[NCC] [MRRC] Advice About Old Amps

[Earl Morse]

Hal,

Go QRO and leave the LP category for me!  ;-)

Powering up old amplifiers isn't hard, it just takes a little finess.  Get a variac, disconnect the plate HV from the tube and start by bringing the thing up at 10% AC input.  Leave it there for a day, then increase it to 20% and let it set for a day, then 30% the next day, etc until 10 days later you are at full AC input.

During this time the caps should reform if they can.  Also during this time the filaments have been on and may burn off any gas that has formed in the tubes.

Next hook the HV back up and tune the amp.  Low power at first.  Watch the tubes, if you start getting that purplish glow of a gassy tube back off the power before it arcs.  On 3-500z tubes the getterer is supposed to be on the plate and removes that gas when you heat it up to reddish orange or so.

I had a couple of SB220s and a SB1000 that I brought up this way after one blew the fuse when first powered up after a long storage.  The real trick is bringing it up in such a way that it doesn't arc over and do even more expensive damage.

Here's a link on the topic as well:
http://www.eham.net/ehamforum/smf/index.php?topic=72672.0

Check www.w8ji.com as he has a bunch of stuff too.

Earl
N8SS



--- hal at japancorporateresearch.com wrote:

From: "Hal Offutt" <hal at japancorporateresearch.com>
To: "North Coast Contesters" <ncc at contesting.com>,	"Mad River Radio Club" <mrrc at contesting.com>
Subject: [MRRC] Advice About Old Amps
Date: Thu, 24 Jul 2014 10:04:48 -0400

I could use some advice from you QRO folks or electronics wizards.

I have two old amps I'd like to sell.  I need the closet space they are occupying.  Here's the situation:

1.  Drake L7

I bought this new back in the mid-80's and used it through 1999 when it was working fine.  It had moderate contest use during those years.  After I moved away from W1 land, I decided to stick with LP so It has been stored in a second-floor closet since then.  Cosmetically it is nearly perfect.  I had to replace the power supply caps once and at the time I bought an extra set from Drake (ten caps made by Sprague) which I have stored in a ziplock bag, hopefully to keep out moisture.    

I'm no electronic engineer and have no time to cope with repairing the thing if I turn it on and something blows up.  I believe that for equipment that has been unused for a long time, you are supposed to apply a very low voltage and gradually increase it to cook away the moisture, but I don't have any experience and I don't have the necessary equipment to do this.  So I am thinking that I should not even plug it in and just try to sell it "As Is" on Ebay or similar.  Note:  this model does not work on 10 meters.

What should I do?  

Anyone want to make an offer?


2.  Heath SB-230 - Free

Same situation as above except that I bought this used in the 1990's, I suppose because the Drake did not work on 10 meters.   After I bought it I found it was a mess inside and I had to replace the caps and maybe other components (I really don't remember) but I got it working and used it for several years.  I have no idea if it works now.  Probably not.  If anyone wants to pick this up, they can have it free.  Is there any point in trying to sell it on ebay if nobody here wants it?

Thanks!

73, Hal W1NN
Medina, OH (30 minutes SW of Cleveland)
_______________________________________________
MRRC mailing list
MRRC at contesting.com
http://lists.contesting.com/mailman/listinfo/mrrc