JJ'844 TUBES

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Atur7fret1
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JJ'844 TUBES

Postby Atur7fret1 » Thu 05/23/19 4:52 pm

EL 84 TO JJ844. Do I have to make a cathode bias resistor change. Or can they just be switched out .
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crgfrench
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Re: JJ'844 TUBES

Postby crgfrench » Fri 05/24/19 7:42 am

They are a direct replacement. I use these interchangeably in my Fullerwell circuit. No bias change required
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Rippleman
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Re: JJ'844 TUBES

Postby Rippleman » Fri 05/24/19 7:47 am

I have a 1974x that needs new tubes. It's a used amp, but new to me. Does anybody know if there's a written procedure or manual somewhere for step by step instructions. I've replaced tubes in amps before but I'm certainly no expert.
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geoff 1965
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Re: JJ'844 TUBES

Postby geoff 1965 » Fri 05/24/19 8:44 am

here's the owners manual,can't see anything in it for replacing tubes but if you get a matched pair of el84's for the output and a balanced ecc83 for the phase inverter "V2" you should be good.
M3310.034_1974X.pdf
is it a genuine marshall or a kit amplifier?
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crgfrench
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Re: JJ'844 TUBES

Postby crgfrench » Fri 05/24/19 9:17 am

Rippleman wrote:
Fri 05/24/19 7:47 am
I have a 1974x that needs new tubes. It's a used amp, but new to me. Does anybody know if there's a written procedure or manual somewhere for step by step instructions. I've replaced tubes in amps before but I'm certainly no expert.
Realizing this post regards JJ844s, if you're retubing a Marshall 1974X you might want to consider the Marshall branded el84s -- TAD has matched pairs available, https://www.tubeampdoctor.com/product_i ... anguage=en
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Atur7fret1
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Re: JJ'844 TUBES

Postby Atur7fret1 » Fri 05/24/19 9:29 am

It's a copy of a tube depo 18 watt brit. With a trem .I sourced all the parts .lots of mods .hi low speed on trem, master volume .parasites on v1 pico f r ad. Have tried JJ s on power tubes and tung sol el 84s also 1 tung sol +1jj .that worked great! I myself do not get matched sets slight differences gives odd order harmonics little more distortion. 1 F&TCap 22uf 500volt also seamed to help with tone. Got most parts from Tube Depot classic tone iron from tried. Matched tubes for hi fi ok for mono guitar I think it's a bunch of hype.
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roadshow
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Re: JJ'844 TUBES

Postby roadshow » Fri 05/24/19 11:56 am

Referring to the manual posted, interesting picture of the circuit board and wiring. Too bad it's low res and there aren't more pics.

I wonder if anyone has opened one of these up and taken picture showing all the details?
Last edited by roadshow on Fri 05/24/19 4:27 pm, edited 1 time in total.
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geoff 1965
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Re: JJ'844 TUBES

Postby geoff 1965 » Fri 05/24/19 12:07 pm

yeah that was in reply to "Rippleman" and that's why i asked if his amp was a genuine marshall,i've been on this forum for over 3 years and have only ever seen kit builds!
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roadshow
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Re: JJ'844 TUBES

Postby roadshow » Fri 05/24/19 1:29 pm

geoff 1965 wrote:
Fri 05/24/19 12:07 pm
yeah that was in reply to "Rippleman" and that's why i asked if his amp was a genuine marshall,i've been on this forum for over 3 years and have only ever seen kit builds!
Here's one I just pulled from a Reverb 1974x ad, and then one I found in a web search that looks like a good copy due to the controls wiring that is just lavender and gray, tube protectors...:
insides.jpg
insides2jpg.jpg
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Rippleman
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Re: JJ'844 TUBES

Postby Rippleman » Tue 05/28/19 7:59 pm

Thanks for the link! It's a Marshall reissue 1974x from 2011
geoff 1965 wrote:
Fri 05/24/19 8:44 am
here's the owners manual,can't see anything in it for replacing tubes but if you get a matched pair of el84's for the output and a balanced ecc83 for the phase inverter "V2" you should be good.
M3310.034_1974X.pdf
is it a genuine marshall or a kit amplifier?
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Rippleman
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Re: JJ'844 TUBES

Postby Rippleman » Tue 05/28/19 8:14 pm

I'm happy to take some pics of the guts on this one. But I'll need basic instructions. I removed the bottom "kick-panel". However, to get behind that top panel, should I lay the amp carefully on it's face, or leave it standing up when unscrewing the top panel?
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geoff 1965
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Re: JJ'844 TUBES

Postby geoff 1965 » Tue 05/28/19 8:24 pm

Rippleman,
at last a genuine marshall on the forum!
i'm lost for word's except have you heard of "reverse engineering" and what are your camera skills like "especially high resolution close up's" !!
you can leave the amp stood up to remove the top panel,just be careful and make sure it's unplugged from the mains and don't poke around inside the chassis! not sure if it has a bleed resistor so the capacitors could have voltage in them!
appreciate this the amp look's good!
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roadshow
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Re: JJ'844 TUBES

Postby roadshow » Tue 05/28/19 8:53 pm

geoff 1965 wrote:
Tue 05/28/19 8:24 pm
you can leave the amp stood up to remove the top panel,
Are you sure? Looks to me like it would be best to have the amp laying on the front face. Then, after you unscrew the outer 4 screws you would lift the back board with the amp chassis out (disconnecting the speaker first, of course). Then laying the chassis down with the back board up unscrew the screws attaching the board to the chassis. You may have to strategically place a couple blocks of wood to balance it evenly. At that point the chassis is open and the pictures can be taken. That's what it looks like to me.

I wouldn't take any more of it apart. I'd leave the turret board alone, we can pretty much surmise what's below there from the top.

And I agree, it's great that we may soon have pictures of a true late model 1974x and all of it's wiring glory!!!
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Rippleman
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Re: JJ'844 TUBES

Postby Rippleman » Tue 05/28/19 9:02 pm

That's what I'm thinking too. Just the 4 silver screws are removed, after the speaker and power are disconnected. At that point, everything should slide out in one piece - internal components and controls attached to the panel. If I lay the amp flat on its face, then I can lift the panel straight up and then set it on a table.
roadshow wrote:
Tue 05/28/19 8:53 pm
geoff 1965 wrote:
Tue 05/28/19 8:24 pm
you can leave the amp stood up to remove the top panel,
Are you sure? Looks to me like it would be best to have the amp laying on the front face. Then, after you unscrew the outer 4 screws you would lift the back board with the amp chassis out (disconnecting the speaker first, of course). Then laying the chassis down with the back board up unscrew the screws attaching the board to the chassis. You may have to strategically place a couple blocks of wood to balance it evenly. At that point the chassis is open and the pictures can be taken. That's what it looks like to me.

I wouldn't take any more of it apart. I'd leave the turret board alone, we can pretty much surmise what's below there from the top.

And I agree, it's great that we may soon have pictures of a true late model 1974x and all of it's wiring glory!!!
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geoff 1965
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Re: JJ'844 TUBES

Postby geoff 1965 » Tue 05/28/19 9:25 pm

yeah i think you're both right,i was presuming the chassis was bolted to the cabinet seperate from the back panel. just be careful when you remove the panel and keep your hands away from the capacitors.
if you create a new post for the pics with say "marshall 1974X" as the subject it will be easier for people to find in future when searching the posts, i bet this will get a lot of interest & comments!
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