You should have some B+ voltage in standby, on the reservoir capacitor, and you should see that on one side of the standby switch. I want to know if the B+ voltage changes from standby to play with no tubes installed. The bias pot is working and you have negative voltage on the control grids. It won't have any effect on the B+ until you have tubes installed.
So I think that I was taking the B+ readings from the wrong capacitors. forgive me for being a noob. Which ones are the reservoir caps?
The reservoir is the capacitor fed by the rectifier. That voltage will be on one side of the standby switch, and it should remain high regardless of the standby switch position.
martin manning wrote: ↑Tue Apr 29, 2025 2:30 pm
Voltage goes up when you switch from standby to play? That isn't making sense to me. Are you measuring here?
Yes I have measure from there, 330vdc to 405vdc
I have noticed I think I have the Half winding wires the wrong way round on the Output tube, does this have polarity?
What to you mean by half winding wires? The blue and brown plate leads from the output transformer? They definitely have "polarity," you will have oscillation if they are swapped, but only if the power and PI tubes are installed. An oscillation will drag the B+ down, but you are supposed to be measuring without the tubes installed for now.
martin manning wrote: ↑Tue Apr 29, 2025 3:05 pm
What to you mean by half winding wires? The blue and brown plate leads from the output transformer? They definitely have "polarity," you will have oscillation if they are swapped, but only if the power and PI tubes are installed. An oscillation will drag the B+ down, but you are supposed to be measuring without the tubes installed for now.
I am the biggest silly billy here, THE FILTER CAPS WEREN'T GROUNDED!!!
I pulled out the ground leads through the PCB holes and they were cut when I did the rebuild, how silly of me! I have check all ground leads and it was just those two. arguable my most important ones!!
Now the readings are around 460-470vdc when in standby and play mode.
That's better. Check your bias voltage range again. If it looks good, i.e. you have something like -50 to -60V, set it to the lowest value (most negative), and put the tubes in.
martin manning wrote: ↑Tue Apr 29, 2025 4:08 pm
That's better. Check your bias voltage range again. If it looks good, i.e. you have something like -50 to -60V, set it to the lowest value (most negative), and put the tubes in.
Set to -50. Accidentally shorted the Cathode of V6 and it started making a humming noise. I will revisit this but looks like I’m on the right tracks… hopefully that humming does not persist when I power on again.
I’m not far off whacking it through my G12-65w Cabinet!
I’m really not trying to nag, but did you address the stereo jack sockets on the speaker and effects loop? I ask because you will start to damage the output transformer if you power it up with a short circuit, which I *believe* the first photo shows (I could be wrong).
timrobertson100 wrote: ↑Wed Apr 30, 2025 7:10 am
I’m really not trying to nag, but did you address the stereo jack sockets on the speaker and effects loop? I ask because you will start to damage the output transformer if you power it up with a short circuit, which I *believe* the first photo shows (I could be wrong).
Sir, I will never consider you nagging.
Yes I sorted that. Here’s a photo for you to check.
Does it matter what output jack I use for the dummy?
I’ll get more pics tonight as this is abit out of date. But I J hooked the connection. I think I’ll start using other wire next.
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Thanks. It's a bit grainy, but it looks like the speaker jack is plugged into a stereo socket - that's OK in itself, but please verify the wiring.
On all the sockets I've used, solder lugs are on the opposite side to the mechanical connection, like this:
Screenshot 2025-04-30 at 11.35.54.png
Please check if yours is like that - if so, you might find your black wire connects to the jack tip and ground, and the blue wire connects to the ring, which doesn't exist on the mono jack, thus also to ground.
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