Twin Reverb.... PT bad ?

[ThermionicScott]

Those voltages are kinda low for a '73. (340-0-340 and 63 on the schematic, not accounting for the rise in wall voltage since then.)
What does the filament winding read?

- Scott

[Doc Stitches]

So would those voltages cause it to blow fuses?

Filament reads 6.7

[ThermionicScott]

So would those voltages cause it to blow fuses?

Filament reads 6.7

Those HT voltages aren't making sense. For the full-wave rectifier in your amp, they should be 340ish, and if it were for the later UL amp, they would be more like 180ish (bridge rectifier).

I'm starting to lean toward the PT being bad. Perhaps there is an internal short that only blows the fuse when current is being drawn?

To the m-e-f brain trust -- if the impact caused one of the mounting bolts to contact the laminations, could that cause the transformer to lose efficiency and blow fuses? Perhaps removing the bolts and replacing the insulation could fix it.

- Scott

[Doc Stitches]

That is a good idea, Scott. Why didn't I think of that ? I'll follow that advice. Also I just rechecked the volts to bias....290 55 290...I will also put in new diodes in the bias section....are In5408 OK ?
I'll straighten out the chassis a re-solder all those joints......off to buy a 50 watt Weller...$$$

Doc

[Doc Stitches]

Hey Scott..........guess what ??? .......... I tested bolts to the copper plates/ribbons on the PT ( for continuity ) and yup.....there is lamentation damage

What would I use for insulation ? Should I go ahead and re-insulate top and bottom?

Jim

[Doc Stitches]

My mistake on continuity test ( just checked my 65 Bandmaster PT, as working model ).........but I will follow your advice on insulation issue.
Doc

[Doc Stitches]

While I have the PT transformer out of the chassis can I test the voltage with the bolts removed ?
Doc

[Doc Stitches]

73 Twin Reverb update......YES...

Just want to say thanks for all the great advice....The Twin LIVES... the Bias components had gone "south"....and they weren't coming back !

When I added 2 100v caps and all new diodes....BINGO......this thing sounds amazing.

Thanks again for all help
Doc.....................................I still don't understand why I am only getting a 190v reading on the 2 HT wires of the PT ??? What am I doing wrong ? I took it to an amp tech yesterday and he said it was fine....340 ish on both HTs. Yes I still confess to being a newbie

Doc

[52 Bill]

What sort of meter do you use? Some will not measure AC voltages very well.

[Doc Stitches]

Eclipse Pro's Kit and a Radio Shack....both digital

[Enzo]

Is your meter set for AC volts?

Plug the probes into a wall outlet, do you get roughly 120VAC there?

[Doc Stitches]

Hey Enzo....My meter is set to AC and wall outlet is 117V.

Black lead to chassis and Red to HTs on Bias board.....The PT is in the chassis.

Doc

[Enzo]

OK, so we know the meter is 100%.

Maybe I am not reading you right. But is your B+ voltage OK on the tubes? If so, I might think your odd reading is an artifact of the rectification.

[Doc Stitches]

Wow....duh.....I had the meter set on AC not DC .....( or maybe someone changed it when I wasn't looking )..............I think I have had my head inside this Twin tooooooooo long ??
B+ at Pin 3 is 409 DC and the HTs are 302..............the amp sounds great.
Would you recommend anything else ?

[Enzo]

If the amp is working, stop fixing it.