The Amp Garage

Raoul Duke wrote: ↑Thu May 16, 2024 8:02 pm Not hearing any weird noise from the PI or OT, so I guess V3b plate wire is ok where it is for now?

Do you mean the OT primary connections/NFB?

It's the same as placing two same-value resistors in series to reduce voltage instead of one at the same total resistance. In the case of two resistors, half of the voltage is dropped in each one, current is the same, so half the power (V*I) is dissipated in each.

Thinking about this more and running some numbers here is what I've come up with. Voltage dividers are linear (though a pot may have a different taper) meaning if you think of the divider as attenuating a certain percentage of signal voltage, it does not matter if that input is 10V or 50V, the rati...

Kagliostro wrote: ↑Thu May 16, 2024 9:01 am but I'm not able to figure why at 1/3 of the voltage as output the dissipation will not ne high

At very low voltage the current draw is reduced. Power is I^2R, and the reduction in I^2 becomes dominant.

I see it has the pro tour option, 12 chassis mounting bolts ;^)

Yea, sorry for the diversion. If you went ahead and wired the rest of it up you'd have been fine. Hopefully the learning was worth the trip!

Raoul Duke wrote: ↑Wed May 15, 2024 2:00 pmMakes sense - the second ground reference wasn’t in the circuit - so it compensated by pushing all the voltage to one (grounded) side. Do I understand that correctly?

That's it. I seem to recall the same question coming up in your 102 build.

Do you have heater leads connected between the two sockets? If not that would explain it. I thought I saw a back/white twisted pair.

That says that the 150R from 2 isn't connected to ground.

Yes. If you disconnect the PT heater leads you should measure ~150R to ground from pins 7 and 2. There are two diodes and a resistor across those pins, but that shouldn't affect the measurement significantly. P.S. If you measure pin 2 or 7 to ground with the heater leads connected, you should see ~7...

I’ll go over everything one more time, but I’m fairly certain that I don’t. Is it safe to measure heater voltage with the leads off the socket and just hanging in the air? No problem. Measure across the leads since you have removed the ground reference. The only other thing I wonder about is the te...

Ok, replaced the heater ACTs with 150R and fired it up. Now I have 6.2vac on pin 2 and 0 on pin 7. With or without tubes you should get about 6.3 across the heater string and half of that from each side to ground. Are you sure you don't have any part of that network grounded other than the 2x 150R?

The 10u 160V IC cap's ESR is not out of line. Check the chart that came with your Peak. Are there caps with lower ESR? Sure, and in some applications such as SMPS with high ripple current it's necessary for adequate life. Those old Mallory's appear to be good, but if that amp is going to be a player...

Do you have 150k resistors to ground from pins 2 and 7 instead of 150 ohm?

Heater voltage was 2.9vac at pin 7 and 6.9 at pin 2 - but 6.2 measured across 2 &7; panel light consistent with this as well. Don't understand this... If pin 2 to pin 7 is 6.2, I would think pins 2 and 7 should both be ~3.1 to ground. Is the only load you have on the heater circuit the panel lamp? ...