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

[David G4FTC]

Hi Victor,

> There are various ways to protect meters,

Please enlighten me.

David G4FTC
________________________________
From: Victor Rosenthal <k2vco.vic at gmail.com>
Sent: 09 October 2024 10:31
To: David G4FTC <g4ftc at hotmail.com>
Cc: Kouichi Ueno <kueno at wine.ocn.ne.jp>; Amps reflector <amps at contesting.com>
Subject: Re: [Amps] about the WARC bands of the Heathkit SB-220.

Back to back diodes across a meter will not protect, for example, a meter with a 1 ma movement. The forward voltage drop of about half a volt is enough to destroy it.
I speak from personal experience.
There are various ways to protect meters, but this is one that doesn't work.

Victor 4X6GP

On Wed, Oct 9, 2024, 09:32 David G4FTC <g4ftc at hotmail.com<mailto: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


________________________________
From: Kouichi Ueno <kueno at wine.ocn.ne.jp<mailto:kueno at wine.ocn.ne.jp>>
Sent: 09 October 2024 00:36
To: David G4FTC <g4ftc at hotmail.com<mailto:g4ftc at hotmail.com>>
Cc: amps at contesting.com<mailto:amps at contesting.com> <amps at contesting.com<mailto:amps at 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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