I would tend to agree with Peter.
The surplus 813 is probably one of the available tubes with best W/$,
but a factor may be the cost of the HV power supply.
This is one of the problems with most inexpensive power tubes,
they either require a fairly high HV potential or forced cooling.
I recall what probably was the most inexpensive PA I ever made; a 2 x 813
single-band amp for 80m
[used in 1979 as an IPA (!) ]. Total cost: 200 SEK (approx. 50 USD today) , of
which the ex-microwave oven power transformer (95 SEK + carriage) took half.
If a prospective builder already has the HV power supply, it might be a better
choice to select tubes
after the voltages available instead of the other way around.
Finally a question to the list;
A TMC PAL-500 amplifier + PS recently followed me home.
Are there any chances of finding scanned schematics somewhere among the
distinguished membership?
73/
Karl-Arne
SM0AOM
----- Original Message -----
From: "Peter Chadwick" <g3rzp@g3rzp.wanadoo.co.uk>
To: <amps@contesting.com>
Sent: Wednesday, August 10, 2005 4:40 PM
Subject: Re: [Amps] TV sweep tubes and 6146s
> For 400 watts, I think you might get it with 4 6146Bs, with 1400 on the
> plates. You would need lots of cooling, no speech processing, a pulser for
> tuning, a big box of spares and no SSTV or RTTY.
> There's a big difference between what you may be able to do, and what is
> worth doing. In terms of watts/ $, surplus tubes like 813 etc are probably
> the best. I've seen 4CX250B pulls as low as $8 each, so despite needing a
> blower, they could be the way to go - a pair of them should give 400 watts
> out.
> As Karl Arne said, the peak cathode current capability of the 6146 isn't as
> great as a sweep tube, so you need a lot more plate volts.
> Asking around can get you things even cheaper - over the years, I've been
> given a pair of good 4CX1000 tubes and a brand new socket and chimney for
> them, and a spare breech block base, and a pair of vacuum variables..........
> 73
>
> Peter SM/G3RZP/P
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
> ========================================
> Message Received: Aug 10 2005, 12:52 PM
> From: "Peter Chadwick"
> To: craxd1@verizon.net, amps@contesting.com
> Cc:
> Subject: Re: [Amps] TV sweep tubes and 6146s
>
> Back when I had almost limitless supplies of 6146Bs, I ran a pair at 1200
> volts on the plates. They lasted well, provided you didn't run steady
> carrier, and gave about 180watts PEP out with 3rd order IMD at about -28dB
> relative to PEP. They were rated in plate modulated Class C servicve at
> 600volts on the plates, so had the potential to hit up to around 2400 volts
> or so peak. This suggests that pushing them much beyond about 1400 or so
> would probably be dodgy. However, at that , you copuld maybe get 400 watts or
> so. On the other hand, some of the transmitters we did with 3 6146Bs and
> about 800 on thenplates would hit 200 watts PEP out at -27dB rel PEP third
> order: others would only hit 100 watts at the same IMD. Of course, there were
> variations in the driver IMD to consider, too.
>
> Incidentally, I'm not sure I completely agree with all K9STH's comments on
> 6146Bs. Tx's that I've designed have got down production lines in enough
> quantities to have used over 10,000 6146Bs in their construction, so I figure
> I can claim some experience.
>
> 73
>
> Petere SM/G3RZP/P
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