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Vintage Tape (Audio), Cassette, Wire and Magnetic Disc Recorders and Players Open-reel tape recorders, cassette recorders, 8-track players etc.

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Old 14th Mar 2019, 1:45 pm   #21
ronbryan
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Default Re: Copicat MK2 - No Echo

The tuning capacitor across the oscillator coil (between red wire and yellow wire on osc coil) should be 2200pF (2.2nF or 0.002uF), not the 200pF shown on your tag board drawing. What is its value in fact?

The capacitor feeding the record head and the 100k resistor should be 200pF, not the 0.002uF (2200pF) shown.

The 0.5nF capacitor to ground shown between the junction of the 100k/0.1uF does not exist in the circuit diagram. You could try disconnecting it as it will bypass some of the recording signal to ground.

The capacitor connecting the triode grid (pin 9) to the oscillator coil should be 0.002uF (2200pF) not the 200pF shown on the tag board drawing.

It is not clear whether these incorrect values are component insertion errors, misreading of component identity or drafting errors.

The -23V on the triode grid would indicate that it is oscillating strongly.

Ron

Last edited by ronbryan; 14th Mar 2019 at 2:07 pm.
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Old 14th Mar 2019, 1:50 pm   #22
ms660
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Default Re: Copicat MK2 - No Echo

Ron beat me to it....Also the bias feed capacitor is shown as a different value in the layout as to what's shown in the linked schematic.

Lawrence.
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Old 14th Mar 2019, 5:47 pm   #23
Michael Why
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Default Re: Copicat MK2 - No Echo

The component values have come from either reading the original values if they can been seen ( and then testing to make sure they are somewhere near) or removing and testing if i cannot read the markings or colours

Anything i replaced was with the same original value as what was already there

I had noticed many differences from the schematic's not only in the record/bias section but right through , extra or very different values but the colours/markings are confirming whats actually there

the capacitor between the red/yellow on the coil reads 156pf and it is marked as 200pf , i have not replaced these ( as i didnt have the correct ones ) so these are original and definitely accurate but incorrect values

I will make the changes you listed and report back

Cheers

Mike
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Old 14th Mar 2019, 6:09 pm   #24
Alistair D
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Default Re: Copicat MK2 - No Echo

Have a look at this site, http://wem-owners.com/schematics/copicat-schematics/ there are a few valved copycat schematics. Perhaps one of these is a nearer match to yours.

Al
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Old 14th Mar 2019, 6:30 pm   #25
Michael Why
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Default Re: Copicat MK2 - No Echo

Ok , changed everything as Ron's instructions - new layout attached

The voltages on pins 1-9 are similar to previous results

One thing i did notice , the voltage on pin one is 235v but on the other side of the 200pf cap going to the record head its -0.5v - is that ok ?
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Old 14th Mar 2019, 6:31 pm   #26
Michael Why
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Default Re: Copicat MK2 - No Echo

With the layout attached this time

Mike
Attached Files
File Type: pdf WEM 1959a Layout.pdf (284.7 KB, 3 views)
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Old 14th Mar 2019, 6:51 pm   #27
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Default Re: Copicat MK2 - No Echo

This schematic of a MK111 shows what appears to be 470pF connected between the junction of the 0.1uF and the 100k to chassis:

http://schems.com/bmampscom/wem/Copicat_mk3-1.jpeg

Lawrence.
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Old 14th Mar 2019, 9:09 pm   #28
ronbryan
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Default Re: Copicat MK2 - No Echo

Do you have access to anything that can measure the bias oscillator frequency, such as an oscilloscope or frequency meter? It would be useful to see the bias frequency, which I guess would be around 40kHz and to scope the record signal through the input stages.

Have you checked the tape path, cleaned the tape heads etc as suggested by TimTape in post #2

Have you cleaned the head selection switch contacts as Martin suggests in post #7?

If you suspect that there is still no record signal, can you check that the 100k resistor from pin 6 of the bias oscillator is not open. This large resistor is chosen to drive the record head with a current.

I've had another look at your neat tag-board drawing and there are a few component values detailed that are different to the MkII circuit diagram.

Pin 1 (anode) of the middle valve should go to a 100k resistor, not 680 ohms.

Pin 6 (anode) of the middle valve should go to a 0.05uF, not 0.005uF

The resistor between the echo and sustain pots should be 1M not 220k

The resistor going to pin 6 (anode) of the first ECC83 should be 100k not 470k, although the photo does show that a 470k is actually fitted. The Mk III shows this as 47k, which would cut the gain a bit.

The value of the resistors mounted between the two volume pots that form the summing bridge network should be a pair of 1M (560k shown) and a pair of 470k (220k shown)

The 390k and 2M2 in parallel between the pots should be 1 x 470k. The 470k and the output wire should be connected to the junction of the 1M bridge resistors, with other end of the 470k still going to the echo pot wiper (middle connection).

Ron

Last edited by ronbryan; 14th Mar 2019 at 9:19 pm.
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Old 15th Mar 2019, 11:12 am   #29
Michael Why
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Default Re: Copicat MK2 - No Echo

Success !! -almost

Changes to components made as Ron listed and the output moved from pin 2 to 4 on the tag strip where the 470K and 1M resistors meet

I am getting an echo now , with all the pots on max i can hear maybe two or 3 repeats. If the volume of the guitar is 10 then the repeats are coming through maybe 3-2-1

the tape heads are clean and the faces look in reasonable condition. The record head was not original - it was from a later Mk4 > model. I swapped this for one of the play heads as it looks to be sitting a little high on the tape ( thinking if i am getting a good sound on 2 of the 3 heads i know where to look )

The switch block is in pretty poor mechanical condition so i have the longest repeat switch jammed closed

I will try swapping the ECF80 for the 82 and try each play head in turn to see if i get anything different. Will put a new tape on as well just in case

Cheers

Mike
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Old 15th Mar 2019, 11:14 am   #30
Michael Why
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Default Re: Copicat MK2 - No Echo

latest version of the layout
Attached Files
File Type: pdf WEM 1959b Layout.pdf (277.0 KB, 11 views)
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Old 15th Mar 2019, 11:57 am   #31
ronbryan
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Default Re: Copicat MK2 - No Echo

I've had a quick look at your updated layout.

The wire from the top of the 'sustain' pot should go to the junction of the two 470k resistors that are located between the volume pots, rather than the junction of the two 1M.

Ron
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Old 15th Mar 2019, 2:20 pm   #32
Michael Why
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Default Re: Copicat MK2 - No Echo

Thanks thats much better

Still a little quiet maybe 10 - 6,3,1 with everything on max but much clearer than before

Cheers

Mike
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Old 15th Mar 2019, 3:03 pm   #33
ronbryan
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Default Re: Copicat MK2 - No Echo

You say it is still a bit quiet. Have you looked at the attenuation network of resistors on the switch bank? Are they an array of 220k and 100k resistors as shown on the Mk II circuit diagram?

The 25uF electrolytic capacitors on the replay ECC83 cathodes will affect replay amplifier gain. Have you checked or swapped those?

Ron
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Old 15th Mar 2019, 11:08 pm   #34
Michael Why
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Default Re: Copicat MK2 - No Echo

I had replaced 2 of the 25uf's but was missing the other two which arrived today , I replaced those and also used the switch block ( with new resistors ) from the other copicat , both made a little improvement

Its a bit noisy but i have all the components stood up off the board so i can get at them so all the long leads are probably acting like antenna's. now its pretty much working i will fit these properly and see what its like

Cheers

Mike
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Old 15th Mar 2019, 11:53 pm   #35
ronbryan
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Default Re: Copicat MK2 - No Echo

The 0.5nF (500pF) capacitor that went between ground and the junction of the 0.1uF and 100k that I suggested you lift off in post #21 was probably intended to reduce the bias signal feeding back into the record amp (the Selmer Echo 300 has a twin T bias filter in that location). You could try re-connecting that capacitor to see if it reduces some of the noise.

Ron
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Old 16th Mar 2019, 4:00 am   #36
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Default Re: Copicat MK2 - No Echo

Quote:
Originally Posted by Michael Why View Post
Its a bit noisy...
Some of that noise may be due to the permanent magnet erase head in this early model, mentioned earlier. Expect low frequency "bumping" sounds. Many cheaper cassette recorders had the same.
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Old 16th Mar 2019, 5:41 pm   #37
Michael Why
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Default Re: Copicat MK2 - No Echo

I am going to give it a good clean out so will report back in a couple of days once itís been stripped and rebuilt

Good point Timtape, spare erase magnets are still available so will try a new one

Cheers

Mike
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Old 23rd Mar 2019, 10:58 pm   #38
Michael Why
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Default Re: Copicat MK2 - No Echo

Hi all

So full strip down and clean , pots, switches and sockets all changed. I am getting a good strong echo now and all seems to be working ok apart from one problem.

There is still a lot of noise. I would not call it a hum it’s more a random but frequent static. I have noticed if I touch the metal front panel with something metal I get a crackle which is picked up by the record head and played back. Does this sound like a bad earth somewhere or as this was never designed for a 3 wire supply has this introduced an earth loop. I have tried disconnecting the earth wire and still the same
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Old Yesterday, 2:47 am   #39
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Default Re: Copicat MK2 - No Echo

If you're touching something and there's a change, then that means there's a misconnection somewhere. Similar to touching the grid of a powered valve with a probe.

In my limited troubleshooting expertise, I would check the resistances of all marked ground connections, and the links between signal ground and PSU ground - if you've changed the earlier grounding scheme (live/neutral to live/earth/neutral) then you could have upset the balance of signal grounds between your equipment. If you aren't sure where the current is flowing between your components, have a check. The shields between units shouldn't be providing a better path to ground than the circuit!
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