get the voltage needed. It gave me  1/2 inch bright blue spark modulated by 60 (cycles) so it sounded pretty bad.
The aluminum foil was taped to the 1/8 inch window glass and wires captured under it.
I felt like Frankenstein with tue blue glow in the glass and the blue spark filling the air with ozone for a satisfying atmosphere…😉
It was my neighbor wanting the bars and noise to stop on his TV that cut my piracy career short…
We jumped to a couple of knight kit walky talkies with regen receivers and I put up a long antenna and we got 6 miles on 27mHz with 100mW.
Meanwhile, I built a Knight kit regen shortwave receiver and listened to 75 meter AM and Don Chester and his friend from Paducah “Con?”  Used to feed my imagination. Cannot remember Con’s call W4???. He liked to imbibe with 807s while he talked and his enunciation and his personal skills deteriorated until he  finally ran down. It was great fun. Don had a fantastic signal from Tennessee. May have had a pair of 4-1000s modulated by Likely a full KW+ 😉 I liked those guys because, like my local me tors, they built everything they ran on transmission and talked about the technical stuff.
Always favored building over anything else. I even built my own SSB crystal filter from some old surplus FT- 455khz crystals and built a lot of antennas.
Got hooked on VHF and UHF and W9UWL and I worked on his Moonbounce station for several years on 2meters.
When I got back after retirement, my love for long waves and AM rose from the ashes and glows as brightly as it ever did.

It sounds as though your entire family are Radio engineers. My family are all builders of something or other. Electrical Contractor, Tool and manufacturing Company, Race Car builder and I am the Electronics Radio guy, though I also make flutes since 1997. I like it because it does not interfere with my radio passion and resonant pipes also have standing waves, impedance, admittance, etc, so it is not as alien as one might think. A conical bore instrument is a two port negative resistance oscillator- amazingly! The universe uses ideas over and over.

[DMOD]

I am starting this topic because I figure someone here has experience in this area of expertise.
I am building up a pair of 4-1000As or 3-1000z tubes in an amplifier that will serve as a SSB linear and an AM linear amp.

I am wanting to put the RF deck in a simgle 15 x17 x 6 chassis.
I have a beautiful pair of Raytheon 7.5volt at 21Amp filament transformers, but they are bulky at 4x5x5 and weigh 12 lbs each.

They take a lot of precious real estate under my chassis, however, and I realize that the total power for both tube filaments 7.5 x21 x2 = 315 watts.

I happen to have a 400VA  Surplus toroid transformer, and it is only 5.25 inches across and a bit over 2 inches thick. I figure to mount it on one of the 6 inch interior walls of my 6 inch deep chassis across from my tube sockets and run the filament chokes across to the sockets.
I have both, #9 and #10 magnet wire for a pair of center tapped windings.
Two windings allow separate cathode current meters and separate cathode bias diode stacks so the tubes can be balanced.

My questions are:

1-Has anyone on here wound a filament winding on a toroid?

2- Is it possible to wind each filament winding as a bifilar winding?
I have wound RF transformers this way and it works great to achieve perfect phase balance, so why not a filament power transformer wound over existing windings?
Has anyone done this?

I know that I can just calculate turns by winding 10 test turns to calculate turns per volt and to design for a bit over 8 volts so it will be right under load and after IR losses and core losses. Any insight on how much more is helpful, too 8.5volts unloaded??

The technique proposed is to pair two wires together and wind them like a bifilar rf transformer. The ends that are together (or a single wire doubled and a loop at the beginning will be the center tap of the winding.
Unlike a linear winding tapped at the center, the center tap will be at one end rather than in the center.

Figure to save time and expensive copper wire by, asking  and hoping for expert advice.

Finally, awg 10 theoretically is rated at 21 amps in transformers, so it should work.
The #10 is easier to wind than the #9 though the #9 is rated at 25 amps.

Advice? Thank you in advance.
73, Mike

I have done it for my homebrew 813 SGM transmitter.

I needed an 813 filament source so I wound 48 turns of #14 on an Antek AS-1209 with a centertap to measure Plate current.

ER Issue #390 also has an 813 Amp article in which the author did something similar.

Phil - AC0OB

[K9MB]

I am starting this topic because I figure someone here has experience in this area of expertise.
I am building up a pair of 4-1000As or 3-1000z tubes in an amplifier that will serve as a SSB linear and an AM linear amp.

I am wanting to put the RF deck in a simgle 15 x17 x 6 chassis.
I have a beautiful pair of Raytheon 7.5volt at 21Amp filament transformers, but they are bulky at 4x5x5 and weigh 12 lbs each.

They take a lot of precious real estate under my chassis, however, and I realize that the total power for both tube filaments 7.5 x21 x2 = 315 watts.

I happen to have a 400VA  Surplus toroid transformer, and it is only 5.25 inches across and a bit over 2 inches thick. I figure to mount it on one of the 6 inch interior walls of my 6 inch deep chassis across from my tube sockets and run the filament chokes across to the sockets.
I have both, #9 and #10 magnet wire for a pair of center tapped windings.
Two windings allow separate cathode current meters and separate cathode bias diode stacks so the tubes can be balanced.

My questions are:

1-Has anyone on here wound a filament winding on a toroid?

2- Is it possible to wind each filament winding as a bifilar winding?
I have wound RF transformers this way and it works great to achieve perfect phase balance, so why not a filament power transformer wound over existing windings?
Has anyone done this?

I know that I can just calculate turns by winding 10 test turns to calculate turns per volt and to design for a bit over 8 volts so it will be right under load and after IR losses and core losses. Any insight on how much more is helpful, too 8.5volts unloaded??

The technique proposed is to pair two wires together and wind them like a bifilar rf transformer. The ends that are together (or a single wire doubled and a loop at the beginning will be the center tap of the winding.
Unlike a linear winding tapped at the center, the center tap will be at one end rather than in the center.

Figure to save time and expensive copper wire by, asking  and hoping for expert advice.

Finally, awg 10 theoretically is rated at 21 amps in transformers, so it should work.
The #10 is easier to wind than the #9 though the #9 is rated at 25 amps.

Advice? Thank you in advance.
73, Mike

I have done it for my homebrew 813 SGM transmitter.

I needed an 813 filament source so I wound 48 turns of #14 on an Antek AS-1209 with a centertap to measure Plate current.

ER Issue #390 also has an 813 Amp article in which the author did something similar.

Phil - AC0OB

Thanks Phil,
I had forgotten the 813 article in ER.
I am actually planning a very similar 2x813 amp to drive my 4-1000a and 3-1000z rig.
The running of the 813s horizontal will give me a low profile design and I actually have that ANTEK 8-800 tranny.
Will only need a very clean 100-200 watts with low 3rd order IMD
Will just need 20-30 watts from my FLEX5000A then and hopefully 400-500 watts carrier on AM.
Glad to know that piggybacking filament windings works well.
73, Mike

[KD6VXI]

My first two way setup was a Uniden 3 knob cb, a broken K40 antenna and a Tyco train transformer.

I'll never forget my first radio check.  Yeah, we can just barely make out what you're saying under the hum.

Me, not knowing better cranks the lever on the train transformer farther to the right.

How about now?

--Shane
WP2ASS / ex KD6VXI

[K9MB]

My first two way setup was a Uniden 3 knob cb, a broken K40 antenna and a Tyco train transformer.

I'll never forget my first radio check.  Yeah, we can just barely make out what you're saying under the hum.

Me, not knowing better cranks the lever on the train transformer farther to the right.

How about now?

--Shane

WP2ASS / ex KD6VXI

Shane,
I was 13 and ignorance and wreck lessness were my chief attributes, so that lever was irresistible…😉
Brought back to reality when the Lionel transformer started smelling hot, so throttled back to just get enough blue spark for my 1/2
Inch gap…😂😂
My career as an
Outlaw was short lived, though. Within a year, got my novice and built up a Knight T60.
Much better CW note and better range on 40 and 15 meters.😎

[w8khk]

My career as an
Outlaw was short lived, though. Within a year, got my novice and built up a Knight T60.
Much better CW note and better range on 40 and 15 meters.😎

Cool to have a Knight T-60 as a novice.   But did your's look anything like this one?  There is no place to plug in a crystal, as the holes were repurposed for DDS menu buttons.  The rig is a work in progress, recovered from an estate sale recently.  It is making RF, but the screen modulator is still under construction.