Hi All,
I think I'm going to be in need of some help. I've just mad a silly offer on an old guitar amp (spares/repair) and it was accepted! I have to say I know very little about these early Charlie Watkins amps. I've yet to collet it but I've attached some pics.
Thanks
Rob
Many thanks Al
Best Regards
Rob
I picked it up last Thursday.
My initial thoughts are its not bad for its age but needs some tiding up. What I have notices is the large greeny coloured TCC electrolytic as show in the pic in post #1 has a lead that has pulled away from the board and taken some board track with it (I will get a pic when I can). This explains the continuous mains hum that it has (its not working that badly to be honest). Also the 10" original Elac speaker as a very small tear in the cone which is causing noticeable horrible flapping sound. I'll repair this with some thin garden weed cloth that I have (the mesh type) with some PVA adhesive.
If its working and (I will give it a thorough check over) is it worth changing any components at all??
I'm planning to put a new 12" celestion alnico blue in it.
Many thanks
Rob
There are lots of "mustard" caps so that's good. The blue electrolytics may be getting poorly by now. I'd probably change the lot as an insurance policy. The resistors look like carbon compo. Measure them and repalce any that are out of tolerance.
Thanks Jeffrey,
I'm not sure if the blue electrolytics are old Plesseys so they have probably done well to last 50 years or so and have no issues in replacing them. I think you will correct about the resistors but they are a deep mauve body colour rather than brown so I'm not sure of the manufacturer but will measure to see how they have stood up to time too. I'm still concerned about the small piece of pulled circuit board track - I have read that this can be glued back using superglue - I cant say that I have every tried this myself?
Best Regards
Rob
If the electrolytics are Plessey rather than Mullard I'd replace on sight.
If a PCB track is in trouble or even missing I'd normally use a bit of tinned copper wire to reinforce it. If there's a big component on the board, such as a large axial capacitor, I'd consider drilling 2 holes and using a tie-wrap to reduce stress on the solder joints. Always provided that the holes won't damage anything else.
(11-11-2019, 09:42 AM)Bushbaby Wrote: [ -> ]but they are a deep mauve body colour rather than brown so I'm not sure of the manufacturer but will measure to see how they have stood up to time too.
These sound more like Piher carbon film rather than carbon composition (a closer picture would help). If so, they will probably be within spec. If any are out of spec, I wouldn't necessarily jump to replace them without first considering what they are doing. Few audio circuits are all that demanding, and in many cases, the usual 30% or more drift that you can get from carbon-comp resistors is not an issue. Occasionally it might matter, but as I say, it's worth thinking about it before replacing. If nothing else, the thought experiment might be a useful learning exercise.
One exception to that - when you have high voltages across high value film resistors (say, >100V and >100k), then they can go high or open-circuit. I explained my understanding of the failure mode a few years ago:
https://golbornevintageradio.co.uk/forum...8#pid46468 (post #14 if the link doesn't take you straight there).
If this was a transistor radio or something that ran on similarly low voltage rails, then Piher carbon-film resistors have an excellent reliability record, as well as being really rather beautiful to look at.
I will add some more pic over the next few days.
My initial thoughts that this doesn't appear a cheaply constructed board albeit it would have been built at cost. One thing I have noticed is that it has a lot of of thin cabling.
Overall its a pity it wasn't constructed on a tag board.
Not a bad buy for £150 - I've seen one sold in the US albeit it far better condition for just over £900 indicating that these were used by the Beatles. Certainly, at the time this one was built (I've not seen the date stamp on the TCC smoothing cap yet but I'll lay money its older than 1965/66) they would have been using Vox amps typically AC30's.
Best Regards
(11-11-2019, 10:47 AM)Mark Hennessy Wrote: [ -> ]These sound more like Piher carbon film rather than carbon composition (a closer picture would help).
I copied it into Paint and blew it up to make it easier to see. Despite the obvious loss of quality, I would say that all but 3 of the resistors are Piher carbon film - I'd even put money on it (and I only bet on certainties!). I would say the other three are carbon film too.
All of the blue electrolytics are Philips (Mullard) and there is a light green HT decoupling can electrolytic which is TCC so the chassis mounted smoothing is probably from the same stable.
There is an electrolytic with a virtually clear covering. Not possible to determine what make but I have come across Philips like this in the past instead of the usual blue.