Wem Watkins Copicat Mk4

[pcc32pcc32]

Hi, no doubt this question has been asked many, many times before.

I've got a Wem Watkins Copicat Mk4, which I am partway through restoring, it was in a sorry state when I got it.

I've completely recapped it, right now the dry sound is working perfectly. Using the footswitch, (and also swell and sustain knobs) I can toggle between dry and echo.

But, as I've said, dry works a treat, but if I try and turn on the echo there is no echo. There is a load of regular noise, which I assume is the tape moving across the heads.

Has anyone seen this before and got any suggestions?

I am at the point of changing out all the transistors to see if it's a problem with amplification either pre the write head, or after the read head. I would also consider buying an oscilloscope to work out exactly what is happening. But before I do either there might be something straightforward that I've missed. Thanks in advance for any help.

[stevehertz]

Probably not your answer to the problem, but you never know: https://gearspace.com/board/so-much-gear-so-little-time/1134...leshooting-wem-watkins-copicat.html

Another one here: https://golbornevintageradio.co.uk/forum/archive/index.php?thread-7894-3.html

[sortedradio]

Copicats can be very fussy regarding tape loops. I've known old loops and some made from the wrong tape formulation to produce little or no echo. The other thing to do is check that the record bias oscillator is working. It should be around 44kHz. You can check the playback heads by pressing all the buttons down and gently touching each playback head with a screwdriver, it should produce a click. Also make sure the push switch contacts are clean.

[Radio Wrangler]

Oscilloscopes are not usually sensitive enough to see the voltages coming from a tape head, so one alone won't necessarily unravel your problem. It should see the signal and bias voltages at the record head, though.

Re-capping is dangerous. Unless your workmanship is of a very high order, it is easy to introduce more faults than it fixes. Electrolytics the wrong way round, dry joints solder-splash shorts, wrong part bought, fake part bought.... Some sets do indeed need almost all changing, but those previously bitten change one at a time and check it works. This can save an awful lot of time in diagnosing what went wrong. We've all made mistakes.

Especially in the US, re-capping seems to have become almost a religion and the first go-to action when something isn't right. We've had many, many people here on the forum after it didn't fix things. Some got helped through finding all the faults and getting it going, but a large proportion of them gave up.

For diagnosis od your copicat, a small audio amplifier would be useful. Connected to the record head you should get a very strong signal. If not, work your way backwards through the record amplifier to find where the signal is being lost. You should get a quiet sound from each replay head. If so, then go trqcking it through the replay amplifiers to see where it stops.

It's honest-to-goodness slow sleuthing rather than trying to jump suddenly to an amazing conclusion. If you've traced the fault the long way, you can be confident in your conclusion and you are making progress by knowing what you're doing and following a trail of solid evidence rather than guessing.

David

[pcc32pcc32]

Thanks for all the advice. I'll go away and try to see what I can do. The consensus seems to be that it might be a tedious lot of fault finding, which was what I was planning on, so no loss there.

I've had another fiddle around with things just now and I can get an echo from one of the replay heads. Albeit it very quiet, and almost completely drowned out be background noise. But an improvement!

SortedRadio-The record bias oscillator is the funny looking component on the small circuit board by the motor? How do you advocate checking the output frequency of that?

Radio Wrangler-I may have made a mistake, generally my workmanship is reasonably good. I've built my own amplifier and quite a few pedals, among other things. If you'd seen the inside you'd have realised I has no choice!

If I'm understanding you, I should connect an amp to the record head. Then play my guitar, and I should get decent output, this proves that the circuit just short of the record head is working. Although not necessarily the head itself.
Then connect the amp to each of the reply heads. This then proves the replay heads are working. As long as the record head, as how else would the signal find itself on the tape.

Cheers

[Techman]

You'll only hear a recording on the other heads if the bias oscillator is working. If it isn't then you'll just hear a very low and distorted sound. You'll need a scope to check the bias oscillator or you may possibly be able to measure its voltage at the record head with an AC digital voltmeter that can handle that frequency.

[Vintage_RC]

Some multimeters have very good frequency measurement capability such as the Aneng 8002. This could be helpful in checking the bias oscillator without a scope. The 8002 does require the signal to cross zero when measuring frequency so a series capacity might be needed.