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Old 3rd January 2004, 03:01 AM   #11
zzz is offline zzz  Canada
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with a shorted turn still lurking in the secondary? doesn't sound very likely.

has anyone ever opened 300 series hammonds? I wonder how hard it is to rewind the secondary.

(just sent an email to handmade electronics. who knows, maybe they'll agree to exchange it)
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Old 3rd January 2004, 03:07 AM   #12
Magura is offline Magura  Denmark
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Are the trafo's new??

In that case its much more likely that they simply ****** a turn.

So give it a shot

Magura
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Old 3rd January 2004, 03:17 AM   #13
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This may sound whacky, but you said that one transformer is right below the other. If so and it is out of phase (or in phase) with its neighbor, the two clashing magnetic feilds may be bucking and causing heat and noise. Try to reverse polarity on one primary and see if it changes the noise level.
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Old 3rd January 2004, 03:24 AM   #14
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Quote:
Originally posted by Magura
Are the trafo's new??

In that case its much more likely that they simply ****** a turn.

So give it a shot

Magura
I found out that it hums even without HV secondary connected (having one filament winding is enough). yah, I can believe that they may have missed a turn and I guess that could technically put some unbalanced dc on the secondary. I'll look into that.

and yeah, the transformers are (were) brand new before I put them in the amp.

Quote:
Originally posted by Brian Donaldson
This may sound whacky, but you said that one transformer is right below the other. If so and it is out of phase (or in phase) with its neighbor, the two clashing magnetic feilds may be bucking and causing heat and noise. Try to reverse polarity on one primary and see if it changes the noise level.
yah, I thought about that too, so right now I'm running wires to an external LV transformer.
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Old 3rd January 2004, 05:28 AM   #15
zzz is offline zzz  Canada
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ok, I'm retarded. going on a hunch, I decided to replace the diodes with some new ones (they are $1.25 a pop, so I have a handful of them) and color me surprised when hum moved to another transformer! I looked down through the socket (amp's upside down for testing/taking measurements) and noticed that one of the diodes in guilty transformer's bridge is not glowing. I wiggled it, it lit up, and voila -- the hum is mostly gone.

isn't this lovely?

(admittedly, there's still some residual buzzing but it's very faint. I'll figure it out.)

so, now I suspect that the problem's not in the transformers or diodes but rather in the poor contact between the diode tubes and their sockets (full-wave becomes half-wave => tons of unbalanced DC current through the secondary => hum and heat). 6cj3 pins look rather oxidized and while the socket contacts are still clean, at some point they'll tarnish too. is it possible to treat them somehow so that neither would oxidize as much?
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Old 3rd January 2004, 05:40 AM   #16
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conductive silicon grease will prevent oxidization commonly known as dielectric compound
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Old 3rd January 2004, 06:49 PM   #17
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Rewinding mains transformers......I've done this many times, but HT windings are usually next to primary; i.e well into bobbin and that means removing all the other windings on top. It's false economy re using unwound wire. If the tranny is vacuum varnished impregnated; core and iron; the going-is-going to be tough splitting laminations from the core, especially if they have been press machine inserted.
Warming the core many help. The best tool to wedge E & I laminations from each other is an old thin pocket sized steel ruler with an end slightly sharpened and a small hobby hammer and work alternate ends... Invariably one looses the first set. Once the bobbin has been separated from the core, you will need to set up a marndrel to count the turns.

It's not the nicest new-year-job for anyone.......especially on a cherished tranny......

rich
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Old 3rd January 2004, 10:00 PM   #18
EC8010 is offline EC8010  United Kingdom
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Default Your problem might be...

Are you are using American TV efficiency diodes in European sockets? The European B9D socket has exactly the same pin positions as the American Magnoval, but the European pin diameter is slightly larger, causing all sorts of problems if you accidentally use (for example) a 12CL3 in a socket intended for an E55L.
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Old 3rd January 2004, 10:07 PM   #19
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Hi,

Quote:
causing all sorts of problems if you accidentally use (for example) a 12CL3 in a socket intended for an E55L.
Not again, please..........

For Pete's sake magnoval sockets and novar sockets are NOT one and the same type.

Confusing one for the other is just asking for trouble...
Dealers are selling one for the other now too or what's going on?

Gosh....

Cheers,
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Old 4th January 2004, 12:20 AM   #20
dhaen is offline dhaen  Europe
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Default You CAN teach an old dog new tricks...

Magnoval vs B9D difference....

I didn't know that

Thanks for the info
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