Brownface Potentiometers

[strat100]

V7 pin 3 - 446v
pin 4 - 451v
pin 5 - -49.3v
pin 8 - 25.2mv
V8 pin 3 - 446.3v
pin 4 - 453v
pin 5 - -49.6v
pin 8 - 26.2mv
I also have 1k5 grid stoppers on pin 5 of the power tubes.
I also swapped the output transformer leads to no avail.

[martin manning]

With only 25 mA (assuming you have grounded the cathodes through 1 ohm resistors) your bias is very cold, only 11W. It should be more like 18W, Vpin3 x Vpin8.

[strat100]

Sorry Martin have got a pair of 6p3s-e tubes in not 6l6 i just use them for starting an amp up.

[martin manning]

I see. The 5881 on the schematic are 23W tubes anyway, so I should have suggested 14W dissipation. 6p3s-e are listed a 20W, so things look reasonable.

[strat100]

Changed tubes to JJ 6L6 and rebiased signal on pin 5 with grid stopper is fine but pin 3 is horrible loud and distorted and sounds out of tune is this looking like the output transformer?

[martin manning]

Could be. Do you have another one to sub in?

[strat100]

As it happens yes i do same transformer from same supplier
https://modulusamplification.com/f-styl ... 3295-p.asp
Will have to wait start my shift pattern tomorrow night.

[strat100]

Just tested the output transformer primaries resistance to the b+ winding 183 ohms on V7 and 88.2 ohms on V8 then tried both primaries to ground both read well over 1m and it just carried on going up, then tried 8 ohm tap to primaries 1m and still going. 8 ohm tap to ground 2.3ohms.

[martin manning]

That seems to indicate shorted primary turns. The resistances should be much closer than that.

[strat100]

Thats what i thought too ,brand new transformer too

[martin manning]

How does the other one measure?

[strat100]

more or less exactly the same

[martin manning]

It would be pretty strange to have two defective ones. You could try the "super secret transformer test" if you have a neon bulb: https://www.premierguitar.com/the-super ... mer-tester
Some discussion on that here: https://ampgarage.com/forum/viewtopic.php?f=6&t=35771

[strat100]

Thanks Martin will have a look when I get home from work tomorrow

[strat100]

Just tried the resistance between the blue( 183) and brown (88) and got 97 ohms, I wonder if the colours are the wrong way round. What's easiest way to find the correct b+ wire?