Capability of Sony/Tamradio SE Output Transformers - diyAudio
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Old 2nd June 2010, 06:29 AM   #1
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Default Capability of Sony/Tamradio SE Output Transformers

I have a pair of Tamradio SE output transformers that reportedly came from a Sony R-R tape recorder/s. I would like to use them in a Schade-style partial feedback amp. There all sorts of tube complements I could use, and I'd like to try them with something more authoritative than the original (so I've heard) 6AU6/6AQ5 complement. One possibility would be to use a 6LR8 with the triode used on top of a JFET in a cascode. Another possibility would be a suitable pentode (there are several that come to mind) paired with a 6P14P-EV. Anyway, I'd like to have some sort of idea of the quiescent current used in the original application to give me some idea of what I can get away with.
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Old 2nd June 2010, 01:48 PM   #2
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Got a model number for the RTR?
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Old 2nd June 2010, 05:00 PM   #3
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Tapecorder TC500 is the most common source for these,

I can dig out measured ratios for at least a couple of these. 8 & 600 ohm taps on ~5k primary IIRC. Medium sized and very nicely made. Shipped with speakers that may have reached 125 Hz.

dave
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Old 2nd June 2010, 07:50 PM   #4
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The specs Planet 10 mention lead me to believe that my transformers came out of a Tapecorder 500, as they have a 5k primary, and the 8/600 ohm secondary taps.
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Old 3rd June 2010, 05:10 AM   #5
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I did some looking around, and I found a schematic for the Sony tape recorder in question, or at least one very similar. The output amp uses a 6AU6 + 6AQ5, with feedback from the 6AQ5 plate to 6AU6 cathode. The 6AQ5 looks like it's pushed to its max dissipation or a little beyond, as the cathode resistor is 250 ohms, resulting in 40-50 mA plate current for any reasonable plate voltage (from looking at the plate curves). The screens are each tied to B+ through a 2K resistor and bypassed with a few microfarads.

This tends to indicate that it would be possible to use the transformers with the pentode half of a 6LR8 with some respectable bias current, so 6LR8 it will be - nice little spud....
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Old 4th June 2010, 03:18 AM   #6
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Just to drive the point home, the transformers were out of the feedback loop. Some pundits said that this tape deck sounded wonderful, which would tend to indicate quality iron, especially as I'm not precisely blown away by the overall design. Let's see if the spud I'm proposing (I think I'll call it "Spudnik") will do better.
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Old 4th June 2010, 11:39 PM   #7
kevinkr is offline kevinkr  United States
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I think you will find it worth the effort, all of these Sony/Tamradio OPTs seem to have been quite good. My understanding is that many of them have permalloy cores.

Have fun!
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Old 5th June 2010, 03:48 AM   #8
mach1 is offline mach1  Australia
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They display quite a bit of inductance for a small unit - I measured 16H @100Hz
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Old 5th June 2010, 04:11 AM   #9
pjanda1 is offline pjanda1  United States
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Permalloy cores? How does one tell? Maybe I shouldn't have sold mine. . .

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Old 5th June 2010, 05:21 AM   #10
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Permalloy/nickel-iron cores are generally whitish in appearance - my transformers look like they have the usual dark gray silicon steel stack.
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