1965 Supro

[Doc Stitches]

I do not know if there is only one HV wire going up from power chassis as there is only the 8 pin coupling plug. Do I need to test all pins of that plug with amp on ? Tubes out or in for test. If so, when ? Now or after I have replaced the multi cap can and the power filter cap ?
I have rebuilt a multi cap can on a Vibro Champ, so I am sure I could do that on this amp but would rather just buy a new cap can from Tubes and More. They have a 450v 20, 10, 10, 10 for $36 bucks. I'll order the parts and resume the testing.
I have a 64 Deluxe Reverb that I replaced all caps and resistors on, the Vibro Champ ( cap can rebuild ) and a Champ. I am not to sure about "marring" 2 amps for test purposes. Good idea, though. Time is on my side and I am in no hurry on this Supro. Without a schematic/layout it'll get done when it gets done.

[The Dude]

It shouldn't be too hard to trace out that connector and see what's going on.

(Guessing) There will be a couple of filament wires, probably 2 wires for the power switch, ground, B+, signal feeding amp. That's 7 pins. Maybe another ground? Maybe one pin is unused. Maybe I forgot something. At any rate, the connections should be fairly obvious. Draw yourself a little diagram and get to labeling.

[Doc Stitches]

Is 475v multi cap instead of 450v good enough ?

[The Dude]

Yes. In that case more is better.

[nevetslab]

From the new photos you've posted, we can see there are only six wires on the Octal plug cable, being 2 wires for the heaters, 2 wires for the AC Mains switch, Ground and V+ to run the preamp tubes. The push-pull wires for the power tubes can be seen (Brn/Wht and Red) running to the right-most connector attached behind the octal socket on the amp chassis. Not sure what the left 2-pin connector is. If you don't have a signal cable from the preamp plugged into that right connector, that's why there's no signal.

Looking at the power tube socket wiring, I see the heater wiring using Blue and Blu-Wht on pins 2 & 7. Pin 8 is tied together with teh Grn wire, and has a 220 ohm power resistor connected to Gnd, so this is a Cathode-biased output stage. I see Brn and Blu cloth-covered wires from the primary of the Output Xfm primary, and the left tube socket uses pin 1 as a tie pint for the Center-tap of the O/T Center-tap. It comes from the rectifier tube at pin 8, with the 1st stage filter for this by way of the blue wire connected to the cap can. Then, we see a 350 ohm power resistor from that filter stage to the axial leaded power supply filter, having a date code of 6518. That dates this part as 18th week of 1965. So, you'll want to replace that cap as well as the plastic bodied Mallory electrolytic caps up in the preamp, and any other electrolytic caps we're not seeing. You'll see similar date code on the cap can, and I'd guess the amp was manufactured in mid-late 1965, maybe 1966.

Not sure where the screens tie in..I do see them tied with an orange wire on pins 4, with a YEL wire that disappears under that axial power supply cap.

On the replacement caps, the lower voltage parts (probably cathode bypass), you can go with higher voltage ratings with similar capacitance values, as today's caps are much smaller, and the higher voltage raging parts are more linear/better. With the power supply filters, same or higher voltage ratings.

Where you had a plate voltage above 420VDC, I'd look at the decoupling resistors in the power supply filter string, or perhaps the plate resistor on that stage, as that voltage is too high.

So, we now know a lot more than we did. Forward progress.

[52 Bill]

Where you had a plate voltage above 420VDC, I'd look at the decoupling resistors in the power supply filter string, or perhaps the plate resistor on that stage, as that voltage is too high.

I'd also check to see what the voltage at pin 3 is on that tube. The high plate voltage could also be sign that the tube is not conducting.

[Doc Stitches]

Thanks for all the helpful details.

Just ordered all parts from AES

I'll do what I can 'til parts arrive.

Doc