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 Post subject: Magnavox ouptut power and transformer selection
PostPosted: Mar Sun 03, 2019 8:29 pm 
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Hello all I recently obtained a Magnavox 306H Windsor. I am in the process of evaluating its electrical condition with the intent to restore, and currently have the amplifier on my bench. Well unfortunately the output tranny is open on one side of the primary so i'm in search of a suitable replacement. Magnavox in its advertisements claimed that this push pull parallel 6l6 amp was rated at 45 Watts output. Color me skeptical. I'm guessing they were using "music power" or whatever their marketing department thought thought they could get away with :).

Why do I say this? The current output transformer physical size just doesn't seem like it would support that. A replacement Hammond 50 Watt transformer absolutely dwarfs it in size and will not fit at all on the chassis when its installed in the cabinet. The current tranny fits underneath the 2 inch high chassis and the core measures 2.8 by 3.4 by 1.2 inches. I think I have found a suitable replacement tranny from edcore. It is rated at 30 watts and still substantially bigger at 3.8 by 3.2 by 1.5 inches. I know the its not completely accurate but that is roughly 60% more iron in the edcore tranfromer rated at 30watts.

So I would like you all to check my reasoning. I think this 30 watt edcor will be more than enough to accommodate the requirements of this amp. As it is i'm going to have to modify the chassis to accommodate it physically so before I go thru all this trouble I thought I would check here first.

According to Sam's the original transformer has a 3800 ohm CT impedance and the Edcor CXPP30-3.8K is an exact match in that regard.

Steve


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 Post subject: Re: Magnavox ouptut power and transformer selection
PostPosted: Mar Sun 03, 2019 11:10 pm 
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Location: Rochester NY USA
6L6 or 6V6? There were several Magnavox quad 6V6 amps, quite common and an original output transformer might be around. For that matter, there are many 6L6 P-P transformers in the 4K range. If you can find one with the same core size, you can swap end bells with your transformer and it will drop right in.

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 Post subject: Re: Magnavox ouptut power and transformer selection
PostPosted: Mar Mon 04, 2019 1:26 am 
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I have never heard of a Magnavox with PPP 6L6s. PPP 6V6s, yes, as Tom suggests. Approximately 20 watts output per channel, so a 20 watt transformer will be fine. If someone has been trying to run PPP 6L6s the power transformer may be toast -- the heater current is much higher than for 6V6s.

-David


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 Post subject: Re: Magnavox ouptut power and transformer selection
PostPosted: Mar Mon 04, 2019 2:18 am 
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Thanks for the input guys. Just Google or on here search for Magnavox Windsor. It is indeed a push pull parallel 6l6 amp. Amp-111.

I thought about just using a 6v6 maggie transformer as they seem to be of similar size but the have a different primary impedance. Quite a bit higher.

stee


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 Post subject: Re: Magnavox ouptut power and transformer selection
PostPosted: Mar Mon 04, 2019 4:24 am 
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Indeed it is. Much older than the Magnavoxs I was thinking about. Could be 45 watts but with an inadequate transformer.

-David


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 Post subject: Re: Magnavox ouptut power and transformer selection
PostPosted: Mar Mon 04, 2019 3:52 pm 
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The PPP 6V6 amps (AMP142) show a 3700 Ohm output transformer, according to Sams.

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 Post subject: Re: Magnavox ouptut power and transformer selection
PostPosted: Mar Mon 04, 2019 7:54 pm 
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Tom Bavis wrote:
The PPP 6V6 amps (AMP142) show a 3700 Ohm output transformer, according to Sams.


This is excellent. Perhaps it will not be that hard to find one afterall. I don't remember which 6v6 amp I checked that had the higher impedance. I just assumed all the 6v6 PPP amps would be the same.

Steve


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 Post subject: Re: Magnavox ouptut power and transformer selection
PostPosted: Mar Mon 04, 2019 8:03 pm 
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Judging from the schematic of the 142 i doubt is has 16 ohms output since it basically drive 4 speakers in parallel.


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 Post subject: Re: Magnavox ouptut power and transformer selection
PostPosted: Mar Tue 05, 2019 11:51 pm 
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Location: Eastlake, Michigan
Sams indicates a Merit A-3133 as the replacement transformer. PP Parallel 807/6L6, AB1, Pri 3300 ohms CT 240ma, 55 watts max, Hammond P-T1750Q is close, but pricey. Heyboer might do better.


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 Post subject: Re: Magnavox ouptut power and transformer selection
PostPosted: Mar Sun 10, 2019 9:03 pm 
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thanks mr ed that merrit is just about the same thing as the Hammond.


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