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Old 27th February 2006, 02:55 PM   #21
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Location: Alps:Tube amp designs over 150W, SMPS guru.
Quote:
Originally posted by rickl

I even use ---------- ear muffs for some suspect gear.


rick

Ahha'... I detect someone who is scary of a good bang ?

Eyes are more important. Watchout with TO220/larger plastic packages with a suspect psu... these devices behave as small handgranades when exploded..... the bang isn't signifigant but the fragments can damage eyes.

Actually listening carefully on warm up can reveal alot of duff components and misbehaviour. For example a full bridge rect gone half wave can make a mains transformer throb esp when a variac is used.

richj
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Old 27th February 2006, 04:53 PM   #22
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Default Questions

Could someone please answer the following questions asked in post #
13. I may need to get and install parts.

1.Am I correct in assuming that the " coupling capacitors", for the 500C, are the four .047 's, 2 per side, which connect a pin on each of the 7591's and the 12AX7's?

2.All are W. German and have a black band on the ends closest to the 7591's. Is that the + end?.

tomtt
I shotsome pics this morning. I will see if I can manage to post the one with, what I believe are, the coupling caps.

Thanks to All, Vic
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Old 27th February 2006, 05:05 PM   #23
anatech is offline anatech  Canada
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Hi Victoria,
The 0.047's sound like the coupling caps to the output tubes, there are others. Anything in that package is likely a coupling capacitor.

The band indicates the lead connected to the outer foil. These capacitors should not be polarized.

Happy hunting Victoria! (I like your full name)

-Chris
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Old 1st March 2006, 04:09 PM   #24
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Default Some Progress!!!

Thanks guys, you made my day!!! Yesterday was my 75th birtday and you made it FUN!!

The big brown truck brought the variac yesterday AM. I hook up the Fisher 500C and took about 5 hours to get to line voltage. Nothing blew up, No tubes flashed or glowed like light bulbs!! But no sound.

This morning I let it idle at 70V for a couple of hours, wiggled the tubes, and now I have *very* low sound in both channels. Also static when using the the volume or mode switch.

I probably ought to clean all the switches. Is deOxit the stuff to use? If the low level sound persists,
what would you suggest next?

Anatech
The "Victoria" is a result of being told I couldn't use "Vic" when I registered for these forums.

Thanks, Vic
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Old 1st March 2006, 05:19 PM   #25
anatech is offline anatech  Canada
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Hi Vic,
Yes, DeOxId is the correct stuff, whether it's Caig or GC. If you still have a bottle of the red "Quietrol", that would work also.

Low sound could be a leaky coupling cap or low B+, check the voltage readings. You may have an entire set of weak output tubes. Test them (all of them, why not?)

-Chris
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Old 1st March 2006, 05:47 PM   #26
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Vic,

Congrats on 75 years! I don't have expectations of getting there myself. Question. Why did you wait so long to try to appreciate these tubed gems?
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On April 01,2012, my radioastronomy Project TARGET SETI search succeeded. The signal came via extradimensional subspace, not radio waves. I now get a lot of 'visitors'. I took my avatar pic of one friend watching me in my work yard from just 20 ft. away.
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Old 1st March 2006, 06:08 PM   #27
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Default Checking B+

Anatech
Can you tell me how to do this or point me to an online explanation? I do have an old US Military book called "Basic Theory and Application of Electron Tubes" Feb 1952. Cathode Bias is one of the things discussed, is that what you are talking about? I also have a schematic for this unit. Like I said earlier, I am not the second coming of Tesla (but I did write my thesis on his turbine in 1960), and I have little past experience with electronic gear. I have a Fluke 8012A Digital Multimeter. Is that adequate?
As any aside, my Mother was born in the Stratford/Kitchener area.
Thanks, Vic
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Old 1st March 2006, 06:14 PM   #28
anatech is offline anatech  Canada
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Hi Vic,
Your meter is fine for this. Do you have an oscilloscope? It's good for checking ripple on supplies.

Your book, Basic Theory and Application of Electron Tubes, should be able to give you the basics. You want to make sure all your B+ voltages are in the ballpark from the rectifier back. Very warm filter caps are not a great sign of health, they will get slightly warm. Measure the B+ voltages (be careful please!) and write them down. I may have the schematic, I'm sure others can help too.

Kitchener is not that far from here! They still build great furnature there.

-Chris
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Old 1st March 2006, 06:56 PM   #29
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Default Fisher 500c Schematic

I have a schematic of the 500C but it is 633k. Too big to post. I can email it if you want it.

rick
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Old 1st March 2006, 09:54 PM   #30
anatech is offline anatech  Canada
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Hi Rick,
The one I have is smaller. Yours might be a higher res.(cool) So please send it.

bhome at sympatico dot ca

And many thanks!

-Chris
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