Output Transformers?

[Degajoe]

I finished recapping and modding a Fisher 460A amplifier for stand alone use. Before I fired it up I discovered one of the output transformers had an open leg. The output tubes are 6BQ5s and the transformer part # is T812-217. How do I go about finding a suitable replacement? Is there some way of testing my good transformer so I know what to order? There is a set on ebay, the add says NOS early 60s, quad 6BQ5/EL84 output transformers pair. How do I know if they will work? Any helpful advice is appreciated.

 

[s-petersen]

if you use anything but an original transformer, the feedback circuit will have to be retuned

 

[Brice]

You should ask Gary at TRS for a quote to rewind your OT. He does an excellent work.

 

[Degajoe]

Classic Tube Audio quoted $225 for a rewind.

 

[primosounds]

Classic Tube Audio quoted $225 for a rewind.

OUCH! that is a hefty price for such a little transformer. If you can not find another pair of stock outputs, it might be better to just get some Fisher or similar outputs and use those instead. It is easy to do static tests via a meter. Just measure the primary resistances to the center tap and each half should be very close. The other transformer should have similar measurements. On the secondary you would be just measuring the resistance between 0, 4, 8, 16 ohms or whatever the 460 has. The resistance reading between the 2 output trans should be similar. If you are concerned about the feedback, you could install a pot for the feedback resistor and adjust it to your taste or in combo with a scope find the right amount and put in a fixed resistor.

 

[larryderouin]

Dejajoe; The 460A is a variant of the original 440A 6BQ5 Amp from 1961. The 440A('61), 460A('62), and 490A('63) all use the 218-117 transformer (61 Custom electra to 63Custom Electra Consoles). The 481A is a 64 and no parts information is available although I would suspect it's just a re-numbered amp in the same family and uses many if not all the same parts as the 490A.

 

[s-petersen]

Sometimes the lead opens up at the joint of the wire to the lead and is reparable with minor surgery,something to look at if you are going to toss it anyway.

 

[Degajoe]

When I removed the cover there was a nice hole burnt through the paper exposing the toasted windings.

Thanks for the help gentlemen, an AK member has contacted me and has a suitable replacement.