Recent JTM45 Build

[ToneMerc]

Here's one that I just finished up, I was going after a 65' JTM vibe.

Metro chassis & backplate
SteveUK JTM45 plexi faceplate
Brian H repro turretboard & fuseholder
ToneMods plexi block logo
Heyboer custom trannies (440V on plates) & 3H 352-114 choke
RIFA lytics
Welwyn MF & Iskra CF grid resistors
NOS Mustard caps
NOS Piher CF & Morganite CC resistors
NOS Radiospares mica caps
NOS Bulgin AC socket & plug
NOS Woven tube retainers
Belling & Lee fuse holder
Ext bias adjust
Modified "Larry" grounding scheme

TM

[selloutrr]

Very nice build

[Teleguy61]

Nice.
Bet it rips.

[Structo]

Dang!
Nice replica!

Love all the NOS stuff.

How does she sound?

[M Fowler]

Now thats how to build them, very nice.

[tribi9]

Holy crap! That is a really neat amp.

Congrats.

[David Root]

Wow! If that's not a pro-level build I don't know what is. Pity that NOS KT66s are so expensive. I bet it sounds just as good too.

I see a real Mullard 5AR4 too. Are the 12AX7s Mullards? And where did you get that Marshall logo?

[ToneMerc]

Thanks guys, I appreciate the kind words. I think the most rewarding part was sourcing some of the parts, last count was 8 different countries.

Soundwise, I was surprised that it is not as bright as what I thought it would be. I actually may go back and install a 100-150pf bright cap to give it just a little edge when the volume is turned down. Like most JTM circuits it's a little bass heavy, but I don't think its flubby.

A gain monster it is not, it has a nice rootsy grind, why anyone would want to put a MV on one of these is beyond me.

V1= Mazda ECC83, V2&V3=Telefunken 12AX7 diamonds

The logo actually came from Canada.....Tone Mods, IIRC.

VintageHeadBox had agreed to make me an early 65' head cabinet(smooth blk tolex, small gray feet, leather handle, T piping), but they vanished about 3 months ago just before I sent them payment....I was one of the lucky ones.

I would love to have some NOS GEC KT66s, it just too many fakes around for me to trust em. Actually, I want try the Mullard EL37 instead.

TM

[David Root]

Interesting choices. I would love to try a Mazda but they are hard to find and not inexpensive, to say the least.

I have heard that Telefunken 12AX7s in the PI don't react well to being overdriven, however that could be a HiFi thing that wouldn't really apply in MI amps. I have some used ones but have not tried them in Dumble circuit PIs. What is your take on that?

[ToneMerc]

Yeah, I lucked up found the Mazda, although you would be surprised whats out there once you start to turn over rocks outside of North America. However, I've pulled the Mazda for the second time and installed a Mullard RI and I think that will stay for now. That may change if I decide to knock preamp voltages down 10-15 volts.

Honestly, I've never tried the Tele's in a Dumble style circuit

[crbowman]

I think this would probably impress Ken Bran himself.
Way to do it RIGHT TM!

[Noel Grassy]

Sweetassedmofo lookin' build. Niceness Tonemerc!

Is that a Selenium diode in the bias circuit? How in hell did you source half
that stuff? Diligence I'm sure.

If you want to build the old style head eventually, I sourced the correct rail
from an old carpet installer's boneyard of metal trim in the US. I used 1/8th
inch solid brass rod for the piping though.

Noel Grassy.

[Structo]

I see that there is a bias trimmer on the board but you say you have an external adjust?
Is that it between the PI and power tube?

[ToneMerc]

Sweetassedmofo lookin' build. Niceness Tonemerc!

Is that a Selenium diode in the bias circuit? How in hell did you source half
that stuff? Diligence I'm sure.


Noel Grassy.

Thanks Noel

That NOS tophat germanium diode I sourced from all places my last local parts shop. Its something that I had walked past it dozens of times and never really paid must attention to until I needed to find one, that was luck.

The other stuff; one just has to look(worldwide), look and look and be patient of all things. It took me almost 6 months to gather up everything and my #1 rule was that I refused to pay crazy prices for stuff.

The thing is in the beginning I never intended to use NOS Mustards or Piher resistors or a period correct board type . I started gathering Pihers last August for a #40 build and said since Marshall used Pihers I'll use a few for this JTM build and it just cascaded.

Mike

[ToneMerc]

I see that there is a bias trimmer on the board but you say you have an external adjust?
Is that it between the PI and power tube?

Yep, it's a 20K 2W Clarostat(green) pot. Currently the internal pot is set so that with a Russian(GT HP) KT66 the sweep on the ext pot is -37.5 to
-47.5 VDC.

I initially fired it up with supposely a matched pair Ruby(Chinese) KT66s and the internal pot I had to set differently to get a similar range up top. I would have used them, but the delta between the two was almost 9mA, whereas, the delta between the GTs was only .7mA.