[BC] Re: Vanguard & Vanguard II

[Phil Alexander]

On 17 May 2005 at 7:34, DHultsman5 at aol.com wrote:

> The Vanguard was the original 1 kW single tube transmitter.  It was  
> essentially a linear amplifier,  which had final amplifier efficiency of  
> approximately 36-40%.  

Heh, heh, on a VERY good day with a dummy load. <gggggg>

> The low level RF stage included a modulator all  solid state.  The 
> transmitter sounded pretty good. If it was tuned for  maximum power the sound 
> and modulation degraded.

When properly tuned for modulation, it was FLAT from 20 Hz to beyond 20 kHz
with under 1% THD. If the load was well matched it sounded better than FM.

> Phil can probably give more details on both transmitters.  As I recall  the 
> final was a 4CX3000 tube.

Correct.

> The broadcast industry just could not accept the clothes dryer style or ice  
> machine style cabinet at the time.  I recall many engineers stating  that..  
> "it didn't look like a transmitter.."

Remember that it was contemporary with the BC-1T when it first came out.
It was ultra-radical, especially for Gates.

> Also during that period Gates continued to make their Class B modulated  
> Class C RF Amplifier transmitter for the old salts that couldn't stand the  
> linear amplifier.

Or couldn't UNDERSTAND it. <ggg>
>
> Gates later took essentially the same hardware and placed it in a standard  
> rack cabinet and called it the Vanguard II.  Phil can probably tell us the  
> difference in the two products.

Essentially, not much. The II included all the fixes that developed for the
original design - minor stuff that made the exciter/driver more stable and
somewhat easier to tune correctly PLUS a built in dummy so you could tune
it on the dummy and KNOW the box was OK, and that the real problem was your
load. The frame was the same used for the contemporary BC-1G and later 1H.
Basically, the difference between a V and V-II was about the same as the
difference between a late model 1T and 1G, which is to say packaging and
marketing with typical first generation design clean-up.

> Comments about power consumption may be more hearsay because using only one  
> tube in linear with only one filament as compared to four filaments may be  
> closer than we all think.  As I recall the two transmitters available at  the 
> time of the Vanguard II, was the BC-1H. I will look I think I have manuals  on 
> both products.

Actually, the V-II overlapped most of the BC-1G and BC-1H production. Of course
those were basically the same boxes with 807 tube drivers replaced by SS in 1H.

> I only worked on two of these units.  One always sounded bad and I  suspected 
> the load. 

Count on it!  Think about how a Smith chart of the load will affect a class A !!

> I suggested that they have the load checked , they  didn't and 
> continued to complain about the transmitter. 

If only you had had a network analyzer. <g>

Really, what I'm saying is that a bridge would have helped, but the analyzer
would clearly show the need for reactance adjustment on a Smith chart display.

> The other sound bad  when I arrived 
> but basically was loaded too tightly and clipping on positive  peaks.  I 
> retuned and it sounded much better.

With a good load, they could be made to sound better than anything else on
the band, but sadly, those were few. IMHO the efficiency advertising was
a mistake because it encouraged mis-tuning to try to get it. Secondly, the
guy who designed it didn't understand the realities of AM transmission
systems. BTW - He's also the same guy who gave us the TE-1 FM exciter and
the VP-100, so I'll make no further comment and let that speak for itself.

> The first Vanguard I saw was at KNUZ, 1230 in Houston.  The station  was 
> clean and loud for a 1 kW in Houston. They later upgraded to the Vanguard  II.

Properly installed and maintained by someone who understood it, there was 
no better transmitter. The V-II was a better physical fit in most plants and
it included all the engineering fixes, but it was very complex in its 
simplicity. <g>

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




-- 
No virus found in this outgoing message.
Checked by AVG Anti-Virus.
Version: 7.0.308 / Virus Database: 266.11.12 - Release Date: 5/17/05