Marshall 68 50 watt build nos parts
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Marshall 68 50 watt build nos parts
69 SuperBass Plexi
12000 Series Bulid
73 1987
68 Nos 50 build
2554 Combo
2550 Silver Jub stack
71 LesPaul Deluxe
68,71,73 4x12
12000 Series Bulid
73 1987
68 Nos 50 build
2554 Combo
2550 Silver Jub stack
71 LesPaul Deluxe
68,71,73 4x12
- neikeel
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- Location: Suffolk, England
Re: Marshall 68 50 watt build nos parts
Tell us more?
Whose trannies?
I see you used late split cathode with mustard byasses on the cathodes, but an earlier 56k slope resistor (presumably with 250pF cap and early spec 0.1uF PI outputs?
Did you try it as shared cathode first? That would be mor in keeping with the JTM front plate, thought about a tube rectifier -that spec is quite sweet (late black flag)
Whose trannies?
I see you used late split cathode with mustard byasses on the cathodes, but an earlier 56k slope resistor (presumably with 250pF cap and early spec 0.1uF PI outputs?
Did you try it as shared cathode first? That would be mor in keeping with the JTM front plate, thought about a tube rectifier -that spec is quite sweet (late black flag)
Neil
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Re: Marshall 68 50 watt build nos parts
Merr.n Audio Trannies. Didn't try with shared cathode. Also didn't think of tube rectifier ( I sold the 2 gz34 Mullards I had) Never had a tube rectified amp yet. The 15k that's coming is for this amp Amp sounds really good though. HAd a problem with no sound when finished. Used a 1 meg under the 68 on v2 DUH the 820 I had was to short and thought I used a 1 k. Dumb mistake.
69 SuperBass Plexi
12000 Series Bulid
73 1987
68 Nos 50 build
2554 Combo
2550 Silver Jub stack
71 LesPaul Deluxe
68,71,73 4x12
12000 Series Bulid
73 1987
68 Nos 50 build
2554 Combo
2550 Silver Jub stack
71 LesPaul Deluxe
68,71,73 4x12
- neikeel
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- Joined: Tue Dec 06, 2005 8:31 am
- Location: Suffolk, England
Re: Marshall 68 50 watt build nos parts
You should try the shared cathode. What you have now is quite a 'blend' of specs, of course if you like it cool but it is not like anything that ever left the factory!beaulieu wrote:Merr.n Audio Trannies. Didn't try with shared cathode. Also didn't think of tube rectifier ( I sold the 2 gz34 Mullards I had) Never had a tube rectified amp yet. The 15k that's coming is for this amp Amp sounds really good though. HAd a problem with no sound when finished. Used a 1 meg under the 68 on v2 DUH the 820 I had was to short and thought I used a 1 k. Dumb mistake.
Neil
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Re: Marshall 68 50 watt build nos parts
so I should try shared ...what about the the 68 on v2? remove it?
69 SuperBass Plexi
12000 Series Bulid
73 1987
68 Nos 50 build
2554 Combo
2550 Silver Jub stack
71 LesPaul Deluxe
68,71,73 4x12
12000 Series Bulid
73 1987
68 Nos 50 build
2554 Combo
2550 Silver Jub stack
71 LesPaul Deluxe
68,71,73 4x12
- neikeel
- Senior Member
- Posts: 7231
- Joined: Tue Dec 06, 2005 8:31 am
- Location: Suffolk, England
Re: Marshall 68 50 watt build nos parts
Just for nowbeaulieu wrote:so I should try shared ...what about the the 68 on v2? remove it?
Neil
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Re: Marshall 68 50 watt build nos parts
10-4! Guessing I should also remove the 4800 on vol 1 pot as well.
69 SuperBass Plexi
12000 Series Bulid
73 1987
68 Nos 50 build
2554 Combo
2550 Silver Jub stack
71 LesPaul Deluxe
68,71,73 4x12
12000 Series Bulid
73 1987
68 Nos 50 build
2554 Combo
2550 Silver Jub stack
71 LesPaul Deluxe
68,71,73 4x12
- neikeel
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- Joined: Tue Dec 06, 2005 8:31 am
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Re: Marshall 68 50 watt build nos parts
Same! Just use a ceramic 100pF instead.beaulieu wrote:10-4! Guessing I should also remove the 4800 on vol 1 pot as well.
If you have the right spec and a good guitar with decent pots, caps and pups these are the plexi amps that you pretty much dime on the front panel and then control the volume and dirt with the guitar controls.
Neil
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Re: Marshall 68 50 watt build nos parts
Her ya go Neil. Tthe cans on top are 50/50. What did these amps have? 32uf? I have a dual 32 on the board. I didn't put the 15k in yet!
69 SuperBass Plexi
12000 Series Bulid
73 1987
68 Nos 50 build
2554 Combo
2550 Silver Jub stack
71 LesPaul Deluxe
68,71,73 4x12
12000 Series Bulid
73 1987
68 Nos 50 build
2554 Combo
2550 Silver Jub stack
71 LesPaul Deluxe
68,71,73 4x12
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Re: Marshall 68 50 watt build nos parts
The vast majority of the 50w JTM's ran a GZ34 rectifier. These amps ran a single element 32uF/450v filter cap for the mains which was mounted top side next to the valve rectifier. The inside filter cap (mounted on the side of the chassis) is a dual element 32uF + 16uF/450v for the screens and PI. The pre-amp filter (on the tag board) is a 32uF + 32uF/350v dual element cap. The solid state rectifier version (diode rectification) of the 50w JTM seemed to show up at the very end of the JTM line before they switched to the JMP panels. There doesn't seem to be all that many of them from what I've seen. These amps run a single element 32uF/450v filter cap for the mains filtering which was mounted top side where the GZ34 use to be mounted. The screens and PI filter cap is a dual element 32uF + 16uF/450v mounted top side next to the 32uF/450v mains filter cap. The pre-amp filter (on the tag board) is a 32uF + 32uF/350v dual element cap.
- neikeel
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Re: Marshall 68 50 watt build nos parts
For the BF 50s I have seen Tazin is correct.
I find uppin the mains filtering beneficial so would leave that at 100uF( 50+50 in parallel). If you want a greasy feel to the amp 16uF screens is best and PI at 32 although I am not sure Marshall ever made a 50 that way - AFAIK 16 screens and 32 PI more normal?
The way Mark has it now is mid 68 JMP spec (my 68 lead has two 50/50 up top and 32/32 on the board with diodes mounted on the PT)
I find uppin the mains filtering beneficial so would leave that at 100uF( 50+50 in parallel). If you want a greasy feel to the amp 16uF screens is best and PI at 32 although I am not sure Marshall ever made a 50 that way - AFAIK 16 screens and 32 PI more normal?
The way Mark has it now is mid 68 JMP spec (my 68 lead has two 50/50 up top and 32/32 on the board with diodes mounted on the PT)
Neil
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Re: Marshall 68 50 watt build nos parts
From what I've seen Marshall did wire the amps both ways; 16uF for the screens and 32uF for the PI; also 32uF for the screens and 16 for the PI. I think the desending way (32uF screens, 16uF PI) is more common and perhaps the correct way.
- rgorke
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Re: Marshall 68 50 watt build nos parts
Looks great Mark. Makes me want to finish up collecting the parts for mine. How do you like the shared vs the split cathode?
I am planning on a tube rectified "model" as well.
Neil, is there another "option" other than Mustards for the bypass caps? WIMA?
I am planning on a tube rectified "model" as well.
Neil, is there another "option" other than Mustards for the bypass caps? WIMA?
"If you make a mistake, do it twice and smile and let people think you meant it." Jan Van Halen.
- neikeel
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Re: Marshall 68 50 watt build nos parts
The correct 400v green WIMAs are even harder to find!rgorke wrote:Looks great Mark. Makes me want to finish up collecting the parts for mine. How do you like the shared vs the split cathode?
I am planning on a tube rectified "model" as well.
Neil, is there another "option" other than Mustards for the bypass caps? WIMA?
Neil
- rgorke
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Re: Marshall 68 50 watt build nos parts
Is there any noticeable difference in tone between WIMA and Mustard caps in the bypass positions?
"If you make a mistake, do it twice and smile and let people think you meant it." Jan Van Halen.