• 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.

SHAG project – simple hybrid with opamp front-end

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Hi All, another project is coming out. Had a half-dozen of 5687 and few PREM trafos ($5 ea) kicking around and wondered how that would mate with NE5532. The purpose of this one is a utility, for occasional hook-ups.

An externally hosted image should be here but it was not working when we last tested it.


Breadboarded it sounded quite ok, on some leftover pcb with messy wiring:

An externally hosted image should be here but it was not working when we last tested it.


With 2 tubes + 2 OPTs per channel it pumps out about 5Wa of good sound. Can be downsized to a single of each, with up to 3 Wa, in this case the HV secondary has to be switched to 180 V tap. The secondaries for opamp are added on top of AnTek mains, 2 x 76 turns of some small wire. With just the capacitors the hum is under marginal level.

An externally hosted image should be here but it was not working when we last tested it.


Some small no-name Blutooth module will work as a source, luckily it has no DC on the outputs. Not installed yet (the power circuitry for it is neither shown on schematics).

(My previous completed project – SHAX)
 
. ..got it playing by now, what is left to fit the top cover:
An externally hosted image should be here but it was not working when we last tested it.


After heating up the HV settles to 260V with 80 mA quiescent, 8 mA per a triode == 2Wa idle dissipation. No bias adjustment, but luckily I got 2 pairs out of 6 tubes matched within about 15%.
 
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Been completed and put in service:

An externally hosted image should be here but it was not working when we last tested it.


There is a LED spectrum "analyzer" used mostly for sensing the standby mode, excuse me such the blasphemy, but it looks nice:

An externally hosted image should be here but it was not working when we last tested it.


Now I'm getting back to SHIII, which by the time quite grew towards the Hi-Fi quality SHIII project, All-Pentode PP
 
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