[BC] Re: Vanguard

[Phil Alexander]

On 17 May 2005 at 7:45, DHultsman5 at aol.com wrote:

> Agreed on the scope.  I wish I had available any bridge during that  time 
> period... Was the OIB available then?  If the modulation didn't sound  good and 
> waveform didn't look on the scope you could retune the final and make  some 
> difference. Also you could look at the waveform at several places within  the 
> driver.
>  
> As I mentioned I think Phil Alexander can probably enlighten us all on the  
> transmitter.

The early OIB-1 was available during that time (mid '60's) but the price was
such that few 1 kW stations would pop for it.

The Vanguard was simply (really not so simply) a class A amplifier and was 
picky about its load. Today, it would be simpler because we understand stuff
like "cusp rotation" for matching loads across a frequency span, but in 1 kW
stations of the mid-60's that would have gotten a lot of blank stares in
most places, especially from the typical Gates clientele who tended to be
small market stations on limited budgets.

Also you had to have a good scope and know what you were doing to tune it.
I think a spectrum analyzer would have helped too so you could see what
was happening to the sidebands out to 20+ kHz. The manual did show a series
of pictures of correct waveforms in the exciter/driver tune up. Anyone here
remember the "horsehead"?

Vanguard installations were either mostly trouble free or nothing but 
trouble, and the difference was the personnel running them. In short,
it was an idea both too far ahead and too far behind its time IMHO, 
and marketed to the wrong audience. It was also one of the least efficient
boxes ever built - maxed out at just over 30% and that was not easy. I 
often wondered how it might have done if marketed by Collins. Probably
much better, but the PDM/PWM idea would have killed it in the end.

Final note, the one that looked like an ice maker or washing machine was
the original Vanguard. The Vanguard II which worked more easily was built
in the same frame as a BC-1H. The Vanguard did have a couple of advantages.
Stereo was simple, just plug in the exciter. Secondly, regardless of the
power level from 0 - 1100 watts, all you had to do was dial it up so it
made hitting multiple power levels of the early PSRA/PSSA days a breeze.
It would do anything you can do now with a PWM box except help with the
power bill. <g> However, you had to know how to talk to it. <ggg>

Phil Alexander, CSRE 
Broadcast Engineering Services and Technology 
(a Div. of Advanced Parts Corporation) 
Ph. (317) 335-2065   FAX (317) 335-9037




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