self split 12au7 output

[allsavy]

I'm in search of a low watt (>2 watt) output alternative to my favorite main guitar amp (fender pro style w/2-6L6 Push Pull pwr section driven by a long tail PI.
This amp (used to be a princeton rev. ll) The last of the point to point fenders!
and is tweaked out just right. Sadly.... it is too @#$% Loud for my apt.

I need less than 2 watts level when driven hard.

Solution ???

What about an alternate (and switchable) low watt output ?

Like diverting the long tail PI output to a single 12au7 wired for push pull operation.

Would this differ from a self split output? (as shown in

The Decimator: Description

is that a PP or a SE output?

btw....
Could I use the existing fender deluxe output tranny? with a PP 12au7?

Thanks, paul.

[Steve Conner]

Self-split is a PP arrangement where the power tubes also function as their own ghetto PI. It's like cathode bias, but you leave the cathode bypass cap off, and the first tube drives the second one through the common cathode connection.

It works OK. I made one as a reverb driver, and while I had it on the bench I tried it as an output stage. But driving the tube with a real PI works better, and you already have one, so you don't need to mess with self-split.

The Deluxe OPT should work. It won't be a proper match, so you'll get less output power than if it were matched. Maybe half a watt, 0.25 watt or something. But that's what you wanted, less output power!

You could also connect an attenuator between the power amp output and the speaker. It just takes a couple of resistors to reduce the power by 20dB or whatever.

[allsavy]

Cool....thanks. Just what I wanted to hear!


perhaps I'll use this output scheme:
lunchbox amp.

Adam's Amplifiers: Lunchbox

All that is missing is a big Dr. Frankenstien throw switch!!!

lol.... how to best handle switching the 6l6's out and the 12au7 in?

lift the 6l6 cathodes???

Can anyone pen a suitable switching circuit?

thanks, paul

[allsavy]

Oh... btw

my fender amp is fixed biased.

[allsavy]

Would I have to scale down the output voltages of my pi to in order to use a 12au7 in place of the 6L6s ?

[allsavy]

I found this power tube switching method but can't make out the type of switch.

http://www.schematicheaven.com/boogi..._blueangel.pdf

[unparalleled]

Firefly uses grounded grid PP.
http://www.sm-electronics.co.uk/imag...efly-inst2.jpg

[allsavy]

Thanks, I saw the firefly but can the grounded grid PP arraingement as such be used with a LTP PI?

wouldn't appear so. ????

[Old Tele man]

..."self-split" is also called single-ended push-pull (SE-PP)

[unparalleled]

Thanks, I saw the firefly but can the grounded grid PP arraingement as such be used with a LTP PI?

wouldn't appear so. ????

The point is that this arrangement removes the need for a phase inverter, you save on valve stages.

[allsavy]

wont need a PI...Yeah you are right. Although I consider my existing LTP (also a 12au7) to be key to the sound I'm used to hearing from this amp (the fender) only I'd like to get pwr tube overdrive at a substantially lower vol.

Actually I don't know how taking the signal from before the LTP would sound ???

Might be easier to figure out a switching scheme though.


hmmm...

[unparalleled]

wont need a PI...Yeah you are right. Although I consider my existing LTP (also a 12au7) to be key to the sound I'm used to hearing from this amp (the fender) only I'd like to get pwr tube overdrive at a substantially lower vol.

Actually I don't know how taking the signal from before the LTP would sound ???

Might be easier to figure out a switching scheme though.


hmmm...

I built a firefly type circuit with a 12BH7 PP output and it sounds just like a big amp overdriven but lower power out.

A 12BZ7 could be interesting on it's own wired PP (one grid grounded) with no preamp stages at all. Gain is 100.
Haven't tried this one yet.

[allsavy]

Yes using a self split PP will eliminate the need for a PI although a SE OT would be needed.

Perhaps this would be the way to go because my trying to figure out how to use the existing power amp stage including LTP PI and PP OT by hot swapping (????) the pair of 6L6s for a pair of smaller pentodes or a dual triode setup identical PP topography seems hard to figure in my head!

Switching between power tube types is one thing but also dealing with using the original OT which has 410v B+ at the primary.... way to much for a smaller tube (s).

Would be easier to just take the signal off of v3 (last stage before the LTP) and send it to a seperate although a single ended self split out put with a small SE OT.

Could take the B+ (around 230v) froman existing preamp B+ node.