[Amps] about the WARC bands of the Heathkit SB-220.
Victor Rosenthal 4X6GP
k2vco.vic at gmail.com
Wed Oct 9 09:33:13 EDT 2024
You can use multiple diodes in series or even zeners for higher voltages.
73,
Victor, 4X6GP
Rehovot, Israel
Formerly K2VCO
CWops no. 5
http://www.qsl.net/k2vco
On 09/10/2024 16:26, David G4FTC wrote:
> Thanks - I can see the logic in that.
>
> You just need to ensure that the voltage across the shunt resistor in
> normal operation never exceeds, say, 0.5V, and that the diodes used can
> handle the fault current.
>
> David G4FTC
> ------------------------------------------------------------------------
> *From:* Victor Rosenthal 4X6GP <k2vco.vic at gmail.com>
> *Sent:* 09 October 2024 13:13
> *To:* David G4FTC <g4ftc at hotmail.com>
> *Cc:* Amps reflector <amps at contesting.com>
> *Subject:* Re: [Amps] about the WARC bands of the Heathkit SB-220.
> Well, for example, if the meter uses the common 'voltmeter' circuit --
> that is, a low value shunt resistor (typically 1 ohm) in series with the
> (for example) cathode circuit and a multiplier resistor in series with
> the meter which allows the sensitive milliammeter to read the voltage
> drop across the shunt, then diodes can be placed across the shunt -- but
> not across the meter terminals.
>
> 73,
> Victor, 4X6GP
> Rehovot, Israel
> Formerly K2VCO
> CWops no. 5
> http://www.qsl.net/k2vco <http://www.qsl.net/k2vco>
>
> On 09/10/2024 15:07, David G4FTC wrote:
>> 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 <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
> <https://harbachelectronics.com/wp-content/uploads/2014/07/SK-220PIC.pdf> <https://harbachelectronics.com/wp-content/uploads/2014/07/SK-220PIC.pdf <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 <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 <mailto:g4ftc at hotmail.com>>>
>> Cc: amps at contesting.com
>> <mailto:amps at contesting.com
> <mailto:amps at contesting.com>> <amps at contesting.com
>> <mailto: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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