Rich wrote:
> I am thinking about building my first amp and was wondering if I could
> use a large tube ( 4-1000a ) at reduced voltage when I first start out
> and then as I build confidence replace the lesser parts with better (HV)
> parts.
Many here would say the 4-1000A is not a large tube!!
You would need to check the data sheet of a tube before deciding whether
it can be used at low voltages or not. Always check the data sheet for
the manufacturer of the tube you are going to use (if you possibly can).
There's quite a selection on my site below.
> I don't like the idea of buying vacuum variable caps and not
> being sure that the amp will work right. I am not looking for great
> efficiency at low voltage but only to prove the concept and all
> supporting parts like soft starts and delays and antenna relays work
> correctly before I go to QRO. Due to band conditions for the next few
> years it will be a mono-bander for 40m to start, 20m and 15m to be added
> later.
> I have smaller tubes I could start with like C1583A's, and 304t's.
>
> Rich, KD0ZZ
It sounds like to could give youself a lot of hard work starting with
lower spec parts and updating them later. What HT transformer do you
use? Are you going to replace that? And the smoothing caps?
I'm sure if you took a well proven design it would work, and so you
would be better buying the bits to work with the tube, and not have to
change them later.
You might be better starting with a smaller tube (250W or so) and
consider you are building the driver for an even bigger tube, and skip
the 4-1000A!
I don't know the C1583A or 304t, but make sure you don't waste much time
on trying to build an amp for which getting replacements will be very
difficult. I once had a 4CV40000A (or similar type number. It was about
40 kW and vapor cooled). The idea of building an amp around an obsolete
and irreplacable (at a sensible price anyway) tube left me to scrap the
thing.
--
David Kirkby,
G8WRB
Please check out http://www.g8wrb.org/
of if you live in Essex http://www.southminster-branch-line.org.uk/
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