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Tubelab Discussion and support of Tubelab products, prototypes and experiments

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Old 9th August 2012, 12:08 PM   #1
kkcinc is offline kkcinc  United States
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Default beginner output power question wpc triode ul cfb

What percentage does output/watts per channel go up when you add ul and or cfb? That is if you know the output in triode. Lets use 8 watts in triode as an example.
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Old 9th August 2012, 12:52 PM   #2
Tubelab_com is offline Tubelab_com  United States
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It all depends......mostly on the tube in use. I have seen tubes like the 307A DHT that make 8 watts in triode, and 8 watts in UL.

Assuming an SSE you will get 4 or 5 watts in triode with a 6L6GC and about 8 or 9 in UL. An EL34 generally makes about 5 or 6 in triode and 9 to 10 in UL. A KT88 or 6550 makes about 8 in triode and 13 or 14 in UL. All UL testing was done with a 5K ohm load and 435 volts B+ with CFB enabled. Triode measurements had no CFB, it is generally not needed.

CFB will generally not increase the output power by itself. It will lower the output impedance, leading to better bass control on some speakers, and it will reduce distortion created in the output tube and the OPT. The reduction in distortion allows a little more power for the same distortion level, maybe 1/2 to 1 watt. It may allow turning the amp up a bit before distortion becomes audible and creating a louder sounding amp.

It DOES reduce the distortion created in low cost OPT's allowing you to squeeze a bit more power through them. The little Edcors and Hammonds seem to respond well to CFB on some speakers.
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