Oh yes...ANOTHER Tsl Marshall!

[Valvehead]

Ok , found another problem part. the BR62 rectifier looks to be bad. No heater voltage at V3 / V4

i have a NTE 53000 here that should work , will try that tonight

[The Dude]

If you change that rectifier, let it stand off the board a bit (unlike the way Marshall does it) to help keep heat away from the board and solder joints.

[Valvehead]

will do sir !

[Valvehead]

Man.....this thing just keeps on giving......

replaced the bridge rect.
now i have 3.5vac on the heaters on all tubes.....except V1/V2 ! measuring v1/v2 my meter just jumps around.

im pretty damn sure i have the rect in there correct , + to + . Maybe this NTE rect isnt correct?

i need to order parts tonight , so i will get a correct rect. and might as well replace those 10uf caps right next to it while i have the board pulled out for the 75th time .

everything else looks ok voltage wise except the low bias

[Enzo]

That you have 3vAC on the heaters tells me you are measuring to ground. What matters is the voltage ACROSS each heater, not to ground. 3vAC on each end usually means 6vAC across the thing, but only if the heaters are ground referenced by a center tap.

But V1/2 run on the rectified 6vDC supply, and that is NOT referenced to ground Measure from pins4//5 to pin 9 and see if you don;t have about 6vDC. And an even simpler test: are those tube heaters lighting up? If they light up, then whatever your readings might look like, the tubes are getting heater power.

Using ground as a reference you are reading a combination of half the AC plus a portion of the rectified voltage.

ground is real handy and often readings are taken with respect to it. But it matters what we are trying to measure. Context matters. If you measure the top of my head to the floor, you get about 5'9", my height. Unless I am standing on a box, or lying down on a sofa. In those cases I might seem to be 8 feet tall or perhaps 2 feet tall. Yet, end to end I still measure 5'9".

[Valvehead]

yes Enzo-- those ac readings were from pin 9 to 4/5 on the pre tubes , and 2 and 7 on the powers. I didnt measure to ground.

v1/v2 heaters are not lighting up---the rest are

[g1]

Check for damaged tracks at the rectifier.
Measuring at the rectifier pins you should have AC voltage at the 2 input pins, and DC voltage at the 2 output pins.

[Valvehead]

I cant see a way to do that with the amp together and running , the rect is buried

[Enzo]

Expose the board and apply 6vAC ONLY to the appropriate pins. Tubes removed. You can use the transformer in the unit if you disconnect the other secondaries, or use 6v from some other transformer yo have. Then you can trace voltage with the board out.

[Valvehead]

Expose the board and apply 6vAC ONLY to the appropriate pins. Tubes removed. You can use the transformer in the unit if you disconnect the other secondaries, or use 6v from some other transformer yo have. Then you can trace voltage with the board out.

Enzo--i pulled the board to try this tonight. the pcb is out and i find that at the PT , i only have 3.7 vac at the heater tap . Thats with no other secondary load at all---heater wires not hooked up

[Leo_Gnardo]

Enzo--i pulled the board to try this tonight. the pcb is out and i find that at the PT , i only have 3.7 vac at the heater tap . Thats with no other secondary load at all---heater wires not hooked up

If I'm not mistook this amp has no fil. winding center tap. So 3.7V from the fil. winding means defective power transformer.

Had a thought, maybe it's set up for 240VAC operation, but you reported earlier you had 520V B+ so that ain't it. Bad PT.... rats!

[g1]

Can you check your meter, or try another? And make sure you still have 120V right at the primary.
I don't know how some of the tubes would light up under such a low voltage?

v1/v2 heaters are not lighting up---the rest are

[g1]

And there are also 4 heater fuses to check, F1 through F4, if you have not yet pulled them and checked with meter.

[Valvehead]

verified with another meter.....should be dang near 7 vac there yes ?

all fuses test ok G1

[g1]

Yes, if you are also measuring the proper voltage at the primary. Be sure to check it right at the primary leads.