ampage
Tube Amps / Music Electronics
For current discussions, please visit Music Electronics Forum. The sunn still shines online!

ampage archive

Vintage threads from the first ten years

Search for:  Mode:  
previous: RJH Can someone provide a usable formul... -- 2/23/1999 8:59 AM View Thread

Re: Formula for output trans match?

2/23/1999 10:14 AM
R.G.

Re: Formula for output trans match?
The "just-right" transformer impedance for a given pair of output tubes is not clearly determinable by a formula. For power pentodes like the EL34, it is usually around 1/9 of the internal plate resistance for best performance. Slightly smaller values give more power, slightly higher values tend to be best distortion. Randall Aiken's note earlier in the forum is a pretty clear statement.  
 
Most of the time the manufacturer built some, tested and tinkered with them and published a recommended value. For the EL34, this is probably 4000 to 4400 for best power, up to 6600 for best distortion at somewhat lower power. The tubes are tolerant of modest mismatches, so the exact value is a matter of taste and design.

 
Replies:
Fred G. See the thread below entitles "Plat... -- 2/25/1999 9:01 AM