Valve amplifier

http://www.youtube.com/watch?v=gPNnIbtXolw

Well worth a watch.

I know they generally fetch an obscene amount of money!
I have got something that my mate is after at the moment, I might see if he wants to do a swap!
Either way I’ll get it off him at the weekend or maybe sooner if I end up in the area, and get it on the bench in my lockup.
I’ll post some pictures as I’m sure a few people here will be interested!
I’m curious as to what I’m going to find, it might have been serviced in the past, or I might be the first to touch it after many decades. Quite looking forward to working on it actually

+ 1 I actually love working on valve amps, they are so much easier to understand than transistors. 

studio45 wrote: + 1 I actually love working on valve amps, they are so much easier to understand than transistors.  Of course, these are the rose tinted spectacles of someone who hasn't had a shock off the B+ yet; I expect that changes one's views on the matter! I like odc04r's dedicated meter idea. I always work in thick rubber gloves, using only one hand as much as possible. That way even if a sharp live wire pierces the glove, I'm not getting a shock right across the chest. Plastic chopsticks are very useful to tap around the circuitry and see if anything is loose, you can even tape your meter probes to them so your hands are as far away from the angry pixies as possible. Fixed an Orange bass amp head last year - six hundred and ninety English volts on the output tube anodes - CRIKEY!

That is a healthy B+, I've only built up to 400V so far - which I had zero problems with but it was enough for me. Not that you should take shortcuts with any HV but in the worst case from 400V I am fairly confident I would live to be angry with myself for being an idiot. 700-800V starts to become somewhat more unknown territory, and you have doubled the chance of it jumping a gap too. Zero room for mistakes there.

Andylaser wrote: odc04r wrote: At a glance you know if it is live, helps concentrate the mind. I had my mind concentrated by a belt of 370VDC which sent me spinning across trhe workshop on my office chair.

Very nice, and all original apart from the paper block capacitor. So nice that it would make a lovely museum piece if left untouched. But I'm sure we'd all rather see (and you'd rather hear) it working to original spec or bettter.

You can expect most of the carbon comp resistors to have drifted up in value. Depending on where they are in the circuit, some will need replacing with modern film types - unless you want to go all the way and replace the lot.

The metalpacks, although very high spec when new, are almost certain to be leaky. Don't be tempted to replace with identical new old stock types. Although the audiophools drool over them (with prices to match), even NOS ones are often leaky. Modern MKT 1813's are the way to go. If you don't like the bright yellow colour you can use them to re-stuff the metalpacks although I wouldn't go that far...

If you intend to sell the amplifier after refurb, keep all the replaced components in a bag and send them out with the amplifier, some buyers like to see the originals (no, I don't know why either...).