[Amps] more sb220 questions

[John Adkins]

Colin--
Thanks for the info re the chokes.  I assume the caps should also be left out.  My major direction
at this point is to address the airflow problem that the modifier caused in shielding the tube
sockets.  After doing that and getting the tubes wired up again, I will again fire it up and see
what's what.  I can check the zener in the meantime, and if necessary, replace it with a diode
string, since that's cheap and easy.

Thanks again and 73
John
w4kv

--- Colin Lamb <k7fm at teleport.com> wrote:

> Date: Fri, 2 Sep 2005 12:30:00 -0700 (GMT-07:00)
> From: Colin Lamb <k7fm at teleport.com>
> To: w4kv at arrl.net
> Subject: Re: [Amps] Amps Digest, Vol 33, Issue 2
> 
> Hello John:
> 
> The 1 mh chokes were only put there because Collins did it in the 30L-1.  They should be left
> out and are an invitation to oscillations.  I have removed the chokes on every SB-220 I have
> worked on and grounded the grids directly.  I have been only following the thread slightly, but
> there is some simple cause for the loss of power output and doing the little things to restore
> to the original configuration will not solve the problem it has.  
> 
> 73,  Colin  K7FM 
> 
> -----Original Message-----
> From: John Adkins <w4kv at yahoo.com>
> Sent: Sep 2, 2005 12:02 PM
> To: amps at contesting.com
> Subject: Re: [Amps] Amps Digest, Vol 33, Issue 2
> 
> Will--
> Thanks for the suggestions.  I've already started taking the amp back to a less-altered state. 
> I've removed the shield from around the tube sockets and am going to put the bifilar choke back
> to
> its original position. right now I'm trying to find replacements for the 1 mH rf chokes which
> the
> modifier removed.
> 
> Once I get the tubes rewired, I'll check on the tube bias and the HV at the plate  In the
> meantime, I'll check to see if the plate choke is open.  I'm planning to replace the PC board
> with
> a Harbach card once Jeff works thru his backorders.
> 
> I don't know whether I posted the page of the restoration in progress:
> http://www.geocities.com/w4kv/sb220-2
> 
> Thanks and 73
> John
> 
> 



		
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