CHAMP ELECTRONICS -" THE VINTAGE VALVE
AMP HOSPITAL"
NOTTINGHAM, ENGLAND
SERVICING A MODIFIED SELMER TEBLE N'
BASS 50
AMPLIFIER HEAD
I just had to put this one on the
web-site…..it was really interesting!
Starting off life as a Treble n’ Bass Fifty, this
had been
completely mod’ed every-which-way-but-lose!
When first
powering it up there was a dreadful hum. The modified phase splitter
would never have worked correctly with the way it had been done, and
basically...........it was just a complete load of crap!
Here
I had already done some “prototyping” to get the
splitter working correctly.
In
the back left-hand
corner, under this mass of components, was an added ECC83 tube and a
relay (the silver thing in the photo). This was all to do with a bias
protection circuit. Now, any bias protection is a good thing really but
hey……this thing was way over the top &
unnecessary
for a mere 50 watt amp with a pair of EL34’s!
I
think the guy who did all
the mods on this amp probably worked in the aircraft business! A lot of
the component types/brands and silicone covered wire lead me to this
conclusion.
Here
the phase splitter is all finished and working well. The big blue cap,
in the middle of the photo, is the second main smoothing
cap….after the 100 ohm “choke resistor”.
This cap
didn’t even exist on the amp and was one of the main reasons
for
the dreadful hum on first power-up! Bottom left-hand corner now cleared
of all the added/unnecessary junk too!
As
you can see here, there are two large power transformers! The one on
the left with the grey top is actually the main power transformer. This
has been changed from the original but was 110 volts only. The one on
the far right is simply an auto transformer for 240 volts down to the
110 volts. This was all very much an overkill and making this amp far
heavier than originally but…..the customer (Tim)
didn’t
have a problem with the extra weight so I left these as-is.
There
had been a modification of two individual pre-set pots for the pair of
output tubes & a balance drive pot too. This had actually been
done
OK, so I left these as they were working well. I did however
rip-out the whole un-followable pre-amp board and components!
The rebuilt pre-amp board and
tone controls….all back to the original T n' B Fifty circuit.
All completely
finished….this one was great fun!! Here is Tim’s
testimonial e-mail:
"Hi
John. Just a quick note to say how pleased I am with the amp.
This Selmer is sooooo loud! It’s far louder and quieter
(hum/hiss
etc) than any Selmer I've ever encountered and its great to find
someone who could bring the old gal back to life. I'm sure it will be
on a stage with me very soon! If only all Selmer’s were this
good!!
Once again, thanks mate. Speak
soon. Tim."
