[Hallicrafters]V15#3 Opened Choke; Shorted BB?

[Phil Barnes-Roberts]

At 01:37 AM 4/3/05 -0500, hallicrafters-request at mailman.qth.net juggled the 
keys to produce...
>From: "W4QG" <w4qg at cfl.rr.com>
>Subject: [Hallicrafters] sp-600 RF Choke question
>Date: Sat, 2 Apr 2005 12:47:48 -0500
>To: <hallicrafters at mailman.qth.net>
>
>  Hello All,
>
>I am in the process of restorring/repairing a SP-600-JX.
>
>During my debug of the circuitry I've discovered that the blocking
>choke for V2 (2nd RF amplifier) is open. (L14) - (No voltage at V2 pin 5).
>
>I am no expert at all on RF chokes, do I need to worry about the Q of my
>replacement choke? I found a 100uH choke in the junk box, can I get by with
>any choke with simular inductance? I'm somewhat concerned that L14 opened
>up, I would have thought that choke would be a very low failure component. I
>have  looked around the adjacent circuitry in the RF deck and I haven't
>found any other  faulted components. I did see some scoring on the switch
>contacts associated with V2 that enguage the tuning assemblies. I did not
>see that scoring on any of the other switch contacts. This rig has already
>had 90% of the Black Beautys replaced before I even started on it.
>
>Anyone have any suggestions?
>
>73,
>
>Paul W4QG

Paul, does it look like one of those Black Beauties was at V2?  If that 
rascal got leaky, or outright shorted, it would take out _something_ 
upstream toward the B+ supply.  Make sense?  And the choke's Q (if it's 
just a B+ isolator, not part of a tuned circuit arrangement - I'm no expert 
on Hammarlunds either) shouldn't make a difference.  You probably don't 
want a self-resonance in the frequencies of interest, and there should be 
bypass caps on either (or at least one) end of it.

And you might post this to the [Hammarlund] list, where there's likely much 
more help in that level of detail...

Good Hunting! es