Does anyone have any info on Supro Delta king amps? I have just got hold of one with next to no output and what does come out is very broken up and distorted.
With no schematic, through elimination I've found that the pre amp section is fine but nothing from power amp. I have swapped the 6l6 but as I've got old ones they may be bad too of course but before ordering a new valve a few voltage and resistance checks seem in order to my mind. Pcb looks OK and main power resistors check out.
Does anyone have a schematic and or suggestions of what voltages I should be looking for around the power amp?
With no signal applied, check DC volts at pins 3,4,5, and 8 of the 6L6 power tubes.
Ok so i get the following:-
Pin 3 = 465V
Pin 4 = 463V
Pin 5 = 0.03V
Pin 8 = 71.8V
Seems like cathode biased and those numbers are ok.
edit: sorry, didn't realize this is a single power tube amp. The voltage at power tube pin 8 seems too high. Pin 8 should tie to a resistor, what is it's color code value and does it measure proper resistance?
Here is a Supro 1959 schematic.
Single ended 6V6.
So having checked pin 8 as G1 suggested there is a power resistor on the reverse of the pcb which was a PITA to get out of the chassis. Resistor is open circuit and brown and each end i guess thats the culprit. R52 is Green, Blue, Brown, Gold, Black. Which i interpret as 560R 5% correct? But what is black band and what wattage do I need?
Pic attached
https://photos.app.goo.gl/vxWLLWRX4Yaog8PH9
1 watt will do fine.
I will suggest a 5W resistor there. This is running a 6L6 with something around 450V supply. As it is a single ended power amp, it could be running the 6L6 up near 30W idle. At 70mA and 400V, that would be around 2.8W on the 560R cathode resistor.
I'm guessing it is a 3W that burned, and would use a 5W replacement.
Good call G1.
I was looking at the Supro 1959 schematic.
I did not see that the OP was running a 6L6.
I figured you must be thinking 6V6 :) and they do specify 1W on the schematic for the 6V6 circuit.
I have my doubts they are running the 6L6 at it's full 30W, but better to be safe, so 5W there will give some safety margin.