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Time to Replace Power Transformer in Magnavox 8802?

oldsmobuick

oldsmobuick

Active Member
My Magnavox 8802 has been fully recapped and new resistors all around. It sounds great but there is some tar leaking from the (original) PT, only a very small blob at the moment, and a vibration that is emanating from the transformer. The vibration is pretty noticeable in a quiet room.

Should I replace the original transformer? If so, Edcor? If so which? I remember looking into this about a year or so ago and I saw an Edcor unit recommended which was about $60. I can't seem to find that thread/PM/email however so I am back to asking the group.

I'm not terribly knowledgeable about how to compensate for mismatches in transformer specs so something that is as "drop-in" as possible is what I'm after.

Thanks!
 
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Does it run excessively hot?

I have a few PTs that look like tar is leaking, but I really think they've just been that way for ages as it doesn't seem to be fresh/currently flowing at any noticeable rate.
 
Heat is warm but not burning hot with a palm on top of the PT. Tar returns slowly if I wipe it off (a small blob will again be present after several days/weeks. I guess the sound of the vibration is more annoying.
 
oldsmobuick said:
This might be the one I had my eye on previously (Edcor XPWR002). If anyone knows whether this would be suitable, let me know. Thanks!
https://www.edcorusa.com/xpwr002
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That transformer is way too beefy for a Magnavox 8802. The XPWR231 (https://www.edcorusa.com/xpwr231) would be much closer to the original, in terms of specs. The 8802's original PT 260-0-260 100mA and had a 3.4A rating on the 6.3V filament winding. The XPWR231 is 260-0-260 160mA and has 2 6.3V windings ... 2A and 3A. You could use the 2A filament winding on the '231 for the rectifier tube, and the 3A winding for all of the rest. I think I read about a @dcgillespie trick to extend the life of a 6CA4 rectifier by tying together pins 3 and 4 together if and only if you are using a separate winding for it that has no connection to ground (which would be the case with my suggestion).

Of course, none of the Edcor transformers will fit in the same hole as the original -- you'll have to vertically mount. But other than that, the XPWR231 should work quite well.
 
oldsmobuick said:
Thanks for that! I'll look at that Edcor unit. 2A is sufficient for the rectifier? I found the thread on the pin 3/4 jump here.
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Yes, the 6CA4 filament draws 1.0A. In my experience, the Edcor PTs have good regulation, so I wouldn't expect the voltage to be too high with only half of the rated load on that winding. The rest of the tubes draw 2.4A total (4*450mA + 2*300mA), which is just about perfect for that 3A winding.
 
You could also get an exact replacement made by heyboer, just email them and see if they have one in stock, or can make one. I have used them for bolt in replacements and the PTs are very good quality.
 
Before replacing the transformer, you could run a test: remove the rectifier and the other tubes. It should run cooler after an hour or so. If so, it should be fine. As for the buzzing, try tightening the bolts holding the end bells on, and holding the transformer to the chassis. That should help.
 
If the 8800 has an extra heater winding, you might consider using it as a bucking winding to drop the voltage a bit. That should help cool it slightly and save it. This assuming it passes the no-load test.
 
Is it buzzing, like a loose winding? Or is it vibrating? Like a electric razor?... Can you feel the vibration in the chassis. does it travel to the shelf? Maybe take off the end bells and look at the shim that holds the core (windings) tight to the laminites or iron stack.... They install a small shim at the factory and these can come loose. I'm guessing a new xmer would be easiest. Good luck....
 
gadget73 said:
If the 8800 has an extra heater winding, you might consider using it as a bucking winding to drop the voltage a bit.
Click to expand...
Thanks Gadget, I do have a bucking winding set up already. You helped me with this amp last year, thanks again!

crispycircuit said:
Is it buzzing, like a loose winding? Or is it vibrating? Like a electric razor?... Can you feel the vibration in the chassis. does it travel to the shelf?
Click to expand...

It's a vibration that is audible because the amp is placed on a shelf and the shelf serves to amplify the vibration. I'll tighten it up and maybe just live with it as long as the tar thing isn't a big deal.
 
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