19th Dec 2014, 11:40 am | #121 |
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Re: WEM Copicat Custom
Edit: looking again it depends which schematic. On one those resistors go to ground, on the other they go to the centre lug of the reverb pot.
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19th Dec 2014, 1:26 pm | #122 |
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Re: WEM Copicat Custom
The wiring is correct.
The common side of the resistors is connected to the chassis. The common side of the switches is connected to the white wire which will go to V3. However there should have been continuity between the sub chassis and the main chassis without the need to add the additional wire, which from previous posts I believe goes to the common negative tag on the smoothing capacitor can You could temporarily remove the wire and use your meter on ohms range to check for continuity between the main and sub chassis.
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19th Dec 2014, 1:35 pm | #123 |
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Re: WEM Copicat Custom
I'm having second thoughts on that. Your wiring seems to correspond to the MK3 diagram with a 6BR8 valve.
However Howard's diagram for the triple ECC83 version shows a different arrangement ie that shown in post #119. As far as I can see either arrangement should work though.
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19th Dec 2014, 1:49 pm | #124 |
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Re: WEM Copicat Custom
I don't suppose there's a connection from the sub-chassis to the reverb control?
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19th Dec 2014, 4:09 pm | #125 |
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Re: WEM Copicat Custom
Glad you mentioned the reverb control because that is what is puzzling me. Yes, there is a wire going from the subchassis to the left hand lugs of both the swell and reverb pots. The middle lug of the reverb pot also has a 470k resistor on it, the other end of which goes to one of the footswitch wires (the other is on the subchassis) and also to a trace on the board...
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19th Dec 2014, 4:22 pm | #126 |
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Re: WEM Copicat Custom
Just used the meter and there is continuity between the subchassis and main chassis, so I didn't need to add that extra wire. I had already removed the one that was going from the 'negative' transformer wire / smoothing cap to the subchassis when I added the extra one (from subchassis to bolt with mains earth wire on main chassis) , i.e. before I tested it with a new C9.
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19th Dec 2014, 4:29 pm | #127 | |
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Re: WEM Copicat Custom
Quote:
This resistor features in both versions, but in each case there is another resistor of 2.2M (6BR8 version) or 1M (triple ECC83 version) in series with it. the junction of the two resistors goes to the base of the transistor.
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21st Dec 2014, 4:38 pm | #128 |
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Re: WEM Copicat Custom
I'm about to do the tests on the transformer, so wish me luck!
By the way I found a couple of other schematics, probably useful for others if they are all linked to on this thread, so: http://www.cornelvis.com/schematics/...mkIII_1965.pdf (clearer version of the one on vintagehofner site) http://tubefreak.com/s-copy.gif same circuit but without the transistor stage |
21st Dec 2014, 5:00 pm | #129 | |
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Re: WEM Copicat Custom
Quote:
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22nd Dec 2014, 3:59 pm | #130 |
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Re: WEM Copicat Custom
I removed C9 and tested the resistance of the smoothers but I don't really understand the results. It didn't seem like anything was charging. Looking at the bottom of the big can with the 3 caps inside I'll call the pins A B C and D going clockwise, A being the terminal which would have the negative transformer wire attached to it. Meter on 20k setting. Between A and B I get 2.7k, between A and C = 7.4k, between A and D = zero. B and C = 4.7k (thats the resistor, I know), B and D = 2,7k (the other resistor, a little high). C and D = 7.4k. I'd guess Looking at the schematic and going by the zero (short?) reading, I'd guess that C15 is dead. Any thoughts?
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22nd Dec 2014, 4:09 pm | #131 |
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Re: WEM Copicat Custom
If the capacitor connected between A and D is indeed short-circuit (zero ohms) rather than open-circuit (infinite ohms) then it is indeed faulty and would explain the problems you had with the transformer over heating.
I assume the transformer secondary is still disconnected, as otherwise you could be measuring the transformer secondary via the diode. Don't overlook the possibility of the wire going to tag D being short circuit to the chassis. To prove the cap is short-circuit you'll need to disconnect all wires and components connected to tag D and measure the cap in isolation.
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22nd Dec 2014, 6:21 pm | #132 |
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Re: WEM Copicat Custom
Ok, disconnected the resistor etc and re-tested between A and D, and it is indeed short circuit, zero ohms. I guess this will mean buying 3 large 20uf caps and soldering them together, or buying a readymade one here http://www.amp-fix.com/images/Spare%...pple%20can.jpg
Nothing shorting out to the sides of the can, I took the opportunity to clean up all these tags of excess solder etc |
22nd Dec 2014, 6:28 pm | #133 |
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Re: WEM Copicat Custom
Definitely faulty then. You may find that buying three new caps and a bit of tag strip works out cheaper than the pre-assembled item.
I don't think it's worth taking the risk of just replacing the one faulty section.
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22nd Dec 2014, 7:12 pm | #134 |
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Re: WEM Copicat Custom
Yes I agree. What would the minimum voltage be? Just checking out prices and I see 450v are cheaper generally, also 22uf seem more common. Also radial seem cheaper, I suppose its possible to use those with a bit of redesigning.
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22nd Dec 2014, 7:18 pm | #135 |
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Re: WEM Copicat Custom
22uF 450V will be fine. You should be able to use radial leaded components, as they'll be much smaller than the originals.
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22nd Dec 2014, 7:22 pm | #136 |
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Re: WEM Copicat Custom
Sorry, I should've waited until I'd taken it out, on the can it says it's 3 x 350v 32uf
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10th Jan 2015, 4:48 am | #137 |
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Re: WEM Copicat Custom
Hi all and happy new year. Still waiting on one cap order but I've replaced the big smoother with 3 caps and a new resistor. I managed to re-use the metal clamp so there was no need for tagboard. Just wanted to double-check with you that I'm not doing anything really stupid. The negative ends of the 3 caps are joined together and one of the red wires from the transformer will go there, and the 3 small red wires are going back to where they were before, plus resistors added as before.
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10th Jan 2015, 7:30 am | #138 |
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Re: WEM Copicat Custom
Hi again, so the other caps arrived. I've replaced C8 (2000pf 630v poly film) C9 (200pf 500v Silver Mica) and C10 (with a 470pf 1000v ceramic - this is the value that was in there, as opposed to what's on the schematic). I haven't resoldered the transformer wires to the heaters and smoothers yet. I tested the other caps just to see if any were short circuit and they seem ok. The small (1/4W?) resistor which is obviously a replacement measures at around 1.8M. I'm a little suspicious of this. Anyway if you could please let me know if you think I should try plugging it in, or if there are any tests which could be done first. I've attached a couple of photos, one showing C9 and C10 replaced, and the other showing the small resistor. Thanks in advance for any tips!
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11th Jan 2015, 8:15 pm | #139 |
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Re: WEM Copicat Custom
Did you change it to the 240V mains tap on the transformer?
1. Use a lamp limiter. 2. Clip your meter (1000V range) across C14 (junction of R27/R28 and chassis). 3. Turn on and keep an eye on the voltage. If it does not rise quickly to 300V and the lamp is bright then switch off and report back here. It should initially rise to 350V or so then fall away as the valves warm up. If it falls below 250V switch off and report back here. 4. Turn off and clip your meter (200V range) across R28 (2.2K) 5. Turn on and monitor the voltage. If it exceeds 50V then switch off and report back here. |
11th Jan 2015, 10:19 pm | #140 |
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Re: WEM Copicat Custom
Hi all,
I don't know if anyone else has mentioned this, but I found this - it may be of use. http://www.amp-fix.com/The%20description.htm The Watkins Copicat A Brief Description The Schematic Circuit Diagram for the version with 2xECC83 + 1x6BR8 Stuart.
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