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_at_dsl.pipex.com
http://www.philpem.dsl.pipex.com/
Received on Tue Dec 24 2002 - 02:52:00 GMT