V2

[WA1GFZ]

My new CDC Viking 2 is setting on the bench. This will be rebuilt for the new station.
I don't think I want to hack it but want to do a few mods.
It ain't class e but covers all the HF bands.

any suggestions. Makes RF but was told modulator not working. Has mod current.

[K1JJ]

Franz,

I think I'd  model it after the Johnson 500.

Get another cabinet to house a HV supply and the new mod iron with a connecting cord between them. Put the new cabinet under the bench.

In the existing Viking II, I would gut the existing audio section and HV supply, giving lots of room. Add a single 813 for the final and an 813 pair triode connected for the modulators. You will have room to add a new pi-network if desired, though maybe that existing strapping one they now use will handle the higher power. All depends on your final HV and the mod iron you intend to use, and final power level. Use an outbord solid state amp to drive the 813 modulators with the standard backwards 8 ohm xfmr. You could hide that amp on the floor too.

The exising RF VFO to the driver is FB. You might need a bigger RF driver giving 5W for the 813, dunno.

That would be some rig and a great winter project..

73,
T

[Tom WA3KLR]

I run mine stock.  Your driver transformer may be open, a typical failure.

I think there are audio mods out there.

[WA1GFZ]

Tom,
I think I will keep it near stock and hack into the PDM V2. Tom vu I have a lot of room in the PDM rig so that is the one to modify. I did a v2 plate modulated years ago and replaced the driver iron and changed to a 6AQ5 driver.
I don't want to make it much heavier to lug around.
The rectifiers are at the top of the list to eliminate. Lots of heater power eliminated will cool the lv transformer down.
I powered it up this afternoon and makes RF with plenty of grid current. I hope to put a mic on it tonight and see why the modulator died. IF I remember it died slowly like a tube going.

[WA1GFZ]

Well,
I'm on the air and making modulation. I notice there is an extra tube in the audio section?

Also my audio pot loses gain above 3 or so like there is some of clipping action going on.

Anybody out there have a schematic for the V2-CDC. It even has PTT so different than the common V2.

Made a brief contact with a guy in Ohio using some new fangled class E thing.

Looks like all I need to do is add an antenna relay and the rig is usable.

[WA1GFZ]

well,
V2-CDC is up and running after a cap job. I need to complain to E F Johnson. They forgot to solder the ground lug for the first audio stage cathode cap in 1953. I noticed a cap and driver transformer were replaced. I bet this caused a number of hours of repair work. Now to solid state the power supplies and remove about 40 watts of useless heat.

[W3SLK]

Frank said:

Now to solid state the power supplies and remove about 40 watts of useless heat.

I wouldn't be so hasty in attempting that Frank. If I recall and there are others here that can back it up, but the voltage drop across the rectifier tubes was engineered in to the plan. So say for instance you were to replace a 5U4, (I'm just guessing here for demonstration purposes), with about 20~40 VDC drop versus a solid state rectifier with 0.6 VDC drop, you may wind up changing the operating parameters of your modulators and finals. I don't know what the actual drop is across the HV rectifiers but I have been advised the same. But then again, what do I know?

[Steve - WB3HUZ]

Mike makes a good point. Could be a problem, although I solid stated the supplies on my V2 and I had no problem. I may have gotten lucky though.

[WA1GFZ]

I solid stated the supplies in my PDM V2 in 1983 without any problems. I think the only issue was the bias supply increased voltage. I'll have to look but I may have changed over to choke input filters to get the voltage back down. I may have added a choke on the bais supply.
I would think the finals and modulators will like more on the plates. This will reduce the temperature rise on the LV transformer.

Tonight I took the VFO apart and found the 18 k resistor to the OA2 measured 40 k so replaced it with 20 K 10 watt. Looks like I need to change out the power lead. I have a nice hunk of teflon twisted shielded 3 conductor. (TST). I heard abunch of guys on 3725 so grabbed the old novice rock from 1966 and popped it in to get on the air. That crystal had not been on the air in 40 years.

I had not worked on a tube rig since I built the pdm v2 soo the first thing I went looking for was the trusty solder sucker. I finally found it but the bulb cracked when I tried to use it. Ended up using a roll of solder wick. The bugger the blob the better the job back then.

[Tim WA1HnyLR]

Hnyello Frank. Its about time I got into the frey. I have also aquired a mint V2-CDC. I have yet to power it up. I am planning on using better mod iron and better driv4er transformer though. I would highly recommend solid stating the power suckplies. One observation I have made is that when most of this old gear was built the usual AC line voltage was 110-115 volts. Take an accurate measure of the fillament voltage at the 6146 PA tubes. Chances are it will be noticeably higher than 6.3v This will shorten the life of the tubes in the long run. In the Viking 1-1/2 transmitter I solid stated all power suckplies. I took BOTH unuesd rectifier fillament windings ,seriesed them up and placed them in series with the 115V primary of the low voltage transformer in the in phase or "buck" configuration. This dropped the phillament voltage to 6.1 -6.15 volts under load. The tubes are real happy with this voltage. The LV/bias/fillament transformer runs much cooler, Collins 32V owners take note!.Being that the LV supply is cap inpoot there will be an increase of voltage. Expect about 330-340 VDC outpoot.You will get more adaquate drive on 10 meters.One mod I did on a V2 you may consider changing the LV suckply to choke inpoot. This will drop the voltage to about 250-260VDC. The values of screen dropping resistors for the oscillator stage may have to be lowered in value.to get good drive on 10 M. A 6AH6 makes a better OSC than a 6AU6. An additional set of relay contacts should be used for the modulator screen voltage control. Get rid of the 20K bleeder with the tap for screen voltage. Take screen voltage directly from low voltage supply  as noted.Using the  choke inpoot low voltage supply requires about -24V biass. Use a zener diode clamp with parallel 100-250-MFD cap across diodes to hold the mod biass steady.If you decide to keep the LV suckply cap inpoot you will need higher mod bias. The reason for the lower screen voltage is to allow the modulator tubes to make more audio power with the stock mod transformer ratio. A higher screen voltage will allow the mod tubes to make more power but only into a lower load impedance.Being that there is an additional tube socket the was occupied by the audio distortomiser you can make use of this socket for a 6AV6 or whatever for additional gain which is needed in the V2. A triode connected 6AQ5 audio driver to be used. Load the driver transformer secondary with a 10K resistor and wrap a loop of negative feedback around the modulator. You can make up a voltage divider from the modulated B+ to the cathode of the newly added second audio stage. This is the route I am planning with the V2CDC that I have. I am curious to see what results you will get with all of this stuff added. I would suggest adding more filter capacitance to the outpoot of all power suckplies. An additional oil filled cap may be added to the HV suckply. Mount it in the space originally used by the  5R4 HV rect tubes. Use a minimum of 100 mfd for the LV suckply and same for the biass. You could take the simple way out. Spend the money and buy a Hammond 75 watt single ended audiophool grade audio outpoot transformer. The 5K impedance model will handle 300Ma of DC imbalance. Use a sound re enforcement type PA amp that with both channels in bridge mode making 500 watts or so of audio be used as a modlator. Unplug the modulator tubes . Plumb in the external modulator sceme. Good luck with it Frank,De Tim WA1HnyLR

[WA1GFZ]

Tim,
I have a copy of the V2CDC manual and Scanned the schematic. I can send you a copy if you provide an email address. It is an 11 meg file though. It is faded but with an eye loop you can read it. The PTT relay switches off the mod screens and there is a screen dropping resistor different than the stock V2. I was on last night with an old turner crystal mic and everyone told me it worked but need an EQ. The driver transformer was replaced and I have a couple ART13 mod transformers. I just want a solid rig to bring to the beach QTH so I can get on. I still have the peak clipper circuit installed and barely hit 100% but the mod resting current is over 100 ma. There seems to be enough gain after changing out the caps. I put 15 uf in the cathodes and .0047 coupling betwen stages up from .001.
Cool idea on putting the 5 volt winding in series with the primary. The HV rectifier fil winding is good for 6 amps so should handle the current and cool down the lv transformer.
I would solid state the audio driver if I really want to go crazy and use FETs and op amps. Then cathode drive the modulators. But then could PDM it.
I don't want to hack this rig too much but plan to really hack the the PDM VE. I want to put an 813 in the final.

[WA1GFZ]

Last night I built the screen regualtor with a pair of 10 watt zeners and 15 K 20 watt resistor.
Holds 337 volts on the screens up to 300 ma mod current.
I had to remove the old screen resistor brackets to make room for the 1 X 1 angle to mount the diodes , 3 bypass caps and dropping resistor. The back one was easy but the front one went through the output variable inductor. I was careful as a cat but it still fell in. From the top it seemed a mile away and I didn't want to drop the panel to reinstall it.
Then I spotted a hunk of 1/4 inch rubber gas line. The head of the screw fit tightly inside.
Second try and I was able to push it into the hole and catch the ground lug and hardware to reinstall it.
That flash back to the red plastic tool that came with Heath Kits.

one more supply to solid state. Tube stuff PITA

[WA1GFZ]

All supplies solid stated, Second 8 uF cap in the HV,
Tim heard 120 HZ so looked on the scope to verify. Added another 400 uf in the LV= gone.
Box a lot cooler now. Now to decide if I want to try a solid state audio driver or play with the tubes.
I also have an ART13 mod transformer that I may try.   
Solid state is so much easier.....

[WA1GFZ]

More testing update:
As Tim suggested Heater voltage is high so plan to put the HV heater leads in series with primary to get closer to 6.3 VAC.
HV pretty solid 765 volts. Man Vacuum rectifiers have a lot of loss when you pull current. I was 100 volts less with tube rectifiers. Extra 8 uf cap made it pretty solid maybe 30 volts sag at mod peaks.
LV about 370 depending on mode.
Bias increased a couple volts no real effect on operation.
Need to reduce the mod resting current 60 ma resting is 46 watts dissipation.