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previous: Whit Stephen, Nice design. I li... -- 1/31/1998 7:50 AM View Thread

Re: 1-watt tube amp for small apartment

2/1/1998 1:28 PM
stephen
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Re: 1-watt tube amp for small apartment
Power and o/p trannys came from a junked Brit amp which had terminal instability as a result of ECL82's and an unfortunate PCB layout.Yeah I know it's annoying when someone throws you a nice design and then says they used recycled (and unspecified) trannys from an old amp,  
 
The power tranny is approx 250-0-250V AC secondary  
and as the OT was intended for ECL82's (rather than EL84's) it's probably at least 10k p-p and may be 12k. I will measure it for you, if you email me a reminder in about a week's time. Although triodes are more load-tolerant than pentodes, the 6SN7 o/p in the Moonlight amp does not work so well into the more common 8k p-p output tranny. It is possible that 12k p-p is a *minimum* load for best results. You could try anywhere between 10 and 20k.  
As power levels are very low here, the easiest source of OT might be a 5 or 6k p-p tranny, with an 8 ohm spkr on the 4 Ohm tap (or 16 on the 8 tap) A cheap "medium-fi" o/p tranny would probably still heve enough inductance and l/f response for a guitar amp, when used in this way.  
If you've got something like 1 to 3 Henrys per k of load, it should work ok. My o/t is wound on a 3/4 by 3/4 core, which is generous for 1 Watt power level. 1/2 inch square would probably be fine.  
That should give you enough to work on. Email me if you need the exact o/t specs. If you build the amp, please let me know what you think of it. I did try several simpler alternatives with mini pentodes, or regular small o/p tubes strapped as triodes, but somehow the p-p SN7 sounded more meaty.  
- Stephen

 
Replies:
Whit Stephen, Thanks, there mor... -- 2/2/1998 8:12 AM