Amps
[Top] [All Lists]

Re: [Amps] Re: SB220

To: "Tony Wanschura" <tonyjw@mindspring.com>," AMPS" <amps@contesting.com>, <zl2aaa@paradise.net.nz>
Subject: Re: [Amps] Re: SB220
From: R.Measures <r@somis.org>
Date: Wed, 5 Nov 2003 04:57:31 -0800
List-post: <mailto:amps@contesting.com>

>Hi Morrie,
>
>I bought an SB220 a couple of years ago.  Here are my thoughts.
>
>You said the amp has the original tubes. If it has had heavy use, the 
>tubes will probably be "soft". If not, the amp may have seen extended 
>periods of non-use, in which case the HV filter caps could be in bad 
>shape. My amp had been on the shelf for years, and the HV caps blew when I 
>flipped the mode switch on the amp to SSB. I replaced the entire HV cap 
>assembly with a new one from Harbach Electronics (see below).
>
>The SB220's T/R switching runs on 120V dc. Modern transceivers can't 
>handle it. You need to rig an interposing relay or install the Soft Key 
>module from Harbach.

Another solution is to remove the wimpy amp control relay from the radio 
and replace it with a 300V, 0.5A NPN switch transistor.  
See diagram in:
http://www.somis.org/440.html
Search for:  "Transistor Installation Note ".
Advertisement:  We sell a parts kit for doing this mod.  Price = 50-cents.
>
>The SB220 uses an old-style, slow, open-frame relay for T/R switching. 
>Modern transceivers switch much faster. This means that your transceiver 
>will be pumping RF through the amp relay contacts before they have had 
>time to close. At the very least, this results in a momentary spike of 
>reflected power, which will cause your exciter output to momentarily  
>"fold back" before coming back to full output.  Maybe not serious if you 
>are an SSB ragchewer, but an intolerable situation for a CW contester or 
>DXer. QSK is out of the question, unless you install a good vacuum relay 
>QSK system like the one sold by Rich Measures.  Use of an interposing 
>relay will exacerbate the problem.
>
>Because of the 220's smart power supply design, filament inrush current is 
>not really as big a problem for the SB220 as it was for other amps of the 
>same time period.  The damaging effect is mitigated if you start up the 
>amp in the CW position (lower plate voltage).  Harbach sells a mod that 
>cures the problem entirely.

However, after doing the aforementioned high-speed switching mod, the 
original relay can be used for stepstart service.  To do this, 2, 10 to 
25 ohm power resistors are needed plus c. a 2k-ohm 2w resistor.  Diagram 
@:
http://www.somis.org/D.a.01.GIF.
>
>SB220 mods by Harbach can be found at: http://www.harbachelectronics.com/. 
> It seems that he has suspended business temporarily, but will return 
>soon. These are excellent mods, and well worth the money.
>
>I love my 220. It just keeps cranking along. A fair price, I think, would 
>be no more than $400 USD.
>
>Good luck!
>
>Tony
>KM0O
>_______________________________________________
>Amps mailing list
>Amps@contesting.com
>http://lists.contesting.com/mailman/listinfo/amps
>
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps

<Prev in Thread] Current Thread [Next in Thread>