J M Noeding wrote:
On Tue, 20 Jul 2004 08:56:15 -0700, Tim Wescott
wrote:



It may be best to pick the least expensive "big" sweep tube for which
you have specs, and parallel enough of them to get the impedance where
you want it to be.

You should also be able to run the voltage down a bit at the tube's
rated current. This will reduce your power output but it'll reduce your
impedance at the same time.

If you use a 3:1 step-down on your output you'll load the plate with 450
ohms. This will require a 1.3A peak current with a 600V plate supply,
and should be good for 300W or more PEP output -- may be easier to start
there than at 5A!


of course, but still the impedance from each tube is high, and it does
not see 50 ohm or whatever load, and still you may need an antenna
tuner.

But I was pulling the leg, since it is not a problem for any moderate
intelligent ham to tune a transmitter. Since I am electronic engineer
and have been working with transmitters it amuses me to see that
colleagues don't understand about PLATE and LOAD, and have really
difficulties to tune a transmitter, other radio amateurs have
commented about the same. It is odd that you need to be an amateur to
understand how to tune a transmitter, and I have never seen it as a
problem, even when I started with a Starflite TX 38 years ago

73, jm
---
J. M. Noeding, LA8AK, N-4623 Kristiansand
http://home.online.no/~la8ak/c.htm

Perhaps if the knobs were relabeled "TX" and "Antenna", and the plate
current meter was relabeled "reflected power"?

I see nothing wrong in principal with wanting to build a no-tune tube
transmitter, although it may be more work than building a
microprocessor-controlled transmitter tuner, and you may run into
insurmountable output-capacitance problems.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

On Tue, 20 Jul 2004 12:08:34 -0700, Tim Wescott
wrote:


Perhaps if the knobs were relabeled "TX" and "Antenna", and the plate
current meter was relabeled "reflected power"?

Can't really remember. Last time I had to assist it was Rohde&Schwartz
10kW 88.8MHz FM broadcast transmitter, and the colleague could hardly
achieve 1kW output, hi. Another ham worked at another medium wave
broadcast station in the summer 1960, and mentioned on an occasion
that "they had no idea how to tune a transmitter", they had some
different transmitters, incl. an old Marconi 10kW TX from 1933.

I see nothing wrong in principal with wanting to build a no-tune tube
transmitter, although it may be more work than building a
microprocessor-controlled transmitter tuner, and you may run into
insurmountable output-capacitance problems.

Well, I see 100pF output capacitance to cause some troubles on 450 ohm

Another problem is that all plate connections to a common point must
be measured to the same length. I am told this is really a problem,
even for a longwave transmitter, the reference transmitter operated on
360kHz as a console radio station, see my page
http://home.online.no/~la8ak/k56.htm

73, Jan-Martin

---
J. M. Noeding, LA8AK, N-4623 Kristiansand
http://home.online.no/~la8ak/c.htm

"David J Windisch" wrote in message ...
The point is, that I don't know what the nomenclature is, and asked for help
with it in the OP.

A quick google on admiral "sweep tube" turned it up: 6LW6. The post
was by Tom, W8JI in 2000.

73,
Mike, KK6GM

impedance for 100pf on 14MHz is -j114, perhaps not so good in a 450ohm
circuit

see http://www.noding.com/la8ak/12345/n12.htm for broadband techniques
with ferrite transformers, and you could always read W2FMI's book
"Transmission Line transformers", but I wouldn't use transmission line
transformers myself

73
jm
---
J. M. Noeding, LA8AK, N-4623 Kristiansand
http://home.online.no/~la8ak/c.htm

(Mike Silva) wrote in message . com...
"David J Windisch" wrote in message ...
The point is, that I don't know what the nomenclature is, and asked for help
with it in the OP.

A quick google on admiral "sweep tube" turned it up: 6LW6. The post
was by Tom, W8JI in 2000.

I just had a look in a couple of references from the
1980s, and the studliest sweep tube mentioned in
the Component Data section of the 1985 ARRL Handbook
is 6MH6, 38.5 watts plate dissipation. Amateur Radio
Techniques (RSGB) mentions 6LF6 (40 watts) and quotes
typical values for tubes like 6HF5 and 6JE6 in ICAS
RF service, both class C and AB1, courtesy Sylvania.

It also mentions that most of these tubes were made
with weird filament voltages for series-string tv
sets. The weird voltage variants are comparatively
plentiful, while the 6.3 volt versions have become
scarce for many types. As a British book it cites
the example of EL509/EL519 (6.3 volt filament), a
scarce tube even then, versus PL509/PL519 (40 volt,
300 mA), readily available.

Reminds me of the black and white Admiral tv set we
had when I was growing up. The horizontal output/damper
tube was a 38HE7. The one that came with the set lasted
years. Once that let go, it ate a replacement every 6
months or so. We finally scrapped it when the picture
tube's emission got too low.

Laura Halliday VE7LDH "Que les nuages soient notre
Grid: CN89mg pied a terre..."
ICBM: 49 16.05 N 122 56.92 W - Hospital/Shafte

Tks, OM. 73, Dave, N3HE

"Mike Silva" wrote in message
om...
"David J Windisch" wrote in message
...
The point is, that I don't know what the nomenclature is, and asked for
help
with it in the OP.

A quick google on admiral "sweep tube" turned it up: 6LW6. The post
was by Tom, W8JI in 2000.

73,
Mike, KK6GM