[AMPS] Solid State 1kw amp

Radiodan W7RF RFpower@radiodan.com
Wed, 3 Jun 1998 21:30:38 -0700


Well now I couldn't resist commenting after the last commercial.

For example, it was just mentioned that "ALPHA 374, 374A and 78 amps (up to
24 years old now) are out
there on the hf bands doing exactly that. Many more ALPHA 87A amps
...snip...>

Well, for one thing the 8874 (only 400 watts plate dissipation) tubes used
in the earlier models are now $435 each (2 or 3 are needed in each amp
described). That makes even just 2 of these little toy tubes cost much more
than the very rugged 3CX1200A7 and about the same price as a 3CX3000A7!!
(both the 3CX1200A7 & 3CX3000A7 are used in the HENRY HF amps).

8874 & 3CX800A7 tubes cannot take much plate voltage (Eimac book says "2250
Volts MAX"  in cathode driven RF service for 3CX800A7) and therefore you
must draw huge amounts of current to make the power.
Better be very close in SWR or you'll draw dangerous grid current because
it's only no-tune for 50 ohms!

Conversely the 3CX1200A7 (Eimac successor to the venerable 8877) is simply a
SUPERIOR tube as you can put 5000 volts on the plate and need to draw much
less current to do the job. Grid dissipation is only FOUR watts on the
3CX800A7 as compared to FIFTY watts for the 3CX1200A7 (or 225 watts for the
3CX3000A7). Complicated and expensive protection devices are not needed with
the single 3CX1200A7 as opposed to any number of 3CX800A7s.

It's hard to run high voltage on the tubes when you use "computer type"
filter capacitors with no choke instead of an oil filled capacitor with a
properly resonated choke input HV supply. Something has got to go when it
has to fit under an airline seat! Of course how many of us ever do take our
amps on airplanes?

Take todays popular "no-tune" tube type design. You better have a near
perfect match EVERYWHERE you operate. Because if you don't it's gonna kick
off on ya! Then wait again for warm up and by then the DX will be on the
next call area and you've missed him. Unless of course you don't mind
backing off the power........

This is all provided you're OK with only getting a pair of 3CX800A7s for
well over $6000.

A much better value would be the 3K Ultra for less $ and it has optional
presets to tune to your favorite spots with a MUCH more rugged design. You
can remote it up to 100 feet away too.
See it at  http://radiodan.com/Henry/Amp_specs/Ultra_info.htm

Available when YOU need us,  no "relaxed" office hours here.

73, Dan Magro
Radiodan W7RF, Portable Clinic
High quality Henry Radio RF Power Amplifiers for LESS!
See the entire HENRY line at  http://radiodan.com/rfpower.htm
http://www.radiodan.com    RFpower@radiodan.com
A trip to our web site is worth the click!


-----Original Message-----
From: Richard W. Ehrhorn <w4eto@rmii.com>
To: 'Dave D'Epagnier' <DAVED@ctilidar.com>; 'amps@contesting.com'
<amps@contesting.com>
Date: Wednesday, June 03, 1998 7:00 AM
Subject: RE: [AMPS] Solid State 1kw amp


>Hi Dave...
>
>-----Original Message-----
>From: Dave D'Epagnier [SMTP:DAVED@ctilidar.com]
>Sent: Tuesday, June 02, 1998 12:51 PM
>To: 'amps@contesting.com'
>Subject: [AMPS] Solid State 1kw amp
>
>...snip...  > of interest is possibly a broadband tube amp design requiring
> no tuning on the HF ham bands, any input is appreciated.
>
>Thousands of ALPHA 374, 374A and 78 amps (up to 24 years old now) are out
>there on the hf bands doing exactly that. Many more ALPHA 87A amps (sold
>continuously since 1991) can deliver even more power with automatic band
>change and tuneup. ...snip...>
>
>FYI, common tubes power require voltages and load impedances which don't
>lend themselves well to high power and wide bandwidth with decent
>efficiencies.
>
>73,    Dick  W0ID/ex-W4ETO
>



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