1977 jmp 50 watt one wire mod help!! PLEASE

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pelvisbuster
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Re: 1977 jmp 50 watt one wire mod help!! PLEASE

Post by pelvisbuster » Sat Dec 23, 2017 10:22 am

Well... To be truthful.. I don't know.. I ABSOLUTELY love the sound that R/T is getting out of these with one wire.. I guess I wanna try the one wire..and of I don't like it..I can remove it.. but with that being said.. doing this the right will give me some experience with it..and upon me not liking it.. I will have the information..and some know how to go the other direction.. the master volume is my work.. the other is not completely.. as I said in posts before, this thing had been tampered with when it came to me.. so , someone else had is hacked up. I did do the experimenting with some components.. so I guess that would mean I'm half guilty of this mess as well.. either way, I'm waiting on a package today with proper caps..

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Re: 1977 jmp 50 watt one wire mod help!! PLEASE

Post by danman » Sat Dec 23, 2017 7:46 pm

R/T has found the values that work very well with his amp. Be prepared t do some fine tuning with different component values because every amp sounds a bit different and everyone hears things differently. You can temporarily jumper components in with alligator clips for testing and fine tuning the sound. Having decade boxes with different capacitor and resistor values is also handy for trying out many values quickly and efficiently. Also, don't be afraid to bias your amp down around 50% as you may prefer the sound versus the standard 70%.

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Re: 1977 jmp 50 watt one wire mod help!! PLEASE

Post by pelvisbuster » Sat Dec 23, 2017 9:25 pm

I'm still learning how to bias tunes well.. all my other amps are "fixed" bias amps . So basically throw in same set of tubes and good to go. But hopefully soon I'll be able to make noise of goodness come from this ole plexi :shred: .. is there a particular tool better to use biasing tubes.. or multimeter do it just fine?

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Re: 1977 jmp 50 watt one wire mod help!! PLEASE

Post by fixer2 » Wed Jun 20, 2018 1:17 pm

:thumbsup: can the RR mod that you have switchable be done to a 50 watt 1968 clone iam looking to build another kit this one having alot lot more gain drive etc
Then my J T M 45 clone which is running great I hear things or read them good and bad about the one wire mod so I think this is better

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Re: 1977 jmp 50 watt one wire mod help!! PLEASE

Post by danman » Wed Jun 20, 2018 5:57 pm

Sure...all of these preamps are very similar to each other. If yours is a shared cathode v1 spec, it may require separating these and fine tuning some component values. All of these mods will require fine tuning anyway to achieve the best sound in each particular amp.

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Re: 1977 jmp 50 watt one wire mod help!! PLEASE

Post by neikeel » Thu Jun 21, 2018 4:14 am

RT one wire actually works best on shared cathode amps

The RR switchable is on SDMs google drive page
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Re: 1977 jmp 50 watt one wire mod help!! PLEASE

Post by fixer2 » Thu Jun 21, 2018 10:47 am

:clap: Does R/T have any layouts of his one wire mod or just do the one wire mod that I find on this forum any then fine tune it with the correct cap for the amount of bite I want and the amount of time more or less treble

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Re: 1977 jmp 50 watt one wire mod help!! PLEASE

Post by danman » Thu Jun 21, 2018 9:19 pm

He has this video...https://www.youtube.com/watch?v=W_4pCaG4z8o and you can also find his post on the "MarshallForum" describing the mod. No layout that I am aware of though.

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Re: 1977 jmp 50 watt one wire mod help!! PLEASE

Post by fixer2 » Mon Jun 25, 2018 10:16 am

:o I will look him up on that forum I like the way his one wire mod sounds Thanks

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Re: 1977 jmp 50 watt one wire mod help!! PLEASE

Post by neikeel » Mon Jun 25, 2018 12:48 pm

I think you will find it is a commercial venture and he will want to work the amp himself.
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Re: 1977 jmp 50 watt one wire mod help!! PLEASE

Post by fixer2 » Wed May 13, 2020 10:35 am

Ok so nobody knows exactly how to do the R/T mod or is it basically a one wire mod.on a different subject how much different or actually what is the difference of a JCM800 it the JCM800 using thre half’s of the two pre amp tubes so is it two or three gain stages.

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Re: 1977 jmp 50 watt one wire mod help!! PLEASE

Post by neikeel » Wed May 13, 2020 4:08 pm

The first three stages are considered gain stages
The tone stack is considered by some as a gain stage but it is actually at unity gain - so not really.

So three gain stages running 3 preamp tubes
Neil

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