The Amp Garage

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? ...

My thought was keep the load similar to the Second Gen to preserve its character, and allow some plus/minus on the level coming out of the OD wrt the fixed divider in the Second Gen layout. The main point is, however you do it, the Ratio control provides for adjustment of the OD output without going...

Looks good now.

Stevem wrote: ↑Tue May 14, 2024 11:20 am Thanks for this test out and post, and yes that’s over a 10% different which is a lot!

My math says over 1000% in ESR. A current data sheet from Mouser indicates IC is part of CDE, and the max ESR for 10uF 160V axial at 120 Hz is 33.157 ohms.

Correct. The cap is a bypass around the upper part of the resistive divider.

I finally got a load of caps to try in my 5F1 based amp. Quick question: Do I put the bright cap between lugs 1 and 2 of the Volume pot, or between lugs 2 and 3? I've seen it mentioned both ways. Or doesn't it matter? Might depend on how you number the lugs. If lug 3 is the input, lug 2 is the wipe...