I'm in the finishing stage of my express build and but I only have 367 VDC on the plates. I saw an earlier thread where someone had the same issue. But the thread does not go into any details about how it was solved. Does anyone have any ideas/solution on how to get the ~400 VDC I should have
Data:
wall voltage is 120.9 VAC, PT is 300-0-300 from toneslut (heyboer). I measure 602 VAC at the secondary side of the PT (yellow wires). I measure 383 VDC at the other end of the 1N4007 diode pairs with it in standby. Goes to first two parallel 40uF filter caps (measured 47uF each) and then to the standby switch. Bleed resistors are 110K 2W in series and they are measuring a 183 voltage drop across each. The 220k bias feed resistor measures 219.6k. Bias is set at -30 VDC.
So far I have removed the bleed resistors and it stayed the same, I have changed the diode pairs of 1N4007s to a single 2N5408 and nothing changed. I make the bias more negative and voltage increases as it should, but -36 on the grids only gets me to 380 VDC on the plates.
This is just a guess but it looks like something is pulling the voltage down (all your numbers look good to me except your actual B+). I would measure voltages throughout the amp, write them all down, and compare to the 'correct' voltages if you can find them. Just think in terms of V=I*R for all your measurements. Your B+ voltage is too low so it appears that current is flowing somewhere that it shouldn't be or too much is current is flowing somewhere. As that current flows through a resistance it creates a voltage drop (V=I*R) so you should be able to spot it just from voltage measurements.
OK I checked all the voltages and in short (no pun) nothing seems out of the ordinary. Other than the somewhat low voltage that is. I'm not sure why I had measured only 367 before. I did change some pre-amp tubes back and forth.
B+1 381
B+2 365
B+3 290
B+4 274
B+5 258
Bias -30
screen current is 6 mA each. Total voltage drop across the 1K sag resistor is only 16 volts. Plate current is around 40 mA.
And all the pre-amp voltages at cathode are very close to the voltage chart I have for an Express. Should I just shut up and play my guitar. If it sounds good and nothing is glowing red except my ears from the volume then why bother??
My wall voltage varies from 120-126 depending on the time of day.