Hi Kouichi
I consider the SB220 amplifier to be one of the best workhorses available.
But it does require some respect to ensure satisfactory performance. Metering
is basic but more than adequate. Above all, it doesn't have any microprocessor
based monitoring systems which cause the amplifier to shut down and only
provide the operator with an incomprehensible fault code!
As I noted before, the amplifier doesn't require any modifications to operate
on the WARC bands.
However I have incorporated the following to my SB220s:
*
Replaced electrolytic capacitors – the SB220s are now about 50 years old and
electrolytics of that age are likely to be suspect.
*
Added a 50 ohm wirewound resistor to the HT anode feed to limit current in the
event of a flash-over.
*
Added back to back diodes across the meters to help prevent damage to the
meters due to excessive current during a flash-over.
*
Added a softkeying module. The keying voltage as the phono socket is +110V DC
which could cause damage to a transceiver's keying output interface. Mine is
home designed/homebrewed but commercial units are available, such as
https://harbachelectronics.com/wp-content/uploads/2014/07/SK-220PIC.pdf
The only fault which I can remember happened with one of the amps and that was
one of the HT rectifier diodes failed. I replaced the whole string with 1N5408
diodes.
73
David
________________________________
From: Kouichi Ueno <kueno@wine.ocn.ne.jp>
Sent: 09 October 2024 00:36
To: David G4FTC <g4ftc@hotmail.com>
Cc: amps@contesting.com <amps@contesting.com>
Subject: Re: [Amps] about the WARC bands of the Heathkit SB-220.
Hi David ,
I have summarized your valuable advice
about the WARC bands of the Heathkit SB-220.
1) On 12m, set the band switch to 10m
2) On 17m, set the band switch to 15m
3) On 30m, set the band switch to 20m
How to operate the Load and Plates
1)Set the load control to maximum capacitance.
2)Apply about 10 watts of drive.
3)Rotate the tune control to find a dip in anode current or a peak in
power output on the external power meter.
4)Adjust the load control for maximum power output.
5)Gradually increase the drive while adjusting the tune and load
controls for maximum power output at each drive level.
6)Repeat the procedure up to 100 watts of drive
Thank you
Kouichi Ueno Ji1FGX/DU9
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