[BC] Power efficiency vs transmission quality

[Milton R. Holladay Jr.]

I was simply passing on J. Fred's offhand remark.
Certainly the 317B lacked the sophistication, more modern tubes, and
headroom of the C. If you didn't have a good set of tubes, you weren't going
to get reasonable performance. With a really hot set, the AMM-3 would hover
around 98% neg and 124pos, driven by a 9200. Unfortunately, the driver would
be reading ~175% pos, creating some audio artefacts.
As I was  intimately familiar with #4 (ex KFI), you can't tell me a whole
lot about it. About $3000/month just for daytime operation; definitely a
power hog, no argument. I believe the XL-60 runs a little less than half
that amount.
Interestingly, as you may have noticed, the name Doherty does not appear in
the manual or literature, just "high efficiency amplifier" as a description
of the grounded grid carrier tube advance of the Doherty design. I found the
'scope to be very unhelpful and misleading, too. The instructions were just
a starting place for tuning.
Adjusting the audio driver balance in a Gates BC-1T w/plate on, or the
driver loading in a BTF-3E  is far more dangerous than adjusting the 316;
you'd have to be very careless to get shocked.
I got the distinct impression that the B was a drawing board to physical
reality type thing, as there were few updates, mods, or follow-up notes.
AFAIK, there were only ~15 made.

In the early 70s, a fellow upstate was building a 50kw site. He went to WBT
to see their MW-50 and to Fayetteville to see their 317C, commenting that it
was like comparing a Chevrolet to an army tank. AFAIK, he's still running
his 317C.
And speaking of J. Fred, did he ever really say "A man is naked without $500
in his pocket" ?
M

----- Original Message ----- 
From: "Robert Meuser" <Robertm at broadcast.net>
To: "Broadcasters' Mailing List" <broadcast at radiolists.net>
Sent: Friday, February 23, 2007 10:53 AM
Subject: Re: [BC] Power efficiency vs transmission quality


> I have worked with J Fred, he even stayed at my house at one time and I
> respect his accomplishments. However, the 317B was way before his time.
> It is a linear amplifier driven by a 316B. There is no way in the world
> a 316B comes close in the modulation category to a 317C series. Trust me
> I ran both at the same time. This is not even a close call. The 316B was
> also a power hog. It was three 4cx5000s screen modulated, no Doherty
> technology.  The linear to make 50 KW was a Doherty but the combination
> does not even run close to the 317 C package in either modulation or
> efficiency.  It was also possibly the most deadly TX package ever built.
> I would not agree that the 317 C-3 was as good as it got for a tube TX.
> I would prefer the MW-50C series, which had the solid state mod driver.
> I had 317 C 2s and worked very closely with Joe Sainton who did many
> mods on them. We jokingly called them 317 2.5 as they got as close as
> you could to a C-3 without extreme surgery. I bought an MW50 C series
> for another station after doing a real world head to head comparison.
>
> R
>
>
> Milton R. Holladay Jr. wrote:
>
> > According to J. Fred, the B and C had about the same overall
> > efficiency, but
> > I've never looked it up to check....And modulation was no problem with
> > good
> > tubes. A mod to bypass the input xfmr would have made it free of audio
> > iron.
> >  Of course, the 317C-3 was as good as it got in tube 50s.
> > The main consideration about tube boxes is whether it was a GOOD xmtr,
> > or a
> > POS. Some of the 50 year old tube xmtrs were a lot better than the 30
> > year
> > old tube transmitters.
> > M