I think the SB200 needs more loading to decrease the grid current?
73
Jim W7RY
----- Original Message -----
From: "Steve Katz" <stevek@jmr.com>
To: <n1miw@cox.net>; "Carl" <km1h@jeremy.mv.com>; "bill price"
<kingofbackswing@hotmail.com>; <amps@contesting.com>
Sent: Sunday, August 09, 2009 9:59 AM
Subject: Re: [Amps] SB-200 6 meter conversion
> 300mA for a pair of 572Bs is a lot of grid current...I suspect the output
> doesn't look very clean, especially if you can do an IMD check (which
> requires a lot of stuff most don't have, but maybe you know somebody).
>
> WB2WIK/6
>
> ________________________________
>
> From: amps-bounces@contesting.com on behalf of Larry
> Sent: Sun 8/9/2009 9:02 AM
> To: 'Carl'; 'bill price'; amps@contesting.com
> 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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