VFO Power Supply

[w9bea]

Good Afternoon All:

I picked up a Heathkit VF1 to run with my DX40 transmitter.  After doing some research, I learned that it is not the best practice to run the VFO B+ and filaments off the accessory socket on the back of the radio, preferring rather an external power supply.  This is due to added chirp on the CW note and added stress/load to the transformer.

So, I am guessing that I need to put a power supply together.  I need 6.3 VAC at 1/2 amp and 250-350 VDC at 15 to 30 mA.

Does any one have a schematic or plans for such an animal?

I have a Heath IP32 on my bench that I will likely use temporarily......  Does anyone see any issues with this?  DO you think the IP32 (400 volt variable supply) is regulated enough to make the VFO happy until I can build something?

Also,  the specs call for 250-350 VDC.  I assume I really ought to have 350 volts as opposed to 250 volts to keep the oscillator more stable?

The DX40 has been a ball so far.  I only have a 7.040 XTAL in the radio and I am thinking some frequency agility ought to be an added plus.  Ready to rock and roll on SKN!

Appreciate the input guys.

73--Wally W9BEA

[kb2vxa]

Hi Wally,

It's been a long while since my last post so some of the gang may have forgotten who I am (;->) but this is an easy one. An external supply is recommended not only for voltage stability but thermal as well. The VF-1 may run second to the Meissner Signal Drifter (Shifter) because it's so temperature sensitive, it takes forever to warm up and settle down. I remember one stable as a rock because it was on 24/7 so your future drift problem may be mitigated the same way.

As long as you stay within the voltage parameters you should be OK. As long as the 0A2 VR tube operating at 150V can have sufficient drop across the 15K 5W resistor connected to pin 5 it will regulate properly. BTW it's pretty easy to build a supply around an old power transformer from a cannibalized receiver, something many old school hams have in their junk boxes.

[n1uvi]

I have built several supplies for VF-1's over the years
The VF-1 uses an OA2  for regulation
your  IP32 will likely work just fine
Just a transformer a 1N4007 and a 50Uf 250 Volt cap
for a supply

[DMOD]

Hi Wally,

Here is a possible PS for you:



Phil- AC0OB

[KA2DZT]

First, do you have any xfmrs to work with??

Building a supply for the vfo should be easy.  The VFO in my HB 6146/813 rig runs from a separate supply.  The Handbook has plenty of info about power supplies.

The VFO you have probably runs on regulated 150 volts, but you'll need to start with about a 250 volt supply then it gets regulated down to 150 volts with a OA2 regulator tube.  You'll need to calculate the correct resistance that is in series with the regulator tube.  OA2 regulators run on about 30 ma max.  So, if you start with a 250 volt supply (250 volts after the filter circuit loaded with about 30 ma).  The supply should have some bleeder current, so add a bleeder resistor after the filter but before the regulator resistor.  Bleeder current can be about 10 ma.  Calculated what resistance you need to drop 250 volts to 150 volts with 30 ma current.  100V/.03 = about 3500 ohms.  Wattage would be I*R, (.03* x 3500) = 3.15 watts, so use a 10 watt resistor.

The way the shunt regulator works is as the VFO draws some current (15-20 ma) the regulator tube draws less current so as to always have the same 100 volt drop across the 3500ohm regulator's series resistor.  These type regulator tubes only have a total range of 30 ma to work with.  The older larger octal type regulators have a max current range of about 40 ma.  These regulator tubes can be wired two ways.  One way will remove the B+ from the VFO if you pull out the regulator tube.  The second way will not remove the B+. So, if you pull out the regulator tube the B+ will go up to the VFO.  With a 250 supply you can use either method.  Study the tube's circuit diagram and you will see this.  The RCA tube manual gives a complete description on how to use these regulator tubes.

The next improvement to a VFO power supply would be to run the filaments on regulated 6.3 volts DC.  This can be done easily with a 6.2V zener diode, if you can get one in the 50 watt size.  You can put the 5 volt filament winding in series with 6.3 volt winding, getting about 12 vac.  Use a single half wave rectifier diode and a big cap to create the DC supply.  Then shunt regulate it with the 6.2V 50 watt zener diode.  This is also a shunt regulator like the OA2.  So you will need to calculate a series resistor for the zener regulator.  If you want to do this I can help you through the design as others could also.  The 5 volt rectifier winding on your xfmr won't be used as you can simply use SS rectifiers for the B+ supply.

Fred

[w9bea]

Hi Fred:

Regrettably, I do not have any transformers to work with (yet).  Going to need to hit a hamfest to find one.

Or perhaps eBay might yield something.

I found both a west coast and a ARRL Handbook of the right vintage that should have the voltage regulators and most likely 1-2 decent schematics.

Phil's schematic also looks good as well.  Uses a bridge I believe.  Then, I found this one:

http://diyaudioprojects.com/Technical/Tube-Power-Supplies/

I was leaning towards a bridge rectifier, but this circuit with the full wave tube rectifier looks interesting....

He uses a 6CA4 as the rectifier,  I need to read the article carefully to see if any of my 5U4's will do just as well.  The author give a treatment to the different type of tubes and their operating values.

Either way, nothing is getting built until I get my hands on some iron.  I do have a nice little chassis and some of the other obvious components in stock...  Need the iron and the right filter caps to glue it all together.  All told, this is highly do-able....

Still investigating and digging in ye 'ol junk box

73--Wally W9BEA

73--Wally W9BEA

[DMOD]

Phil's schematic also looks good as well.  Uses a bridge I believe.  Then, I found this one:

http://diyaudioprojects.com/Technical/Tube-Power-Supplies/

I was leaning towards a bridge rectifier, but this circuit with the full wave tube rectifier looks interesting....

It does contain a solid state full wave bridge rectifier. Since your current needs are modest, 1N4007 diodes can be used.

The transformer I suggested on the schematic was the Hammond 261E6 for simplicity

http://www.hammondmfg.com/261.htm

but you can use whatever dips your plate.   

Phil - AC0OB

[KA2DZT]

Hi Wally,

Sorry to hear you don't have any xfmrs.  What's up with that?  You know that you can't call yourself a real Ham Radio Operator without any spare xfmrs.  Just thought I'd mention it.  Being a ham for over 50 years I have in excess of a 1000 xfmrs and chokes.

The PS you need for your VFO should be simple to build.  You don't need to do too much figuring to build one.  No need for a lot of math, even though I study EE which was all math. 

A 5U4 is way too heavy a rectifier for this type supply.  Most all small power xfmrs will not have a 5 volt filament winding rated at 3 amps which is what is needed for a 5U4.  Most all supplies now being built use SS diodes for the rectifiers.  My HB 6146/813 rig has, I think, 12 separate power supplies.  All of them use SS rectifiers.

For your supply you need a small 50 ma xfmr with a HV winding of about 500 volts center tapped.  That would be 250-0-250 volts. This type xfmr uses a full wave rectifier circuit.  That would be two 10cent diodes.  If you find a xfmr that has a single 250 volt winding (no center tap) then you would use a full wave bridge rectifier.  That's four 10cent diodes.

Years ago, xfmrs like this were a dime a dozen.  Not so nowadays.  Most all consumer electronics today do not even have any power xfmrs, if they do they are just low voltage ones (20-30 volts).

Check with a local ham, if you know any, that may have some spare xfmrs they will part with.

Fred.

[VE3LYX]

 I cheat. I use a pair of 12 volt transformers back to back and a full wave with a pair of 1n40007 with a resistor before the diode in pos side and one between the first an second filter cap. The 12 volts come from the local dump from discarded battery chargers. The one running in front of me right now also has a doubler circuit with a two section filter and has been my MV bench supply for several years. I recently rebuilt it (last Monday) and still love the lil fellow. Very handy, stout enuf supply that it doesn't sag and voltages as I desire. I use a VFO on a DX60B when I need to move around. Nota lot of difference from your deal . It is because of the way those sets are wired for VFO a bit of a pain so an outboard PSU is a great idea. Ideally from y perspective anyway. Always live heater voltage and switchable /keyable B plus (as in PTT operated)would be great. Mine takes about a week to warm up. (actually about 20 to 25 minutes it settles down but it seems like a week. )





   

[DMOD]

Hi Wally,

I think Fred was thinking of something like this:

See Schematic Below


Now you have all kinds of options.  

Phil - AC0OB

[N6YW]

Here ye here ye...
Do you want some cheap parts to build your supply?
The tremolo and reverb amplifier units found in old tube type Conn & Wurlitzer organs are ripe with the parts you need. These come up on Epay all of the time for next to nothing. The audio amps usually go for more money due to the interest of DIY guitar/hifi amp builders, but the other units found in these organs usually get ignored. Also, look for the Leslie C2C preamplifier unit. It has the transformer you need and includes the filament windings good for at least 2 amps. These are used to amplify the tremolo and echo on Hammond organs like the M-1 and M-100 that used an axillary tone cabinet without rotating speakers. Leslie designed and manufactured dozens of different designs and the least favorable tone cabinets have the most sought after parts we builders look for. Sadly, many of these things get tossed into the land fills.

[WD5JKO]

   Lots of good advice thus far.

A few comments...

On Ebay look for a "control transformer". There are many listed, and look for a 50VA with 120V input and 240V output. Then use one of the schematics already posted with a full wave bridge rectifier.

Many have said to leave the filament on. This could mean a separate filament transformer providing 6.3 vac at 300ma. Better yet, have a bigger transformer (maybe 1 amp), use a half wave voltage doubler to make ~ 10 vdc, and then with a 7806 three terminal regulator you will nail the filament voltage at 6V DC, and regulated.

OR....

Looking at the DX-40 HV power supply, there is a 15K series dropping resistor from the 600V B+ to the accessory socket. This would be an easy spot to pre-regulate the VFO B+ to 250V with a power zener diode (like four 62V 5W zeners in series). The value of R22 might need to come down a bit to get proper shunt regulation.

But then you say, I don't want to load down that DX-40 transformer..Sure, get rid of that 5U4, and solid state it (about five 1N4007's in each leg would do). This will drop 15 watts of power. Then take that 5V winding, and use it to 'buck' the incoming AC to drop that level 5V. This will also cool down that transformer, and the whole rig in fact. The little load from the VFO would be negligible so long as you pre-regulate the VFO B+ to 250V, and the filament in the VFO to 6VDC, and you should be golden.

Jim
Wd5JKO

[VE3LYX]

I now use separate heater transformers in all my supplies and my linear. This allows me to keep the set in question ready to go at the flip of switch but it is all warmed up. I have found this to be very handy. For instance on  the 811A linear and my bench supply for the ARC5 sets They are kept live and ready and I have a seperte switch in the Hv transformer primary to turn the Hv off and on. Very handy for me anyway. On the Dx60B and I imagine the DX40 the VFO can be heard faintly in a nearby rx if you have PTT which all these transmitters do with the use of the Key , even in Am mode. That can wear a bit thin after awhile listening to the faint ever changing heterodyne as few in a group are exactly on the same freq. You can turn off the vfo by switching to stndby but the wafer switch is the achillies heel of these rigs so I try to avoid using it more then on or off. The idea of a separate PSU for the VFO is appealing  It could be warm anytime I am in the shack and the power bar on and could be wired in with the other stuff and its B voltage operated by the PTT.
don

[KA2DZT]

Jim,

Very good ideas.  I'm not sure what B+ the VFO runs on.  Last time I saw a DX-40 was 50 years ago, and never had the VFO.  Best thing to do is get rid a the 5U4 and then do the buck with the 5 volt winding.  50% of the heat is gone and the power xfmr runs much cooler, big help.  I still remember burning my forearm on a 5U4 in an old RCA TV.  Some of the sets had two 5U4s that were plugged right into the top end bell of the power xfmr.  Reaching around that corner of the chassis to pull tubes was very dangerous.

As for the control xfmrs, I have used them to make PSs, they work good and they usually are not too high priced.  Ebay has plenty of them.

Like you, I suggested running the filaments on a regulated 6VDC supply.  I used a 6.2 volt zener for my VFO supply.  What this does is it eliminates drift associated with changing line voltage during the normal operation of the station.  Kick on the xmtr and the line voltage sags a bit, enough to cause a slight change in filament voltage causing some drift.

Fred

[KA2DZT]

Hi Wally,

I think Fred was thinking of something like this:

See Schematic Below


Now you have all kinds of options.  

Phil - AC0OB

Phil,

I looked at your PS schematic,  It's a typical PS which is exactly what the VFO needs.  Although, i think your need a supply that yields a higher voltage.  So, a xfmr with a higher winding voltage is required.  Reason is to regulate it down to 250 volts you have to start with at least 325-350 volts.  Everything else would be the same.

Fred

[KK4RF]

Wally,
     I've never  operated a VF-1 or a DX-40 before, but I do run an HW-16 with an HG-10 vfo. I run my vfo using the accessory socket off the back of the HW-16 which supplies all the needed voltages  and to be honest, I have not had any chirp issues when I use it with the HW-16. Perhaps the HW-16 has a more stout power supply in it than the DX-40, but I doubt it. Unless you just want to build a separate power supply for the VF-1 (which likely would have lots of other potential uses) you might consider using the VF-1 with power from the DX-40, assuming that Heathkit designed the 2 units to be compatible with each other. Safety first, however, but I have had no problems running my HG-10 vfo from the accessory socket on the back of my HW-16.
     Just my 2 cents worth. Good luck.    ---Marty, KK4RF---

[kb2vxa]

Hi again,

It seems like some have misunderstood what I wrote previously:
"I remember one stable as a rock because it was on 24/7 so your future drift problem may be mitigated the same way."

By that I meant not left in standby with heater voltage applied, I meant with B+ as well. A heater alone won't keep it up to operating temperature so when not in use it's easy enough to keep it "on". The front panel switch is labeled either off-on-operate or off-standby-on and the key jack on the back has a normally closed switch so when not in use removing the key and rotating the switch on the right to the far right position will do the trick (provided the power supply is on, hi).

I may seem a bit of a hassle but you don't want it drifting when you're operating, that's an even bigger hassle.

[DMOD]

Phil,

I looked at your PS schematic,  It's a typical PS which is exactly what the VFO needs.  Although, i think your need a supply that yields a higher voltage.  So, a xfmr with a higher winding voltage is required.  Reason is to regulate it down to 250 volts you have to start with at least 325-350 volts.  Everything else would be the same.

Fred

According to the DX-40 manual, the accessory socket pin 4 supplies 250 volts to the VF1's 6AU6 circuitry.

For class A amplification, that's what you want:

http://frank.pocnet.net/sheets/049/6/6AU6A.pdf

The OA2 gas regulator tube in the VF1 takes the 250 Volts and regulates the screen grid voltage down to 150 volts via its internal 15k resistor.

If more regulation is required such as for the plate as well, sure, select a higher voltage secondary, size some series voltage dropping resistors, and use four zeners stacked in series, such as 4, 62 V.

Phil - AC0OB

[W1RKW]

Interesting topic.  I have a VF-1 myself that I use with a Johnson V2. It is completely stock.  It needed a little TLC when I acquired it but it has been very stable. I've heard about these instabilities and drifting and have experienced it.  The only problem I had with it were the trimmer caps.  A slight dab of deoxit with a toothpick  on the mechanical connections stabilized the thing considerably. No other mods were necessary. After a 60 minute or so warm-up, it's almost as stable as my FT-102.

[N2DTS]

Was not the vfo designed to run off the transmitter power?
That would be the easy way, and would take very little power.

But if you need parts, just post, I think most guys have more stuff then they will ever use...