WA1GFZ Audio Driver PCBs (all spoken for)

[W7SOE]

I have made some PCBs of Franks fine audio driver circuit, described in this thread by K1JJ:

http://amfone.net/Amforum/index.php?topic=23632.0

I have built one up and it seems to work FB.  One thing Frank pointed out was that I neglected to leave much space between traces carrying up to 300V.  If I check PCB clearance calculators I am on the edge of acceptability.  

With this said I have run mine on the bench for several hours at 300V with no observed problems.

I was going to sell the two remaining PCBs to try to recoup some of the cost but I don't want to do so with the tight clearance on the traces.

I will give the two remaining away to first comers who:

    1)Will build it relatively soon.
    2)Will install it in a xmtr when done.
    3)Will let us all know about the performance etc.

(please don't ask for one if it is going to sit in a drawer!)

PM me if you are interested.

73

Rich

[WA1GFZ]

Wow Rich,
You are living on the edge with no heatsink on the FETs. Even light loaded the phase splitter is dissipating a few watts. The outputs may be higher.
I figured you had everything running fine since there has been no emails in two weeks.

[W7SOE]

Wow Rich,
You are living on the edge with no heatsink on the FETs. Even light loaded the phase splitter is dissipating a few watts. The outputs may be higher.
I figured you had everything running fine since there has been no emails in two weeks.

I had them lightly loaded and I kept an eye on them with an IR thermometer.  They did not get up much past 120-130F.

Rich

[W7SOE]

Both the PCBs are spoken for.

Thanks

Rich

[WA1GFZ]

Rich, Send me an email of the winners.

[WA1GFZ]

It will be easy to do Steve's zener isolation method between grids with this driver.
Just need a pair of zeners of the right power, 5 watt should work for the 807.
Then an isolation resistor resistor to a well bypassed -5 volt zener regulator.
A couple 100 volt caps across the zeners.

[KC2ZFA]

I'm not a winner   but I would definitely help with the cost of another
run that will turn me into one  

[Steve - WB3HUZ]

Nice design. Frank was telling me about it at NEARFest. If you do another run of boards, I'm in for two.

[W7SOE]

If enough people are interested I could do another run.  Perhaps after I get some feedback from those who are building them now.

Rich

[K1JJ]

Nice job, Rich - good to see this project looking professional.

As pictured below, my working prototype has all fets mounted on a single heatsink with small 3/8" fins. None of the fets run warm when driving the 4-1000A modulators full bore. Haven't had a single problem with it since we built it 6 months? ago. No RF in the audio, instability or other problems to be found. Just runs and runs.

On Rich's board, why not bolt a 1" wide, 6" long, custom cut single heatsink right across the fets?  And if more cooling is needed,  slow down a small muffin fan with a variac blowing air down the heatsink fins.

Frank's design is possibly the best out there and simple too. Just one +- ~300V supply needed. It has built-in provisions to accept negative feedback from the modulators - nice feature and very important. I was able to tap my NFB at the secondary of the mod transformer w/o oscillation problems. Anyone with tube modulators should consider building one, especially now that PC boards will be available.  This is the cleanest audio driver you will find anywhere. If you have a good quality mod transformer - and tubes with plenty of headroom, this will put your class C, plate modulated rig into the broadcash transmitter / class E sounding class, caw mawn.

T

[W2XR]

If enough people are interested I could do another run.  Perhaps after I get some feedback from those who are building them now.

Rich

Hi Rich,

Yes, if you do decide to go for another run of these boards, count me in for two each. The circuit could be used to replace the push-pull class A 845 audio driver I currently use with my class B 833A modulator, and I would then be able to wrap the NFB loop around the mod xfmr, instead of the 833A plates. No more problematic driver xfmr. And I could use the second solid-state driver assembly in a future class B 833A modulator for my GPT-750, in the event I ever decide to build a modulator for that rig.

Thanks & 73,

Bruce

[KM1H]

I might as well go for a pair also, maybe a few more. Will be running 810's, 304TL's, 4-400's and maybe 4-1000's.

With W3AM's phase adjuster it looks like I can even use the 1935 all transformer coupled low level preamp, amp and 46's. Then Franks circuit to the 250T modulators feeding HK-354's for some real elderly AM.

Carl

[WA1GFZ]

Tom,
Rich mounted the caps on the bottom to save board area and cost. This forces the board to be up on 1 inch stand offs. I was thinking why not mount it in a chassis with the FETs up against the side wall. An additional heat sink could be added on the outside surface supported by the 5 FET screws coming through the chassis if it still runs too warm. At first I wanted the board on smaller supports so the fets could be mounted flat with the leads bent vertical to accept the PC board hole pattern.
I'm working on a slight design change and as Rich said some of the traces are too close. Also I would increase the hole spacing of the smaller resistors.
BTW Everyone, Tom get the credit for many hours of testing and feedback configuration. It was fun making the simulation agree with the measured performance. I think the first time we tried feedback it fell apart around 3KHz due to phase shift through the driver adding to the phase shift of the iron.

[w8khk]

Please count me in for a pair too!  One for a pair of 810s modding PP 250THs, the other to mod a pair of PP 304TLs by either 304TLs or 4-400s - haven't yet decided which to use for modders.  But a quad of 304TLs, two in the final and two in the modder would look sweet!  The final is done, waiting on mod and PS.

[K0ARA]

Rich... Count me in for two. 

                      Mike

[W7SOE]

One board is freed up as the claimant decide that he could not build it soon.

Anyone else ready to build one?

All gone...

Rich

[KC2ZFA]

It would be nice to hear from those who built using these first-run
boards.

Peter