Transformer Orientation… yet again!

[M Fowler]

The wires on the volume pot either need to be reflowed because the solder is not good or the pot itself is bad.

To make a capacitor discharge tool you need a 220K or larger resistor attached between an aligator clip and a metal tip. You can use a plastic tube or wood. I used a Romex house wiring 12ga piece of copper soldered to a 470K 5w old resistor I had sitting around then other end of resistor soldered to wire with aligator clip this is housed in an round plastic tube so I don’t get shocked.

[beelzebum]

for the pot it sounds like the ground wire is loose if you are not able to turn the volume down, and for the cap discharge, i just use any resistor above about 200k. it just shorts from HT to ground. i dont worry about the shock factor, its mainly to protect the cap. if you discharge most caps to ground without the resistor you will damage the cap. the resistor just slows down how fast the cap can discharge. the best way to make the shorting probe is to just solder alligator clips to the end of the resistor, heat shrink the whole thing and then connect the alligator clips to your multimeter probes. set it for reading your HT voltage and take your reading. you will see the voltage on the cap drop. that way you know when the cap is fully discharged

[Robin]

A cold solder joint seems likely. Its also possible that the pot is bad, or that it was damaged when the ground was soldered to the case. I’ve seen pots damaged while trying to solder to the case with too low a wattage iron. The pot stays too hot for too long and the innards get damaged.

[Kier]

Do I need a resistor with a minimum wattage? As all I have is thousands of 1/4w metal film resistors to hand…

If I can use a 1/4w, I’ll re-flow all the joints and check it over, if not I’ll make a tiny order of 1 resistor and 1 new pot (just in case) lol!

Is it possible at all that when I bent the solder tab over to bring it closer to the pot casing, that the tab may have loosened from the carbon track some to make it intermittent as it is?

I had a play on it today and used an eraser wedged underneath the knob to apply the little pressure and all was sounding great! ha

[Robin]

Sounds like a bad pot, or it could be a cold solder joint.

I’ve never see a pot damaged by bending a lug (expect for breaking the lug off).

You don’t need to get real fancy with the cap discharge probe, a 1 watt resistor would do, in fact, if you unplug the amp, put a test lead (jumper wire) without a resistor from ground to the plate (pin 1) of V1 and turn the amp to the “on” position (be sure it’s unplugged from the mains), the caps will drain in about 20-30 secs. You can short the caps one by one to ground after that just to be extra sure that there is no energy left. I usually just clip a grounded test lead to a plastic handled screwdriver and touch all caps for a couple of seconds. I haven’t been bit yet (hey, did I just jinx myself?).

[Author]

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