On Tue, 30 Oct 2007 09:15:42 -0700, max graff wrote:
Hi guys,
I am planning on building my own valve amp and need a starting point
viz. books, forums etc. Any tips would be of good help.
I have proved to myself that I can solder well and don't have shakey
hands and did EE in my previous life.
Read, read, read...
TAKE NOTE OF THE SAFETY ISSUES. HIGH VOLTAGES CAN KILL YOU.
Unless you are building a kit (not a bad place to start) you are going to
have to know how to choose the necessary bits to build it. Even if you
find a design that you like, there is every chance that some of the
components that are specified are either no longer available or only
available in the US, with accompanying high carriage charges. That
results in having to source near equivalents - not easy in some cases.
You have to remember that in a valve amp all the components are
interrelated. You need to have the valves operating in about the right
region of their curves to get anything like what the design says. That
means that you need the right HT (or B+ for the foreigners), the right
output transformer, the right cathode resistor(s) and the right input
voltage swing from the previous stage to start with. Get any of those
wrong and you're off to a poor start. That means that you need to be able
to draw a load line and read data from it - so there's no getting away
from that reading...
Having said all that, you can have a lot of fun designing an amp on the
breadboard; fiddling the bias while watching test tones on a 'scope until
you find a setting that you like. It needs a bit of test gear, but it's
never wasted. You can get a really good insight into how valves and amps
work that way.
Have a clear idea of what you want before you start.
Don't buy *anything* until you are pretty sure that it will all go
together!
Remember that the one item that makes or breaks an amp is/are the output
transformer(s). Use junk and you can never get top quality sound.
Remember that (particularly for a single-ended amp) the output stage is
just a way of modulating the power supply. If the power supply is poor
you get hum, low output, distortion etc. etc. Good quality chokes and
capacitors will repay their cost in sound quality.
My own recommendation would be to build a simple single-ended amp, with
1/2 an ECC88 for the input stage (it looks like a good driver to me) and
an EL34 triode-connected output stage. All those valves are commonly
available and quite cheap. It won't be very sensitive and only low power,
giving about 6W max from a CD player input. That isn't too bad if you
have fairly sensitive speakers. I don't know if that would do for you,
but IMHO it would be a good beginner's amp. It should sound very nice too.
Something a bit like this:
http://www.angela.com/catalog/how-to/SE.EL34.html You can get those
transformers in the UK. I would like to try the ECC88, perhaps with an
LED instead of the cathode resistor/capacitor instead of the 6SL7 though.
--
Mick (Working in a M$-free zone!)
Web:
http://www.nascom.info http://mixpix.batcave.net
Building my own valve amp
Linear Mode
