Sunday, 16 February 2014

Carlsbro PA60 - Power Up Test

New resisistor and HT fuse in, powe cord into amp, plugged into circuit breaker (safety first).

Power on! Light! Wheeee!

Check HT fuse, just to be sure, and it's blown with no valves in the amp.
New HT fuse = blown

Dodgy capacitor is the most likely culprit according to Foxen and sure enough there's a bit of white fluff by the vent on one of the filter caps, which means it's probably dead, and this is further borne out by a quick voltage test across the caps. Best thing at this stage is to do a 'brute force' recap, so that's more money to spend.

Bah. But learning is good.

Sunday, 2 February 2014

Plumbing the Depths

Retrovive RV-4 in C# standard -> Nine of Swords Burial at Sea -> Blackstar HT-DistX -> Peavey Firebass power amp -> Orange OBC 115

Sub. Ter. Ran. Ean

That is all.

Project: Carlsbro PA 60 Head

As mentioned previously Mr. Foxen of Ampstack has given me a Carlsbro PA 60 to work on.

Carlsbro 60 PA Front

From what I can tell from info-mining the internet this is a early-mid 70s model, probably a late Mk II. All other Mk IIs I've seen pictures of are point-to-point wired whereas this is on PCB, but I cannot find any reference to a Mk III so kind of assuming that at some point during the Mk II being in production it was changed to PCB construction.)

I have done initial solder refreshing and resistor testing. During the course of this testing I learned that sometimes resistors in circuit test at a lower ohmage than they are rated for and that by popping one end out of the board you can make sure they're sound. One of the resistors is duff (cheapo non-original, natch) plus the HT fuse has blown so that needs replacing. There was also a bodged in power cable which I've now removed.

Carlsbro PA 60 Guts

Pretty PCB

Next I'm going to clean up the valve sockets, pots, input jack, etc. and after that is powering up with no valves to check voltages.

Finally here is a bit of random human interest stuff. The amp was apparently built by Trev and tested by people who as far as I know exist only as initials.

Build and Inspection Label