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In Reply to: RE: 20B SET: look ma, no driver tubes posted by Frihed89 on February 11, 2012 at 14:02:28
line-up some time ago. Ultimate Audio has done a review on it; I think I still have the review somewhere if you would like me to have a look and email it (Edit: it is linked from the Wavelength Audio site, see Gordon's post below). I think Wavelength still has spud amps in their line-up, though I am not sure if if the 20A is one of them.I have thought about building such an amp, though despite the single tube they are probably expensive to get working well. Well designed and built circa 14K primary transformers don't come cheap (Hashimoto has one though) and I would rather go all-nickel parafeed for such a beast, alas... Three other concerns for a DIY effort: (1) I don't know if such a beast would be suitably dynamic and have enough musical meat on it's bones, (2) with series feed, would the high gain and impedance make it more or less susceptible to power supply ripple, and (3) what DC filament scheme to use?
I might again consider building one of these someday... my pending speakers should only need about 2W to meet most of my needs so could significantly reduce the step-up, especially if my source puts out a little more voltage than the standard.
Cheers.
Edits: 02/16/12Follow Ups:
They are nice amps. Amazingly quiet, and not just for a tube amp but in general. They are quieter noise floor than most of my solid-state amps too.
nicely built, simple enough design, and well executed. I was thinking of selling mine (along with some NOS no-longer-available AVVT 20B tubes) but haven't gotten around to it yet.
They use a step-up (I forget the brand offhand), then a Magnequest EXO-45 output tranny, and Magnequest choke. DC fils of course. If I was going to hot-rod them I'd probably try a better version of EXO-45 (silver for example, or cobalt) and choke, and maybe a higher-end lundahl step-up or MQ cobalt step-up. I actually have some cobalt EXO-45 and was going to try swapping them in but never got around to it.
-Ed
Gang,
Yea I used the B, the A has too much Rp (Plate Impedance) and requires a higher load and output power would be nothing.
RCA input went into a 1:4 step up and then directly to the Grid, we used custom MagneQuest output transformers in parallel feed and it got about 3W's output power, but really required a well oiled preamplifier.
These sold big when the Horn era hit the US and all those huge amps had tons of hum.
Thanks
Gordon
J. Gordon Rankin
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