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I currently have an Audio Research VSI 55 that puts out about 50 watts with 4 kt120's (formerly 4 6550's). I am looking at the VAC 200phi which is rated at 100 watts with 4 kt88's. Does the VAC really have double the power of the VSI55? How does the VAC squeeze out 100 watts from 4 output tubes?
thanks in advance for the response,
Lolek
Follow Ups:
So, is the circuit topology for a 50 watt amplifier with 4 kt88's different than the circuit for a 100 watt amplifier with 4 kt88's? Is it a superior transformer that enables a greater amount of wattage from 4 output tubes? What are the advantages and disadvantages of using more output tubes for the same amount of wattage?
thanks for all the responses,
Lolek
I certainly hope so, (4) kt88's are a lot of juice!
I'm getting 85 wpc out of my VAC Sigma 160i integrated amp which uses 4 KT88's.
I see the VAC 200 Phi is heavier, so I'll assume bigger transformers. I'm sure Kevin can squeeze out another 15 wpc using bigger transformers.
Opus 33 1/3
I would be interested to see that measured.
A voltage doubler being used to power a class B amp is asking for trouble/bad performance. I once messed around with EL84's running in class B on a doubler power supply. They did well until cutoff, then the doubler sagged, power dropped like crazy, and distortion went way up. The normal practice to make a power supply with good regulation over a wide variety of currents is with a choke input filter, which is impossible on a doubler.
He also admits to removing the balancing resistors across electrolytic caps in series. This has caused pretty serious problems with some rather notorious production amplifiers.
Opus 33 1/3
There's nothing to explain. A class B amplifier fed by a voltage doubler is just a terrible idea. I don't believe the output power claims are possible.
grasshopper have a lot to learn. it's a proven design since 1989
Please do show me the measurements. I've actually tried building amps like that, and I understand why they don't work well.
The datasheet for KT-88 valves specifies a class AB1 operating point that will deliver 100W with TWO tubes.
VTL does it with the S-200 with each channel having four 6550Cs for 200 watts tetrode / 100 triode output.
Yes, in class B PP.
Observe, before you think. Think before you open your yap. Act on the basis of experience.
I friend of mine had a VAC amp that was 100wpc it was originally 80 but VAC offered a upgrade and he had the upgrade done.
Check this!
The VTA M-125 provides 125+ watts from four KT-88s or 6550s without over-driving the tubes.
But with the right transformers in a push/pull circuit it's easy.
Edits: 03/01/15
Manley 120 monoblocks put out 120W from a pair of KT90s. I get great tube life, but suspect that's because I normally run them at pretty low levels.
WW
"A man need merely light the filaments of his receiving set and the world's greatest artists will perform for him." Alfred N. Goldsmith, RCA, 1922
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