HV mA Spec on Large RCA Power Xfmr? - diyAudio
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Old 23rd August 2010, 10:47 PM   #1
duganj is offline duganj  United States
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Default HV mA Spec on Large RCA Power Xfmr?

I have a large, what I think is RCA, power transformer.

Model#:
901620-502

Primary:
0-110-120

Secondary:
290-0-290
5V @ 3A
6.3V @ 12A
5V @ 6A

It weighs ~20lbs.

I found one reference to it on the web (here in a cached yahoo version):
Audio Bizarro - Vintage and Ultra-Fi audio since 1997

I'm planning on using it in a multichannel home theatre amp I'm sketching out, modular, based loosely around the Decware ZKIT2.

While I'm sure that there is the ~200-250mA I would need for 5xEL84, it would be great if I could actually track down a spec for the thing and see what else it might be able to power.

Any suggestions for tracking down these old specs?
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Old 23rd August 2010, 11:01 PM   #2
duganj is offline duganj  United States
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So in a quasi-answer to my own question, I got thinking about what you could power with 12A of 6.3V heaters, and came up with ~12x6L6's or 24x6V6's which assuming 50 and 30 mA of current per tube, gives you 600 and 720mA of B+, respectively.

I don't know how valid those data points are but there's a rough ballpark at least.
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Old 24th August 2010, 12:55 AM   #3
ChrisA is offline ChrisA  United States
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Quote:
Originally Posted by duganj View Post
So in a quasi-answer to my own question, I got thinking about what you could power with 12A of 6.3V heaters, and came up with ~12x6L6's or 24x6V6's which assuming 50 and 30 mA of current per tube, gives you 600 and 720mA of B+, respectively.

I don't know how valid those data points are but there's a rough ballpark at least.
The real answer is to test it. Hook it up to a dummy load and let it run for an hour then reduce the resistance of the dummy load and run again for an hour. Stop when it gets warm to the touch. Be sure and load all the secondary windings.

I would not push an older transformer up to it's limit. Let it run warm but not hot. Also I would not invest the time to build an amp until I'd run the PT with a dummy load for a long time. Make sure it does not hum or whatever _before_ you cut and drill a chassis. You'd be best to discover that the thing vibrates and hums at full load now rather then later.

A 500W resistor can be expensive, some people will use light bulbs in a series for a test load or parts salvaged from a hair dryer or electric frying pan, stove element or whatever. A transformer of this size can take along time (hours) to reach thermal equilibrium so don't just do a 10 minute test.
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Old 24th August 2010, 02:18 AM   #4
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Check out this link:

diytube.com :: View topic - The Dumpster Transformer Topic
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Old 24th August 2010, 02:44 AM   #5
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Hi there:With a masive power transformer and 12A of filiment current available at 6.3V, how about an OTL amplifier using 6c33 tubes. Without the need for purchase of OT's, you can get a fine amplifier for a small cash layout and not have the distorsion from OT's. Writers of several threads suggest that the 6c33 should be run at plate voltages much lower than the other tubes you mentioned, so your transformers plate voltages should work into a supply for the 6c33. Search the site for OTL and also google OTL. ...regards, Michael
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Old 24th August 2010, 02:32 PM   #6
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What's the DC resistance of the HV winding?
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Old 24th August 2010, 03:43 PM   #7
duganj is offline duganj  United States
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Thanks for that electronics world article, thats a useful one.

The DCR of the HV winding is 15.8 Ohms. I haven't measured the no load voltage recently, but working with the rated 290-0-290, going by the chart in the article, I get ~400mA capacitor input.
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Old 24th August 2010, 08:35 PM   #8
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400 mA would result in 2.5 watts of copper loss in the secondary - not a lot for a large transformer. 500 mA (4W loss) might be pushing it for an older part, but should be OK with modern insulation.
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