SET amplifier Q
On Saturday, November 3, 2012 10:00:02 PM UTC-4, Phil Allison wrote:
** Hi all,
a neatly built, home brew SET amp arrived on my bench this week, I
understand it is about 10 years old.
The tube line up is two 300Bs in parallel and one 6SN7 per channel, the HT
is 550 volts and each 300B has its own grid bias adjustment. There is no NFB
used and the PSU has diodes and a metal bridge for DC heaters on the 300Bs.
One of the output transformers ( UBT-1s by One Electron ) was open primary
and two of the Chinese 300Bs were stuffed.
I have one good channel and I so did few tests, grid bias set at -105V and
plate current is close to 55mA per tube.
Max power is 21 watts at 2.2% THD - mostly 3H.
At 10 watts, the THD is 0.85% - mostly 3H.
At 1 watt, the THD is 0.14%, mostly 2H.
The damping factor is 4.5
Signal to noise is -80 dB rel full power.
Input sensitivity is 260mV.
All the above is with an 8 ohm load on the 4 ohm tapping of the OT.
These numbers are a rather better than I expected.
Any comments ?
.... Phil
UBT-1 is rated at 160mA on the primary... Did those 300Bs develope a dead short?
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