[NJARC] NJARC Digest, Vol 73, Issue 22

Fri May 28 00:14:36 EDT 2010

 That is why I use my Heathkit Variable Isolated AC Supply with volt and ammeter this way I can monitor the current. I worked on a Dynaco ST-70 that had the original bias selenium rectifier and had the amp playing in my basement, I went upstairs for 2 minutes to get something when I returned I saw the ST-70 was pulling 3 amps, nominal 1.6 amps. If it wasn't for the ammeter, I could have blown the 45 year old power transformer. 

BTW, the original bias selenium rectifier opened, lost the negative bias to the grids of the EL34's, tubes pulled what ever current the power supply could supply..

Sal

-----Original Message-----
From: John Ruccolo <jr6v6gt at yahoo.com>
To: Jim Whartenby <antqradio at sbcglobal.net>; njarc at mailman.qth.net
Sent: Fri, May 28, 2010 12:06 am
Subject: Re: [NJARC] NJARC Digest, Vol 73, Issue 22

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Hi Jim,

Agreed. Another approach is to substitute a good, regulated bench supply for the 
internal power supply. Let the *bench* supply take the heat -- if the ammeter 
gets pinned, you know you've got a serious problem and need to do some 
resistance checks. (Probably shorted filter cap or shorted diode in those TV 
voltage doubler supplies).

JR

----- Original Message ----
From: Jim Whartenby <antqradio at sbcglobal.net>
To: njarc at mailman.qth.net
Sent: Thu, May 27, 2010 4:56:55 PM
Subject: Re: [NJARC] NJARC Digest, Vol 73, Issue 22

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Honestly, I would do minimal testing until the power supply is in proper working 
order.  A leaky filter capacitor can easily take out the power transformer and 
turn a bad situation worse.  I am beginning to have the opinion that a good AC 
power meter is more valuable then a variac ever could be.
Jim

----- Original Message ----
From: John Ruccolo <jr6v6gt at yahoo.com>
To: victor bellini <victor3d at verizon.net>; njarc at mailman.qth.net
Sent: Thu, May 27, 2010 12:30:53 PM
Subject: Re: [NJARC] NJARC Digest, Vol 73, Issue 22

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Hi Victor,

Look *carefully* where each terminal exits the can. Usually that area is in the 
shape of circle, square, triangle.

If your pix tube is good, you're way ahead of the game. What symptoms do you 
have? What (if anything) is on the screen? Does the set have sound at least?

Regards,

John

----- Original Message ----
From: victor bellini <victor3d at verizon.net>
To: njarc at mailman.qth.net
Sent: Thu, May 27, 2010 10:38:13 AM
Subject: Re: [NJARC] NJARC Digest, Vol 73, Issue 22

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I spoke with Scotty yesterday and he informs me that this is not a tube that 
he can restore. He did agree that this tube is very difficult to test unless 
you have an individual pin rejuvenator tester which I do not. He asked me to 
look at the filament which I had not done (ha) and said that it is a good 
thing if it lights up which it did ...ah progress. Now I realized that the 
three filter caps on top of the chassis had never been changed and realize 
that this may be the problem. I realize that I must change these before 
dropping the cash to buy a new tube. the canister has the usual symbols of 
triangle square and semi-circle but I can't for the life of me find them on 
or near the terminals. I have only changed out one other multi filter 
canister and I am not that comfortable with doing this so maybe a good 
candidate for the next clinic. I see that I just missed one.

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