"N_Cook" wrote in message
...
Hum particularly on clean channel builds up from nothing ,over half an
hour,
and very intrusive 0.3V rms of hum over 8R speaker load and still rising.
Putting a signal in Return, for PA only, is fine but opening guitar input
hum returns.
Owner had replaced all the valves and exactly the same hum.
Hum is negligible on the downstream HTs from HT1. What sort of grounding
problem increases with warmth?
I've not started exploring the low voltage electros around V1 yet, I'm
letting the amp cool down





Couple of other tips on the DSL and TSL amps:

Resolder (and preferably reinforce with wire) the DIN footswitch socket. It
is only held in place by the solder joints which often (always) fail in
regular use.

The back panel PCB mounted mains and HT fuseholders also tend to suffer from
dry joints. Whip off the PCB and resolder them. 3 minutes tops.

The 16 ohm speaker output is a switched socket that disables the 4 and 8 ohm
sockets when used. These often get damaged, becoming a problem when the
other sockets are used instead. Check, repair or replace.

The speaker ohmage selector switch also tends to suffer from dry joints.

(Either of the above 2 problems can destroy the output TX, output valves and
other stuff, so best do it)

The output mute switch is stupidly relying on the switch contact to feed the
signal to the power amp, rather than being a mute. Clean it.




Gareth.