KEL34 refurbishing issue

[goonybird]

Finally refurbed my KEL 34 and it fired up first time.
Work done: rewired Heaters, Replaced all Caps and larger resistors, and anode resistor mod to 2w as recommended.
apart from the 6x Poly Caps and smaller wattage resistors.

All voltages check out ok and sounds fine.
except!

after a few minutes the left channel level drops slightly, but seems to be mainly bass levels.
Sometimes comes back then goes again.

Have swapped over all valves and still occurs.
Replaced the 6 polyproprylene caps with new components (vishay) and thought that had cured it, but on soak testing it came back after about 2 hours
So only Small resistors left as all checked ok. Checked for Dry joints which I was careful to avoid on rebuild.

I do get some low level "Sch" "rustling" sound

The obvious stage is to replace small resistors, unless I have a faulty replaced one? Anode resistor?

I am suspecting a resistor due to the noise, and might try a freezer spray as seems heat related.

But any suggestions in case I am missing the obvious.?

Thank you in advance.

[Richard]

It sounds heat-related doesn't it. Have you checked/cleaned/resoldered/replaced the valve sockets? They are all on the pcb and may have oxidised or the solder joints fractured after many heat cycles. On mine the small 7 and 9 pin ones were sensitive to dirty valve pins causing rustling. A glass fibre pencil is useful to clean valve pins. If replacing the sockets fit an old valve into the socket to set the pins alignment before soldering the pins to the pcb

[goonybird]

Originally Posted by Richard

It sounds heat-related doesn't it. Have you checked/cleaned/resoldered/replaced the valve sockets? They are all on the pcb and may have oxidised or the solder joints fractured after many heat cycles. On mine the small 7 and 9 pin ones were sensitive to dirty valve pins causing rustling. A glass fibre pencil is useful to clean valve pins. If replacing the sockets fit an old valve into the socket to set the pins alignment before soldering the pins to the pcb

Thanks Yes resoldered all connections including Valve pins. I do have a suspicious thing with heater top One of the El34 left Valves and ned to check solder on heater wired at that socket. One new valve kept losing heater. but is intermittant at best, have some odd NOS ones around. Although fault occurred with replacement valve with good heater.

[goonybird]

I could make the fault occur by putting a meter on C8 which Is why I just replace all the Poly caps. So resoldered again valve pins to V5 especially Anode A1 as well as surrounding components.
Seems to have sorted it. Seems the pins maybe a bit short on the ECC82 sockets?

Trouble now is bought a new AV amp and not easy to connect external amps for Stereo Front L&R so might have to sell it on.