Actually the 572B is rated to 54 mc but maybe not to 54 mHz.
It all depends on when and who wrote the spec sheet.
Bright red plates is OK for a few seconds during tune up but is not
conducive to long life in regular use, especially imports. Properly tuned a
pair should show no color at 500W on SSB and just a bit on voice peaks at
750-800W. I recommend running at 60-70W drive, tuning up to peak the grid
current at 100ma, and look at the wattmeter. If its over 700W then reduce
the mike gain for around 600W on a peak reading meter. This keeps tubes and
PS happy for a long time.
Carl
KM1H
----- Original Message -----
From: "Larry" <n1miw@cox.net>
To: "'Carl'" <km1h@jeremy.mv.com>; "'bill price'"
<kingofbackswing@hotmail.com>; <amps@contesting.com>
Sent: Sunday, August 09, 2009 12:02 PM
Subject: RE: [Amps] SB-200 6 meter conversion
> I have had no issues with tuning my 572B tubes during testing, even with
> having the plates glowing bright red. Even though the tubes are not rated
> for 50MHz, how many other tubes are run outside their specs (HV,etc.) and
> work fine?
>
> I would like to convert an SB-220 or 221 - if someone has a junker with
> a
> good transformer but soft tubes they're willing to give me, I'll take it.
> Other than that, I'll stick with the 200 because that's what I could
> afford.
> I can't justify to the wife spending $800.00 on a good amplifier that
> will
> be converted to a monobander and used only a couple of months throughout
> the
> year. $500.00 on a faulty one is pricey too...
>
> I still may convert to the GI-7b, but this was a cheap experiment (zero
> dollars spent on the conversion) that seems to be going quite well,
> despite
> what all of the skeptics say. It's all part of my learning curve with
> amplifiers. If it blows up, so be it. I like fireworks! 73's, Larry N1MIW
>
> -----Original Message-----
> From: Carl [mailto:km1h@jeremy.mv.com]
> Sent: Sunday, August 09, 2009 9:50 AM
> To: bill price; n1miw@cox.net; amps@contesting.com
> Subject: Re: [Amps] SB-200 6 meter conversion
>
>
> The 572B works just fine on 6M at full ratings. This is been discussed
> many
> times on here and should no longer be an issue.
>
> Carl
> KM1H
>
>
> ----- Original Message -----
> From: "bill price" <kingofbackswing@hotmail.com>
> To: <n1miw@cox.net>; <amps@contesting.com>
> Sent: Sunday, August 09, 2009 9:21 AM
> Subject: Re: [Amps] SB-200 6 meter conversion
>
>
>
> the 572b tube is not rated to operate on 6 meters, the sb220 would be a
> better choice.
> i have a sb200 with a gi7b tube that some one started to mod and gave up,
> this fall i will finish it. bill nj2s
>
>
>> From: n1miw@cox.net
>> To: Amps@contesting.com
>> Date: Sat, 8 Aug 2009 22:34:18 -0400
>> Subject: [Amps] SB-200 6 meter conversion
>>
>> I just wanted to report that I have been almost successful at converting
>> my SB-200 with 572B's to 6 meters. I originally wanted to replace the
>> tube
>> with a GI-7B (and still may do so), but decided that I should give it the
>> effort to at least try the 572's to "see what happens". I removed several
>> plates from the tune cap and at the moment, I have a jumper on the output
>> coil at the 1 turn mark - this coil looks like it "might" be original,
>> but
>> not sure since this amp was previously modified for ...ahem... 11 meters.
>> With 30 watts in, I'm seeing ~500 watts out on the bird. Not sure about
>> the
>> accuracy though because the slug I'm using is for 2-30MHz. I plan on
>> connecting up the amp to the digital wattmeter tomorrow to see how close
>> I
>> actually am to the 500 watt mark - it's getting late. I'm also hoping the
>> signal is clean - I don't have an analyzer. Guess some on-the-air testing
>> is
>> needed during off-season.
>>
>> One quick question for you guys who are running modified 6 meter amps -
>> does the amplifier draw more line current after the mod? I seem to have
>> allot of output for little input, and when I approach 70 watts in, I run
>> the
>> risk of tripping the breaker in the house. I'm happy with the 500 watts
>> (if
>> accurate), but wanted to hear someone else's experience.
>>
>> Oh, by the way - I didn't touch the suppressors on the anodes. They're
>> still 3 turns around a 47 Ohm Carbon Comp resistor. I have ~300ma grid
>> current with ~500ma plate current at 500 watts output.
>>
>> 73's... Larry N1MIW
>>
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