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DoomPixie 27th February 2006 01:01 AM

Old Projector amp conversion project
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Hey. I have an old Projector amp theat i bought of ebay and i am trying to convert it to a guitar amp. I have stripped out all the Stuff that related to the projector side of things (or most of it anyway) which made the inside of the chassis a hell of a lot less crammed and i can see roughly what is going on in there now..
From what i can tell it is basically an EL37 PP amp.
There was a 3rd EL37 but that was wired into the Excitor lamp and as far as i can tell (after ripping excitor lamp gubbins out theres no connections to this socket except heater) it has nothing to do with the actual amplifier.
There are two EF40 pentode's which i assume are being used for the preamp and an ECC40 which is a dual triode and i asumed is being used as a phase splitter but on closer inspection it apears to be operateing as two seperate triodes and each is doing something different (but then there would be no phase splitter?? is that possible?? :S )
Anyway, I would Like to know if it would be possible to use 6L6GT valves in it instead of the EL37's as i am haveing trouble sourcign cheap EL37's?? also would it be possible to use a different rectifier other than GZ32? best something i have here mabey a U22 or U50 or something?
It apears to be a VERY old amp, there are no plastic coated wires, they are all cloth coated and most of the caps are wax coated jobbies so i will have be doing a complete rebuild anyway.. or probably more fitting would be to say i only plan on reuseing the choke and output transformer and the really high quality pot's that were on the front that are still flawless in operation and extremely quiet even after all these years ( they have a really nice feel to them aswell)
Many thanks in advance,

Eli Duttman 27th February 2006 01:51 AM


You should be fine using SED ("flying C") 6L6GCs with the O/P trafo. AAMOF, if you can find metal envelope RCA 6L6s at a good price they will work too. Be sure to avoid exceeding power limits either for the the tubes or for the trafo.

NOS European (Mullard, etc.) GZ32s are costly. Perhaps you can find a RCA 5V4GA. The RCA is decent, while being "reasonably" priced.

To stay with an Octal type in the preamp, use the 6SL7.

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