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Post subject: 64 bassman transformer question
Posted: Wed Feb 04, 2015 5:04 pm
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i brought my bassman slowly over 3 hours up with a variac. then, i switched the standby, plugged in the guitar and played for about 10minutes. it sounded really good, then a puff of smoke came out the back and i quickly turned it off.

even tho the variac says 120v, i believe it goes higher.
i'm enclosing a picture showing the green wire to ground.

what would you recommend? could i reattach it to the variac and bring it up slowly again?

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thanks,
mikeB.


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Post subject: Re: 64 bassman transformer question
Posted: Wed Feb 04, 2015 5:41 pm
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MikeB wrote:
i brought my bassman slowly over 3 hours up with a variac. then, i switched the standby, plugged in the guitar and played for about 10minutes. it sounded really good, then a puff of smoke came out the back and i quickly turned it off.

even tho the variac says 120v, i believe it goes higher.
i'm enclosing a picture showing the green wire to ground.

what would you recommend? could i reattach it to the variac and bring it up slowly again?

thanks,
mikeB.


That is a serious short, maybe inside the windings.

It's time to pull the tranny and have it professionally tested.

My guess is it's blown and needs rebuilding or replacement. Trying to crank it up again could well damage other sections of the Amp.

The good news is that there are transformer restorers out there that can rebuild it such as Mercury Vintage, a Div. of Mercury Magnetics and Hammond Manufacturing. There are probably many others too.

But from the looks of it, that thing right now is just a Firestarter. :shock:

Good Luck !

cheers

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Post subject: Re: 64 bassman transformer question
Posted: Wed Feb 04, 2015 5:57 pm
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Mike,

The green-yellow wire is the center tap of the heater secondary wiring. The heater wiring draws the most current of all secondary wires of the power transformer. You cannot use the amp until you find out the source of the excess draw.

The first thing to check is the fuse. My bet is that the fuse is not the correct amperage. After that, look very carefully at the twisted green wires coming off the power lamp. There maybe a worn insulation somewhere along the line. The twisted pair stretch from the lamp, all the way down to the input 12AX7's (Input). Use a DVM set to DC-Ohm resistance to look for shorts. Amp off, power wire pulled from outlet. Main power caps drained.

Pull all tubes AND power lamp. Check green line to green line for shorts. And each green line to chassis for shorts.

Next thing would be to test all tubes for shorts. Do you have access to a tube tester? Esp those 6L6GC's. Shorts in the heater portion to plate of those tubes can cause fuses to pop.

Last thing. Check the power tranny and check for shorts in the primary and secondary. Pull the wiring from the circuit and do continuity checks. Esp shorts from windings to ground (metal case of PT).


Good luck! Keep us informed.


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Post subject: Re: 64 bassman transformer question
Posted: Wed Feb 04, 2015 6:34 pm
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BMW2002Ti wrote:
Mike,

The green-yellow wire is the center tap of the heater secondary wiring. The heater wiring draws the most current of all secondary wires of the power transformer. You cannot use the amp until you find out the source of the excess draw.

The first thing to check is the fuse. My bet is that the fuse is not the correct amperage. After that, look very carefully at the twisted green wires coming off the power lamp. There maybe a worn insulation somewhere along the line. The twisted pair stretch from the lamp, all the way down to the input 12AX7's (Input). Use a DVM set to DC-Ohm resistance to look for shorts. Amp off, power wire pulled from outlet. Main power caps drained.

Pull all tubes AND power lamp. Check green line to green line for shorts. And each green line to chassis for shorts.

Next thing would be to test all tubes for shorts. Do you have access to a tube tester? Esp those 6L6GC's. Shorts in the heater portion to plate of those tubes can cause fuses to pop.

Last thing. Check the power tranny and check for shorts in the primary and secondary. Pull the wiring from the circuit and do continuity checks. Esp shorts from windings to ground (metal case of PT).


Good luck! Keep us informed.


i did check the fuse to make sure it was ok, and it is a 2amp.
yes, i can test the tubes. it is an old knight tester but it should show me that the tubes are ok. i could also put them in another amp to check.

thanks for the info. i'll let you know.
mikeB.


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Post subject: Re: 64 bassman transformer question
Posted: Wed Feb 04, 2015 6:59 pm
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Check all heater lines. Look behind the power lamp for signs of shorts in the holder's connection. Is there a small paper circuit board between the lamp holder's arm and the chassis?

You'll need to pull and check the power tranny. Check the heater windings for shorts. Check the high voltage line for shorts.


Good luck!


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