807 Tube

[SteveH]

All,
Anyone have experience in building an 807 PP amp ? I'd be looking to get about 45wpc out of it or so. From what I have read, I can look for 6L6 circuits and basically plug and play - but I would like some second opinions first.
This far, I am thinking of 450v B+ which would give me about 70mA per tube draw. I imagine that an 8k OPT would be about the right range as well.

Thanks !
Steve

[sorenj07]

I'm not positive but I think i've read elsewhere that a 10K a-a load is best for the 807 in UL, if that's what you're planning. That said, I'm not sure that the grids of an 807 could take 450-500V on the plate - you're probably better off running them in tetrode, you'll have a much easier time attaining high power this way. Edcor has a 10K 60W OPT that would probably suit your needs.

[mesherm]

If 807s are similar to 6BG6Gs you will need a bias supply of close to -100v. I made many amps with 6BG6G and GTs and they all required lots of bias voltage.

[sorenj07]

Would tapping off the HV secondary with a single UF4007 work for a bias supply, or would a separate transformer be best?

[mesherm]

I seem to recall that Shannon or someone used a small value capacitor into a diode and filter network to tap off of one of the HT sides on some circuit. It was like 0.05uF or thereabouts.... I would imagine the higher the cap value the higher the voltage.

[TomMcNally]

Take a look at the schematic in Guitar Amps/Hammertone Six Pack ... there is a nice drawing of the cap coupled bias circuit ...

[kheper]

The 807s have a max screen grid voltage of
300V. Some fancy UL output transformers
have a tertiary tap, which might bring the
screen voltage down, close to 300V. If you
are using a regular UL output transformer
with a %40 or %43% tap, a 20W power
resistor could be used to drop the voltage
down.

Running the output tubes in pure tetrode
mode with a seperate screen grid supply
sounds like the best ticket.

Placing the diodes on the screens is used
to block the flow of AC current from the
screen grids back to the DC source.

[sorenj07]

I think a nice stiff SS-regulated screen supply should suffice. I actually got as far as "should" before I noticed :\

[TomMcNally]

Say Soren,

Suppose said screen supply sparks, sputters, simultaneously sending
spurious strong signals spewing strange sounds speakerwise, should
same screen supplies serious serviceman swiftly sever such service ?

[Sal Brisindi]

Wow,
What ever your drinking Tom, make it a double for me.... :-)

On another note, its scary when you don't know how much crap you have until you start cleaning.. I found a chrome 6v6 monoblock in my garage plus a home brew tube power supply with a 83 mercury vapor tube not to mention a whole lotta other goodies.

I know better than plug something in without doing some preliminary checks first, but I said what the heck... sparks flew in that 83 tube when the heater warmed up... of course I checked the caps after but they didn't show any shorts but with some B+ on them, they probably had a ton of leakage. I killed the 83 tube..

This power supply must put out over 400vdc, the voltage on the secondary was about 820vac, 410vac to the center tap, might not be enough for the Darlings though...

Regards,
Sal Brisindi

[TomMcNally]

Sorry Sal !

Sometimes secondaries short swiftly sending stupendous sparks spewing
skyward ! Sadly, such shows send scared siblings scurrying !

[sorenj07]

sorry to interrupt but I was just updating my profile and I was wondering, Tom, how you got such a nice big avatar! Yellow_Light_Colorz_PDT_49

[Shannon Parks]

We have a few threads here and there discussing the 807 PP that might be worth searching, IIRC. Thermion took a ST70 chassis w/ PA060, a pair of Hammond 1650Ps, and used a stock diytube driver for his 807PP. Works great, sounds great. Max power output does NOT meet the datasheet numbers though. He's only getting 25W. We haven't looked at it, as he liked it as-is so much. Maybe he needs the driver circuit tweaked for more drive. ?

[EWBrown]

For a larger format avatar, you have to "import" it from your own URL or website, or link to another one. That gets around the local pixel size limitations, which are actually larger than on most forums.

My "headbanger" avatar is borrowed from a friend's website, and fills the need, until I can find something more suitable (Yuh, I'm one of those luddites who doesn't have their own website, web space, or other form of web presence. I just use the "Remora" method Yellow_Light_Colorz_PDT_07 Yellow_Light_Colorz_PDT_09

807s are basically identical to 6BG6Gs, but with a 5 pin UX base. 1625s are similar, but with 12V filaments and 7 pun UX style base. All of these are kissin' cousins of the 6L6 and its derivatives.

/ed B in NH

[TomMcNally]

My small pix are 200x150 ... you can also store pictures on this site,
take a look at Shannon's instructions here ....

http://www.diytube.com/phpBB2/viewtopic.php?t=1269