Super pa 100 mods ?

[10349]

Hello Everyone!

First poster here. Big thanks to everyone involved. This is a wonderful forum!

I would like to ask for some opinions for mod suggestions on a 1970 super pa 100w I have.
I think I would like to tweak some bass out of it and tweak a little more gain into it, not looking for a a high gain mod, just a little closer to the a "normal" "plexi"
It is missing logo and a broken switch but pretty close to original in the circuit. It has the stock transformers and some original and other old preamptubes that seems in good working order. I think the amp has been in a closet a long time.
As far as I know only the bias circuit caps and the coupling caps after the Pi and the power tubes re new. And that was made by the tech I hired to check it out before I startet it.
My amp has 47k/5k with the feedback taken from the speaker jack. And I use a 16ohm cab.
It also has 250uf 820 ohms on the cathodes and the super pa mixer circuit robs some gain

So its pretty fat , a bit stiff and very very clean. Reducing the negative feedback , rolling off all the bass on the EQ , setting all unused channels to 6,5 helps some but I have been listenining to overdriven plexis on the tube and it have made me considering some mods .
That or buying a Helios or a BE100
I guess the few components required for modding ought to be about 400 times cheaper than a new amp.

I am not looking for high gain. More of a Zeppelin early ACDC type gain

Where would you start?

Disconnect some channels?
0.68/2.7k on first stage?

Other ideas?


Sorry for a lengthy post. Thanks for reading. And thanks to the Admins of this treasure of a forum.




Ps the amp sits on my 4x12 with serial 10349

[lifer]

really? i had a '71 PA 100w. and i forever hate myself for selling it!!!! LOL

i LOVED it the way it was. talk about a beautiful, smooth creamy tone.

you could tack a 500pf cap to the mixer resistor. but....don't go butchering the thing! Keep it original.

if you don't dig....get another amp.

no need to disconnect channels. (channel 1 is the same as 3. channel 2 is the same as 4.)

[10349]

Thanks for your reply Lifer!
Sorry you parted ways with your super pa , they can be found bargain cheap at times!'
Maybe you'll get a second chance someday ?

Yeah, I hear you. I don't want to go nuts and mod it like crazy.
Another amp could be a solution. Lots of money though.

Sorry I don´t know what you mean with 1is like 3 and 2 is like 4?

I think mine is like this ( it is not thesame as mine the NFB circuit though)

http://www.amparchives.com/Amp%20Archiv ... A/1968.jpg

I got the impression that the 4 ch mixer inputs all interact and that there is gain loss there that can somewhat be reduced by setting the pots to approximately half. But that also adds a bit noise.

Thanks for chiming in!