• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

5Z3P 6N9P EL34B SE amplifier

I finished building a SE tube amplifier after dropping the hobby 35 years ago.
I use this PCB bought from ebay:
1pc Single Ended Tube Amplifier Bare DIY PCB FOR EL34 KT88 6L6GC FU7 FU50 6550 | eBay
The PCB is isolated from the chassis. The only connection between PCB and chassis is the input signal ground connected to chassis safety earth. No hum what so ever and I'm happy with the outcome.
I use a switch to switch the EL34 between triode and pentode mode. It seems to me that triode mode is louder while pentode mode is softer.
Any comment?
 

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zs6bra

Member
2013-03-29 7:06 am
Edenvale
EL34 in triode mode with 6072, SS PSU & ultrapath

Hello, fellow DIYers,
I cobbled up the following (incomplete, needs some resistors values) schematic for paralleled 6072 / 12AY7, (with choke load) driving EL34 in triode mode with "ultrapath" & S/S PSU, with "ultra-fast" soft recovery STTH1210 diodes in FWBR (I know it's not often seen on this forums, just that I have some @ hand, as well as some some massive toroidal PT -225 W!, heavy choke & some nice locally made OPTs (C core, with 0.5 mm silver wire in the secondary)....I would like to use paralleled Solen "fast cap" polypropylene capacitors in the CLC filter. For the output stage operating point I used the recommended value from Amperex EL34 datasheet (OK, 368 V instead of 375, guess close enough to notice), should push about 5-5.5 W out (plenty for my case, with Lowther DX3 in Mauhorns "Signature I", >100 dB/W/m on the business end);

Couple of things still need advise:
- are these diodes (rated @ 1200 V / 12 A, t=48 ns) in need of bypassing with small capacitors (0.01 uF/1 kV) & resistors (470 kΩ / ½ W), like eg DRD PSUs?
- any recommendations re size of DC blocking capacitors? (don't think I am worried about reactances at anything lower than 50 Hz, though)
-any opinions on benefits with DC heating for both stages (space under 12"x 11" chassis is a bit tight, though)....

Any comments welcome!
SE 6072-EL34-SS PSU-ULTRAPATH.jpg