Help - PA Amp for guitar - increasing output?

[Shark_Sandwich]

Do you mean running the two halves of the 6N7 in series instead of in parallel?

[Satamax]

Yep, using them as two gain stages You could try also cascode with full B+ on the top plate

[Rob Mercure]

Hey Max,

You might want to check out the 6N7 basing diagram first - kinda hard to cascode, or cascade, a twin triode with a common cathode! And, again, overall gain doesn't seem to be the problem - and the 6N7s in parallel provide greater current to the PI tranny and "may" allow some excursion into AB2 space. What we need is the amp driven and the 6L6 control grids scoped. Now if one wanted to go to the trouble you could install a separate PI stage, add a PP to PP interstage tranny, and use the 6N7s to pump 10 watts into the 6L6 grids. Not sure why you'd want to but that's the easiest way I can see to get more "umph" from the 6N7s.

6N7s are actually neat tubes and a common pre-WWII design used on with the sections paralleled driving a PI tranny which pushed another 6N7 in PP Class B for a "portable" PA system (as "portable" as the weight of the batteries would allow). They're one of the types that have always been on my "someday" list for a "novel" (at least to me) circuit - I've always wondered what the distortion characteristics would be like in true Class B.

'Nother neat feature of this amp is the choke loaded input stage and the "strange" tone control circuit which taps part of the signal between the choke load and a dropping resistor in the plate circuit. Somehow I believe that is probably doesn't sound like anything else I've got laying around here.

SS noted perhaps too much treble response. While you could shunt a small cap from the input pentode to ground - perhaps 100 uuf to start - increasing the value of the coupling caps and cathode bypass caps would sorta accomplish something similar by increasing the low end. Lotsa room to experiment w/o altering the basic topology.

Rob

[Satamax]

Oups, sorry, my bad. i'm kind of lame tech DIY yellowjacket and a 12 AX7?

[Shark_Sandwich]

Oups, sorry, my bad. i'm kind of lame tech DIY yellowjacket and a 12 AX7?

Ah, that's too easy. :-)

(actually, I thought about that, but I decided to stay all octal, partly because I'm trying to use this platform to learn about tubes, and partly because, well, the thing is OLD anyway.)

It does have a strange tone circuit. It sounds like a balance between highs and lows - not quite a low-pass capacitor filter design, but almost a variable bandpass.