Tim Shoppa wrote:
On Oct 18, 10:04=A0am, (Scott Dorsey) wrote:
I once built a push-pull class C amplifier using 833 tubes, with three
continuously tuned inductors that could handle 80M through 20M.

Kewl. Neutralization in push-pull is in my experience much more
tractable because you just tap off the signal from each phase, feed it
through the neutralization cap which is nominally identical to the
plate-grid capacitance, and into the grid of the opposing tube.
Mathematically the plate-grid capacitance is constant as you change
bands so to zeroth order neutralization may not have to be adjusted
for band changes. Did the same neutralization setting work across the
bands?

No, it didn't. Part of that may have been the RF transformer on the
plates not being completely symmetric and that symmetry changing with
frequency.

i once tried to imagine a scheme where all 4 inductor taps in a push-
pull front-panel-bandswitching scheme were switched with ceramic
switch wafers actually inside each of the coils, and all the wafers
are ganged with plastic cog belts. In the end I went with a much
simpler plug-in coilset scheme.

The plug-in coilset is a good one, unless you suddenly find you want to
talk on a band you don't have a coil set for. I like the whole idea of
being able to continuously tune across all the bands and between all of
them. The problem with this is that you now have expensive big variable
caps or variable inductors, and they are usually sensitive as hell because
of the required tuning range... even a tiny tap and you're out of tune
again.

Sure, but can you get them free out of someone's trash? =A0All the big
planar grid tubes I found being thrown out are destroyed...

It just occurred to me why ham amps with driven grids are so hard to
neutralize compared to diathermy machines that donate their old tubes
to the projects: You don't need to neutralize a diathermy machine at
all!

You know, I haven't heard anyone even mention a diathermy machine in
ages. These days the major ISM band polluters are plywood manufacturers
and WiFi users....
--scott


--
"C'est un Nagra. C'est suisse, et tres, tres precis."

On Thursday, October 15, 2009 at 11:24:01 AM UTC-4, Steve wrote:
A while ago I bought a homebrew amp (80-10 meters) that uses
a single 833A tube. Its beautifully built. So far I have not been
able to find any plans or schematics for an amp that uses this
tube. Has anyone seen an article in QST, Ham Radio, or other
magazine of an amp using an 833A? No luck with a web search.
TIA
Steve W6SSP
p.s.-it has a tuned grid circuit

1980 handbook Page 6-46 Chapter 6 Has a 833A in an amp.

On Saturday, November 11, 2017 at 1:07:24 PM UTC-7, wrote:
On Thursday, October 15, 2009 at 11:24:01 AM UTC-4, Steve wrote:
A while ago I bought a homebrew amp (80-10 meters) that uses
a single 833A tube. Its beautifully built. So far I have not been
able to find any plans or schematics for an amp that uses this
tube. Has anyone seen an article in QST, Ham Radio, or other
magazine of an amp using an 833A? No luck with a web search.
TIA
Steve W6SSP
p.s.-it has a tuned grid circuit

1980 handbook Page 6-46 Chapter 6 Has a 833A in an amp.

Thank you. I have been in the process of building an 833A amplifier for 20 meters and I do have it working but I sure would like to see another builders ideas. Mine is grid driven with about -90 volts on the grid. I get 800 watts output with 3KV under load. I believe the plate current is just over 400 mA and a grid current of just under 50 mA if I remember correctly while writing this with an efficiency of about 63% which I consider OK. I will try to locate this article and if I cannot find it may just purchase the 1980 book from Ebay. 73 WA4QGA El Paso, TX

wrote:

Thank you. I have been in the process of building an 833A amplifier for 20 =
meters and I do have it working but I sure would like to see another builde=
rs ideas. Mine is grid driven with about -90 volts on the grid. I get 800 w=
atts output with 3KV under load. I believe the plate current is just over 4=
00 mA and a grid current of just under 50 mA if I remember correctly while =
writing this with an efficiency of about 63% which I consider OK. I will tr=
y to locate this article and if I cannot find it may just purchase the 1980=
book from Ebay. 73 WA4QGA El Paso, TX

A lot of broadcast transmitters used the 833, and schematics for them should
be easy to find. Bauer 707, Gates BC1G are the first that come to mind.
Some others just uses 833s in the exciter deck to modulate larger finals.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."