Ok, picked up this console cheap and found this little gem inside. I rebuilt an 8802 with a lot of peoples help on this board, and am hoping for some more insight. I'm thinking this power transformer is toast, what do you think? Also the rectifier is burnt on two sides. Jim McShane.....do you sell PT's?
http://i107.photobucket.com/albums/m285/stickman81/IMG_0150.jpg
http://i107.photobucket.com/albums/m285/stickman81/IMG_0150.jpg
http://i107.photobucket.com/albums/m285/stickman81/IMG_0150.jpg
http://i107.photobucket.com/albums/m285/stickman81/IMG_0150.jpg
If the power trafo is shot, as the leaking tar suggests, consider rebuilding as an "El Cheapo". Those undersized O/P trafos will probably work well in combination with triode wired "finals". Salvage the choke and buy the rest of the new power "iron" from Allied.
Jim McShane has all the parts needed to finish the job.
Jim McShane has all the parts needed to finish the job.
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Those amps were not fused, (unless you count the transfo windings as a fuse). As you observe the 5U4 may be shot too. It follows then that the can cap has probably shorted, failing the others. You probably want to replace it before installing a new transformer.
That transformer footprint is pretty common and you are likely to find another on an auction site. A couple years ago I found one NOS at a fair price.
How are the tubes?
That transformer footprint is pretty common and you are likely to find another on an auction site. A couple years ago I found one NOS at a fair price.
How are the tubes?
Eli - you suggested "El Cheapo" on my 8802 also, and I know I'd be happy with the final product - but my electronics training was back in 1984 (& I don't even work in the field anymore). How close to "El Cheapo" is the 9302 stock?
Captn Dave - you're right, the rectifier looks shot.....as well as the right 6EU7 (gone to air). From what I've read, the 9302 should be a bit better on bass than the 8802 with my Klipsch Chorus II's
Captn Dave - you're right, the rectifier looks shot.....as well as the right 6EU7 (gone to air). From what I've read, the 9302 should be a bit better on bass than the 8802 with my Klipsch Chorus II's
A stock Magnavox 9302 uses a paraphase splitter. "El Cheapo" uses a differential splitter. The circuits are quite different.
You are going to incur some costs, including power "iron", regardless of how the unit is made operable again. For quite good technical reasons, only "concertina" and differential phase splitters are currently "in vogue".
If you decide to go the "El Cheapo" route, install some sheet aluminum to fill in the cut out the failed OEM power trafo occupies. The "real estate" gained will be used for new power "iron" mounting. The chassis openings currently used for the rectifier tube socket and the can multi-section cap. will be used for new PSU capacitors. A new opening rates to be needed for the 2nd doubler stack cap., as the rectifier hole will take the 1st doubler stack part. I don't think it will be too much trouble to reuse the space the "Molex" power connector occupies as where the 7 pin mini socket the B- rectifier mounts.
I had a really detailed long post to put up - and then somehow it went away as I was finishing the last sentence!! Grrr.. I'll try to reconstruct it and post it tomorrow.
But for now let me just say the El Cheapo idea is GREAT - and getting the existing power trafo rewound may be the best/easiest (albeit a bit more expensive) route to go.
More soon...
But for now let me just say the El Cheapo idea is GREAT - and getting the existing power trafo rewound may be the best/easiest (albeit a bit more expensive) route to go.
More soon...
LD,
I wouldn't write that tranny off as a gonner just yet. That tar is painted on the outside and that one looks like some kind of solvent or oil dripped onto it from above. Those consoles generally placed the turntable above the amp. Could have come from that or someone oiling a noisy platter, who knows?
Those trannys have the lead holes on the bottom. If anything was to "leak" from the tranny it would show there. Those leads also get some tar at the opening so that doesn't indicate a problem either. You really need to put a meter across the leads to look for a problem. Maybe find another rectifier and fire it up. Don't jump to conclusions from the looks of this one.
Good Luck.
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I send stuff to Gary Brown in Orono Maine - his site is:
http://members.tripod.com/tubes_tubes_tubes/transformerrewindingservice/
But to implement El-Cheapo you need a 40-45 volt winding for the B- supply. You can ask Gary to remove the 5 volt rectifier winding and use that space for this new winding. You only need 25 ma. or so from the winding so there'll be plenty of room for it. As well, the main B+ winding would work great as a 275-0-275 winding, it's likely close to that now. The voltage doubler shown in the El Cheapo supply will be replaced by a full wave center tapped rectifier and a single 400 volt cap.
When you are done you'll have:
1. a 6.3 volt winding that used to power the tuner tube heaters that can now be used to heat the 6AL5
2. a B+ winding ideal for El-Cheapo's audio circuitry when rectified by a cap input filter.
3. a 6.3 volt winding for all the other tubes except the 6AL5. Eli and I recommend you use the 6CM6 as the output tube; it's a 9 pin tube with a 6.3 volt heater and makes changing sockets unnecessary.
4. a 40-45 volt winding that will be rectified by the hybrid bridge for the B- supply.
You're half way home at that point!
Let me augment what Jim said.
The OEM 5 VAC winding is rated for 3 A. or 15 VA. When rewound, it should be 50 VAC at 30 mA. or 1.5 VA, which is plenty to support the 12 mA. B- draw. Power requirements have been reduced.
While the current rating of the 6.3 VAC winding used to support the tuner is unknown, you can bet the farm it's greater than the 300 mA. needed for a 6AL5 B- rectifier. Power requirements have been reduced.
6V6 family tubes, including the 6CM6, draw less heater current than the EL84/6BQ5 draws. 6EU7s and 12AT7s draw the same amount of heater current. The heater draw of all 6 "El Cheapo" signal tubes is 2.4 A. Once again, VA requirements are lower than OEM.
The 275-0-275 VAC B+ winding has to be able to comfortably support a 200 mA. B+ draw in combination with a good sized cap. I/P filter. Since OEM was close to this requirement, it's safe to assume that all well be well. Remember, several VA were recouped from the low voltage windings.
The disadvantage of rewinding the OEM trafo is that it will cost more than assembling several off the shelf pieces of power "iron". The advantages of spending the extra money on the rewind are that you get exactly what's needed, considerable fabrication work is eliminated, and you avoid some expense in buying sheet aluminum. Make a decision and live with it. Trade offs will be with us forever.
The OEM 5 VAC winding is rated for 3 A. or 15 VA. When rewound, it should be 50 VAC at 30 mA. or 1.5 VA, which is plenty to support the 12 mA. B- draw. Power requirements have been reduced.
While the current rating of the 6.3 VAC winding used to support the tuner is unknown, you can bet the farm it's greater than the 300 mA. needed for a 6AL5 B- rectifier. Power requirements have been reduced.
6V6 family tubes, including the 6CM6, draw less heater current than the EL84/6BQ5 draws. 6EU7s and 12AT7s draw the same amount of heater current. The heater draw of all 6 "El Cheapo" signal tubes is 2.4 A. Once again, VA requirements are lower than OEM.
The 275-0-275 VAC B+ winding has to be able to comfortably support a 200 mA. B+ draw in combination with a good sized cap. I/P filter. Since OEM was close to this requirement, it's safe to assume that all well be well. Remember, several VA were recouped from the low voltage windings.
The disadvantage of rewinding the OEM trafo is that it will cost more than assembling several off the shelf pieces of power "iron". The advantages of spending the extra money on the rewind are that you get exactly what's needed, considerable fabrication work is eliminated, and you avoid some expense in buying sheet aluminum. Make a decision and live with it. Trade offs will be with us forever.
Well,thanks Eli & Jim.... I know I will not regret the El Cheapo decision once completed - getting there will be the tough part (for me). I'm a believer in doing it right the first time - so I will most likely rewind the trafo with Gary Brown. These last two posts have shed light on your schematic Eli,was confused as to the seperate parts.
That 9302 is one of the highest regarded and sought after Magnavox amps. They sound great, have plenty of power and are super easy to work on. The feedback circuit is in the amp, too, as opposed to some that go to a different preamp section and have to be rebuilt into the amp. It is a complete amp. If that tranny is good, you will be doing yourself an injustice by trashing it. You should determine what's good on it and just refurb it. You have a classic console amp there. Your desire to build an El Cheapo is going to require a nearly completely from scratch, build. You are basically taking the wheels off a Cadillac and trashing the rest, to start building a VW. Keep the 9302 as is and build your El Cheapo from all new parts.
Good Luck.
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Too Riggght! It is probably in working order unless of course the smell of magic smoke is lingering. I have converted several into stand alone power amps. They are very good little amps and have totally humiliated some highly regarded big brethren. By all means try it before stripping it!
Here's 9304 refurbed that went for $325, you know where. It's not as good as the 9302 because the balance control is not in the amp.
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Everyone has their own opinions, and that's fine. But the stock audio circuit was really built to a price point and (to me) reeks of cut corners and so on. They clearly did better on the power supply, with a real live choke in it!!
And I must confess - I don't lust after console amps.
A properly implemented El-Cheapo will provide truly remarkable performance - IMHO performance FAR beyond what the original could provide. The OPTs will be about the only limiting factor with an El-Cheapo circuit.
It' up to the owner to decide, but I sure hope he goes the El-Cheapo route. That little amp turned into a really stunning performer!!
And I must confess - I don't lust after console amps.
A properly implemented El-Cheapo will provide truly remarkable performance - IMHO performance FAR beyond what the original could provide. The OPTs will be about the only limiting factor with an El-Cheapo circuit.
It' up to the owner to decide, but I sure hope he goes the El-Cheapo route. That little amp turned into a really stunning performer!!
I must confess, I'm not totally decided about how I'm going to rebuild this amp. It sounds like if I rewind the trafo, I circumvent a lot of fabrication normally associated with building the El Cheapo. If I just redo the 9302, I end up with a very nice, sought after amp as well. Because this amp has the balance pot built into the amp....this negates the 390 ohm resistor need in the feedback loop- right?
No. ...The 9302-00 (there are slightly different versions of the 9300-xx series) should have a 3900 ohm , not 390, (or it might be a 2200 ohm) in the feedback circuit from the OPT's. This is the resistor that tunes the feedback to be optimal with the OPT's. It is required. It also influences the driver biasing because it is part of the cathode path to ground, so you can't just pull it.
Not talking about removing anything. On the 8802 I redid, i had to add 390 ohm resistors..... this explains: Magnavox stereo PP console amps and the mysterious balance pot - AudioKarma.org Home Audio Stereo Discussion Forums
This was necessary because removing the molex umbilical opens the feedback loop.
This was necessary because removing the molex umbilical opens the feedback loop.
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