[Amps] Amps Digest, Vol 33, Issue 2

[John Adkins]

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

--- amps-request at contesting.com wrote:


> Date: Fri, 02 Sep 2005 07:46:53 -0400
> From: "Will Matney" <craxd1 at verizon.net>
> Subject: Re: [Amps] more sb220 questions
> To: amps at contesting.com
> Message-ID: <200509020746530370.01667CCE at outgoing.verizon.net>
> Content-Type: text/plain; charset=us-ascii
> 
> John,
> 
> There's several thing that could cause no power output from the amp. That zener diode being one
> which I'd check first. It sets the tubes bias on transmit. No heater voltage. No high voltage
> would also do it, but I assume you checked that. You could still show plate voltage on the meter
> in the amp and not have it on the tubes because of an open plate choke. Another thing to cause
> it would be a bad relay. The amp supposed to use a 3PDT relay with 10 amp contacts and was an
> open frame type. You can use an enclosed one here also. Bad tubes would be the last.
> 
> I'd check the bias voltages first. On receive you should have around +120 Vdc on the C.T. of the
> heater transformer. On transmit it should be around 7 volts (zener voltage). The antenna relay
> switches this voltage through the 3rd contact. Next, check the plate choke for continuity.
> 
> Best,
> 
> Will


__________________________________________________
Do You Yahoo!?
Tired of spam?  Yahoo! Mail has the best spam protection around 
http://mail.yahoo.com