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.
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
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
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.
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....
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....
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.
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!
Have fun!
Permalloy cores? How does one tell? Maybe I shouldn't have sold mine. . .
Paul
Wild Burro Audio Labs - DIY Full Range Speakers
Paul
Wild Burro Audio Labs - DIY Full Range Speakers
Permalloy/nickel-iron cores are generally whitish in appearance - my transformers look like they have the usual dark gray silicon steel stack.
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!
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!
I've been looking at these mini 5K SE OPTs - loads for sale in Europe. I'd be trying out something like 6C4C outputs at 50mA and 300v.
Anybody tried something like that?
Anybody tried something like that?
Andy, can you please share a link/picture/part number?
My attempts of locating those have failed miserably 🙁
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.
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.
Sony 5K transformers at 39Hz -1dB would be useful for small full range Fostex , forget about large bass drivers .
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You can try PL 36 in triode, up the current till they start to glow, then back off 10 %, if the transformer does not sturate you can get 5 watt.
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..
They seem to find favour with type 45 , but at 1 useful watt before distortion climbs rather high your speaker choice is up around 99dB/ 1watt and above
Exactly
I didn't have 45, but pl36 likes a 45 OPT (homemade) and gives 5 watt, and costs 5 euro.
I didn't have 45, but pl36 likes a 45 OPT (homemade) and gives 5 watt, and costs 5 euro.