[Amps] about the WARC bands of the Heathkit SB-220.

[Kouichi Ueno]

Hi David,

Thank you again for the valuable information.

Actually, I do not own an SB220 yet. Right now, it's being sold at an auction in Japan for about $470. 
It's a reasonable price, so I became interested in the SB220. 
However, I was surprised when you mentioned that it has been 50 years
since it was manufactured.

Since I live in the Philippines, the shipping cost via DHL is around $670, which makes me hesitate to place a bid. 
The current owner hasn't done any maintenance on the capacitors, and
spare parts for maintenance are hard to come by in the Philippines.

However, hearing everyone's passion for the SB220 has made me unsure whether I should go ahead and purchase it.

Thank you again.

Kouichi Ueno


On Wed, 9 Oct 2024 06:29:53 +0000
David G4FTC <g4ftc at hotmail.com> wrote:

> 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