[Amps] Tube limits & Beetles

[jeremy-ca]

----- Original Message ----- 
From: "Nils Petter Pedersen" <la7sl at online.no>
To: <amps at contesting.com>; "jeremy-ca" <km1h at jeremy.mv.com>
Sent: Tuesday, September 25, 2007 12:14 PM
Subject: Re: [Amps] 6 mtrs:


>> 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 ??? ...

Well, Ive seen Beetles do 200 mph in the 1/4 mile at the drag strip.

And other souped up models do 100 on the street. There used to be all sorts 
of performance kits available back in the 60's & 70's. I'll even admit to 
installing a Corvair pancake 6 in one along with the Spyder package 4 carbs. 
That was a scary ride but it was almost unbeatable from light to light! I 
made a lot of money with that car.

And yes, 750 W is a bit excessive but that appears to be where the tubes 
appear to be the "happiest" when run at the 100W of drive that the spec 
sheet claims is OK.  And with 40 years of history to compare it doesnt 
appear to hurt them. The primary destroyer of the 572B is mistuning or 
taking forever and resulting in bright orange plates; they can take that 
abuse only so many times before bad things happen. The 6M amp is a set and 
forget affair since the active band is quite narrow.

Carl
KM1H




>
>
> ----- 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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