Fender Super 60 RETURN + 4 Ohm Speaker jack replacement

[kka]

no, I did not experience a hot PT in that super 60 I serviced. Before you keep playing this amp I would strongly advice you to measure all secondary windings (AC voltages) to make sure the PT is not on the brink of shorting out or has already partially shortened out in which case it would get hot and the changed ratio could increase secondary voltages to the point that they cause damage to components before the main fuse would blow.

[brianino]

Thanks a lot .. I'm going to check the PT ... or could be a shortened condenser?

[pdf64]

'The power tubese 6l6 are very close to the transformer but I tried to remove them with a special circuit and it seems that heats the same'

What is the special circuit that you used to replace the 6L6s?
The main thing that affects how hot the power transformer gets (assuming that a component hasn't failed) is the static dissipation of the power tubes. It would be very beneficial to measure the static dissipation of each 6L6.

To do that follow the procedure described in Biasing, the section starting - 'The plate current can also be measured by first measuring the resistance across each side of the output transformer primary ...'.
It is very beneficial to fit a bias adjustment trimmer, as shown as optional in the schematic (R170 and 171) post #1, though a 10k trimmer (R171) seems to be more suitable that 5k, with R170 then being 4k7.
Pete.

[brianino]

hallo Pete,, first of all I'm sorry for my bad English .. but anyway..
The special circuit is an hand-made bias probe that you can see in the picture..
I put a 1 ohm resistor to the cathode pin,, and I implemented the biasing circuit with the 5k trimmer.. Then I have biased the 6l6 with 20 mA each one .. I think it's correct.
Well,, in the next days I'm going to check for the supplie voltages in the circuit,, but I'm beginning to suspect there is a fault somewhere..
tomorrw a friend of mine can land me a temperature gauge so I can have an accurate measure of PT temeperature ..
Thanks for the link you posted

Sandro

[brianino]

Hello,,
with no load (no load at Ht windings, no load 6,3v) the transformer temperature rise from 29° to 40° in less than one hour ..

[pdf64]

That may not be indication of a problem.
Check the temperature rise with normal loading, eg tubes in, no signal.
Pete

[brianino]

Yes, but the test I wrote was the third one..
The first was with the whole circuit working, with an input signal and a 8 ohm resistive load with about 40 W sinewave output 1Khz .. well after 30 minutes the transformer was so hot that I can't keep my hand on it because it was burning!!! but I Had not the temperature gauge.. after I have disconnected the ht transformer from the main board and I have load it with 2 15W lamps in series .. so the transformer was giving about 20 Watts and I checked the temperature and was similar the third test I wrote up ...
more ,, the first test was with the 6L6 in their sockets close to the transformer, the second and third was with the 6L6 in my hand-made probe,, not so close to the transformer ...

sandro