Bad Marshall 2210 PT

[drewl]

Well, that's a shame.
Customer said amp is blowing mains fuse, threw it on a limiter and the bulb is flickering like crazy.

Disconnected secondaries, still flickering.

The 220 and 240 volt windings are good though.

Just 120 breaking down.

[J M Fahey]

Well, that's a shame.
Customer said amp is blowing mains fuse, threw it on a limiter and the bulb is flickering like crazy.

Disconnected secondaries, still flickering.

The 220 and 240 volt windings are good though.

Just 120 breaking down.

What do you men by that?

You connect 220/240V mains to same rating primaries and amplifier or at least the transformer works properly?

Then no secondary is shorted, since magnetically they are all in parallel: one shorts all show (AC) shorts.

[Jazz P Bass]

https://www.tubesandmore.com/product...nt-power-100-w

$80.00

[drewl]

When you turn the voltage selector to 220v or 240v the amp fires up (as much as it can)
So those primary windings seem okay, the 120v - not so much.

That's what I mean.

[Jazz P Bass]

I am not a transformer winding expert but I am having a hard time seeing the failure mode.

[Pedro Vecino]

When you turn the voltage selector to 220v or 240v the amp fires up (as much as it can)
So those primary windings seem okay, the 120v - not so much.

That's what I mean.

Adjusting the amplifier to 240V but connecting it to 120V, I imagine.
If so, maybe using the 120 tap as 0V and the 240 as 120V tap would work?
The short is supposed to be in the other half...

[drewl]

Yes, running 120v into the 220 or 240v taps the amp powers up, just for testing purposes with no output tubes installed.

I suppose I could try what Pedro suggested, just to test it as I wouldn't have faith in the other PT windings since the 120 failed.

[Jazz P Bass]

There must be a soldered wire that goes to each 120/220/240 tap.
So the failure is most likely at the 120 joint.

trying the 120 as 0 may prove that out.

[Helmholtz]

Adjusting the amplifier to 240V but connecting it to 120V, I imagine.
If so, maybe using the 120 tap as 0V and the 240 as 120V tap would work?
The short is supposed to be in the other half...

If there is a short in one half of the primary, it will make the other half act as an AC short as well because of transformer coupling.

[J M Fahey]

When you turn the voltage selector to 220v or 240v the amp fires up (as much as it can)
So those primary windings seem okay, the 120v - not so much.

That's what I mean.

As said before, "one shorted winding ... any of them ... a shorted transformer"

So if on winding seems to work fine ... no shorts there.
And you are ignoring the voltage selector switch and associated wiring ... why?

[drewl]

What do you mean ignore?

FYI, I disconnected the PT from everything to rule out any other possibilities.

[Randall]

Easy enough to employ RG Keen's neon transformer test.

https://www.premierguitar.com/articl...ormer-tester-1

[drewl]

Yeah, one of these days I'll build that.

I built light bulb limiters for home, work and for my son.

[J M Fahey]

What do you mean ignore?

Well, on post #4 you mention

When you turn the voltage selector to 220v or 240v the amp fires up (as much as it can)
So those primary windings seem okay, the 120v - not so much.

so thatīs used to connect windings, so itīs legitimete to ask whether you checked it.
A poor voltage selector contact is one main suspect if trouble reports "flickering" on one winding but not another.
Ignoring it means you do not report testing this important suspect.

FYI, I disconnected the PT from everything to rule out any other possibilities.

Nice fresh news , received much later, not mentioned before.

In any case, even if directly used, 120V tap junction may very well poorly soldered or corroded inside the transformer, which does not mean the winding is bad.

Maybe itīs buried in the winding and so unreachable, but on many transformerfs the enamelled wire is brought outside and soldered to outside leading wire, often means you can reach that point just by carefully slitting varnish impregnated fish paper and exposing those joints.

You might give it a try and save $80+freight+wait time.

[drewl]

Yup, fixed several tranny's over the years that just had a bad connection or blown thermal fuse.