JTM45 Reissue Upgrade Question

[frank9310]

I just traded a monster JCM 800 50 Watt Combo split channel with reverb with massive Drake transformers for a 1999 JTM45 Reissue used at Guitar Center thinking I'll have pure tone now. The first thing I noticed after bringing it home is it hums even when in standby and is really noisy if I run an overdrive pedal such as a Fulltone OCD where the 800 noise was barelay audible if I had the OCD on or off. So I posted a question in the repairs section about this and someone said it's because the poor design of the reissue chassis where they positoned the PT right next to the OT causing magnetic interference and hum. So the fix it I'd need to cut a hole in the chassis and rotate it 90 degrees to eliminate the magnetic interference which I assume is similar to turning sideways with a humming guitar to reduce hum. They also suggest to put a peice of metal in between if I didn't want to go that route which the amp tech tried with zero effect.

Of course if I did any of that, I would immediately make my new $1100 amp worth about $500. The transformers say Drake but look kind of cheap compared to the 1986 JCM 800 T's and while it has a huge bottom end, it doesn't have a whole lot of mid muscle or chunk iike the combo.

So I'm thinking of returning it and getting my 800 back before they sell it unless I can find a solution. I'm more after the Jimi early tones and thought maybe with the right tubes or minor mods I might be able to get close, but I'm not really feeling that. I'm feeling more early Clapton/Bluesbreaker tones. I didn't want to have to get a 100 watt Plexi for their weight and loudness but also not crazy about the JTM45 in that there's only about 20 watts of clean headroom before it starts breaking up while it still doesn't have the chunk or muscle.

So my question is this. With every mod suggested here such as circuit board replacement, and if you're going to do that, you might as well replace the OT and the PT and the Filter Caps and the 5881 tubes with KT66 or EL34s or whatever, and since the chassis is cut wrong, you need a new one of those to eliminate the design flaw. So what's the point of modding a reissue when the only thing left to it in the end is the wooden case? I mean I'm not trying to be smart but is there a reason that makes sense or some type solution where I can get the tone I want without breaking the bank and taming the noise?

[mwm523]

For less than $1000 you could build yourself a point-to-point wired boutique-quality vintage sounding JTM45 that would blow that reissue out of the water.

I would recommend you build one yourself, George's kit will walk you through every step and the end result is far superior to the Marshall reissue.

[frank9310]

Thanks and maybe true but I wouldn't trust my soldering skills that it would have the same quality build level of an amp that was rofessionally constructed plus I just don't have several nights to work on it. Well I do, but my ole lady doesn't agree.. LOL

[mwm523]

Well... not to beat a dead horse, but there's also the option of having Metro build your kit for you for an extra $400. That's really an unbelievable deal, and I wonder how long George will offer this option.

I know I sound like a schill for Metro, but I'm not. I'm just a very happy customer like many others here.

Anyway... To answer your original question, my opinion is no, it's not worth it to sink tons of money into that reissue to try to make it something it's not.

[Mars Hall]

So my question is this. With every mod suggested here such as circuit board replacement, and if you're going to do that, you might as well replace the OT and the PT and the Filter Caps and the 5881 tubes with KT66 or EL34s or whatever, and since the chassis is cut wrong, you need a new one of those to eliminate the design flaw. So what's the point of modding a reissue when the only thing left to it in the end is the wooden case? I mean I'm not trying to be smart but is there a reason that makes sense or some type solution where I can get the tone I want without breaking the bank and taming the noise?

I understand your plight! In my case I upgraded a BBri that had a blown OT. So it made more sense to go ahead and gut it. I replaced the Board, OT, choke and caps, all with Metro stuff. Everything else is stock, PT, chassis, tube sockets and pots. My PT makes a little noise but not enough to warrant changing the chassis or remounting it.

The upgrade kits are for guys who've had there amps for awhile, like them, but want to make them better and guys like me, who've had major issues. I think this is where George got his start.

[Big Jim]

Frank,
I've got to second what Mike said. I would take the re-issue back and get your 800 back if you can. I just built a Metro JTM 45 and I love it. Its quiet, and sounds AMAZING. I had no building experience whatsoever and with a little help from the forum, I got it done. From reading your post, it sounds like you
are kind of going for the 45/100 tone. But when I was looking, most experienced builders were steering me toward the 50 watter, or the 45. If you can solder, read and follow instructions, and have access to a computer, you can probably build any of Georges kits. The forum members are awesome at offering tech support.
Jim

[frank9310]

Hey after working on it a while, I take it all back. It still does hum but not so bad I'm getting used to. Anyway, I popped in some Valve Art KT66s when I found no changes necessary, rebiased to 38mA, swapped some preamp tubes and ran into 2 Celestion JH100 G12C greenbacks and it's now a roaring Jimi beast!

Only thing is I read these need biased hot so wondering what is a good bias setting for these reissues. Also, Im getting a Scumnico from Jim as Scumback so can't wait! Check out the MetroJTM45 clip using one here http://www.scumbackspeakers.com/clips/alnico_clips.html

Thanks guys for the advice!

[thousandshirts]

Ahh, you're in for a treat with that Scumnico. Good stuff. Glad to hear you've found a sound you enjoy.

As far as people saying that the Valve Art KT66 need to be biased hot to sound good -- don't believe a word of it. For some people, some ears, and in some amps, that's absolutely true, but it is not true of all amps and all ears. So just bias it up as you see safe, and as your ears please you (both safe for the tube and pleasing for the ear) and you are DONE.

If you're curious about the 'safe' side of things, you can use your plate voltage readings and your current readings, and use those to calibrate your tubes under their maximum dissipation rating. To do this easily, it would be best to install some 1 ohm bias resistors on your amp, but it depends on how comfortable you are in getting inside your amp.

Here's the Shuguang (Valve Art) KT66 data sheet:

http://www.pentalaboratories.com/Produc ... id=KT66+MP&" onclick="window.open(this.href);return false;

[frank9310]

Ah yes thanks! Cant wait to try the Scumnico. Have you tried one? Im not sure if I should get a 30 watt version to blend with a Celestion G12C Greenback from the JH 45/100 Hendrix Stack as that has an awesome vintage gooey-crunchy low end roar that is spooky as if Jimi walked in the room and cranked it up on his rig. When I tried that with a G12H30th anniversary, that kind of took away from some of the crunch with a tighter low end but added back lots of smooth sustain, tighter and more defined mids and more overall muscle and output.

On the other hand, the Scumnico sounds like great silky, chimey early Jimi all the way which I think would be a better combination overall for the particular vintage sounds I'm after. However, the clip I heard didn't have a lot of crunch but that chime and swirling mids and sweet highs are to die for. Not that it isn't capable of the gooey crunch like Red House Woodstock, just that the particular clip didn't demonstrate it if it does compared to what I'm hearing with the greenbacks.

So I'll ask Jim but would you recommend say a 65 watt Scumnico in a 1x12 to make it easy to get around with a nice 1x12 open back cab or the 25 watt Greenback to retain some gooey-crunch (if the alnicos in general lack that) along with a 30 watt Scumnico in a closed back?

Here's the G12Cs http://www.areyouexperienced.net/celest ... eakers.htm

Thanks guys for the terrific advice!