[Amps] TV sweep tubes and 6146s

[Karl-Arne Markström]

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 at g3rzp.wanadoo.co.uk>
To: <amps at 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
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> ========================================
> Message Received: Aug 10 2005, 12:52 PM
> From: "Peter Chadwick" 
> To: craxd1 at verizon.net, amps at 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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