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In Reply to: RE: Warmer sounding output tubes in VTA 70 posted by airtime on August 17, 2016 at 07:29:19
Bob Latino and Roy Mottram,I don't care for the choice of the blue metal oxide resistors used in many places.Notice the resistors I used on this particular board and this actually actually removes most that sterile sound you are experiencing in an otherwise very fine amp.Also,you may want to try a different paper in oil cap like a vitamin Q or Pyramid,as opposed to the K40y feeding the interim stages.
"For every complex problem there is an answer that is clear, simple, and wrong" H. L. Mencken
Follow Ups:
Including tantalum and Riken carbons in a few key positions. I used mostly Dale and a few PRP metal films everywhere else.
I'll get the metal films out of there at some point, along with the Auricaps, which I know how much you love, based on your posts from eight to ten years ago. That's an attempt at sarcasm, if anyone's wondering. Mike had some pretty unflattering things to say about these caps in his posts way back when.
The Auricaps aren't that bad.The only thing I don't like about them is the stranded leads can pose problems like when humidity sets in,the leads going into your cap body can separate and let moisture in.This is turn can cause cap failure overtime.
"For every complex problem there is an answer that is clear, simple, and wrong" H. L. Mencken
Not certain if they were Carbon Comp or Carbon Film and I could not locate (just now) the info on Bob Latino's website.
Hum - which resistors did you change? And where can I get VitQ's?
charles
Please observe that Mikey followed Jim McShane's sage advice and mixed the dielectric materials up. Both K40s and Solen film/foil parts are in that build.
Mixing dielectric materials up lets you hear the amp, instead of hearing the capacitors.
Eli D.
All of them.I just buy the boards from Roy and build them my own way..Charlie,if you change the plate and cathode resistors to carbon film along with the grid resistors,this will solve a lot of your problem..You can use Vit Q,Pyramids,or astrons but change resistors first.
"For every complex problem there is an answer that is clear, simple, and wrong" H. L. Mencken
Now this is from a schematic I found online because my papers are still in boxes. And this schematic has 12AT7 where as mine uses 12AU7.
Are the resistors you are talking about the following:
Splitter R1 grid
Cathode Inverter R23,27,25
Grid output tubes R33,35
I think that was all I see.
charles
Mike, carbon even over Dale metal films?
when I unpack my stuff and get an actual shop area that will be the first thing I'll do. But it's going to be a while.
So plate, cathode and grid - basically take out all the metal film and use carbon film.
If you go the fix-it route --- try to mod one section, at a time. That way, if you go further from desired end-point... it'll be easy to reverse the mod. I like starting at input, then phase inverter sections.
IMHO, Wholesale mods are a way to instant insanity.
8^)
Right on Steve! I learned that the hard way many years ago.
"For every complex problem there is an answer that is clear, simple, and wrong" H. L. Mencken
I can't agree more.
And yes that was the plan. First the invert, followed by the splitter and then the output grids. Most of the time that ONE upstream part is all you need.
charles
The Sylvania 5932 is one of the warmest output tubes of the 6L6 family. In my experience. Max dissipation is around 22 watts per tube, IIRC.
6L6GA are also a bit warmer in the midrange, but have lower dissipation ratings, 18 watts max.
what plate voltage can those stand? I think a vta st70 puts 430-440ish on em.
I'm pretty sure it can use the 6L6. I'll email Bob and ask???
Yeah, best to contact designer or manufacturer of your unit.
Good luck, in the hunt for perfect tone!
8^)
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