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modifications to compact EL84 amp

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I really like the simplicity of this circuit and the EL84/6BQ5 output tubes. However, I would like help with the following modifications:

1) Increasing power to greater than 10 watts.

2) Possibly changing the driver tube. I haven't heard much about the 6C4, but I know it is out of production. How about an ECC99 or 6SN7? I read in the circuit description that it only needs to swing 11 volts.

I'll need some detailed assistance, as I'm just starting out.

Regards,
Eric
 
diyAudio Senior Member
Joined 2002
HOLD ON...

Hi,

Planet10 is correct,loose the tone control...

Up C4 to 470 mF,up C2 to 0.22mF and your going to have a little powerhouse.

The 6C4 should still be around at reasonable prices,check Antique Electronic supply.

All of this won't yield a a more powerful amp but the upgrade will give quite a bit more headroom and better bass performance.

Heck,I may build one for the bedroom system...:cool:

Cheers,;)
 
diyAudio Senior Member
Joined 2002
6C4 = 1/2 of ECC82

Hi,

personally id drop the resistor splitter thing, use a 6SN7/6CG7, use 1/2 for gain, and 1/2 as a cathodyne.

And loose the elegance in the process for what?
A dB or two?

If you need the power look elsewhere I'd say??:(

I dubbed this the "Tiny Penthode"

BTW,a nice compact circuit can be made using a pair of ECL86s this way...call it the "Pocket Amp"

Cheers,;)
 
Would a ONE resistor mod retain the elegance? Remove the ground at the low end of the cathode resistor and add another 100-200 Ohms from that point to ground. The balance of the output stage will be improved. Calculation of the wattage is left as an exercise for the reader (translation...Where did that calculator go?). Of course you'll need more drive voltage - nothing is free. But it isn't hard to find a tube with more gain than a 6C4.

For more power, you'll need more than 250V, especially with the extra drop of the added resistor.
 
elegance

perhaps this has still some more elegance:
 

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simplicity

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:
 

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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. :bigeyes:


jD
 
diyAudio Senior Member
Joined 2002
CONSERVATIVES.

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,;)
 
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