1985 Marshall JCM800 2205 Split Channel

Overview

Back when I first started playing guitar, I quickly learned what a JCM800 was, and dreamed of one day owning a high end tube amplifier. At the time, I was playing on a Vox AD30VT, a great amp in hindsight, but really limited in what it could do for me. So with some saved money, and help from my Dad (a fellow guitar player and understand-er of the need for a tube amp) I set out on a teenage journey to pick out the best possible amp for me, with the intent of trying just about every amp I could play and buying a single amp to last me forever (ha ha!).

After weeks of searching, testing, comparing, reading forums, watching youtube clips (which were noticeably lower quality back in 2009 when I started this search), I came across a JCM800, two channel, in a local guitar center. I didn’t know anything about it but I distinctly remember playing it and thinking it was just about the best thing I’d ever heard - but out of my budget. When I went back to see if I could make a deal, it was gone already. Before I fully understood these amps, I also played a 1982 model 2205 in small local shop and found it extremely disappointing. Skipping ahead, I ended up with a Marshall TSL instead - see that page for more on this story.

That first JCM800 split channel stuck with me though, and I always hoped to find one that sounded like that one again. Finally, with a full decade more of knowledge to help me understand that there were pretty drastic revisions to the circuit of these amps, I knew what I was looking for - a later revision with more gain and a new location of the tone stack in the circuit. These amps released at the end of 1981/early 1982 and this is the original circuit. In the past, thanks to internet wisdom, I expected the later circuit to appear only in 1986 and later, but this particular amp has a 1985 date code and has the later circuit. It’s easy to tell the two apart by pulling out the V2 tube, if the boost channel remains the same in volume/gain, then it’s the later circuit. I think it’s safe to say the revisions made it to production models sometime in late 1984, as I’ve seen others online with 1984 models with the earlier design. There are actually 3 revisions of this circuit, one coming very late in the run, 87-90, but the latest version is very similar with the only difference being a bit more gain on the boost channel - it’s difficult to find useful schematics for these to really show the differences.

This specific amp still has the original caps, although it does have a full set of new tubes. I’m pleased to report that there’s no cap related issues, despite their age they are still performing great. I’ve heard caps that are regularly powered up last longer than those neglected and unused for years, and with the fairly discolored front side of this amp, I think it’s safe to assume it’s been in regular use the last 35 years - and the way it sounds, it’ll get regular use from me too.

The boost channel is very old school in its gain structure, and doesn’t have much bass to it like a modern amp. Between the separate channel volumes and the master, it’s surprisingly easy to tame to studio/practice volumes, but sounds much meaner turned up. There’s almost no taper after 3 on the master, so once you are up there you may as well go all the way because at that point it’s already at full tilt volume wise. I’ve found the best tones I get from the boost channel are with the gain and bass maxed, and treble rolled down to around 4. The mids control has a great sweep on this amp, going from an old school thrash metal tone with ease rolled back (maybe with the treble at 5 or 6 too), but I usually leave it around 6 and it’s great and thick. This channel has diodes that provide extra clipping of the signal for a bit more distortion. These diodes can be changed out for different types as well, although I think it sounds so good stock I don’t intend to do this. Some players don’t like diodes, but I don’t really notice much of the trademark graininess that goes with them in this amp - at least, it doesn’t sound any worse than a 2204 with a diode boost pedal in front. This kind of thing is really up to player preference, though I’d expect with the right diodes installed nearly any player would be happy.

The normal channel is very clean - and very sensitive to volume changes. Even with the master set low, it’s very loud by 2 on the dial. You can get a little grit from this channel up to 10, although it does bleed ever so faintly into the boost channel when set this high (it’s really barely noticeable, earlier revisions were much worse here). One nice trick - since this amp has a great tube buffered serial effects loop - is to throw a volume box in the loop and use that as a “final” master volume. This allows you to crank up the normal channel volume wherever you want it to get a nice dirty clean tone, and have a little better control over the balance between that channel and the boost channel - at first managing 4 volumes seems a bit strange but in this configuration, just treat the normal “volume” as a gain control and you’re all set. Even the boost channel sounds a bit different in this configuration, by turning up the master and the channel volume down, that channel takes on a slightly different character - you might like it either way, it’s nice to have both flavors.

I suppose my only complaint about this amp is that the reverb is fairly rudimentary. It’s a bit too short of a tail, bright, and not all that lush. It’s a tube driven accutronics tank, so all of the components are there for a great reverb sound, I think it’s implementation is just not ideal. It was Marshall’s first attempt at onboard reverb though, and while I haven’t had the next iteration (the JCM900DR), I do have a JCM2000 TSL and the reverb on that is absolutely fantastic, so they got it right eventually. At the very least, having the reverb on doesn’t detract from the sound at all, so I usually leave it around 5 (which is barely on) for a little atmosphere. I am using a single button footswitch, but with a two button I could switch channels and also turn the reverb on and off, so if I were gigging with this amp I’d probably max the reverb and just switch it on only when using the clean channel, or just use a pedal in the excellent effects loop - just a shame to let that real spring sound go to waste.

One last note, during this era it was getting very difficult to find mass production EL34 tubes of sufficient quality for Marshall. The luxury of modern new production tubes didn’t really come into play until the late 90s, and quality/consistency of chinese made tubes in the late 80s was hit or miss. Many Marshall heads around this time are configured for KT88/6550 tubes instead, since those were more plentiful. This amp is equipped with a pair of these tubes - and unlike EL34s, generally can handle a lot more power. Some modern amps even use a pair of KT88’s like this for 100w output, to put it in perspective. With that in mind, don’t expect the classic EL34 power amp breakup with this amp, and also it is capable of much louder volumes than you might expect from an amp rated at 50w. That 50w RMS rating is based on a clean sine signal, using a guitar and cranking up the volumes and gains into overdrive and all holds are off.