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6B4G PPP idea

I got bored today and tried to come up with a 6B4G PPP amp. This is really rough so take it easy on a design newbie. The phase splitter is an input transformer, the main gain stage is 2 pentodes (6SJ7 or EF86, because thats what I have), the drivers could be any number of things 6SN7s or these 1626s I got. I'm mainly unsure about the negative supply for the drivers and the output tubes. I was hoping to run them both off of one supply and have some balance adjustment for the output tubes. So here it is, it will at least give you an idea of what I'm thinking of, even if its rubbish.

Athos
 

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Even though 'm not getting any traction on this thread, I'll post what I fiddled with today. I lifted the frontend from the new Millett amp, and gave the CFs CCSs so that, "I think," I can keep the whole thing balanced. Rubbish?

Athos

PS, I think I could run the CF's CCSs off on the negative supply I use for the Bias and the input.
 

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revintage

Member
2007-05-30 4:12 pm
Move the coupling caps from between two drivers to between the second and the output tube. You will need a negative supply. This will be the way to let the amp work in A2 where grid current is drawn.

Also I wouldn´t go for 6SJ7 or other low Gm tubes. Instead a good triode with mu 40-60 and no GFB. Maybe a triode-strapped 6SJ7 will do, but I haven´t got a clue.
 
Ok the caps are between the CF and the output tubes, and the driver's CCSs share the negative supply. I think that a single -50 to -60 negative supply can be used for the input, drivers and the output tube bias. Thanks for the input!

Athos
 

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revintage

Member
2007-05-30 4:12 pm
Move the coupling caps from between two drivers to between the second and the output tube. You will need a negative supply. This will be the way to let the amp work in A2 where grid current is drawn.

Sorry, didn´t check my writing before posting:eek:. I ment the other way around. Off course the text should read:

"Move the coupling caps to between two drivers from between the second and the output tube"
 
Sorry, didn´t check my writing before posting:eek:. I ment the other way around. Off course the text should read:

"Move the coupling caps to between two drivers from between the second and the output tube"

Ahh that makes more sense :). So maybe something like a 6SL7? I should also mention, that a preamp with a little gain is before this amp(56/76 preamp), so it doesn't have to be geared for a CD input.

Athos
 

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How about D3a?

here is some work I did last night. I lifted the bias scheme from Miles Prower's Vixen amp, Thanks Miles. The other thing I've been playing with is the E-linear verses Schade feedback. Thanks for looking, sorry about all the schematics, but I guess you can see the learning/thought process.
 

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Forget about Schade, it is for making pentodes work like triodes. You have nice linear DHT-triodes that need no feedback.

D3a is somewhat wrongly biased. It likes something like Ua=20mA and Ra 10k.

Ahh, good point. Yeah I forgot change any of the values in the schematic, which are all really preliminary anyhow. So now the pentode/triode input question. Here's what I got on hand in enough numbers to populate the input position, 6SL7, D3a, 12AX7, 6SJ7, EF86, 5842, 5687, 6SN7.
Thanks

Athos56
 

hemgjord

Member
2007-04-24 10:55 pm
Obviously I did not read what Revintage wrote either, I read what he meant :)

But that is OK now. However you need to move the biasing network to bias the CF's instead of the outputs.
The output tubes are biased by the cathode voltage of the CF. To bias the output tubes you adjust the CF grids.
As it is set up now the CF grid is at gnd potential and that will give you a few volts POSITIVE voltage at the CF cathode which is direct coupled to the output grids. I.e. you have a few volts positive bias on your output.

/Olof
 
Now for more practical concerns, parts selection. Should I go for the cheapest option, the Russian 6S4S, which runs between $15 and $20 per tube or the Sovtek 6B4G, at a little over $60 bucks a tube. Or even go for the Sovtek 6A3, 2A3 or even the Sino 2A3. The output transformers are going to be Edcor 25w, 2.5k units, for $40 they are really economical.

Athos