The AM Forum

Well, here is my attempt at an 813 rig.  Here were the design goals:

1) The whole rig including VFO/RF driver, modulator, HV PS, and final must fit into a nice 17 1/2" high rack cabinet I already had.

2) All hollow state except for power supplies, no switching supplies, just good old silicon rectifiers.

3) Completely self contained, just hook up a receiver, antenna, and a mic.

4) 1 KW input just like in the good old AM daze

5) Must run off 120 VAC @ 20 A  (This will be my bar rig!, no 220)

6) 160 to 10M frequency coverage.  WARC bands with XTAL OK


Here it is in the final stages of being built.  It already produces RF to spec but I need to work on the audio.  The mod transformer hasn't been installed yet nor the audio driver.

More pics later if anyone is interested.  A bit more cosmetic work is needed since the guy I used as my engraver of the brass has gone bankrupt last week so the temp labels.

Bery, vely cool looking 813 rig, Chuck!

A one-of-a-kind. Very attractive front panel.

Did you use a plate-screen dropping resistor rather than a self-mod screen choke?  

It looks like the mod xfmr will sit on the upper chassis.  Will you be using a modulation reactor or unbalanced DC current?

Curious why the SO-239 coax connectors are recessed.   A Bird thru-line?

Yes, more detailed pictures!  A view of the bottom if possible.  

This is a perfect time since I'm still laying out my own 813 rig.

T  

Hey Tom,

A few design notes:

Yes, a 20K screen dropping resistor using two 10K/100W resistors in series.  This gets rid of a screen supply and a choke!

There is no bias supply.  Not needed since I use a relay and its coil in series with the grid resistor that trips in at about 10 mA.

This relay controls the application of HV through the series Ruskie HV relay in series with the B+ supply so no B+ unless there is at least 10mA
of grid current.  BTW, a 24V relay with the spring relaxed a bit can be used here.  It will kick in at about 10 mA.  Test a few...interesting

Anyway, the mod transformer is from a GPT-750 I got from Tim.  I removed it from its hermetically sealed can, got rid of the PCB's, and will
mount it behind the 572B's.  I adjusted the gap spacer to handle about 400 mA before saturation, it took about two 0.015" spacers.  Still
has about 14H of inductance and is good to about 50 Hz.

The VFO is a Globe V-10 modified and the driver is a Globe HG 303 very heavily modified, I would say just about redone.  It had the low profile
I was looking for since the V-10 and the HG-303 would fit with a standard 5 1/4 " rack panel side by side.

The plate supply uses a Triad 3300VCT transformer rated at 650 mA and with the capacitor bank (6 X 1000 Mfd/450V) produces about 2300 VDC

The two SO-239's are from the internally mounted Dowkey relay.  You will see the top connector going up to the loading cap with a banana plug through a piece of coax.

One SO-239 goes to the antenna and the other to the receiver. A turn key rig was the goal here like the old Globe Kings...

More later....

Chuck

Amazing rig, OM.

There's a lot to see when enlarging the pictures and carefully studying.

I like the big heatsink plate caps. Yours is a "no air" convection cooled rig which is exactly what I am doing with my 813s this time... quiet shack.

I wonder why the loading cap is raised an inch on metal spacers?

Cool on the 10mA grid current triggering the Ruskie HV relay. I can see the HV lead from the PS to the vac relay. So no need for protective fixed bias.

FB on the Globe VFO and driver. Self-contained.

Do you think there is any operational or linearity/ IMD difference between using a screen resistor vs: a screen choke?

I'm curious why you don't have  .001 bypass caps across the meters?  Is that just an old practice like TVI filters of the 50's?  I've never seen any difference without them, but still use them from habit.

That shade of blue for the cabinet is my favorite  - for all the rigs here.

I can see when you finally get the brass engraved panel labels it will be a real beauty. Wish I had the patience to attend to the finer details like that... ;D

T

If like mine, loading cap raised to allow for right angle drives.

Absolutely beautiful Chuck.

Bar rig. I love it!

Thanks for sharing.

very nice...look forward to hearing you from the bar....Steve

A little more progress today.  Finished the modulator which is on the same chassis as the RF to keep this thing compact.

Added a spark gap which is visible behind the 572B modulators through the front window.  Should be interesting to see when they arc.

Haven't done the audio driver yet but modulated the rig with 60Hz from a 120V CT transformer driving the grids and at 60 Hz it looks pretty decent.

One issue is that the mod transformer buzzed a bit with that 60 Hz drive.  Not sure how it will be on talk back with audio.

I will have to remove the RF/Audio deck so I'll take a pic under so you can see how I did all the mechanical drives. 

Looks like there is a bit of interest in this stuff.  Haven't been on this board for over a year now but happy to share.

Next rig after this is an amplifier using FOUR 304TH's in parallel, grid driven. I'm taking bets on if I can make this work on 160 through 40 M

Getting bored....I guess

Awesome work Chuck! Can't wait to hear it!

Chuck, this is a beautiful transmitter and very interestingly laid out in front of the panel and behind.

Aside from amazing craftsmanship, to be able to fit all that function in a compact space is a feat by itself.

jon

Well more progress but a setback due to Chink capacitors!

In order to meet the limited space on hand, I chose to use 6 X 1000mFd/450VDC caps in series in the HV supply I bought on Epay from China.  100K/5W resistors across each to help equalize the voltage drop.  Bottom line is that wasn't enough!

Major crapout with much nasty smoke from that stack of capacitors.  I had slowly raised the voltage across this stack and measured the voltage across each capacitor, very equal.  All seemed well right up to the 2300 VDC level.


While checking the rig out after going though 160 to 10 M measuring output, one cap blew, spewing its juices everywhere.  Replaced that cap with the one of the extra spares I bought.  Same thing happened!

Damn Chink capacitors do NOT hold up to their voltage rating in these values!  Lesson learned....I would expect a capacitor to work at 80% of its working voltage.  And this is after forming them in...

Here are a few photos of the rig after the power supply failure.

More, the middle pic below is the RF driver which is a modified Globe V10 VFO and a heavily modified Globe HG 303 with 160M capability added.

Under the skirts...Before the power supply crapout, I got 700+ watts out on all bands, including 10M !

Tuning on 10M was a bit touchy since I am running a Q of close to 40 on that band but it was stable.

I found on Epay some 100 mfd at 2500VDC polyester caps that are pretty small, 3" dia by 7" long that will replace the 6 X 1000mfd chink electrolytics that died.

These are made in France (by cone heads) and used in laser power supplies.  They will "just" fit in where the electrolytic caps were I hope.  

The two pin plug you see connects to the driver when installed in the rack.  You can see where that plugs in in the second photo above this. I use a pi net going from the 5K output of the driver to the 1.8K input to the 813's. There is no 50 ohm intermediate impedance needed.  This keeps component values reasonable since the output cap on 160 going into the grids and 1800 ohm resistor is only 420 pF.  Thats the cap labeled as driver on the final and controls the grid drive.

The design goal of this rig was simplicity, minimal iron, and minimal component count, except for metering and the steam punky/1930's look....

How did you do those right angle drives? They look different than the Millen ones you sold me.

Looks like you also disassembled the turns counters and rebuilt them on the face plate - very nice!

Lots of interesting things to be hidden under the skirt!  ::)

John

Yes, is it possible to see more of the drives? I always have 3/8" capacitor shafts, and everything else from drive to knob is 1/4". How's that work?

So, on the Chinese caps that blew up, might it have been the large ripple current, that is, the repetitive peak-charging current of many amps? That will heat up caps of cheap make. Was there any warning, such as the appearance of corona?

amazing work !

please more pics on the exciter...the 303 looks like a
very nice MOPA.

John - The Millen drives are exactly the same as the ones you got from me.  I removed the metal shield that covers the gears and trimmed the 1/4" shaft that comes out the back to be flush with the body.  Looks better that way, I think.

On the vacuum variables, the plate tuning cap already had a 1/4" shaft but the loading cap had a 3/8" shaft.  I unscrewed the shaft from the cap and turned it down to 1/4" in my lathe, leaving about a 1/8" of the 1/2" shaft for the bearing.  I do this on all the vacuum variable caps I use.

More pictures to come of the RF driver.  The driver is two separate pieces, the V-10 VFO and the HG-303 bolted together.  They fit perfectly on a 5 1/4" (3U) high rack panel side by side.  I added a couple of relays switching in extra inductors to get the HG-303 on 160M.  The V-10 already has 160M output and the HG-303 doubles it for 75M.

Still can't find an engraver for the brass to label the functions so I may stay with the labels.  This damn chinese virus is taking out too many small businesses around here!

On the failed power supply caps, yes, I think it was the ripple current that probably took them out.  Never had that problem with Sprague or CD US made caps.  I have a 50 ohm resistor in series with them to limit the peak ripple current and to add some additional RC filtering.  It does hurt the regulation slightly but including the transformer secondary resistance limits the peak charging current to under 20A. I never bothered to measure the ESR of these caps.

The best high capacitance caps (40 - 100uF @ 3 - 5 KV) I have found are the Russian plastic caps on Epay that cost as much to ship as the cost of the cap!  I use two of the 40uF/5KV in my 4-400A rig.  Very low ESR and a peak current rating of 200A.

Patrick - one of the shafts on mine were 1/2in. I used one of these to adapt it.

https://www.amazon.com/gp/product/B07K3X3X1D

Chuck,

Is there no need to have a support for the right angle drives? I supported mine.

John

No need at all if you do not use any flexible couplings.  The right angle drive will "float" and adapt to any minor variations in centering of the drive shafts. 

You will find that even going through the right angle, turning torque is smooth with little resistance.  You will need a bushing going through the panel for the 1/4" shaft from the tuning knob.  As you can see I disassemble the turns counters and mount the drive gears for the counters on the 1/4" shaft and mount the counter directly on the back of the panel.

The band switch is also driven through a right angle drive the same way.

Some time ago, being interested in reduction of peak rectifier currrent, I looked into what would amount to replacing the equivalent of that 50 Ohm resistor and its I2R losses, with a very small choke having 50 Ohms reactance at 120Hz. The choke resistance was to be minimized to lower I2R loss.

For those that don't want to read the whole thing, there would be very little to gain by substituting the 50Z choke for the 50 Ohm resistor. It's only for those chasing minute increments of efficiency and hang the cost.
1.) The DC output voltage result was only 3.7% higher (2411 vs 2501VDC).
2.) Peak to peak ripple with the resistor was 83V, and 81V with the choke.
3.) The ripple waveform and regulation was not affected materially as the 66mH value is less than 3% of the critical value at the load current simulated.
4.) The worth of either a resistor or a small choke as a repetitive peak current limiter increases as the impedance of the plate transformer is reduced.

-------

The choke in this case would be 66.3mH (XL=50 Ohms). A minimum practical resistance, consistent with exploring the possibilities, would be 1 Ohm on such an inductance, and there was very little to gain in any sort of 'residential plate supply' situation by making the choke's resistance lower, say, 100 milliOhms.

A capacitor ESR of 0.5 Ohm was assumed, which should reflect a best case situation with a good capacitor plus the wiring, connections, and everything else between the rectifier and the load. A 2200-0-2200V transformer and a DC load resistance of 2600 Ohms, representing a peak load current of about 950mA, was assumed.

What was learned is that the impedance of a practical power transformer is almost always so high as to dominate the situation. The peak current (@ 170 Ohms impedance) would be limited to 3.6A without the 50 ohm resistor. In a second situation where an overkill-transformer's impedance might be around 20 Ohms, the peak current came out to 7.8A.

Adding a 50 ohm resistor after the rectifier brings the two postulated transformers from the aforementioned 3.6 and 7.8A, down to and 3.2A and 5.1A.

Replacing this with a 66mH inductor (50 Ohm XL) having DCR of 1 Ohm gave peak current results of 3.5A and 5.01A, and 3.7% more voltage than the result with the 50 Ohm resistor.

Well, I just received the French capacitors from Ebay.  They are 100uF @ 2500 V non polarized.  Physically they fit where the crapped out chink electrolytics were.  I measured the peak charging current (Tek current transformer probe) under a 700 mA load and it was 16.8 A  The plate transformer I'm using is 3300V CT and measures a 65 ohm dc secondary resistance.  I removed the 50 ohm series resistor and all seems well.  The rectifiers can certainly handle the peak repetitive current so that resistor isn't really needed.  I left the HV supply on for most of the day at about 2400 V and no crap outs!

More pictures to follow when I complete the rig.  I've made minor changes to the design to make it work better on 10M and to the cosmetics.  After all, all these rigs are a work or art!

Beautiful work, Chuck.   Very impressive!!!

Update:

The HG-303 Globe transmitter is probably one on the worst rigs released!  After chasing parasitics and other stuff, it turns out that using this rig as a driver was not easy!  I have three of these things and they all exhibit the same instabilities.  No wonder they didn't sell many. 

So....the when I had time over the last few weeks I fixed it.  Too much stuff to mention, but it is an excellent starting platform for a driver, unfortunately, I had to redesign most of it.

Now the 813 rig is working unconditionally stable and in an interesting discovery, it works on 6 Meters!  While checking out performance on 12 Meters I noticed that at minimum capacity on my 813  plate tank cap there was a spike just below 6M!  The final was apparently doubling.  So...thinking that perhaps 6M was in the future for this rig, I decided to try driving it with 6M drive instead of the 24.95MHz.  Modified the HG303 to do 6M output and driving the 813's directly with 50 MHz resulted in more output!  About 450W out at 700W input, vs 200 out when doubling but very tricky tuning.  I did the series resonance trick on the screens and that fixed it.  Now if I want 6M I need to switch the screen bypassing.  Not sure yet but maybe I'll do this.  How about an 2 X 813 rig that does 160 through 6M?

NOTE: I use my spectrum analyser when tuning up new rigs to look for parasitics and harmonic rejection.  Without this I would never have discovered this!  An absolutely invaluable tool!!!

160 through 6 - I like that very much. It's great.  :)

Hi Chuck, very nice job !!  Interesting on the capacitor failure.... something to keep an eye on.

On your 4  304TLs in parallel - I believe it will work on 40 meters no problem.  I had a rig with a pair of 304TLs and that one worked quite well on 40 meters.  Then I added a 3rd 304TL and it still worked on 40 meters.  So, I suspect yours will as well with 4 304TLs.  Watch out for parasitics (but you know all about that sort of thing).  That was the challenge with my rig.

I used a balanced grid input circuit (for neutralization) and a PI section output.

Yup...running triodes is a challenge in RF service!  Many years ago I built a pair of 833A's in push pull using the B&W 1KW plug in tank coils with the swinging link. (Modulated it with a pair as well)

I used a balanced input with cross neutralization.. It worked very well on 160 through 10M

Sold that rig.  Then.....

Built another rig with a pair of 833A's in parallel instead of push pull,  Pi network output, balanced grid input to get the 180 degree shift for neutralization.  That rig worked well, but I had to put a control on the front panel for the neutralizing capacitor since neutralization didn't hold up across more than two bands! 

Anyway, that's what I'm going to try.  Four 304TH's in parallel, Pi Net output, balanced grid input using the National Radio MB-150, and a front panel control for neutralization with dial indicator to set the neutralization when I change bands.  Nothing wrong with that, more knobs on old buzzard rigs are required !  The filament heater power is crazy for 4 tubes, but this will be a room heater.

I'm not expecting anything more than a high frequency end of 40M BUT I will try for 20M!

This will be a Winter project...

Stay tuned, I've got all the components.  Color me bored with all this coronavirus crap...

Chuck

Just tuning around on N1SDR's SDR and ran across Chuck operating his new 813 rig. It was about 1:10 PM today and conditions we not the best. He was talking with Glen WA3GPE  somewhere in 3 land who was a bit stronger than Chuck.


I originally posted a audio sample on here but it sounded horrible not because of Chucks rig, but because I had it set up to record via the web cam microphone. YUK! 

Maybe someone else hear him and can post the audio? He sounded very good to these ears!

One design/implementation detail that is missing is anything related to the audio driver or modulator.

If the tubes in the modulator are triode connected (that is the assumption), and the mod transformer has that much inductance, it should be possible, with the proper audio driver, to achieve very good results using a direct coupled audio driver.

I have done this with excellent results - getting almost class E audio performance, at least down to about 30 cycles.  The rig would properly modulate triangle waves, which is what I use for testing.

Because the only phase shift in a proper, direct coupled modulator is in the transformer itself, it is possible to run a reasonably high amount of negative feedback and include the modulation transformer in the loop.

In my particular implementation, I included a high level, 3 diode negative peak limiter (which was of course not in the feedback loop).

Anyway, curious about the audio driver, etc.  ;)

From Tom K1JJ

They are quite old buzzard and I think they were part of the 833A tube socket kit made by Eimac. I think RCA took a stab at it but their socket would not flex on the filament mount as well as Eimac. I think there are plate caps that may radiate heat more efficiently than the Eimac, but they have their own cool factor look which is more modern than the Eimac. What's this note about? To let the younger guys on here know where to source the cool old stuff ;D ;D ;D

I have some them here and one problem I have has is that some will not tighten down without using a mini vice grip. I wonder why that is. Smaller diameter caps on the tube or some other problem?

The 813 rig fully integrated into the main operating shack.  Added a few cosmetic improvements including a tuning chart for 160 through 10 Meters.  The 51J4 is used for the receiver when using the ART-13 or the 813 rig.

The side mounted dbx 286 is the only audio processing I'm using with the rig.

I've been using it quite a bit on 40M lately.

BTW, that Atwater Kent horn speaker works and I can select it or the Hallicrafters speaker with the switch mounted at the top of the 286.  It makes for a very interesting sound, kind of like going though a narrow band audio filter which actually improves intelligibility on marginal signals.

Great picture!! Beautiful equipment. Good Job!!  Very Cooool !!!
AG5UM

I'm admittedly a meter freak...It is SO NICE to see all yours match :D

It can be a daunting task to achieve that.

I have hundreds of just Westons and Westinghouses here, and still acquire more to be able to have complete sets for projects.

Good job!

73DG

I saw this when you were building last year. Very nice to see in set up for operation.

Great job and a beautiful transmitter.

Greg

Dang!

That is one fine looking rig.
Love the switches and the jeweled pilot lights.
The whole things looks first class.

Don't forget to put your callsign on it somewhere.

                   _-_-bear

YES YES YES! Matching meters!