Fender Super 60 ...little power on clean channel

[Doc Stitches]

I can only get low volume on clean channel....sound is good....new filter and tone caps.
I tried new preamp tubes ....no difference.
Changed power tubes....no difference.
Overdrive channel is OK.
Any ideas ??
Doc

[Enzo]

Since the other channel works OK, we would not suspect the power tubes.

If you already swapped preamp tubes, then the circuit has the p[roblem.


Go down the row of preamp tubes, check voltages at the plates, pin 1 and 6, of each tube. You want to see reasonable B+ readings. If any of the readings are the same as the B+ itself, then that triode is not conducting for whatever reason (or it is a cathode follower stage). Likewise look at all the cathodes. They should each have a small voltage related to tube current and cathode resistor. Cathode followers would have large voltages of course. I have not looked at the schematic yet. Zero volts on a cathode also indicates a triode not conducting. Non-conducting triode? Look first to see if the heater is running on both sides.

If the tubes are running OK, then apply a signal to the input, and trace it stage by stage through the channel.

[Jazz P Bass]

Non-conducting triode? Look first to see if the heater is running on both sides.
.

Good point, Enzo.
Had exactly that on a HR Deluxe.
One heater pin broke off at the socket.
So always check at the socket.

[g1]

How low is it? One of the original complaints with the design of this amp was that the clean channel was fairly weak compared to the OD channel. Seems to me it was pretty tough to get the clean channel to break up at all.
But it sounds like yours is more than a little weak. That era of Fender was somewhat prone to opto-coupler faults. Most of the tubes are shared between the two channels, so if OD channel is ok, it's less likely to be tube related.

super_60_rack.pdf

[g1]

Forgot to mention, check the screen resistors. A power tube not doing it's work will be far more noticeable on the clean channel. If you have to replace one, put it on the foil side, don't even think about trying to flip the board.
If it's the normal weak clean channel due to design issue, crank the mids.
For those who stumble across this thread looking for mods regarding the clean channel stock weakness, there are some interesting notes from the designer posted by kitchking on page 1 of this thread: Fender Super 60,112 & 210 Owners! - Telecaster Guitar Forum
Apparently some parts were hand selected for each amp due to variations in the opto couplers, tubes, and pots. This is probably why some have reported resistor values that don't match the schematic.
Also more detailed mods here: Fender Super 60 Mods - Telecaster Guitar Forum

[Gtr_tech]

+1 on the opto failures.....