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Discussion in 'Amp Tech Center' started by itsa68, Mar 16, 2016.
Good news everyone! I have fresh voltage measurements!
Ac in: 308vac
After rectification: 322vdc
So b+: 322v
6v6 (1) is as follows
Pin 3 (b+ through OT): 317v
Pin 4: 289v
Pin 6 (bias): 18v
6v6 (2) follows
Pin 3: 310v
Pin 4: 286v
Pin 6: 18v
12ax7 stage one
Stage 3 (phase inverter)
Bias (anode): 46v
Any comments or suggestions welcome! Thanks folks
I still have not seen a 5e3 use a power transformer with such low secondary voltage. My hunch is that I need a 350Vac PT instead of this one, which looks like a 300v. However, I'm a bit strapped for cash right now so I won't be able to order another one in order to test this theory.
You originally said you were getting 414 for b+, without tubes.
A 5v4 will bring it up, but you may need solid state diodes to get it much higher. You can wire 2 diodes in a old tube socket and plug it in.
It will also work fine with 322v , just maybe a bit dirty.
A GZ34 rectifier will boost the voltage almost as high as solid state so if you want to stick with a tube give that a try.
How does the amp sound? Still have the ratty tone?
How is the circuit grounded to the chassis? You need a big iron to solder directly to the chassis or you can end up with a cold, noisy joint.
I hate to say it but your layout is nowhere near optimal. I would have put the rectifier in the upper left "empty" socket and drilled some new holes to put the tone and volume pots over by the preamp tubes. As someone stated earlier, your layout may be conducive to oscillations, noise and hum.
After assembly, I've been realizing the gravity of my layout sins. I did update the heater and grounding schemes with notable improvement. But if the general layout of the amp needs to be changed, perhaps I'll disassemble and reassemble soon. Ah well, this is how we learn!
I plugged the 5u4 back in earlier today with no sound improvement. I could check the voltages later.
Your voltages actually look ok- definitely within 20%. Is it still 'flarping?' And by Pin 6 (bias) you mean Pin 8, right?