Converting JMP 50 to JTM specs (Filtering question)

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Danhalen
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Converting JMP 50 to JTM specs (Filtering question)

Post by Danhalen » Tue Oct 19, 2010 9:01 pm

I am well on my way to converting my JMP 50 to "JTM 50" specs. I did not necessarily set out to do that but that's the way it is going and I love the way it is sounding. I currently have 50uf mains, 32uf screens and pi, dual 33 preamp. My question is this:

Is it safe to use a 32/32uf for the mains and pi, while using a 16/16 for the screens?

So the setup would be one half of the 16/16 for the screens and then one half of the 32/32 for the mains and the other for the pi.

I realize I could also replace the screens/pi cap with a 16/16 but I was just trying to figure out a way to lower the screens filtering to 16uf while maintaining the 32uf I have on the pi. Thanks! :toast:
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Re: Converting JMP 50 to JTM specs (Filtering question)

Post by Roe » Wed Oct 20, 2010 5:29 am

jtm50s have 32uf for everything. personally i prefer at least 47uf on the mains
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Re: Converting JMP 50 to JTM specs (Filtering question)

Post by neikeel » Wed Oct 20, 2010 4:23 pm

I am with Roe on this, I actually prefer 100 on mains, with 32 screens, PI and x2 in pre-amp, but of course I prefer split cathode in preamp of 50 watters.
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Re: Converting JMP 50 to JTM specs (Filtering question)

Post by shakti » Thu Oct 21, 2010 1:43 am

JTM50s had a 32+16uF mounted on the inside of the chassis. IIRC 16 for the PI and 32 for the screens.
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Re: Converting JMP 50 to JTM specs (Filtering question)

Post by Roe » Thu Oct 21, 2010 4:22 am

I assume the earlier amps had 16uf on the PI while the later amps had 32uf
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Re: Converting JMP 50 to JTM specs (Filtering question)

Post by shakti » Thu Oct 21, 2010 9:27 am

I have photos of a late '67 JMP with tube rectifier and the 16+32 cap. I'm 99% sure it's original.
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Re: Converting JMP 50 to JTM specs (Filtering question)

Post by Roe » Thu Oct 21, 2010 9:49 am

interesting, I've seen pics with 32uf in all positions (I believe some were on the marstran page)
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Re: Converting JMP 50 to JTM specs (Filtering question)

Post by Danhalen » Thu Oct 21, 2010 11:18 am

Oh wow this is interesting. I'm sure you're both right seeing as how much these amps seem to vary.

Is there anywhere to still find a 32\16 cap? I am curious to see what 16 on the screens would sound like on this amp. So to get 32 on the mains was there a dual 16 jumpered?

I am starting to think that I may build a black flag 100 watt. I love EL34's and low filtering! Ghosting and all.
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Re: Converting JMP 50 to JTM specs (Filtering question)

Post by SteadyEddie » Thu Oct 21, 2010 1:21 pm

I'm interested in a 32/16 can also, so I can get 32 on the screens and 16 on the PI. Right now I've got 16 on each and I think the screens want a little more tightness.

Edit: Found on here, it's pricey: http://www.vibroworld.com/parts/tech15.html" onclick="window.open(this.href);return false;
One thing you can do is get a 16/16 cap can, and get an axial 16uf cap, put that in parallel with the side you want to make 32.
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Re: Converting JMP 50 to JTM specs (Filtering question)

Post by neikeel » Thu Oct 21, 2010 1:28 pm

http://cgi.ebay.co.uk/NOS-ERIE-HUNTS-16 ... 5d2b520474

:wink:
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Re: Converting JMP 50 to JTM specs (Filtering question)

Post by Danhalen » Fri Oct 22, 2010 7:40 pm

OOoh that's purty looking! Thanks for all of the into everyone.
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