New Project Ideas?

[ncusack]

Hello,

Recently I picked up a transformer pulled from an old organ amp. It was originally powering a quartet of el84'2 along with 5 12ax7's. The Voltages recorded using a variac at 120VAC are as follows

590V w/ CT
35V w/ CT
7V no CT
6V no CT

I was thinking of doing something like this with it but with a pair of el34's instead.



I'm not sure if the voltages would be suitable. If this is a viable option please let me know or if you guys have other suggestions let me know.

Cheers

Neill

[phsyconoodler]

Yes it would work fine.No 5v tap for a rectifier but the EL34's don't need lower voltages.
  Just change the phase inverter and screen resistor values to a Plexi or 2204 and you will be fine.
It will have about 415v or so on the plates and you could make it fixed or cathode biased.It will kick ass.
 

[jojokeo]

No 5v tap for a rectifier 

Phsyc - I think those are likely unloaded readings so the 6V may be 5V and the 7V would be the heaters. Most if not all old organ amps used tube rectos.

[ncusack]

jojo your right all the voltages here are unloaded measurements. When the circuit is built they should all drop a bit.

psych - by 2204 PI values do you mean 2x1M a 470R and 10K?

[phsyconoodler]

Yes.The EL34 won't sound good with EL84 PI values.

  You can use negative feedback or better yet have a switch to lift it if you want a more open tone/

Good call on the unloaded voltages.Makes sense.However,you still might like to use a diode rectifier unless you cathode bias it and hit it with some current.Then the EL34's will sing nicely.