Hot Rod Deluxe troubleshooting advice needed

[Oldmactech]

Bought a troubled Hot Rod Deluxe awhile back to try to learn a little about amp repair in my spare time. Seems previous owner had tried some sketchy repairs so I’m already behind.

I did a Fromel kit repair and replaced the caps and the 5 watt resistor. Ended up exposing traces at the resistors as the previous guy destroyed some pads. The 2 Zener diodes looked suspect to I replaced them also.

Now I getting the following:

Clean channel is ok, all controls-reverb, tone etc function. Haven’t tried full volume yet.
Channel switching non-functioning. Channel switch light blinks but does not go to red.

Oddly, power tubes are not glowing like normal. Checked Voltages from filter caps and there are in the mid 200’s not the 440’s as supposed to be (not looking at schematic or a DMM so approximate)

Voltage at the 5w resistors is -16.55/+16.55 (supposed to be -16/+16.

Any advice to starting troubleshooting?

Thanks.

[The Dude]

Low B+: I'm thinking you might be missing a ground. Did you remember the green ground wire by the input jacks? Or maybe something else disconnected or loose.
On the low voltage supplies: 16.5 is plenty close enough. Nothing to worry about.

[Jon Snell]

The question is, was it not switching before you replaced these components.
If that was the case then check the work before you replaced the components otherwise, check your work.
Low HT could be a bad connection, it could be a capacitor in the wrong way around, it could be a diode with a bad connection to the first filter capacitor. Etc, etc etc.

[Mick Bailey]

Also, check the heater supply to make sure it's OK (nominal 6.3v).

[Oldmactech]

Jon Snell- was not switching before I replaced the caps. Caps are installed correctly but I will re check the continuity.Thanks for the diode suggestion.

Mick Bailey- a bit of a novice here, a hint on how to test the heater supply voltage would be appreciated. (I’ll be trying to figure it out from the schematic also)

[glebert]

Word of advice, if you are going to do amp repair get a DMM, even a modestly priced one and get comfortable measuring AC and DC voltages. And always think about safety first, I will usually wear rubber gloves or keep one hand behind my back.

[Oldmactech]

Thanks for the advice. I do have a DMM and have done a good bit of voltage testing but you can never be too careful and the rubber gloves idea is solid.

[Mick Bailey]

Check the heater voltage at the pilot light - set your meter to AC volts and take a reading across the terminals of the bulb holder.

EDIT: the reason for checking the heater voltage is because the power tubes are not glowing like normal. It also helps to cross-reference the the low HT - a low heater voltage as well as low HT points to a transformer wiring issue.

[Oldmactech]

Reading 4.56 at the bulb holder. Jumped around for a few moments settled at that.

[Mick Bailey]

That's too low, though be sure to scratch through any oxide coating with your probes to get a good reading. These amps often read on the high side - sometimes towards 7v or more. Did you unplug the power transformer leads when you worked on the amp? If so, take a look a the table on the schematic and make sure your wiring corresponds according to your local mains voltage.

Just to double-check, remove the tubes and check the heater voltage again, just in case one or more tubes is pulling the voltage down. Unlikely, but not impossible.

[tdlunsfo]

Just to confirm, you don't have the amp on a dim bulb do you?

[Oldmactech]

Yes, it is on a dim bulb circuit. Maybe why the voltage is low?

[g1]

Yes, that is why the voltages are low. If it's not blowing fuses you don't need to be running it on the bulb.
Plug it in to the wall and redo any voltage measurements.
If you haven't tried it without the bulb, that may even be why the switching didn't work.

[Oldmactech]

Thanks.
The switching didn’t work before the limiter but I retouched some solder and replaced the Zener diodes so might be good now….