Theo wrote:
"Sam Goldwasser" wrote in message
...

The transformer is good for 1500 to 2500 VRMS at 0.5 A or more.


I would check to see if these transformers are continuously rated, I seem to
recall they are rated for intermittent use only.

Theo



They are also built to have high leakage inductance, for current
limiting when you put your steel coffee cup in there. This is done by
having physically separate windings and a laminated-steel wedge in the
window in the core. You have to knock that wedge out.

There was an article in QST or QEX about using microwave parts to build
power supplies for linears. Very interesting. Very scary, considering
that the author also used old refrigerator drawers as the case...

I saved the pieces from my old microwave in case I ever want to build
something that puts out more than 5W.

--

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

Hi Tim,

There was an article in QST or QEX about using microwave parts to
build power supplies for linears. Very interesting. Very scary,
considering that the author also used old refrigerator drawers as the
case...

Just curious: Do people still build linears with tubes and HV supplies
or is it much cheaper now to use transistors? Mine were all tubes but
that was about 20 some years ago when FETs and BJT were just way out
there in terms of cost.

Regards, Joerg

http://www.analogconsultants.com

Just curious: Do people still build linears with tubes and HV supplies
or is it much cheaper now to use transistors? Mine were all tubes but
that was about 20 some years ago when FETs and BJT were just way out
there in terms of cost.

As one example: Ameritron builds solid-state ham-band amplifiers of up
to 600 watts output (their "ALS" series). Starting at the 600-watt
point, and going up to the 1500-watt legal limit, Armitron's amps are
all based on tubes. There are legal-limit HF amps which use only a
single tube (e.g. a 3CX1500A/8877 triode, running at about 2500 volts)

According to a talk I saw recently, commercial television broadcasters
have moved almost exclusively to solid-state RF amplifiers for their
newer stations. No one set of transistors can provide thenecessary
power, so the amps use a large number of smaller modular amplifiers
operating in parallel - I think the basic "brick" we were shown was
capable of a couple of hundred watts. I haven't seen any ham-band
amplifiers using this modules-in-parallel approach, although I'm
sure one could be built.

--
Dave Platt AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

Hi Dave,

Thanks for explaining. 600W is pretty good power already. Since the commercial amps are bricks it seems they must have good protection against sudden mismatches as well.

I remember when I had a coil in the antenna open, which was immediately followed by an exploding coax cable portion. The tubes didn't even flinch but in the 70's just the opening coil would have immediately destroyed even a small transistor amp because the SWR network wasn't fast enough to shut it down.


Regards, Joerg

http://www.analogconsultants.com

On Fri, 25 Jun 2004 23:28:12 -0000, (Dave Platt)
wrote:

According to a talk I saw recently, commercial television broadcasters
have moved almost exclusively to solid-state RF amplifiers for their
newer stations. No one set of transistors can provide thenecessary
power, so the amps use a large number of smaller modular amplifiers
operating in parallel - I think the basic "brick" we were shown was
capable of a couple of hundred watts. I haven't seen any ham-band
amplifiers using this modules-in-parallel approach, although I'm
sure one could be built.

In broadcasting, the station is usually operating on the same
frequency all the time, so simple Wilkinson dividers/combiners (which
are frequency specific) can be used, which effectively isolates the
modules from each other, when one module fails.

However, a ham linear amplifier is typically required to operate in
the 1.8-30 (or -54) MHz frequency range, which complicates the
divider/combiner issue.

Paul OH3LWR

Dave Platt wrote:
According to a talk I saw recently, commercial television broadcasters
have moved almost exclusively to solid-state RF amplifiers for their
newer stations.

I suppose this is kinda OT but tubes (usually, klystrons or various
modifications thereof) are still generally used for high power at UHF.
IIRC solid-state UHF transmitters are available up to about 30kw or so,
but larger stations require as much as 110kw to achieve the desired
effective radiated power.

Tubes do indeed seem to be a thing of the past at VHF, where powers
beyond 50kw are generally not necessary.
--
Doug Smith W9WI
Pleasant View (Nashville), TN EM66
http://www.w9wi.com