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Tube DIY Asylum Do It Yourself (DIY) paradise for tube and SET project builders. |
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Tube DIY Asylum Do It Yourself (DIY) paradise for tube and SET project builders. |
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In Reply to: Akai m-8 reel-2-reel transformed to SET mono block amp project. posted by potlicker on July 10, 2006 at 17:59:22:
I have one of these that I meant to rework one day as well. It uses 6BQ5 output tubes, single ended. It was sitting in a cupboard gathering dust until I read your message. I remember trying it out and thinking the frequency response was a bit lacking, especially the top end. I thought maybe they rolled it off purposely as 12 to 15kHz was considered high enough back then? The SE transformers are not huge, but should work OK. They are bigger than some cheap Hammond SE transformers I have used and got acceptable sound from. Still, no reason why it can't be made to work.The preamp tubes are a twin triode, 12AD7, so that socket is perfectly setup for a 12AX7, and a 6267 (EF86) pentode. The pentode is the one with the rubber vibration reducer on it. This last is not so useful in my opinion, as I prefer triodes, but you might experiment.
Mine is basically built as 2 mono blocks. You can remove them and run them separately. In mine, there is a transformer/choke to derive the 100volts AC that they run on (our power is 240 VAC), so for that reason, I have left them in the original wooden case with the transformer for now, and just removed the (broken/worn) tape mechanism.
[ aside: I also have a mono R2R from AKAI with a very similar amp module (just one of course) that I turned into a guitar practice amp, and also, a chassis from a smaller/later stereo R2R that uses 6BM8's. That last one has an excellent sound.]
When using an amp from a tape recorder, the main inconvenience is that the circuitry runs through a huge switch, that is connected to the record button/lever of the old mechanism, and it is also sometimes sprung loaded. This one is a large, but simple slide switch - not so bad. Even if you can disconnect it from the mechanism, and manually set it in the desired position to use the amp, I'd prefer to remove it from the circuit and avoid future problems and sound degradation. Then there will be a bias oscillator tube (6AR7) that can probably be eliminated (probably should be).
Anyway, to sum up, you have 2 chassis, power iron and power supply circuits (tube rectified and choke filtered), output iron, 5 sockets in each chassis (one is the rectifier), VU meters So plenty of scope. I think I'd strip out everything else (maybe retain the circuitry around the 12AD7 and the 6BQ5 output) and start afresh.
You've got me interested in having a play with it again :-)
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Follow Ups
- Re: like this one? - ffrr 01:31:40 07/11/06 (1)
- Re: like this one? - potlicker 09:01:33 07/11/06 (0)
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