JTM45 RI mods

anis258 · February 9th, 2005, 10:07 AM

Hi there, I just wanted to know what mods JTM45 RI owners have done and how it worked out tonally... I'm going to retube (with KT-66s), but as a not-so-techy guy, i'm not sure about the type of filter capacitors that i should replace with (ie brand, values) and how i can source them. I've looked at http://www.raw-sewage.net/jtm45ri_mods.html but am still a bit unsure about the filter caps. Thanks for any help:)

1612112 · February 9th, 2005, 08:45 PM

I ran KT66's in my bluesbreakers and did not change the any of the filter caps. The only trouble I had was physically fitting the tubes in the tight space. They sounded way cooler than the 6L6s
pjb

bluesbishop · February 9th, 2005, 11:45 PM

The Most important mods you can make on a JTM45 are change the tubes to KT66's, replace the output transformer, and the caps with Sozos.

Many guys like replacing the PCB board with a Point to Ponit board...makes mods, and tweaks easier.George at Metro amos is a really good guy and can help you get the sound your looking for. http://www.metroamp.com/index.php

Here is a sound file of george with one of his JTM45 kits, and a set of KT66, this file is with the Valve arts, but george has up samples on the forum with various tubes.

http://www.digitalsoundplanet.com/Me..._000024902.mp3

The Blackface Bassman and the Jtm45 are my Favorite amps...nothing beats them for just pure great tone :-)

Ken

elgorgon · February 10th, 2005, 05:27 PM

Quote:

Originally Posted by 1612112

I ran KT66's in my bluesbreakers and did not change the any of the filter caps. The only trouble I had was physically fitting the tubes in the tight space. They sounded way cooler than the 6L6s
pjb

While it still sounds good (to me at least) with the stock filtering it doesn't sound like a real JTM45 until you lower those filter cap values. Takes away much of the boominess.
You want to get a 16uf/16uf 450v (or higher voltage rating) and a 32uf/32uf 500v (or higher voltage rating).
You'll also need a real GZ34 or Copper Cap version for the rectifier to get the JTM45 tone. The Sovtek is not a real GZ34.
The 330uf cathode bypass cap change to 250uf isn't as integral - both boost frequencies far below the guitar's output (a 5uf will cover all guitar frequencies).
The mixer resistor change will open up the sound as well, and should be done if you want the original tone.

JTM45blues · February 10th, 2005, 11:17 PM

I had one I highly recommend that you use the 32x32 and 16x16 values for those caps, find LCR's if you can, but the JJ's also work well. Also, I loved the sound of the KT66HP's by Groove Tubes, these are "high power" (HP), and are very robust tubes, with a big, plump midrange that you'll fall in love with.

Try to find a Mullard 12ax7 or three if you can also for the preamp, but if you can't the new JJ 12ax7's are very good, and Ei's are nice too, when you can find one that isn't microphonic.

I also changed the OT in mine to a Mercury Magnetics, and while it added some more detail, it wasn't nearly as noticeable of a mod as the tubes and filter caps.

anis258 · February 11th, 2005, 02:12 AM

any recommendation as to which GZ34 to buy (non-NOS)?

JTM45blues · February 11th, 2005, 06:14 PM

You may want to try a nice JJ 5ar4, inexpensive, easy to find, and will last a long time.

February 9th, 2005, 10:07 AM	#1 (permalink)
anis258 NEW MEMBER! Join Date: Dec 2004 Posts: 9	JTM45 RI mods Hi there, I just wanted to know what mods JTM45 RI owners have done and how it worked out tonally... I'm going to retube (with KT-66s), but as a not-so-techy guy, i'm not sure about the type of filter capacitors that i should replace with (ie brand, values) and how i can source them. I've looked at http://www.raw-sewage.net/jtm45ri_mods.html but am still a bit unsure about the filter caps. Thanks for any help:)

February 9th, 2005, 08:45 PM	#2 (permalink)
1612112 Tele-Meister Join Date: Nov 2004 Posts: 229	Leave the power supply alone... I ran KT66's in my bluesbreakers and did not change the any of the filter caps. The only trouble I had was physically fitting the tubes in the tight space. They sounded way cooler than the 6L6s pjb

February 9th, 2005, 11:45 PM	#3 (permalink)
bluesbishop Tele-Meister Join Date: Jan 2005 Location: Fort Myers, FL CHICAGO Native!!! Age: 45 Posts: 106	JTM45 mods The Most important mods you can make on a JTM45 are change the tubes to KT66's, replace the output transformer, and the caps with Sozos. Many guys like replacing the PCB board with a Point to Ponit board...makes mods, and tweaks easier.George at Metro amos is a really good guy and can help you get the sound your looking for. http://www.metroamp.com/index.php Here is a sound file of george with one of his JTM45 kits, and a set of KT66, this file is with the Valve arts, but george has up samples on the forum with various tubes. http://www.digitalsoundplanet.com/Me..._000024902.mp3 The Blackface Bassman and the Jtm45 are my Favorite amps...nothing beats them for just pure great tone :-) Ken

February 10th, 2005, 11:17 PM	#5 (permalink)
JTM45blues Tele-Meister Join Date: May 2003 Posts: 421	I had one I highly recommend that you use the 32x32 and 16x16 values for those caps, find LCR's if you can, but the JJ's also work well. Also, I loved the sound of the KT66HP's by Groove Tubes, these are "high power" (HP), and are very robust tubes, with a big, plump midrange that you'll fall in love with. Try to find a Mullard 12ax7 or three if you can also for the preamp, but if you can't the new JJ 12ax7's are very good, and Ei's are nice too, when you can find one that isn't microphonic. I also changed the OT in mine to a Mercury Magnetics, and while it added some more detail, it wasn't nearly as noticeable of a mod as the tubes and filter caps.

February 11th, 2005, 02:12 AM	#6 (permalink)
anis258 NEW MEMBER! Join Date: Dec 2004 Posts: 9	any recommendation as to which GZ34 to buy (non-NOS)?

February 11th, 2005, 06:14 PM	#7 (permalink)
JTM45blues Tele-Meister Join Date: May 2003 Posts: 421	You may want to try a nice JJ 5ar4, inexpensive, easy to find, and will last a long time.