[Amps] 6 mtrs:

[Nils Petter Pedersen]

> And yes, when it is operated properly the IMD is excellent.

I can not argue against that as I have never had the chance to test one of
your conversions. ....
Also, my points in the mailings are of a general nature, and not 
spesifically
pointing to your construction.
But driving a pair of 572B's to 750W output  looks to a retired E 
professional
like pushing an old VW beetle to 100MPH would look to an auto engineer:
Risky,- at best :-)
May be I am too conservative ??? ...


----- Original Message ----- 
From: "jeremy-ca" <km1h at jeremy.mv.com>
To: "Nils Petter Pedersen" <la7sl at online.no>; <amps at contesting.com>
Sent: Tuesday, September 25, 2007 5:47 PM
Subject: Re: [Amps] 6 mtrs:


> 750W is key down. Youre forgetting that many still use CW for chasing DX 
> on 6M. When operating on SSB I always suggest loading to the max to 
> establish a point and then reduce power with the mike control and follow 
> the Ip and Ig in the Tuning Section of the SB-200 manual. An operating and 
> test result procedure is shipped with every amp.
>
> Some hams will always over process and overdrive an amp, it is not limited 
> to a 6M conversion.
>
> And yes, when it is operated properly the IMD is excellent.
>
> Carl
> KM1H
>
>
>
> ----- Original Message ----- 
> From: "Nils Petter Pedersen" <la7sl at online.no>
> To: <amps at contesting.com>
> Sent: Tuesday, September 25, 2007 9:49 AM
> Subject: Re: [Amps] 6 mtrs:
>
>
>> Hi all !
>> I have so far not contributed to this discussion, but as a long time ham
>> (1968) as well as a professional, I would like to say a few words:
>> I think it is possible to make a pair of 572B's work relatively well on 6
>> meters by careful design taking the tubes internal construction into
>> consideration.
>> In the early days of VHF there were not too many tubes available designed
>> for these frequencies. So manufacturers often operated tubes well above 
>> max
>> frequency ratings. I remember an RCA Nera TV transmitter operating near
>> 200Mhz using a pair of tubes rated at a max freq of 50 Mhz for full 
>> ratings.
>> The construction was unconditionally stable and several units were 
>> produced,
>> indicating a good repeatability. The transmitter ran at abt 60% of max 
>> power
>> ratings given at 50Mhz. And this is what worries me most about the
>> conversions discussed here. They say they get 750 watts or more from 
>> those
>> units.
>> Manufacturers max rating for two tubes ICAS is 600 watts below 30Mhz ! 
>> It
>> is obvious to me that 750 watts ICAS at 50 Mhz is way out of all good
>> engineering and operating practices !  Say 350 watts and I would probably
>> accept it, but I would NOT recommend it. Why should we push all
>> limits when we have suitable tubes at reasonable prices that will give a
>> much more reliable unit ? If it is just to prove that it can be done, I
>> understand it,
>> but to make a bussiness out of it ?  It is at best very questionable
>> engineering practices in a unit that is promoted for sale. But can it be
>> done ? Certainly !
>> Is it repeatable ? Most certainly ! Is it to be recommended ? Most 
>> certainly
>> not !  I have myself built a 2 meter FM transmitter using EL-95 as a PA.
>> That is an AF amplifier tube ! No freq of max ratings is given. It is
>> strictly AF amp. And it was run well above its max power ratings ! So 
>> sure,
>> it can be done,-
>> but would I recommend it ? NO !!  And I would love to have one of those
>> converted SB200's on my desk, tune it to 750w, apply a two tone test
>> signal at 750watts PEP , and watch my spec. analyzer ! I would also love 
>> to
>> see it at 500w pep ! IMD -32dB ?? Hardly :-)
>>
>> _______________________________________________
>> Amps mailing list
>> Amps at contesting.com
>> http://lists.contesting.com/mailman/listinfo/amps
>>
>
>
>
>
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