WEM Copicat Schematic request

[valvusmusicus]

Hi
Does anyone have a schemo for the above please-have a playback/rcd fault, in that there is a rumbling/white noise all over the delayed signal
Have checked all the obvious-just need to check a schematic to check components.
Have changed tubes, PSU caps, decoupling caps and checked continuity of a ll solder joints

Thanks all

V

 

[tinn]

I attached a schematic of the MK2
http://www.backfromthesixties.co.uk/Pages/Site_Map.aspx
has a nicely redrawn schematic as well.

There are many versions. Which one do you have?

Try to isolate the problems.

Clean and demagnetize all heads.

Pull out the bias genarator tube.
For extra safety,  put some tape or cardboard over the record  head, to prevent the tape from being recorded with some noise (dc eventually running through the rec head)
put a prerecorded tape on.
Does that sound ok? evtl. repair playback section.


If that is ok go to the erase/record section:
Early copycats don't have an erase head, the bias in the record head is trying to erase most of the old recording.

some copicats have erase magnets which can be adjusted (distance to tape)

Listen to the recording signal with a 1Meg probe/amp at the Plate of the rec amp.
Check the bias oscillator and the 200pF cap.
Is the oscillator running stable?
Maybe the rec head is worn down and needs less biasing, try 150 pf.
as well it can  be that you need a new rec head.


In models with erase head, it is advisable, to short the rec head first an check the erase head "solo" before starting with the rec amp section.

Good luck,

Tito

 

[Tubefreak]

There is one on my website, came with the unit.

Maarten
Tubefreak.com

 

[valvusmusicus]

Hi all
Thank you very much for that. I have now fixed the problem
It was the verision with 3  12AX7's-not a 6BR8 bias tube. I thought I had removed all the nasty Hunts caps-but there is a -005uF one Id missed that was nearly hidden by others. Problem in the playback circuit-all sorted
Thanks again for all the help

Cheers

V