Got my eye on a '79 2204. Insights please

[Frank Araneo]

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

 

[V-man]

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

First thing I saw. Clearly a 6550 to EL Conversion being a US model so bias resistors should have been adjusted. The handwritten Imp note shouldn’t be Marshall’s doing (not IME)… perhaps an uncertain tech or owner who monkeyed around with mods/taps? Also, I am guessing the red lead on the far rt on the board is not stock?

 

[BlueX]

Maybe the pictures in this thread can be of help. It's my late '79 2104, Scandinavian EL34 version. Fusing, and maybe PT and OT, might differ.

NAD: 2104 - Couldn't get it out of my head

Got a new Marshall today, 2104 from 1979/1980. Saw a 2104 about a month ago (see thread below) and now another popped up so I got it. S/N 05012L which should be 1979 (L). Inspection label dated 5/1/80 (5th January 1980?). Speaker code T3120 which seems to be the correct type (G12-65, Ceramic...

www.marshallforum.com

 

[Frank Araneo]

First thing I saw. Clearly a 6550 to EL Conversion being a US model so bias resistors should have been adjusted. The handwritten Imp note shouldn’t be Marshall’s doing (not IME)… perhaps an uncertain tech or owner who monkeyed around with mods/taps? Also, I am guessing the red lead on the far rt on the board is not stock?

Right. I forgot to mention about the bias caps. It is running EL34s, and my understanding is those caps are supposed to be .08 uf? The Marstran schematic (below) shows the resistor in parallel with the bias pot is supposed to be 56K for EL34s and 47K for 6550s. This amp has what appears to be an unmolested (original) 56K there, suggesting it's for EL34s. There's no voltage selector, suggesting it's a US model. This amp is currently stocked with EL34s, but that doesn't really prove anything!

https://www.marstran.com/2204_pwr.gif

 

[dtier]

Gut1
1) Stock is a 10k ohm cathode bias resistor. There is a pot (10k?) in series with what looks like a 1k ohm resistor.
2) The 2.7k is there.
3) The shielded gray wire looks stock.
4) Someone had soldered something across the 820 third stage cathode resistor and removed it. Likely a capacitor.

Gut2
Something was soldered across the first stage plate resistor and removed. Likely a capacitor again.

Gut6
Someone was likely experimenting with connecting the violet feedback wire to different impedance taps.

The grid leak/bias feed resistors for the output tubes have been replaced with 220k, and the first bias dropping resistor has been changed to a 150k for the EL34 tubes.That work looks professionally done.

 

[cliffenstein]

I have a 79 2204 and it's absolutely awesome. Do you have a chance to play this? Mine is stock with 6550's. I've never played through one that had a conversion done.

 

[Frank Araneo]

Gut1
1) Stock is a 10k ohm cathode bias resistor. There is a pot (10k?) in series with what looks like a 1k ohm resistor.
2) The 2.7k is there.
3) The shielded gray wire looks stock.
4) Someone had soldered something across the 820 third stage cathode resistor and removed it. Likely a capacitor.

Gut2
Something was soldered across the first stage plate resistor and removed. Likely a capacitor again.

Gut6
Someone was likely experimenting with connecting the violet feedback wire to different impedance taps.

The grid leak/bias feed resistors for the output tubes have been replaced with 220k, and the first bias dropping resistor has been changed to a 150k for the EL34 tubes.That work looks professionally done.

Thanks very much dtier.
"Stock is a 10k ohm cathode bias resistor. There is a pot (10k?) in series with what looks like a 1k ohm resistor."
I'm assuming that pot would adjust the brightness of the Bright Channel? I like that idea.

 

[Frank Araneo]

Yes, I

I have a 79 2204 and it's absolutely awesome. Do you have a chance to play this? Mine is stock with 6550's. I've never played through one that had a conversion done.

Yes, I can demo it. I wanted to get some insight from the experts here before I make the trip. So far I haven't heard anything that would dissuade me from making the trip. At $2,300, the price seems fair given the current market.
I have a '76 1987 with 6550s and an '86 4210 JCM800 combo with EL34s. The 6550s sound great. I believe the two channel 4210 is a 2205, and I've never played a 2204.

 

[dtier]

Thanks very much dtier.
"Stock is a 10k ohm cathode bias resistor. There is a pot (10k?) in series with what looks like a 1k ohm resistor."
I'm assuming that pot would adjust the brightness of the Bright Channel? I like that idea.

It will affect the bias of the second stage. Only one channel on the 2204 with high and low sensitivity. The second stage is a "cold clipper" and is a distinctive part of 2203/4 sound. Asymmetric distortion with lower gain. The pot will adjust that stage warmer. At 1k it will have much more gain. That sounds good but moves away from the signature tone. I would ask that it be set at 10k if possible for a demo. The amp overall looks great on the inside.

 

[Frank Araneo]

It will affect the bias of the second stage. Only one channel on the 2204 with high and low sensitivity. The second stage is a "cold clipper" and is a distinctive part of 2203/4 sound. Asymmetric distortion with lower gain. The pot will adjust that stage warmer. At 1k it will have much more gain. That sounds good but moves away from the signature tone. I would ask that it be set at 10k if possible for a demo. The amp overall looks great on the inside.

Thanks again! I'll schedule a trip.

 

[Blacksabbath1987]

there nothing wrong with this a few upgrades to the good my dad has this leave it alone buy it play it and enjoy it

 

[Blacksabbath1987]

there nothing wrong with this a few upgrades to the good my dad has this leave it alone buy it play it and enjoy it

If your where as old as it is you need some upgrades to Lol it’s been around I’d buy it with no hesitation and what ever it needed do it there badass

 

[VERVEHAMMER]

Very nice condition!

Onward to Victory!

 

[Central Scrutinizer]

Hope it works out for you.

Road trip!!

 

[LoudStroud]

Yep, my ‘79 2204 has been a lifetime favorite. Bought it back in ‘93 or so and it’s still in the fold. I had monkeyed with gain stage and bright cap values a bit early on, but fairly quickly put it back to stock, where it remains.

Looks good. Git it.

 

[Deftone]

I have a '79 JMP 2204 myself. It's an awesome amp. Mine is an original 6550 USA amp like @cliffenstein



It's the most organic sounding and more forgiving of speaker choice than my other two JCM800 2204's. It's definitely my #1.

 

[Blacksabbath1987]

There you go Marshall and Orange ruled the roost when it came being loud and proud we our lucky to even have these coming out new like they our it’s unheard of and the specs our pretty good. Quit reading and go get it I think it’s cool they have the 20 watts I even went out and bought 2 myself when they went on sale

 

[Frank Araneo]

If your where as old as it is you need some upgrades to Lol it’s been around I’d buy it with no hesitation and what ever it needed do it there badass

Well, I'm 22 years older, so I know what you mean!

 

[Frank Araneo]

Hope it works out for you.

Road trip!!

Thanks! Trip scheduled this week.

 

[TheOtherEric]

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 a mod. 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.