modifications to compact EL84 amp

[planet10]

Originally posted by Tom Bavis
Remove the ground at the low end of the cathode resistor and add another 100-200 Ohms from that point to ground.

Which cathode resistor?

dave

[analog_sa]

Don't want to sound negative but i've tried liberating EL84 pentode amps from negative feedback and the results have been quite lo-fi. Anyone been luckier?

cheers

peter

[Jaap]

perhaps this has still some more elegance:

[Jaap]

what about this ?

[Joel]

Jaap,

1) How are the tubes biased in your push-pull example?

2) What do these designs have to do with the original posting?

[fdegrove]

Hi,

Something is missing there.

Cheers,

[Jaap]

The thread is also about simplicity and elegance, but you are right I don't see a el84 in these designs. By the way I have used 2A3, 300B and 6B4 but yesterday I fired a simple 6N1P cap coupled EL84 se-amp. Of course everybody should start with the el84 in the first place. Boy what a good amp is this ! I used a small fourty year old outputtransformer and the amps rocks. Of course no feedback.

here is the powersupply of the PP 6B4:

[electrode10101]

Mods as per fdegrove;

I don't know if I'd go as far as putting a 470uF cap in the p.s., in that C4 position. Seems to be overkill, and could significantly reduce the life of the 5Y3 and the power tranny. 50-100uF would be more than enough. I guess I've seen a few barbequed amps with hi value caps in the power supply. It's not pretty.

If you really wanted it to sing, try using film caps in both positions; say a 20uF for the first cap, and anything or combination of caps (space limitations) at or over 40uF. That would sound even better.

Agree with .22 for C1.

Play safe; keep one hand on the chassis, one hand in your pocket.


jD

[Joel]

Originally posted by electrode10101
Agree with .22 for C1.

Actually with the 500k ohm Rg, 0.1uF would already be overkill.

[fdegrove]

Hi,

I don't know if I'd go as far as putting a 470uF cap in the p.s., in that C4 position. Seems to be overkill, and could significantly reduce the life of the 5Y3 and the power tranny

It won't.The only thing that could happen is the choke going into saturation..but it won't.
If you value awesome dynamic range and deep,solid bass...follow my lead.

If you really wanted it to sing, try using film caps in both positions;

A waste of money in front of the choke,after it..yes.
While you're at it you can make an electrolytic cap sound as good as a filmcap by decoupling gradually.

Cheers,