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Capability of Sony/Tamradio SE Output Transformers

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wrenchone

wrenchone

Member
Joined 2004
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.
 
wrenchone

wrenchone

Member
Joined 2004
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....
 
wrenchone

wrenchone

Member
Joined 2004
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.
 
K

kunja

Member
Joined 2009
Tamradio for Darling amp?

I've got a tc-500a that I salvaged the Coral drivers and the 12ad7 from. Now I'm thinking of building my first tube amp and was wondering if these transformers would be suitable for a Darling amp project? Has anyone used them for that purpose? Thanks!
 
45

45

Member
Joined 2008
They really look poor in terms of frequency response. They don't even make 15KHz @ -1dB that was a target response for quality transformers back in the 50ies (see Olson 6F6 amp criteria, for example)....

As tested by Tubelab in a 300B SE amp, a Hammond CSE125 or an Edcor XSE15-5K perform a LOT better in every aspect, especially distortion at various levels and high frequency response. DC current applied about the same in 50-70 mA range.
 
45

45

Member
Joined 2008
Perfectusaudio said:
Sony 5K transformers at 39Hz -1dB would be useful for small full range Fostex , forget about large bass drivers .
Click to expand...

I was talking about the other end. Most of them don't make 20KHz at all. High frequency response is poor. With $20-25 you can buy a small Edcor that can go up to 40KHz and also performs better in any way you want to look at it.

If you can buy these transformers for $5-10 max it might be ok. More it's not worth..
 
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