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[AMPS] RE: Counterpoints and corrections to Radiodan

To: <amps@contesting.com>
Subject: [AMPS] RE: Counterpoints and corrections to Radiodan
From: w4eto@rmii.com (Richard W. Ehrhorn)
Date: Fri, 5 Jun 1998 19:28:34 -0600
Hi Guys...

For any who care, here are a few factual counterpoints to Dan's post of 
6/3.  Warning! Some of my comments may seem to border on "commercial." If 
you object, please feel free to hit <Del> now.

1. A long list of astute and thoroughly seasoned, primo world-class contest 
operators, for whom winning is top priority & who can afford the very best 
(e.g., OH2BH/EA8BH, N6TJ/ZD8Z and W6QHS/W6NL) have owned and used one or 
more very "popular no-tune tube amplifiers" (i.e., ALPHA 87As) since 1990. 
In years past, top-tier contesters W2PV AND K2GL (R.I.P.) had their 
world-beating multi-multi stations outfitted with 6 to 12 ALPHAs each. Can 
you believe that if ANYTHING better had been available for this toughest of 
amateur radio uses they wouldn't have known about and used it?

2. Our amps have carried a standard 4 year, non-prorated factory warranty 
since 1990. Extensions to 8 years are available. (What's yours, Dan?)

3. Blather about 3CX800A7s and "delicate grids," and about alleged frailty 
of HV filters using stacked electrolytic capacitors, is misguided and/or 
self-serving nonsense. In fact, 3CX800A7s and 8877 or 3CPX5000A7 series 
tubes, with electrolytic HV stacks in ALL the HV supplies, are used in the 
majority of vacuum tube rf power amplifiers for big medical MRI systems 
(e.g., GE, Picker, Philips, Toshiba, Elscint). Those guys and their 
hospital/ clinic customers won't tolerate down time at $1000+/hour billing 
rates.

4. Some of the world's biggest manufacturers of semiconductor chip-making 
systems (where a failure can destroy up to $100k or more of in-process 
silicon) use vacuum tube rf generators powered by ~6kV supplies up to 
      ~15kW dc output. And some of the very newest employ stacked 
electrolytic HV filter caps virtually identical to ALPHA's in design, 
components, and processing. Guess what - nary a "properly resonated filter 
choke" in sight.

I've injected a few more notes below, where relevant...

> -----Original Message-----

> From: Radiodan W7RF [SMTP:RFpower@radiodan.com]
Sent:   Wednesday, June 03, 1998 10:31 PM
To:     'Dave D'Epagnier'; amps@contesting.com
Subject:        Re: [AMPS] Solid State 1kw amp

> 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

5.  ...that is, don't require...

> 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.

6. Huge! Roughly an amp for "maximum legal power" -- maybe as much as 2 
amps (!) if you aren't restrained by such matters. By comparison,  50-120V 
solid state devices must draw WAY huge currents.  So what's your point?

> Better be very close in SWR or you'll draw dangerous grid current because
it's only no-tune for 50 ohms!

7. That's simply and absolutely untrue. PLEASE see note 12 below.

> Conversely the 3CX1200A7 (Eimac successor to the venerable 8877)

8. All my friends tell me the 3CX1200A7 is an improved successor to the 
troubled 3-1000Z - with very little electrical or mechanical resemblance to 
the widely-used (in amateur, medical & critical industrial systems) 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.

9. With competent engineering, highly effective protection is neither very 
complicated nor very expensive. BTW, wasn't the brute-force approach what 
made the USSR so successful in the long run?

> 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.

10. This is complete technobabble and nonsense. See notes 3 and 4 above.

> 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?

11. More of us than own fork lifts?

> 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!

12. I don't believe you've used one enough to learn how they actually work, 
have you Dan? Even if you accidentally use an "Oops!! Wrong-band!!" antenna 
- or feed full power into an open or short-circuit in the middle of the 
night - the reflected power protection system prevents damage by switching 
the amp to standby in milliseconds - and it takes about one second to 
reset.  If you want to read the specs, see our web site.

All the best to you anyhow, Dan.  We all make mistakes.

         [SORRY GUYS - I absolutely promise I won't do this again.
              Banish me from the reflector if I do ... PLEASE!]

73    Dick  W0ID  -SK-

... snip ...

>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!




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