Weird howl--Marshall

[Chuck H]

So this amp has never passed a guitar signal then? I promise that it couldn't have if wired that way. You're lucky the short wasn't in the other direction from pin 9 PI to 4/5 of V2 because that would have been blowing fuses (at best) or could have burnt your filament winding (at worst).

[The Dude]

I can't see how that's possible with an amp that "sounded like Angus". If your drawing is correct, you had a direct short across the heater winding of the PT. There should have been no heaters, no sound, and likely a blown fuse.

Edit: The above assumes heater starts from the left of your drawing. If the transformer comes in from the right, no shorts, but there wouldn't have been heater voltage to anything left of the PI and still no "Angus".

[Valvehead]

yes-----i just moved the wire from pin4/5....to pin 9 ..

dont ask.


and yes---the amp rocked yesterday---LOUD. i have not tried it tonight..its 1230pm.......and yes its still humming...with no pre tubes...and MV on 0 .

[Valvehead]

I can't see how that's possible with an amp that "sounded like Angus". If your drawing is correct, you had a direct short across the heater winding of the PT. There should have been no heaters, no sound, and likely a blown fuse.

Edit: The above assumes heater starts from the left of your drawing. If the transformer comes in from the right, no shorts, but there wouldn't have been heater voltage to anything left of the PI and still no "Angus".

yep======sounded great. see why im confused?

id post video....but all technology is failing right now....cant upload 4 second vid on here...cant upload vid on tinypic......frustrated---walking away tonight.

[g1]

Once you get your devices up and running again, some quality well lit pictures of the guts might help.

[Valvehead]

with it wired wrong as above , at the filaments....is it possible i hurt the windings in the PT ?? Amp has been on many times with it like that..didnt blow fuses...sounds great ...just the hum.......

i can order a 6.3vac filament trans to try that (un wiring the fil tap thats in there now )

[The Dude]

Very unlikely the transformer. Measure the VAC across filament winding and see.

[Chuck H]

I think there's been some error in the observation and reporting. Because the amp would not have worked wired as per the above diagram. In this light it's impossible to say if the transformer could have been damaged. Why are you un wiring it? I think you should just check to see that it's correct, correct it if it's not and take measurements to see that it's working properly.

[Valvehead]

Very unlikely the transformer. Measure the VAC across filament winding and see.

6.4vac

[Valvehead]

Havent found the problem----even tried a separate 6.3v filament trans ....went back through all the grounds...ALL the grounds .....im stumped.

heres the hum--amp is on about 4 on the mv .

https://www.youtube.com/watch?v=_M-KXEmVabI

[drewl]

The filament voltage is coming from the power tubes on the right, it "may" have worked with half the filament voltage on V1 and V2 when wired incorrectly.