[Heathkit] How about the SB-220?

[Mike Hyder --N4NT--]

Marvin, you're welcome.  I'm sending this to the reflector so as to expose 
my ideas to flying barbs.

I'll give you my experiences briefly.  When the FCC ordered that amps no 
longer could cover 10 meters (approximately 1977), I ordered an SB-220 kit.

Once, there was a big bang in the amp -- some say it would have been caused 
by a parasitic oscillation.  Rich Measures belongs to this school.  I 
installed new tubes (one was ruined by the bang) and installed parasitic 
suppressors -- NiChrome coils.  Measures sells them.  Look here and specify 
your amp model when ordering: http://www.somis.org/Price-Info.html

I use Ten-Tec rigs and run 35-45 WPM CW.  My main consideration is that the 
transmit relay in the SB-220 presents over 100 VDC across the back-panel 
jack and current sufficient to cause pitting to the contacts in a 
transceiver's relay.  You can buy a small circuit called the SK-220 Soft-Key 
for the Heathkit SB-220 or SB-221 from this website: 
http://www.harbachelectronics.com/main/page_products_sb220__sb221.html 
This is a very worthwhile modification.

They also sell a module called the SS-221 Soft-Start which I believe is NOT 
NEEDED AT ALL, don't waste your money (read about that on Measures' site).

I have a full QSK amplifier but greatly prefer my SB-220.  Here's why:  The 
Ten-Tec rigs have a drop-out delay on the relay which switches an amplifier 
to transmit.  That delay is to prevent the rapid clatter of the amplifier's 
relay.  But there is a most salutory effect to that.  When the amplifier 
switches to transmit, there is sufficient signal coupled from the antenna 
through the antenna relay and into the transceiver.  So when I'm working QSK 
at perhaps 45 WPM and start to transmit, my receiver becomes much quieter --  
but enough of the other guy's signal comes through for me to hear him, even 
if his signal is perhaps S4 or so (maybe much less) because the signal is 
still well above the noise level.  I keep my transceiver's drop-out delay 
set to maximum.

With the age of the your amp, here's what I'd consider doing to it:
First, remember that the 3-500 tubes must be operated vertically!  I'd 
remove the front spacers on the feet to make the amp sit level on the desk.
a. I'd oil the fan motor as suggested by Rich Measures
b. I'd install that SK-220 Soft-Key circuit.
c. If the electrolytics are original, I'd replace them.
d. I'd REPLACE the equalization / bleeder resistors across each electrolytic 
capacitor per Measures, whether or not I replaced the electrolytics!
e. I'd make sure I had installed the NiChrome parasitic suppressors from 
Measures.
f. I had trouble with the big zener diode used for PA bias.  The Harbach 
RM-220 Rectifier/Metering Board fixes this problem.
g. I'd take Measures' advice about removing the interlock from inside the 
final cage and I'd use "Stove Black" or as he said, "black liquid shoe 
polish" to paint the inside of the final compartment (including the cover to 
same).
h. If I had lotsa money, I'd buy a spare fan & motor and a spare antenna 
relay (just in case).  I was stationed in Ethiopia for some three years and 
developed a great fondness for spares.

But my main points are these:
Don't convert the amp to QSK.
Do install an SK-220 circuit (or build your own circuit).
Otherwise consider ALL of Measures' ideas.

The SB-220 is a great amp.

73, Mike N4NT

----- Original Message ----- 
From: "Marvin Moss" <mmoss at mindspring.com>
To: "Mike Hyder --N4NT--" <Mike_N4NT at embarqmail.com>
Sent: Friday, August 21, 2009 04:59 PM
Subject: Re: [Heathkit] How about the SB-220?


> That is a good one.
> Thanks.
> Marvin
>
>
>> [Original Message]
>> From: Mike Hyder --N4NT-- <Mike_N4NT at embarqmail.com>
>> To: <mmoss at mindspring.com>
>> Date: 8/21/2009 03:43:24 PM
>> Subject: Re: [Heathkit] How about the SB-220?
>>
>> Look here: http://www.somis.org/
>>
>> particularly here: http://www.somis.org/SB220ci.html
>>
>> 73, Mike N4NT