Help checking '85 JCM 800 - any red flags before buying?

XTRXTR

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My 1983 2204 works perfectly with no mods, unless you call adding output tube cathode resistors as a mod and its filter caps and output tubes have been replace several times each. That's just normal for a tube amp that gets used.

I don't use it now because I don't want the tolex to get further beat up and I build my own rack mounted 2204s for the road and use other Marshall speaker stacks.
 

Deftone

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I've yet to look inside my '85 2204 but I'm sure it's a mess. The seller (MLP Forum) claimed it was "modded and returned to stock" It even has a couple extra holes in the front panel.....
IMG957288.jpg

That said, once I matched it up with the right speaker combo...holy shit! It sounds amazing.
 

V-man

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I've yet to look inside my '85 2204 but I'm sure it's a mess. The seller (MLP Forum) claimed it was "modded and returned to stock" It even has a couple extra holes in the front panel.....


You ”have yet” to look inside a drilled-through used Marshall???

Please tell me this is a NAD and you are pulling the panel as we speak!

NFW could I buy a used amp online sans gut shot, nor could I keep myself from delving in to see what I have and what I want/need the tech to look at, regardless of whether I saw pics or not.
 

LPman

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Update: I decided to pass on this hacked Marshall since I couldn't try it in person and the seller was not a man of too much words.

Regarding prices: 1500 EUR is the norm all over in the EU (not in Reverb - it's 1800-2000 EUR there believe it or not - but even in local marketplaces where there are no additional fees) You can go local in Germany, Austria or Italy, that's the price they sell. I don't understand how these generic late 80's 2204s became so expensive, but that's the case around here.

Regarding the horizontal vs vertical input, with 2204 models I don't have a preference, they are 99% the same. If I would looking for 2203, I would only go for the earlier ones naturally.

Btw, I already owned a 2204, it was an early '78 JMP MK2 but with a replaced Dagnall UK PT that produced 450 VDC plate voltage instead of the 370-390 VDC of those late 70's and early 80's 2204 models. And the percussive, fast response of that amp was golden. Those crystal clean lows without any flubbiness and sag is what I'm looking for in a 800. I believe that the closest I can reproduce that tone is with a post-'82 2204 when the PT changed for the higher voltage version.
 

XTRXTR

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My '83 white 2204 mkII head has all that, I still IMO have not heard a better amp but I keep it indoors now and use my rack mounts for live with a Variac.

My wall AC is 120 to 127 depending what time I play, plate voltage gets to 483. You would think summer would be better for the line voltage. Desert/high plains climate, too many Air Conditioners, should be swamp coolers in the dry heat, One fan. AirCon has two large fans. So the power station puts out higher Voltage and I live about 20 miles from a 965 MW non nuclear power generation site, just small towns (< 1000 pop) between here and there. Used to be nuclear then they shut down and slowly installed three bldg generators on natural gas. Might as well be a Gigawatt. With the Flux Capacitor!!! lol Not even in the top 100 largest plants in the US.

I'm contemplating a sag resistor or building a switchable bucking transformer maybe target 117V depending on the switch Higher or Lower. That variac is heavy. I'll probably test both just to see what added sag would do.
 

Derrick111

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Regarding the horizontal vs vertical input, with 2204 models I don't have a preference, they are 99% the same. If I would looking for 2203, I would only go for the earlier ones naturally.

I was the same way until I learned that the guy who made me want JCM800s in the first place used later ones. Plus a friend had a later on that I thought sounded stunning after the bright cap was changed. I realised there are really good ones throughout the time of the JCM800. I happened onto an '86 and it is a force of nature to be reckoned with. So I don't go by years anymore, I go by my ears.

My '83 white 2204 mkII head has all that, I still IMO have not heard a better amp but I keep it indoors now and use my rack mounts for live with a Variac.

My wall AC is 120 to 127 depending what time I play, plate voltage gets to 483. You would think summer would be better for the line voltage. Desert/high plains climate, too many Air Conditioners, should be swamp coolers in the dry heat, One fan. AirCon has two large fans. So the power station puts out higher Voltage and I live about 20 miles from a 965 MW non nuclear power generation site, just small towns (< 1000 pop) between here and there. Used to be nuclear then they shut down and slowly installed three bldg generators on natural gas. Might as well be a Gigawatt. With the Flux Capacitor!!! lol Not even in the top 100 largest plants in the US.

I'm contemplating a sag resistor or building a switchable bucking transformer maybe target 117V depending on the switch Higher or Lower. That variac is heavy. I'll probably test both just to see what added sag would do.

All you need to do is either build one of these VINTAGE VOLTAGE ADAPTER or buy a commercial made one like the Brown Box. If you are knowledgeable enough to safely build it, you can do it for around $10-$30 in parts including adding your own digital voltage meter from Amazon or elsewhere like the brown box has.
 

LPman

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I like a 800 which hits like a jackhammer. When the notes kick like a drum. No sticky, saggy feelings, the response of the amp to the strummed notes is as fast as lightning. The player, the guitar and the amp is one. Can be unforgiving, but that's what I'm looking for. Master at noon, preamp at noon.

Then if I want the saggy, squishy power amp saturation I dime the master to 8 and get the big glasses cookin and let that machine gun tone of the 800 melt to mercury.

The ideal amp would be my '78 2204 which had the replaced high voltage Dagnall with the tasty stock Mustard caps and the plexi style small box head. I don't really like the look of the later heads. I was crazy to let that one go.
 

XTRXTR

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It is a whatchamacallit that lowers the AC, there are various designs to achieve it. Buck-boost type raises or lowers by the same amount say 10% depending which end you put on the source/Wall. From what I gather its a boost transformer if it raises voltage, and a buck if it lowers. e.g. 120 to 108 is a buck and 120 to 132 is a boost.

The vintage voltage adapter is a buck type design but as pointed out in the last sentence it can be wired to buck or boost if the line is connected to center tap B then A is a boost +6V and C is buck -6V

Buck or Boost terms have been around transformers and switching power supplies for sometime I guess. I only just looked into it recently.

Rob Robinette called his design a Bucking Transformer. I like his layout but it would be nice to have -6V for my amps and -12V if I ever get an old 60s model Marshall or Fender, or if they keep pushing the voltage higher, over time we might see 130V. Rob uses percentages of reduction I guess because in real life the transformers used to Buck act differently with actual wall AC applied - what ever that may be. This was posted in 2013 so the costs are off but simple enough.
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