Where/who can do JTM45 tuneups?

PaulO · Post by **PaulO** » Thu Feb 16, 2006 7:50 am

I have a fairly new JTM45 reissue. For all I know it is operating where it should be (nothing to benchmark it against).

I noticed at low volumes it sounds thin. Different cabs make huge differences in sound. Cranked up it sounds much fuller. but it just sounds thin and anemic, and I tend to gravitate to a DSL100 when playing. Has to be something I can do to it. I love the vibe of it.

I would like to get someone to look over the JTM and if not running where it should, do modes as required.

Can someone point me to a link so I can contact someone who is good at this stuff?

Thanks,

Paul

Ricky Lee · Post by **Ricky Lee** » Thu Feb 16, 2006 9:05 am

The amp bias is probably set to the cold side, typical of a new stock Marshall, however, that's probably the least of your problems. Marshall's new amps are built with less than quality pieces/parts, such as those grey legos found on the PCB. Just changing those to Sozo "Mustard caps" makes a world of difference in sound quality. Changing tubes will have a possitive effect as well, since Marshall uses about the worst tubes one could find. As far as someone tuning the amp for you, there are plenty of us here on the forum that can do that for you, but our tune up will most likely be more of an upgrade than a simple tuneup i.e. changing the PCB to a PTP board, replacing tubes and maybe even output tranny. If your somewhat mechanically inclined you could make all the upgrades yourself, it doesn't take a rocket scientist to upgrade Marshall type amps and George, has done a great job with the JTM 45 instructions. They're like painting by numbers, so to speak and pretty much straight forward. Hope this helped.

bvmjethead · Post by **bvmjethead** » Thu Feb 16, 2006 9:11 am

https://weberspeakerscom.secure.powweb. ... r_page.htm

Read this......

Search these forums as well, I've got alot to learn yet but I've learned ALOT since coming and reading till my eyes bleed.
If all else fails I'm sure George will work on it for you.

[urlhttp://www.metroamp.com/services.php[/url]

PaulO · Post by **PaulO** » Thu Feb 16, 2006 9:12 am

Yes, I can do some on my own. With instructions I did a whole bunch of mods to my Blues Junior amp and it turned out great.

I don't really want to attempt biasing because it sounds a little more complicated.

Can you or someone email me the George instructions?

I will plan to purchase items from Metropoulos Amps as they seem to have all the right stuff.

Thanks a bunch!!!

Paul

bvmjethead · Post by **bvmjethead** » Thu Feb 16, 2006 9:15 am

You CAN do biasing yourself. Click the above Weber link.....

You just need to be careful and patient. Find out how it's done and carefully proceed.

Like I said before if all else fails call George and ship the amp to him.

http://www.metroamp.com/services.php

neikeel · Post by **neikeel** » Thu Feb 16, 2006 10:13 am

I hope others here agree with me but I started the whole amp building thing sitting in the same position 2-3 years ago.

First question is are you bridging lo Channel I to hi Channel II (guitar in hi Channel I)? Try this first, this can thicken it up a bit particularly when bias on ouput valves is correct typically 32-40mA range for the 5881s that are stock (they seem to come set at 22-25mA way too cold but gives longer tube life of cheap valves).

If you are looking to improve your amp in a cost effective way IMO I suggest:
1) Get a NOS Mullard or Brimar ECC83 for V1 (any non-microphonic ECC83/12AX7 will do for V2/V3 for the moment).
2) Get a pair of KT66 output valves GEC are first choice but expensive George has some excellent modern ones which sound v. good - sound clips everywhere! set bias typically to 38-40mA at idle (you will learn about % of plate dissipation calculation later).
3) Replace grey lego caps on stock board first with Sozo caps (guess where to buy them......)

If you are into serious fiddling next get PTP board kit with 'vintage' sozos or NOS mustards and use carbon comp resistors in the 'tone' circuits. Whilst you have the board out put in a Mercury Magnetics/Heyboer/Marstran output transformer and swap the filter caps to lower values. Then put NOS valves in V2/V3 (I actually found some USA 7025 valves which sound better than Mullards in these positions but that is probably heresy and maybe me having a bad day

)

The above are only MY personal observations others may disagree.

It is all here on the forum or try legendary tones site.

Careful you will get addicted

PaulO · Post by **PaulO** » Thu Feb 16, 2006 10:21 am

Yes, I am bridging channels 1 and 2, and run the head thru a 1960BX cab.

I noticed my cheap Les Paul Junior makes the amp come to life much better than my Strat or LP. Strat sounds very thin (single coils) while the Strat pushes it to distortion fast (humbuckers).

I can certainly replace tubes. Heck its only money.

Do you have a shot of where that lego thingy is located on the board?

Thanks a bunch,

Paul

Ricky Lee · Post by **Ricky Lee** » Thu Feb 16, 2006 10:33 am

PaulO wrote:Yes, I am bridging channels 1 and 2, and run the head thru a 1960BX cab.

I noticed my cheap Les Paul Junior makes the amp come to life much better than my Strat or LP. Strat sounds very thin (single coils) while the Strat pushes it to distortion fast (humbuckers).

I can certainly replace tubes. Heck its only money.

Do you have a shot of where that lego thingy is located on the board?

Thanks a bunch,

Paul

The LEGOS are those rectangular shaped gray caps located on the PCB bard. Changing them can be difficult and if NOT carefull when soldering you can damage the board itself, that's why the PTP board is a better option for upgrading on-board components such as resistors and caps eytc...

neikeel · Post by **neikeel** » Thu Feb 16, 2006 10:36 am

The lego thingies are little grey bocks of plastic which are soldered to the single sided PCB you can see inside the amp. These are the signal capacitors. The type and specification of these capacitors affects the way the guitar signal is processed in the amp. You will see that they are of different values 0.022uF (x5) and 0.1uF (x3) plus a 0.1uF on the presence pot.

I take it you are safe with high voltages and know how to discharge the filter capacitors?

If not search andd read the forum for a while longer before doing anything other than replace valves (but you will need to bias the output valves to get them to work effectively.

If your strat is thin but the P90's are ok you could just snip off one of the leads on the little pink/buff capacitor on the channel I volume pot, just inside the edge of the chassis front, this will help thicken things up at low volumes with a strat but will sound the same wide open.

PaulO · Post by **PaulO** » Thu Feb 16, 2006 10:39 am

Well, I built my own Heathkit amp when I was about 15 years old ... but that was nothing more than laying out parts and soldering them in.

I know about grounding caps allowing time for the built up electrons to dissipate.

Yup, I'll probably kill myself.

I'll read on! This is a fantastic site with a wealth of information. My problem is cutting to what I need quickly.

Thanks for your help!

God save the Queen.

Paul

neikeel · Post by **neikeel** » Thu Feb 16, 2006 10:43 am

Who he?