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[Amps] Drake L7 issues- update

To: <amps@contesting.com>
Subject: [Amps] Drake L7 issues- update
From: 2@mail.vcnet.com (Richard)
Date: Wed, 12 Jun 2002 09:53:44 -0700
Randy

>Thanks for the suggestions to date.
>
>I have made a little more progress
>
>Using a good light source, the existing caps look fairly bad. The one with 
>the lead cut loose measures a dead short on the VOM, and two others look 
>like 
>they are slightly deformed at the top end with swelling inside. 

they are history/RIP

>Cant see the 
>diodes and resistors yet, but dont intend to take the boards out until I get 
>the new parts. 
>
>The good news is that the old Drake undersized (2 watt) glitch resistor 
>didnt 
>blow,  which I am reading as a sign that the immediate problem was upstream 
>in the power supply, and not on the amp rf deck (scraping load cap not 
>withstanding).  

agreed

Undersized is right. A 2w resistor does not limit peak fault current at 
3kV.  Some 10w resistors will. 

> I never did hear any "noise" from the rf deck, and the 
>initial power up reading on the plate meter shows that one leg of the 
>voltage 
>doubler was not operating to begin with. 
>
as a one legged FWD should do.

>Looks like I can get some 105 degree computer grade caps from Mouser for 
>about $9 each if I buy more than 10, and they are about 1/4 the size of the 
>old ones. 

I would buy 16 so that I had a complete extra set.
>
>I wonder if I should replace the two giant 50k 50 watt dropping resistors 

yes

>which have the unusual mounting scheme at the top of the supply. They 
>measure 
>ok, about 10% low, but there was at least one thread on this board that i 
>found which indicated that they sometimes give an arcing problem from the 
>mountings. Seems like drake could have simply put another winding on the 
>transformer instead of  using these things to get 120 volts from 2500.
>
I would remove R-9, 10, and 11.  A 10k - 100k, 0.5w resistor across the 
NO cathode relay contacts will cut the tubes off.

-  R. L. Measures, a.k.a. Rich..., 805.386.3734,AG6K, 
www.vcnet.com/measures.  
end


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