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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> http://lists.contesting.com/mailman/listinfo/amps
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