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In Reply to: RE: In the background you say?... posted by Steve O on March 29, 2015 at 16:36:20
Looks to be the QS KT 88 60 watt monoblock. Yeah it ran a GE 5AR4 hard, pushing a 320 uF cap. You could optional have a 70 uF cap right after the rectifier. The GE's lasted, though as did the Mullards and Mastushitas.
Commie tubes provided fireworks, with or with the 1812 playing.
The cap seems to installed in the space for the rectifier, which may be marginal for the space required by the screw terminals. don't know how that large cap is installed
Follow Ups:
"Yeah it ran a GE 5AR4 hard, pushing a 320 uF cap."
Why would anyone do that?
Torture the tube, transformer and the first cap with those high charging currents?
A 5ar4 has a limit for the first cap of 60uf and that's only when the proper resistance per plate (rt) is provided (different values ranging from 75 to 200 ohms depending on the AC voltage applied).
If you increase this resistance the cap value can be a higher value but without the proper resistance the cap would need to be lower in value.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
But, I've seen this in several 1980-90 era amps. Seems almost like it was done on purpose, to keep you buying $$$ tube rectifiers. Should have used solid-state rectification, if large first stage filtering was needed.
routinely did this on the early 60 watters,8417 and KT 88, at least as long as the GE's were available. Tough damn tube.
I remember asking him about the over valued caps in the first stage. His reply was have you had any issues? I had to say no, none at all, and as a matter of fact, those GE's ran for years.
Curiously, with the advent of the commie crap, we have to toe the line concerning the ratings, and even allow for greater allowances....
Mike ended the practice when the GE plant closed down of course.He did briefly modify the units for two 5AR4's, but returned to the single GE's.
Having a design solely dependent on one type/make of tube is kinda odd. I can understand this philosophy in the 1940-50s, when tubes were plenty and really the only choice. But, in the 1980-90s, when it was well known that most tube manufacturers were closing their doors... strange.
Ever try on of those Weber Copper Head replacement rectifiers in those AS amps?
Thanks!
Mike started building in the early 80's. tube production was still going on strong. GE was not to close their plants til 1992. In 18989 Mike told me he had something like 4000 5AR4s. he has 6000 sylvania 8417's too
Matstushita 5AR4's and Mullards could hold up to the stress he loaded them with. I believe he ended all rectifier tube production in the mid 90's, because the new stock were horrible.
Those are just silicon rectifiers (most likely 1N4007) with a 53 to 100 ohm wire wound resistor to drop/sag voltage and a NTC Inrush limiter. Not bad if you don't want to modify your equipment, but not really a tool for sound improvement. I would not want to bake a pair of diodes in a metal can with a power resistor and an inrush limiter.
Edits: 04/02/15
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