Got my eye on a '79 2204. Insights please

[LoudStroud]

Since we're having a bit of a '79 2204 appreciation moment, here's mine...

 

[Chris-in-LA]

My 2204 is later, an '86, but it very quickly became my favorite amp. So much so, I built a few 2204 clones because I couldn't get enough of that tone!!

 

[Frank Araneo]

Gut 2
The amp was built with a capacitor across the 100k plate resistor (Br-Bk-Y, under the gray wire). This cap doesn't show up on most/any schematics, so a "clever" prior owner or tech removed it, probably thinking incorrectly that it was added by a "clever" prior owner. Or perhaps there's a good reason to remove it?

Gut 3
The EL34 conversion looks pretty well done, except 2 things: (1) the resistor to the right of the two bias caps, tucked in next to the diodes, should be 220k (R-R-Y) but it isn't. I think there's some leeway there, so probably no big deal. And (2) there should be a 5.6k (Gr-Blue-R) on pin 5 of each power tube, and the wires going to the 220k bias pair (R-R-Y) should connect to that instead of direct to pin 5. This is commonly missed on EL34 conversions, but I don't know how important they are or why they're there. But I do know Marshall has them on EL34 units.

Overall looks GREAT. $2300 would be an appropriate price if it's cosmetically beat up. If in great shape, then $2300 is a steal.

Thanks, Eric.
"

The amp was built with a capacitor across the 100k plate resistor (Br-Bk-Y, under the gray wire).

Do you know the value of that cap? I'm wondering if it's the 100 pf cap (C2) cap referred to in the attached Marstran schematic that shows " *Not present on earlier versions of the circuit.". The schematic shows that cap in series.

http://marstran.com/22032204_pre.gif

"

The EL34 conversion looks pretty well done, except 2 things: (1) the resistor to the right of the two bias caps, tucked in next to the diodes, should be 220k (R-R-Y) but it isn't. I think there's some leeway there, so probably no big deal.

Yeah, it's a 200k (R-Black-Y) instead of 220k.

And (2) there should be a 5.6k (Gr-Blue-R) on pin 5 of each power tube, and the wires going to the 220k bias pair (R-R-Y) should connect to that instead of direct to pin 5. This is commonly missed on EL34 conversions, but I don't know how important they are or why they're there. But I do know Marshall has them on EL34 units.

Yes, I see that resistor on the control grid on other EL34 gut shots and on schematics. Pretty easy "fix".

 

[cliffenstein]

My 2204 is later, an '86, but it very quickly became my favorite amp. So much so, I built a few 2204 clones because I couldn't get enough of that tone!!

1986 JCM800 2204
Mojotone 2204 clone
Valvestorm 2204 clone

How is your Mojotone 2204? Is it the British 800 one is it the British 50 (JMP) one?

Mine is the British 800 one and it is incredible...when other guitarists borrow it at my band's gigs they freak out about how great it is!

Mojotone 2204 vs Valvestorm 2204?

 

[TheOtherEric]

...
Do you know the value of that cap? I'm wondering if it's the 100 pf cap (C2) cap referred to in the attached Marstran schematic that shows " *Not present on earlier versions of the circuit.". The schematic shows that cap in series.

http://marstran.com/22032204_pre.gif

Nope; the cap in question is across the plate resistor for V1a, which is R4 on the schematic you linked. If you search for some gut shots of 1979 2204s, you'll see it there. But it's not on later 2204s. Sorry I don't know the value. But I wouldn't bother adding it back; I'm no expert but I suspect it's function is similar to the 100pF you asked about that Marshall put on later units on the tube socket (across pins 6 & 8) to block radio frequencies or oscillations or something like that. Marshall ditched this cap on the plate resistor, so it's likely not useful.

 

[Frank Araneo]

Nope; the cap in question is across the plate resistor for V1a, which is R4 on the schematic you linked. If you search for some gut shots of 1979 2204s, you'll see it there. But it's not on later 2204s. Sorry I don't know the value. But I wouldn't bother adding it back; I'm no expert but I suspect it's function is similar to the 100pF you asked about that Marshall put on later units on the tube socket (across pins 6 & 8) to block radio frequencies or oscillations or something like that. Marshall ditched this cap on the plate resistor, so it's likely not useful.

Got it. Thanks again!

 

[science]

Greetings.

I'm attaching a few pics. Haven't played it yet, but before I make the trip I'd appreciate some comments/insights/advice. A few things that looked a bit peculiar to my newbie eyes right off the bat:

Gut 1:
1) the variable resistor at the first input stage on the board (left). Is that supposed to be a 1M? I suppose having a pot there could be a good thing for the tweaker in me.
2) Isn't there supposed to be a resistor (2k7?) in parallel with the .68uf mustard cap?
3) The gray wire connecting V1 and the 68K resistor. I believe that's right, but the solder looks new?
4) The solder for the 820K resistor above the "Marshall" printing doesn't look original.




Gut 2:
The solder for the 100K "hiding" under the gray wire doesn't look original (upper left on board).

Gut 3

'79 2204

www.flickr.com

Gut 6 impedance
Correct?



Transformers look original:





It appears that the filter and bias caps have been replaced?

Thanks again in advance. This place is THE best!

Frank

The pot on the first resistor is wack but I suspect they did what everyone tries to and put actual gain in the stages as wired. Can't do it that way, had to rewire the sockets to be chronological of layout. Just oscillated turned up. Curious. 1st one was 820 ohms and 100uf. then 10k Rk on the second stage then 820 on the 3rd one. The .68 was for the 2k7 on the 1959 not this one. Boards were overlapped.

 

[Trem man]

They're such great amps if working properly and you can get a decent deal on it. Anything that's amiss can be put right by a good amp tech. As long as the Drakes are original that's the main thing, imo.

 

[Chris-in-LA]

How is your Mojotone 2204? Is it the British 800 one is it the British 50 (JMP) one?

Mine is the British 800 one and it is incredible...when other guitarists borrow it at gigs I play they freak out about how great it is!

I got the Mojotone British style 800 2204 kit a few years back, it's the one with the full size JCM800 chassis. Sounds really good, almost exactly like my stock 2204. I also built 2 Valvestorm versions, one with a Chris Merren OT and one with a Marstran OT. You would struggle to tell the difference blindfolded.

 

[cliffenstein]

I got the Mojotone British style 800 2204 kit a few years back, it's the one with the full size JCM800 chassis. Sounds really good, almost exactly like my stock 2204. I also built 2 Valvestorm versions, one with a Chris Merren OT and one with a Marstran OT. You would struggle to tell the difference blindfolded.

Very very cool...yeah, my JCM800 Mojotone is incredible.

 

[Frank Araneo]

The pot on the first resistor is wack but I suspect they did what everyone tries to and put actual gain in the stages as wired. Can't do it that way, had to rewire the sockets to be chronological of layout. Just oscillated turned up. Curious. 1st one was 820 ohms and 100uf. then 10k Rk on the second stage then 820 on the 3rd one. The .68 was for the 2k7 on the 1959 not this one. Boards were overlapped.

Thanks, Science. Would you consider this to be a relaible (definitive?) schematic for this amp? I know it's for 6550's but the pre-amps should be the same. I'm trying to determine what "stock" is. Thanks

https://el34world.com/charts/Schematics/files/Marshall/Marshall_jmp_mastervol_50w_2204u.pdf

 

[Vinsanitizer]

Greetings.

I'm attaching a few pics. Haven't played it yet, but before I make the trip I'd appreciate some comments/insights/advice. A few things that looked a bit peculiar to my newbie eyes right off the bat:

Gut 1:
1) the variable resistor at the first input stage on the board (left). Is that supposed to be a 1M? I suppose having a pot there could be a good thing for the tweaker in me.
2) Isn't there supposed to be a resistor (2k7?) in parallel with the .68uf mustard cap?
3) The gray wire connecting V1 and the 68K resistor. I believe that's right, but the solder looks new?
4) The solder for the 820K resistor above the "Marshall" printing doesn't look original.




Gut 2:
The solder for the 100K "hiding" under the gray wire doesn't look original (upper left on board).

Gut 3

'79 2204

www.flickr.com

Gut 6 impedance
Correct?



Transformers look original:





It appears that the filter and bias caps have been replaced?

Thanks again in advance. This place is THE best!

Frank

They sure don't make 'em like they used to. The inside of a DSL, TSL, JVM, looks like a PC motherboard or 8.

 

[dtier]

Thanks, Science. Would you consider this to be a relaible (definitive?) schematic for this amp? I know it's for 6550's but the pre-amps should be the same. I'm trying to determine what "stock" is. Thanks

https://el34world.com/charts/Schematics/files/Marshall/Marshall_jmp_mastervol_50w_2204u.pdf

That is not the correct schematic for the 79. It is for the 76 non-cascaded version. There may not be a 79 6550 schematic out there but several that are close.

 

[BlueX]

Thanks, Science. Would you consider this to be a relaible (definitive?) schematic for this amp? I know it's for 6550's but the pre-amps should be the same. I'm trying to determine what "stock" is. Thanks

https://el34world.com/charts/Schematics/files/Marshall/Marshall_jmp_mastervol_50w_2204u.pdf

I was told that this was the schematic for the cascaded pre-amp in my '79 2104 (the bottom one for 2103, 2203, 2104, and 2204): https://www.drtube.com/schematics/marshall/jcm800pr.gif

 

[dtier]

This is the power section from the same site.

https://www.drtube.com/schematics/marshall/jcm800pw.gif

 

[Frank Araneo]

I was told that this was the schematic for the cascaded pre-amp in my '79 2104 (the bottom one for 2103, 2203, 2104, and 2204): https://www.drtube.com/schematics/marshall/jcm800pr.gif

Thanks very much BlueX! That looks more like it.

 

[Frank Araneo]

This is the power section from the same site.

https://www.drtube.com/schematics/marshall/jcm800pw.gif

Thanks very much dtier. Very helpful!

 

[TheOtherEric]

That is not the correct schematic for the 79. It is for the 76 non-cascaded version. There may not be a 79 6550 schematic out there but several that are close.

There's a schematic dated Feb 1978 for 6550 tubes. I found it a couple weeks ago on one of the main schematics sites using Google. It's titled "50w MASTER VOL (MODEL 2204) REV" and shows Unicord. I printed it but didn't save the file. :

 

[Frank Araneo]

There's a schematic dated Feb 1978 for 6550 tubes. I found it a couple weeks ago on one of the main schematics sites using Google. It's titled "50w MASTER VOL (MODEL 2204) REV" and shows Unicord. I printed it but didn't save the file. :

Thanks Eric. I saw a version of that; it was kinda hard to read. dtier and BlueX directed me to these schematics for pre-amp and power sections for 50w and 100w JMPs:

https://www.drtube.com/schematics/marshall/jcm800pr.gif

https://www.drtube.com/schematics/marshall/jcm800pw.gif

 

[KirkD777]

Greetings.

I'm attaching a few pics. Haven't played it yet, but before I make the trip I'd appreciate some comments/insights/advice. A few things that looked a bit peculiar to my newbie eyes right off the bat:

Gut 1:
1) the variable resistor at the first input stage on the board (left). Is that supposed to be a 1M? I suppose having a pot there could be a good thing for the tweaker in me.
2) Isn't there supposed to be a resistor (2k7?) in parallel with the .68uf mustard cap?
3) The gray wire connecting V1 and the 68K resistor. I believe that's right, but the solder looks new?
4) The solder for the 820K resistor above the "Marshall" printing doesn't look original.




Gut 2:
The solder for the 100K "hiding" under the gray wire doesn't look original (upper left on board).

Gut 3

'79 2204

www.flickr.com

Gut 6 impedance
Correct?



Transformers look original:





It appears that the filter and bias caps have been replaced?

Thanks again in advance. This place is THE best!

Frank

My favorite amp of all time was my '79 JMP 50W. Stupidly I let it go because I was living in NYC and thought I would never use it again. I'm 53 and worked at a vintage music shop in the 90s. I've played or owned every classic amp made pretty much. But that '79 was my favorite. I finally found a pedal that nails the sound of that amp. I just use it alone with my Supro Black Magick. It's the Freidman Small Box. I know this has nothing to do about your questions but it has completely filled that sorry hole in my life. I think they're around $200 but my friend made me a clone of it. He hooks me up. I would watch some videos on the pedal but it's all I use. Just like I plugged straight in to that '79. Just a heads up as most Marshalls from those days can sound different. My buddy's Facebook page is

No One Cares Pedals

No One Cares Pedals. 1,904 likes · 14 talking about this. Custom made-to-order guitar pedals.

www.facebook.com

Great guy and you can pick your own graphics. I chose the cover of a Thin Lizzy record called Black Rose. Anyway he just follows the circuit and uses the best parts. And they are guaranteed for life. So that's a bonus. Plus it will save you some money. His name is Chris and tell him Kirk sent you. But no matter which way you go I really can't recommend that pedal enough. Easy way to get that sound for sure. Plus all the vintage amps I've bought recently are finally just getting too old. I always seem to have an expensive problem. Kinda over them.

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