Tony Duell wrote:
I'd love a
valve power amp but it would need at least one Phono
input, th= ree
Aux inputs (PC, radio and CD player) and tape recorder in/out. All
stereo.
If you build your own, then you can have whatever combination of
inputs you want...
Always useful. Need another input? Add another valve and some
extra
connectors :)
Catch is, the
only valve amps I've ever seen like that:
A) Look cool (but where are the Magic Eye VU meters?)
B) Keep a room warm in Winter (not necessarily a bad thing)
C) Cost a lot. We're talking =A3300-=A3400 here...
OTOH, I *could* buy a few 1T4s or similar and a pair of EM84s and
build a= n
1T4 = DF91. That's an RF/IF pentode. It could be used for audio
output, but at _very_ low power...
Which explains why it was used in the RF section
of R. A. Penfold's
"Two-valve SW Radio" project (published in EPE October 2001). But not why it
was used in the audio amp section...
EPE also published a 6V to 90V step-up converter in the February 2002 issue.
Whether it will work on 12V (well, 13.8V) or if I can get 200V out of it is
another question entirely. Might be fun to build a portable valve amplifier
with a built-in rechargeable SLA battery.
You'd be better off considering something like
EL84, EL34, or even
better KT66 or KT88 valves (the real GEC ones if you can find them
[1]) for the output stage.
EL84: B9A connector, Pentode. Should make a good audio
preamp if not a power
output stage.
[1] A camera shop (!) closed down locally last year.
They had some
valves that were used in cine projectors which they sold off for
\pounds 1.00 each, all brand new, boxed. Most were Mullard
EF86/ECC83/EL84 types (I think a total of 8). But the other 2 were
GEC KT88s (!). Of course I handed them a tenner and took the lot...
:)
And I get to pay a fiver per valve plus ?1.60 for the sockets...
amplifier
myself. Now if only I could find a decent book on
electronic design that gives more than a passing "These things are
obsolete" mention= to
valves...
You're not looking in the right place!. IIRC, the Radiotron
Designers
Handbook has been reprinted (at least it was in-print as a reprint a
few years ago). Mullard's 'Circuits for Audio Amplifiers' is not hard
to find (either second hand or a reprint). There's an excellent GEC
book called something like 'An Aproach to Audio Amplifier Design'
which _starts_ with the Williamson and goes on to kW-power amplifiers
(!).
Now I know what I'm going to spend what's left of my electronics
budget on.
Second-hand bookshops are well worth looking at...
Chevet (IIRC) and Chelmer Valve Co. had some of those books, IIRC. I think
www.valves.uk.com have a few of them too. That's where I've been getting
prices from.
Later.
--
Phil.
philpem(a)dsl.pipex.com
http://www.philpem.dsl.pipex.com/