Capability of Sony/Tamradio SE Output Transformers

wrenchone · 2nd June 2010, 06:29 AM

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.

Tom Bavis · 2nd June 2010, 01:48 PM

Got a model number for the RTR?

planet10 · 2nd June 2010, 05:00 PM

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

wrenchone · 2nd June 2010, 07:50 PM

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.

wrenchone · 3rd June 2010, 05:10 AM

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 · 4th June 2010, 03:18 AM

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.

kevinkr · 4th June 2010, 11:39 PM

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!

mach1 · 5th June 2010, 03:48 AM

They display quite a bit of inductance for a small unit - I measured 16H @100Hz

pjanda1 · 5th June 2010, 04:11 AM

Permalloy cores? How does one tell? Maybe I shouldn't have sold mine. . .

Paul
Wild Burro Audio Labs - DIY Full Range Speakers

wrenchone · 5th June 2010, 05:21 AM

Permalloy/nickel-iron cores are generally whitish in appearance - my transformers look like they have the usual dark gray silicon steel stack.

2nd June 2010, 06:29 AM	#1
wrenchone diyAudio Member Join Date: Feb 2004 Location: Silicon Valley	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.

2nd June 2010, 05:00 PM	#3
planet10 frugal-phile(tm) diyAudio Moderator Join Date: Oct 2001 Location: Victoria, BC, NA, Sol III Blog Entries: 5	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 __________________ community sites t-linespeakers.org, frugal-horn.com, frugal-phile.com ........ commercial site planet10-HiFi p10-hifi forum here at diyA

4th June 2010, 11:39 PM	#7
kevinkr diyAudio Moderator Join Date: Sep 2004 Location: Boston, Massachusetts Blog Entries: 6	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! __________________ "Extraordinary claims require extraordinary evidence." - Carl Sagan

5th June 2010, 03:48 AM	#8
mach1 diyAudio Member Join Date: Sep 2004 Location: Brisvegas	They display quite a bit of inductance for a small unit - I measured 16H @100Hz __________________ Au rutti wop-bop-a-loom-bop-a-boom-bam-boom - Richard Penniman

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2nd June 2010, 01:48 PM	#2
Tom Bavis diyAudio Member Join Date: Jun 2002 Location: Macedon NY	Got a model number for the RTR?

2nd June 2010, 07:50 PM	#4
wrenchone diyAudio Member Join Date: Feb 2004 Location: Silicon Valley	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.

3rd June 2010, 05:10 AM	#5
wrenchone diyAudio Member Join Date: Feb 2004 Location: Silicon Valley	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....

4th June 2010, 03:18 AM	#6
wrenchone diyAudio Member Join Date: Feb 2004 Location: Silicon Valley	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.

5th June 2010, 04:11 AM	#9
pjanda1 diyAudio Member Join Date: Jan 2005 Location: Boulder, CO	Permalloy cores? How does one tell? Maybe I shouldn't have sold mine. . . Paul Wild Burro Audio Labs - DIY Full Range Speakers

5th June 2010, 05:21 AM	#10
wrenchone diyAudio Member Join Date: Feb 2004 Location: Silicon Valley	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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