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In Reply to: Re: DIY posted by hitsware on December 23, 2005 at 07:45:00:
When I got the resistor upgrade from Atma-Sphere for the M60 kits I had built, the resistors were for each grid and for each plate of the output tubes. I was told one advantage was being able to measure across the plate resistors so you could match tubes.Recent posts here from Ralph suggest they no longer use resistors at the plates, but at the cathode instead. I would think you could also use the cathode resistor to measure tube performance.
As for finding bad tubes, wouldn't it be easier just to pull out the tubes one by one and look at them? That's how I found my latest one -after a heart-stopping zap in the speaker gave me a hint. It took only a few minutes to check the tubes and examining them is a nice zen-like exercise that at the least renews one's respect for tube design and manufacture.
Follow Ups:
> one advantage was being able to measure across the plate resistors so you could match tubes.Makes sense
> they no longer use resistors at the plates, but at the cathode instead.
Makes sense too. Helps swamp out variations in the tubes.
> I would think you could also use the cathode resistor to measure tube performance.
Right.
> wouldn't it be easier just to pull out the tubes one by one and look at them?
I don't know much about tubes, but I would think plenty could go wrong with no obvious physical manifestation at all.
> a nice zen-like exercise that at the least renews one's respect for tube design and manufacture.
I'd use a meter accross the cathode resistors, and ogle my spares for mystical insight ........... :) ........ mike
> they no longer use resistors at the plates, but at the cathode instead.
> Makes sense too. Helps swamp out variations in the tubes.I think that was also what the plate and grid resistors were meant to do.
> I don't know much about tubes, but I would think plenty could go wrong with no obvious physical manifestation at all.
The tubes in question have fusible links. The blown links are what the original post is about. Whether they are blown or intact can be determined by just looking at them.
> I'd use a meter accross the cathode resistors, and ogle my spares for mystical insight ........... :) ........ mike
For this common failure visual inspection is a lot easier than disconnecting the amps and opening them up for testing.
While zen-like tube gazing may be good it is seldom done. The positive experience of examining the tubes and gaining respect for their complex manufacture happens at the best moment to counteract the negative effect of having a tube go bad. With my budget I have had to come up with philosophical approaches to the cost of tubes.
Bill Layer said something about designing a tube tester devoted to the specific needs of Atma-Sphere users, but I haven't seen any mention of it since. I found a schematic for a tube tester. It's complex but maybe could be pared down to just octal base for a start.
?
(this is the right tube, right?)
?
(this is the right tube, right?)
> ?
> (this is the right tube, right?)
Not 6sn7. 6as7 the output tube. Go here:
If you're only worried about catistrophic(sp?) failure then OK ....
Geez ........... Quite a 'forgiving' circuit ! :)
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