Epiphone Valve Jr repair question

[Gonzo1999]

Hello! A friend of mine has an old Epiphone Valve Jr that wasn’t working, so I offered to take a look at it.    I thought I’d identified the problem, but now I’m confused.  Here’s a quick description:

Symptoms: the heaters on neither of the tubes seem to getting any voltage.  Voltages elsewhere on the board seem to be ok (considering there is no tube draw).   If I pull off the primary transformer heater connections and measure them directly, the AC voltage reads in the ~6.5V range - so that seemed good.

Initial diagnosis: I first thought (maybe mistakenly) that the bridge rectifier or the rectifier filter cap could be the issue.  Replaced those both on the board but did not solve things.  I then decided to recreate the heater portion of the circuit off the board (using a new bridge rectifier and cap, as I bought 2 replacements each), but I’m not sure I understand the results.  I was expecting to measure 6.5V DC for the output of the rectifier (not connected back into the circuit yet), but instead measure about 0.6V DC. 

Does this make sense?  Any thoughts on what might be going on?   I must not be understanding something…

Thanks so much for anyone who has any ideas.

[sluckey]

I then decided to recreate the heater portion of the circuit off the board (using a new bridge rectifier and cap, as I bought 2 replacements each), but I’m not sure I understand the results.  I was expecting to measure 6.5V DC for the output of the rectifier (not connected back into the circuit yet), but instead measure about 0.6V DC. 

Was the only thing connected to the filament secondary your test bridge/cap?

[Gonzo1999]

Yes.

[rake]

Did you check C12 ?

[sluckey]

Connect a 47Ω resistor (and nothing else) across the filament winding. Measure the acv across the resistor. What have you?

The resistor will be dissipating .8W if winding is good. So best to use a 3W resistor. 1/2W will work for a couple seconds which should be long enough to get a voltage reading if meter is already hooked up.

[Gonzo1999]

Thanks so much for the responses.

Yeah, I replaced C12 on the board, and in my ‘off the board’ circuit I also used a new C12.
In both cases I see very little/no voltage after the rectifier bridge. 

I’ll give the resistor test a try and report back.  Thank you!!!

[Gonzo1999]

Closest I’ve got right now to 47 ohm is a 100 ohm 5W resistor.  Will I be ok with that?

[sluckey]

Closest I’ve got right now to 47 ohm is a 100 ohm 5W resistor.  Will I be ok with that?

Yes. Just want some kind of load. If voltage is still very low when connected to the resistor the transformer is bad.

[Gonzo1999]

Apologies, this is going to be a dumb question - but just to make sure I understand - place the resistor between the two ends of the filament winding and read ACv across the resistor, is that correct?

[sluckey]

yes

[Gonzo1999]

It does indeed seem to be the PT heater winding itself.  Voltage is essentially zero (0.03 ACV) when adding the resistor.  Thanks so much for the help, I would not have figured this out otherwise.

I guess this thing is probably not worth fixing at this point…?  Perhaps use the chassis for something better…

[bmccowan]

There are lots of options out there for that chassis. The Smokin Joe 1 thread from just a few days ago is a good example and there are several others on the Wattkins Forums - http://www.sewatt.com/vj-mods It should be fun.

[vintasonic]

If you want to replace the transformer, something like one of these would probably work, have to do some math to check current draw
P-T261C6   17.5   250V C.T. @ 45 ma   6.3V @ 1A
P-T261E6   29   250V C.T. @ 91 ma   6.3V @ 1A
P-T261G6   45   250V C.T. @ 130 ma   6.3V @ 2A
https://www.amplifiedparts.com/products/transformer-hammond-plate-filament-or-bias-63-v-auxiliary
-or-
https://www.amplifiedparts.com/products/transformer-power-120v-primary-325275v-63vct-5v-secondary-fender-champ
(ignoring the 5vac winding)