Tube and schem question

[trem]

I have this old projector amp laying around. It looks like one lead of the 120 comes into the center of one of the tube sockets, and then the other lead hits the tag board.
The schem shows a In-Put Transformer, but not a PT. It does have an OT.
I cannot really understand all of the schem. It does use some high voltage (heater voltage) tubes. I would ditch those and just use a 12AX7 and then 2x6BH6.
I was thinking I could gut the chassis, keep the OT, and go with (it currently runs 2x50C5 in the output) 2x6BH6 power tubes.
I can then either buy a PT, or scrounge one I have laying around.
Do you guys think I can do a "basic" BF Fender preamp into a 2x6BH6 output with the OT in this amp.?
If so.....Would I be able to use both triodes of an AX7 for the preamp/tone stack...another AX7 for the PI, and then run that mess into a pair of 6BH6.?
Thank You
the schem is on page 19

[Amp Kat]

IMO if you want to change the Topology it would be much more difficult. Think it would be cool to see how it sounds and maybe tweek a few things. The interstage transformers are interesting tstl and may give you a really unique tone. You may have to change some cathode values and plate but if you are going to strip it you may as well just use the parts and build a real Fender clone with the parts and a more easier layed out chassis and board.

[J M Fahey]

1) although you seem to be aware of this, please let me scream from the top of the Church tower:
THIS IS A DANGEROUS LIVE CHASSIS ac/dc amplifier.
It shows an input transformer for the Mic input, maybe to offer better impedance matching but much more important, to avoid killing the announcer/operator.

Power output is puny, probably around 3 or 4 W RMS.
You need to use a 120:120V isolation transformer , pull that input transformer and rewire the first pentode with a high impedance input ... and just plug a guitar there and play.
If you want to build a classic Fender amp, just go get the proper parts and build it; whatever you can cannibalize from this one is not much and limits your design big way, not much result for a lot of effort.
Use it as is for a raw lo-fi sound, where it will excel.
Or as a harp amp

The "extra" 50C5 is an oscillator, probably a high voltage generator (1945 technology SMPS?) for the "exciter" tube, part of the optical sound track reader, it must have needed a higher voltage that what can be gotten out of an ACDC 110V supply.

[trem]

Maybe my OP is not clear, so I will reiterate.....
I am gutting the chassis and using a "normal" PT.
Wondering what I can build (good idea about the harp amp BTW) with the remaining OT and projector chassis/cover.?
Thanks

[J M Fahey]

Just thinking aloud:

1) 6BH6 are *not* power tubes, by any means.
While even puny 50C5 are.

2) Redefine what power tubes you will use, or suggesting is useless.
Hint: check the impedance favored by those 50C5 and choose something compatible.

[trem]

10-4.
Thanks
I was avoiding the 50C5 because of the heater voltage.
So looking for something similar to a pair of 50C5.....
...if Load Resistance is 2.5k for one tube, Class-A, at 120 plate volts
how do I figure for a pair of these in a P-P amp.?
Thank You

NJ7P SQL Tube Database Query

[jazbo8]

The "easiest" conversion would be 6CU5 or 12C5, but either one will require a separate filament transformer so you can use the stock OPT, then again to get better sound you may want to upgrade the OPT anyhow...

Jaz

[J M Fahey]

Really don't know.
You must first find what that OP is so you can get suitable "normal" (6.3 or 12.6V filament) tubes .

[trem]

Yeah -
Let me pull the OT loose, put some voltage across it, and see what we get.
Then a better decision can be made.
Thanks Again