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In Reply to: Re: Caution! posted by Russ57 on December 30, 2003 at 11:29:40:
Thank you Russ for this very important clarification about the bias caps as I was very confused about the positive/negative thing in all these can caps.About the electrolytics to replace the can caps, I didn't find anything rated at 500V or more, so I didn't buy the caps for C1 (C53). Any hint is welcome here, maybe to connect some in series?
For the other two cans I found the following, let me know if my choices are ok. They are not special brands, but mainly Elna plus Jamicon, Pec and Samwha.
C3:
100uf/50V + 47uf/50V to replace 150uf/50V
220uf/50V + 33uf/63V to replace 250uf/50V
47uf/63V to replace 50uf/50VC2(C24):
47uf/450V to replace 30uf/400V
22uf/450V to replace 20uf/400V
4.7uf/250V to replace 5uf/250VThanks
Raul
P.S. A thing about the coupling caps to replace: in my amp, the four caps coupling the 7199s to the 6BQ5s are four .068, not two .06 and two .04.
Follow Ups:
I have two Sherwood S-5000 schematics, the one of rather bad quality that's available on the net (http://www.triodeel.com/s5000.gif ) and another from a 1960's copy of a Sam's photofact. I was using this last one because it's a better quality copy and because the other says "Serial No. 959000 and up" while mine is a 5121XX.
But after all these helpful messages that I got from many of you after my request for help, I found that something was wrong in the schematics I was using. So I carefully compared the two and I found that I was following a wrong schematics.
The two schematics, for example, show the the bias supply rectifier with the two "diodes arrows" pointing into opposite directions: the Sam's (that I followed) has them pointing to the filter cap (as I did yesterday), while the "net's schematics" has them pointing toward the power transformer (as some of you told me to do).
Again: the 47 ohm 5W resistor (that is on my amp) becomes a 33 ohm 7W in my schematics.
Another: in my amp the can capacitor C2 (C24 on the "net" schematics) is a two sections (30/20/400V) can, and not a three sections (30/20/400-5/250) as the Sam's parts list states (and as I reported in my post above).
So, if the correct schematics is the one from the net, yesterday I installed the two 1N4007 diodes in the wrong way, and tomorrow morning I'll install them again as per the "net schematics" direction (arrows pointing to the transformer). AS HERE WE NEED NEGATIVE VOLTAGE, IS THIS THE CORRECT WAY TO INSTALL THEM, RIGHT?
Then I'll should be able to see if only the selenium rectifier was damaged from the short or if also the filter cap(s) suffered. However, as there was a low bias also before the accident, I think that I will replace at least also that bias filter can cap.
Of course, following your advices, I will pull the tubes and I'll check the voltages before putting them on again.
Raul
Or having a response from you, as if I were speaking to the dark blue sea. Maybe, getting over-zealous, my fault again??This phenomenon is common to this asylum. I don't need people to thank for me but at least, I want to know the inmates have read my listing and got better ideas.
The selenium rectifier due to age, would cause a higher voltage drop across itself and hence lower bias. a leaky cap will do the same.
Sorry Koo,
Of course I read carefully your posts and were these that put me in the doubt that something was wrong in my schematics. I have two schematics with opposite directions for diodes and by being a newbie I was very confused by this. I would have written to you to ask some more detail but I saw that you are not accepting emails. So after reading all the other emails I began to understand how all these things of positive/negative, bias and not bias caps work. Then I posted my conclusive opinion that my schematics was wrong.
Today I will replace the wrong diodes and I'll see what happen, then I would have posted the results and of course I'm very grateful to everyone that answered to help me. Sorry if I seemed ungrateful to you.
Raul
I am a professional engineer and I am willing to give my advice (though the risk is on your side) and share my experience. Nowadays, this asylum is overwhelmed with advertisments(or better say, pre-advertisements) and Ebay grieves and it's driving me mad, too.When you post some topics really pertinent to the Asylum, very few people would respond.
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