WEM Custom 15

[ppppenguin]

Some Siemens electrolytics look rather like blue philips but with a clear plastic cover. While they, and blue Philips, are good electrolytics I still reckon it's worth a bulk replacement.

If the resistors are carbon film, as Terry has suggested, they ought to be OK.

[Mark Hennessy]

I copied it into Paint and blew it up to make it easier to see.

Well aren't you a clever boy!

However, there's no need to go to all that trouble - simply hold Ctrl while turning the scroll wheel on the mouse to zoom it in the web browser. Or Ctrl and the plus/minus keys. Ctrl+0 to reset to 100% when done.

Obviously I did zoom in, but know better than to state absolutes based on a low-res photo on an internet forum. Especially a photo that wasn't taken by the OP, who hadn't actually collected it at that point in time. Though he did subsequently mention "deep mauve resistors", which swings the odds back. Whatever, I was 95% convinced, but have been jumped on too many times over the years.

The other ones look like Iskra - also carbon film. I'm 95% convinced of that

https://www.vintage-radio.net/forum/show...p?t=125025

Also very reliable in my experience. My earlier comments about high-ish values and high-ish voltage still applies, however. Those Piher types were notorious for failing in Telequipment 'scopes, though to be fair to them, they were seriously over-volted, and lasted for decades before they'd risen in value enough to cause noticeable problems. They switched to Mullard (now Vishay) VR37 later on, and those remain a good recommendation for high voltage situations:

https://www.vishay.com/ppg?28907&quality

[Bushbaby]

You can now see where the TCC cap has pulled away from the board. I'm surprised it hasn't been held down given the size its just held by the soldered joints.
Mark - you are spot on re the resistors. 

Whats you thoughts in general - apart from the flux left over from the soldering (!!) I dont think it appears too bad, but what do I know?

Best Regards

               

[ppppenguin]

Unusually, components are monted on the print side of the board. A good way for larger parts to pull the print off the board. If you relace that big green cap, the new part will be a lot smaller. To repair that damaged track I'd drill a couple of small holes so that I could loop some tinned copper wire through the board to provide a good anchor for the cap. Or fit a pin that has a shoulder on the non-print side.

The flux residue is nothing to worry about. Some people like to clean it off and a clean board looks nice unless you do it really thoroughly it can even make things worse.

[Craig]

Since that electrolytic is well away from the valves, hot melt is another method of attaching a capacitor to a board.

[Mark Hennessy]

Thanks for the better quality pictures. Resistor spotters can now rejoice

The 100k and 56k are indeed Iskras. They're unusual for film resistors, as they don't have the characteristic "dog bone" shape that's caused by the metal end caps under the finish. But if you look at them from the right angle you can see the spirals of the film. They're good resistors.

The other ones - e.g. the beige 100 ohms - remind me of the sorts of resistors I used to see in Philips gear.

It is a curious bit of PCB design. It's tempting to assume all the components are "surface-mounted", but I can see some holes drilled in it, so perhaps it wasn't done that way to keep costs down to the absolute minimum. I can't help wondering if the PCB layout became mirror-imaged during production (we've all done it!), but no-one spotted it until thousands of boards had been made. Silly of me, but the thought amused me More likely it was done that way to facilitate the assembly into the chassis, with all those short wires between the PCB and the valve holders, etc...

Earlier Terry thought he'd spotted an electrolytic with a clear sleeve - that's actually a film cap (220n), and likely OK, but might be worth checking for leakage.

That small tear in the speaker diaphragm is nothing to worry about IMHO.

[Terry]

Yes, Mark - the 220n WIMA stands out very clearly now!

As for the 'surface mount' PCB arrangement, I think there is a very simple answer.

Take another look at it and visualise it with the print on the underside.

Now work out how you would gain access to it to replace a faulty component ...

[Bushbaby]

I did think that WEM type equipment was at the cheaper end of the amplification market. The Fender Bronco 68 amp I have is virtually prehistoric in comparison with the board and components used on it.
It does appear that the hardest bit of work I will have on this is the bent and buckled metal speaker grill. I did think about replacing this with WEM speaker cloth until I saw the cost of any bits that can still be purchased! they are more than I paid for the amp in the first place.

[Terry]

In my experience, VOX amps were built like the proverbial battleship with all components mounted on tag boards.

A very interesting piece of kit was the Klemt Echolette, as used by the Shadows.

This had three record heads, two playback head, an erase head and a twin speed motor and could produce a wide range of effects.

The one thing it couldn't do though, was to make the fascinating range of sounds that the Watkins Copycat could produce.



These are the noises that introduce the Tornadoes' recording of Telstar.

Note the magnet erase 'head' on the left in the picture!

I've never played with one but I think that there was sufficient gain in the sustain path to generate feedback round the tape loop itself without any input and which could be varied by altering which heads were in use.

[Bushbaby]

Hi Terry
I have indeed played with one of these when I was first playing guitar in my teens and they are really good fun and very effective. I would dearly like to get hold of another one but they are just so expensive to buy now!

I've just picked up a new 12" Celestion alnico blue speaker for this amp which I can wait to try. I've a wee bit more work to do before I'm in a position to fit this though.

Best Regards