What resistance do you get between A1 and A2?
Finished Crack build, need help with low voltages [resolved]
- Thread starter timindq
- Start date
This sure is an odd one. Can you measure the resistance of the 22.1K resistor across terminals 4 and 5? You should be able to do this with it soldered into the circuit (with the amp off of course).
Either the 22.1K resistor is open, or there's some bizarre short in the circuit that I can't see that's pulling the voltage at T5 down.
-PB
Either the 22.1K resistor is open, or there's some bizarre short in the circuit that I can't see that's pulling the voltage at T5 down.
-PB
Good morning,
The resistance across t4 and 5 measures 22.1k. I also measured the resistance from t5 to ground with the 12AU7 in place; this measured similarly to the A1 to A2, as if a cap is in circuit.
After work today I will recheck all wiring and see if I made a mistake somewhere that I missed the first time I checked.
Thanks again.
The resistance across t4 and 5 measures 22.1k. I also measured the resistance from t5 to ground with the 12AU7 in place; this measured similarly to the A1 to A2, as if a cap is in circuit.
After work today I will recheck all wiring and see if I made a mistake somewhere that I missed the first time I checked.
Thanks again.
You should be able to measure from T5 to ground without too much fuss, is it the same as T1 to ground?
I borrowed a better meter and performed resistance checks. T1 to ground and t5 to ground are basically the same starting at 30k and going up until I remove the leads. If I reverse the leads the circuit reads short. If I leave the reversed leads on points the the resistance will eventually climb as before leads were reversed.
Man I wish I had an analog meter.
Man I wish I had an analog meter.
Last night I did a thorough visual check of the wiring on my Crack. I see no discrepancies. Have to admit it is a easier now that I'm familiar with the thing.
After checking and measuring voltages again I decided to resolder the 22.1K resistor at t4 and t5. Voltages remained the same after touch up. T4 224VDC and T5 8VDC.
Wish there was one of those head scratching emoticons.
After checking and measuring voltages again I decided to resolder the 22.1K resistor at t4 and t5. Voltages remained the same after touch up. T4 224VDC and T5 8VDC.
Wish there was one of those head scratching emoticons.
Try putting the resistor back in. I believe the resistor may not have been properly installed, and wasn't allowing half the 12AU7 to conduct.
-PB
-PB
Reinstalled the resistor and measured 22.2k ohms from B5 to A1. I used these points to ensure I wasn't moving any part of the resistor's connection. I then measured voltage at T5 and it was 9VDC. This measurement was with the 12AU7 in place and without the 6080 installed.
Voltage at T1 is 90VDC. The other side of tube seems to be working fine.
Tim
Voltage at T1 is 90VDC. The other side of tube seems to be working fine.
Tim
Just to be thorough, try swapping the 22K resistors.
Also, with no tubes installed, what DC voltages do you get at:
Terminal 21
Terminal 2
-PB
Also, with no tubes installed, what DC voltages do you get at:
Terminal 21
Terminal 2
-PB
Hmm, OK, those voltages indicate 11mA of current draw with no tubes installed. I bet if you remove the 22.1K resistor between 4 and 5, you'll discover that your voltage at T2 will pop up a bit.
I'm still suspecting a short around the socket. It may be debris in there, look for something touching A1 that shouldn't.
-PB
I'm still suspecting a short around the socket. It may be debris in there, look for something touching A1 that shouldn't.
-PB
Swapping the resistors did not help. But I read your last response and went back and checked the tube sockets. I saw no issues but did wiggle them about and blew some air at them.
I then checked voltages and no longer had the drain at T5!!!
I plugged in the 12AU7 and both LEDs lit!!!
I'm going to give the tube sockets a thorough cleaning and try it out.
Another plus: with all this turning on and off and measuring voltage and resistance, I have yet to shock myself!
Thanks for the help and please let me know if there is something I should do before proceeding.
I then checked voltages and no longer had the drain at T5!!!
I plugged in the 12AU7 and both LEDs lit!!!
I'm going to give the tube sockets a thorough cleaning and try it out.
Another plus: with all this turning on and off and measuring voltage and resistance, I have yet to shock myself!
Thanks for the help and please let me know if there is something I should do before proceeding.
Yeah, we may never know what was stuck in there, but I'm glad the drain is gone. The sockets are two pieces of ceramic that are riveted together, and it's possible that something worked its way in there.
In any event, if all your voltages look good, go ahead and give it a listen!
-PB
In any event, if all your voltages look good, go ahead and give it a listen!
-PB
IT SOUNDS WONDERFUL!!!
Seriously, no hiss, no hum, k.d. lang never sounded so good. With the music on pause I maxed the volume and still heard nothing but silence.
Thanks again for your help Paul. You can relax for a little while as I'm going to listen like this for a couple weeks before building the Speedball...We'll see how patient I am.
Seriously, no hiss, no hum, k.d. lang never sounded so good. With the music on pause I maxed the volume and still heard nothing but silence.
Thanks again for your help Paul. You can relax for a little while as I'm going to listen like this for a couple weeks before building the Speedball...We'll see how patient I am.
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