[BC] Gates BC-1F

[Phil Alexander]

On 21 May 2005 at 9:39, Chris Edwards all560 at yahoo.com wrote:

This is a bit stale, but since it's a topic near and dear,
I'll try to reply. I do love the old BC-1F, not because I
found the audio that great, but because it was a real moose
on the RF side and reliable as a Swiss railroad.

> http://lists.radiolists.net/pipermail/broadcast/2005-March/004586.html
> 
> Uh,  Phil,  have you ever actually HAD one of those
> UTC LS 1kw mod transformers?   

No, I never got the chance. Maybe that was a good thing
according to your comments. <g>

I always had good luck with the smaller HA meeting spec.
One in particular would do 30-15k virtually FLAT to +40
with a pair of 6AQ5's in P-P Ultra-linear using a 6C4
split load phase inverter as driver. I don't know how
many times I used that circuit in the late '50's and
'60's.

> And driving 833's with beam pentode 807's in a cathode
> follower to replace two class-A, direct-heated 845's
> with the perfect combination of input,  driver,
> modulation transformers and reactor??????

Yeah, because my experience was far from perfect, and I
later found good reason to believe my experience was not
unique. Secondly, they weren't ALWAYS class A, they were
often AB1 verging on AB2.

To appreciate the reason for the change you need to have 
some play time with the good GREEN boards used in the 
BC-1G. Static AND dynamic balance were simple with the
addition of a couple of pots. <g>

> Come now!   The BC-1F was totally unique in all the
> world.  And I still have the 15 ips reel tapes from
> 1965 to prove it!
> 
> Anyone who ever had a 1E knows why the 1F was built in
> two cabinets.  

Actually, it was a single cabinet made to look like two,
but I understand your point. However, its footprint
was bigger than some 5 kw boxes made just a few years
later, and a small footprint became the name of the game
by 1962 if you wanted to sell boxes. Once all stations
were permitted remote control, the days of the big boxes
for small transmitters were over.

> And anyone who ever ran a 1F for years,
> then lost a modulation component and had to live life
> with the poor substitute of those used in the 1J,  1T,
> 1G or 1H knows what I mean.  

I ran a fair number of audio proofs on the 1F and was
never that impressed with the results because the
modulator was not great at 30 Hz nor was it very
efficient above 10 kHz. 

> To me,  the name "Basler"
> (like "Orban") will always be profane.  

Just curious, where do you put Chicago and Electro in 
this  pantheon? There was a period when much of Gates 
iron came from them, and ISTR some of it went into 1F's.

I don't think you should hold Bob responsible for
filling a demand of the industry and doing it better
than many others of the day. I don't think there are
ANY AM stations that would trade a 9200 for an SA-39. 
<g> Bob and Frank have both done their part to keep
listener acceptable sound quality on AM as the 
adjacent channel and power line interference have
made that more and more difficult.

Time marches on, and our choice is doing the same or
being left in the dust of history.

> "Thordarson" - now there's a name to reckon with.

Since the 1F I did most of the work on was not that far
away from them, I got to know them quite well, and
agree they were really great; not only the iron, but
their service was outstanding. I even had the president
of the company show up as the emergency delivery man one
Sunday afternoon when I was off the air. Although the 
name survives, alas, it's no longer the same company.
Their bread and butter was TV, and when it stopped using
their iron, that was the end of a great tradition.

> The 6BG6 problem was in the octal sockets,  used on
> some of the very first PC boards ever made.  In the
> typical AM transmitter room (150 degrees,)  it was not
> uncommon to find a 6BG6 hanging by it's plate cap,
> after the socket came unsoldered from the board.

There I take issue. The problem with the 6BG6 was it
was a TV horizontal output tube. The RCA receiving
tube manual had a warning in LARGE type that said,
in effect, "THIS TUBE MUST BE MOUNTED VERTICALLY BASE
DOWN."

When mounted horizontally, the filament structure 
sagged and the tube shorted, ZAaaappp! The 807 was
considered by RCA to be a TRANSMITTING tube and was
suitable for operation in any position. (Which
the military uses clearly confirmed. <g> )

> (Same with the Gatesway series audio console and its
> 6BQ5 tubes in the monitor amp.  They'd go into thermal
> runaway and melt completely off the PC board.  

Not nearly as common a problem as the 6BG6 board failures.
I did one of the service bulletins for board replacement
in the BC-1T.

> The later units had the bend-down pins...and scorched
> sockets!) Otherwise,  the 6BG6 IS an 807.  Virtually
> no difference in them.

Perhaps superficially, but RCA had a different opinion.

Really, the big difference in the BC-1T was the 
transmitter with the 6BG6's would burn up the board
after burning out a few tubes while the 807's sat there
and ran and ran and ran .... and ran. <g>

> Have you actually built an audio amp with either of
> them?   Try it!   You'll hear what I'm saying in an
> instant.  Inherent (dynamic) intermod of 10-20%.

Built a few around 807's in P-P and P-P ||, but I
preferred 5881's, EL-34, and 6550's for straight audio
work. The 30w chrome Mac's with EL-34's made great
program and monitor amps if modified a bit.

> Sure, all the later transmitters had better specs.
> With a sine wave.   

For better or worse, we lived and died with the sine
wave performance because that is what the FCC demanded.

> But,  do you know,  I spent my
> late teens with a BC-1F,  and have been trying to get
> back to that sound ever since?  And I've had them all.
> 
> By the way,  the 1F did quite nicely out to 15khz
> under dynamic conditions.  

Not in my experience, but that may have been a variation
in boxes.

> The modulator overloads
> were slow dashpots,  and typical plate current
> excursions of an amp or better per tube on highs were
> common.  

I've seen I(mod) L and R pegged out and the plates 
varying between orange and yellow dynamically on a 
1F playing "The Theme from Mondo Cane." That was the
one with a lot of HF organ in it, and it did test the
modulator of any transmitter.

> Still,  the 833's lasted years,  

If you wanted to pass a proof with something other
than a pencil, they didn't.

> and the 845's decades.  

The problem wasn't the tubes it was the driver xfmr.
Once I put in Thordarson's the performance was better
on THD.

> The feedback complimented the iron perfectly,  and 
> the result through a reasonable AM receiver was 
> astounding.  Loud,  crisp,  and with a way of 
> handling lower mids that Gates/Harris never
> again achieved.  

I liked it because it was a reliable moose that was
easy to get in and work on, but was never that 
impressed with its audio high end. In those days I
could hear out to about 19.5 kHz and did some
interesting sound work for people like Johnny Cash
and Ray Charles before groups traveled with trucks
full of sound gear. There's no denying that the 1F
was meant for rock, but for overall sound quality,
I'd have to give the nod to the Vanguard, which was
anything but a moose.

> RCA did.  Once.  In the 1MX.  But it
> was only close,  and harder than the 1E to maintain.

I never worked on one, but I understand the basic 
design originated with Raytheon in the RA-1000.

Part of the "magic" was the heavy RF drive from the
813. It could develop all the 833's needed on positive
peaks.

> Today,  of course, it doesn't matter.   All audio is
> being processed (and programmed) to replicate the
> sound of 3-bit PCS.  And,  with every technical
> "advancement",  radio recedes further into the QRM.
> But it was once great.  And I have the tapes to prove
> it...

There are cycles both in human preferences and in
technology. Once full digital becomes a fact and a few
years are spent on codec improvement, we may again see
quality sound on AM. The only question is finding
quality material that also attracts and audience. I'd
much rather live in the future than the past, you see.

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





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