I fixed the problem with the humming (thanks for the help), but after about 30 mintues. The amp just died. A bit fed up with my inability to get the speedball working properly, I removed it and reverted it to stock again. Now, nothing is working. I am getting no voltage readings from anything except T. 21 which is within spec at 218. Both of the diodes were still fine until I was checking the (lack) of voltage in the input socket. The diode at A8 lit up for a few seconds and after that, the diode at A3 had blown. The power tube is still lit up however. Perhaps I should buy a new kit and start over.
If it isn't one thing...
- Thread starter moviedave
- Start date
If you get no voltage readings for anything except T21, then the 270 Ohm resistor leaving T21 is loose and not making contact (or the black wire that runs with it).
-PB
-PB
Those are both essentially zero. How is the fuse?
If you pull the fuse out, you can measure the resistance across the fuse. If your meter has a setting to beep for continuity, this is a good setting to use to be sure it's still in-tact.
After that, start with the AC voltages at the power transformer with the Crack plugged in and the power switch on.
Between power transformer terminals 1 and 2, you should see 110-125V (meter set to AC volts, black probe on T1, red probe on T2).
Between power transformer terminals 4 and 5, you should see 6.3V (meter set to AC volts, black probe to T4, red probe to T6).
Between power transformer terminals 6 and 7, you should see 150V (meter set to AC volts, black probe to T6, red probe to T7), repeat for 9 and 10. (These may be higher since I don't believe your amp is drawing current through this winding.
Let us know if all those check out.
-PB
After that, start with the AC voltages at the power transformer with the Crack plugged in and the power switch on.
Between power transformer terminals 1 and 2, you should see 110-125V (meter set to AC volts, black probe on T1, red probe on T2).
Between power transformer terminals 4 and 5, you should see 6.3V (meter set to AC volts, black probe to T4, red probe to T6).
Between power transformer terminals 6 and 7, you should see 150V (meter set to AC volts, black probe to T6, red probe to T7), repeat for 9 and 10. (These may be higher since I don't believe your amp is drawing current through this winding.
Let us know if all those check out.
-PB
Ok, so power is getting to the power transformer, and the transformer is doing it's job.
Next you will want to check the ground buss, and to do this set your meter to DC resistance and clip the black lead to terminal 20, then probe 14, 12, the sleeve of the headphone jack, and terminal 3.
If all of these are approximately zero, then go ahead an power back up and check the voltages of the unstriped terminal of each capacitor: 21, 13, 15. If you have no tubes in the amp, all these voltages will be about the same, if you have tubes plugged in, they will each be a little different.
-PB
Next you will want to check the ground buss, and to do this set your meter to DC resistance and clip the black lead to terminal 20, then probe 14, 12, the sleeve of the headphone jack, and terminal 3.
If all of these are approximately zero, then go ahead an power back up and check the voltages of the unstriped terminal of each capacitor: 21, 13, 15. If you have no tubes in the amp, all these voltages will be about the same, if you have tubes plugged in, they will each be a little different.
-PB
Noob moment, butI'm not sure what you mean by sleeve of the headphone jack. The bottom metal part measured zero, the two upper (metal things that hold the headphone in place) all measured 2.5k since they are connected to the resistor. Everything else measured zero resistance.
For the voltage readings, they are all zero.
For the voltage readings, they are all zero.
What are the voltages on the unstriped sides?
OK, this is helpful, you have narrowed down where the problem must be.
You have AC voltage at the power transformer, and now I would double check that you get ~160V AC between terminals 18 and 19.
We would then immediately expect to see 160-200V DC between terminals 20 and 21, but you reported that this is 0V.
To ensure that there isn't a short downstream of the power supply that is drawing the rail down, temporarily remove the red wire that leaves 13U and attaches to the 8 pin socket, then retest the power supply. If it is still 0, I would suspect a short in the diode wiring, and you could verify this by measuring the resistance between 20 and 21, or by looking for diode leads that shouldn't be touching (if the legs to the same terminal, they can touch, if they don't, they will short circuit your high voltage supply).
-PB
You have AC voltage at the power transformer, and now I would double check that you get ~160V AC between terminals 18 and 19.
We would then immediately expect to see 160-200V DC between terminals 20 and 21, but you reported that this is 0V.
To ensure that there isn't a short downstream of the power supply that is drawing the rail down, temporarily remove the red wire that leaves 13U and attaches to the 8 pin socket, then retest the power supply. If it is still 0, I would suspect a short in the diode wiring, and you could verify this by measuring the resistance between 20 and 21, or by looking for diode leads that shouldn't be touching (if the legs to the same terminal, they can touch, if they don't, they will short circuit your high voltage supply).
-PB
If terminals 1 and 2 are only at 6.4V, then you may have a loose wire or melted switch that is not letting the full 120V through.
-PB
-PB
