CHAMP ELECTRONICS -" THE VINTAGE VALVE
SERVICING A CARLSBRO CS40-60 Mk I PA AMPLIFIER WITH GZ34
To the best of my knowledge this was the first-ever series of Carlsbro PA amps.
Its title I believe is a CS40-60 PA. The assumption here being that it was 40 - 60 watts? It featured 2 x EL34's for the output and a GZ34 rectifier.
I acquired this at a good
price.........as a gift for my Australian friend Mervin (Doctor Valve). It had no power transformer, and the output transformer was duff too! On these very first PA amps, the speaker output sockets and the Bulgin power-in were all on the wooden back panel.
With Mervin being here for a five week
visit, we both decided that as this one was so bad and rusty, we should strip it completely and "start a-fresh!" All the very first
Carlsbros used an R.S. (Radio Spares) choke and yes....that is the one in the photo!
Ready to do some more serious stripping. On doing
this, when it came to remove the knobs, the grub-screws were so rusted we had to smash all the knobs off.......shame! Furthermore, the same thing applied to the
pot-nuts; there was no way that these were going to budge! We had to hack-saw all of them off too!
As for the circuitry, this amp used
a pair of EL34 output tubes in cathode bias which, to be honest, would probably have made it more like 40 watts in reality. You can see here the pair of 470 ohm cathode resistors and one of the two by-pass caps...the other looking like it might have "blown itself apart!"
OK, here we go. Back from the stripping, cleaning, and
powder-coaters.......what a lovely job they have made of it, as always.
Piecing the hardware back together,
with the speaker outputs and impedance selector now in place on the rear of the chassis.
The RS choke now tested, cleaned,
lacquered, and re-fitted.
Well on the way with the rewiring......compliments of Mervin......as after all it is his baby, so I left him to get on with it!
Now fitted with my own Champ 60 watt output transformer!
God I'm good! My Partridge look-a-like transformers are cool! Mervin and I call the process "Partridged!"
The amp all finished.
Underside of the power
supply with HT fuse fitted now. Also both Merv & I thought it a good idea to put this baby into fixed bias, but retain the GZ34. I built a bias board for him with individual 20-turn pots for each tube. (I had put a bias winding on the power tranny anyway in anticipation of
The top all finished.
Originally these had both transformers with closed end-bells, but....with my open framed "Partridged" look transformers........she looks pretty cool!
Mervin is going to make a new back panel for her when he
gets back to Oz.
Love these knobs too.....they suit the old Carlsbro's really well and
make the whole thing really cool! Lovely job well-done.