My official JTM45 kit build thread. Pics & CLIPS ADDED

franc · Post by **franc** » Sun Sep 02, 2007 2:48 am

Be careful when jumpering resistors!!!

That is not a good idea in general!

Jumpering the 68ks is not a problem, but jumpering the 100ks will raise the voltage at the plates which is not good!

mushmouth · Post by **mushmouth** » Sun Sep 02, 2007 3:58 am

franc wrote:Be careful when jumpering resistors!!!

That is not a good idea in general!

Jumpering the 68ks is not a problem, but jumpering the 100ks will raise the voltage at the plates which is not good!

Lesson learned. Thank you...

SO. NEW TESTING BEGINS NOW:

TESTING PART 1:
Pulled all tubes. With no tubes in:
Rectifier socket:
Pin 2&8 = 4.96V
Pin 4 and 6 = 323.2/323.4

Output sockets:
Pin 2 and 7 = 3.454/3.454
Pin 2 and 7 = 3.467/3.463

Preamp Sockets:
V1-
Pin 4: 3.483
Pin 5: 3.483
Pin 9: 3.483

V2-
Pin 4: 3.481
Pin 5: 3.481
Pin 9: 3.481

V3-
Pin 4: 3.483
Pin 5: 3.483
Pin 9: 3.483

TESTING PART 2:
Rectifier tube installed--
Rectifier voltage at pin 8: 313.5
Voltage at standby switch: 313.9

Install Preamp tubes--
V1-
Pin 1: 217.3 (AND 320.6!!!, see note below)
Pin 3: 31.14
Pin 6: 172.9
Pin 8: 1.192

V2-
Pin 1: 184.4
Pin 3: 1.206
Pin 6: 323.9
Pin 8: 186

V3-
Pin 1: 240
Pin 3: 44.3
Pin 6: 230.9
Pin 8: 44.3

(Note, when I first read V1 pin 1, I got 320.6 instead of the 180 the chart desires. I shut amp off, pulled the tube and inserted the sovtek and got 218 now on pin 1. Shut amp off. Turned amp back on to test all of V1 with the sovtek and I got 320 AGAIN on pin 1 with the swapped sovtek tube now. I wiggled the tube, then got 218 again. Same glitch to 320V on pin 1 with 2 different tubes... I put the JJ back in, 320 again on pin 1 and was able to wiggle it until it started reading 217 on that pin. That sounds like socket, right? Could that be something??)

UPDATE:

WELL GUESS WHAT??

When I was getting 320 on pin 1, it was hard to find a spot wiggling the tube to get it back down to reading 218. It occurred to me that since it was hard to find a spot while wiggling it where it would go back to reading at 218, it was probably sitting at 320 most of this time and maybe that's how it'd read when it wasn't working. So I went back in, installed the power tubes, took a pin 1 reading on v1 and it was still down in the correct range and NOW NORMAL CHANNEL WORKS!

So... BAD V1 SOCKET, right? Shit, I wish I had picked that up at the store today! lol

mushmouth · Post by **mushmouth** » Sun Sep 02, 2007 10:10 pm

Took out all the troubleshooting components and got the allen bradley's all back into place. Everything is working great. As soon as I receive it, I'll replace that dodgy V1 socket.

I also put that old stock mustard cap I scored in the bright channel's first .022 slot. There is a noticeable difference between the sozo and beige resistors, and the mustard and AB's. The AB's sound a little harsh right now, but they have had no break-in yet. Though it's definitely more aggressive with the old mustard and ABs. More present. More "at the front of the speaker", if you get what I mean by that. We'll see if that remains true after the AB's settle down.

Thanks to everyone, especially Toner and Franc, who provided so much help with this build. You guys made it immensely easier for me to become "unstuck" when I'd run into a wall.

PS: This amp sounds incredible! Sound clips will come once I tame these resistors...

I'll do before and afters...

franc · Post by **franc** » Mon Sep 03, 2007 1:06 am

Good to hear you located the problem!!

Have fun with your amp

bluze81 · Post by **bluze81** » Mon Sep 03, 2007 11:37 am

congtrats mushmouth! glad to hear you have it,now rock-n-roll time, bluze81

NY Chief · Post by **NY Chief** » Mon Sep 03, 2007 1:07 pm

Let 'er rip, Mush! Open the windows I wanna hear from here!

mushmouth · Post by **mushmouth** » Mon Sep 03, 2007 9:21 pm

NY Chief wrote:Let 'er rip, Mush! Open the windows I wanna hear from here!

Odd, because earlier I pointed it out the window and shattered house windows down the entire block when I hit the A chord during a chorus of Highway to Hell. You didn't hear that???

franc · Post by **franc** » Tue Sep 04, 2007 6:51 am

I think I might have heard you...

toner · Post by **toner** » Tue Sep 04, 2007 11:39 pm

mushmouth wrote:Odd, because earlier I pointed it out the window and shattered house windows down the entire block when I hit the A chord during a chorus of Highway to Hell. You didn't hear that???

I think I heard the police sirens afterwards!

How's the amp mushmouth? Did you replace the V1 socket yet? Please post some sound clips when you can!

mushmouth · Post by **mushmouth** » Wed Sep 05, 2007 11:55 am

toner wrote:
mushmouth wrote:Odd, because earlier I pointed it out the window and shattered house windows down the entire block when I hit the A chord during a chorus of Highway to Hell. You didn't hear that???
I think I heard the police sirens afterwards!

How's the amp mushmouth? Did you replace the V1 socket yet? Please post some sound clips when you can!

Yup, they actually had a matching socket at the guitar store here so I picked it up, installed it, and everything is great. I took a reading at V1 pin 1 and it was 181.2, so even that is at a proper number now.

It was too late to crank it last night. I want to run through the entire testing sequence now that everything is working properly and see where all my readings are sitting before I do sound clips. My B+ was a bit low to start with and George suspects rectifier tube might be dropping it too low, so we're going to swap that out.

Sound clips in the next several days. Promise.

mushmouth · Post by **mushmouth** » Wed Apr 02, 2008 12:29 am

I'm way late with this, but I threw up a mic tonight and made a few quickie sound clips. My 57 was pointed too near the cone center, as you can hear.

I'm replacing all the caps with NOS mustards next week, so I figured I'd get the stock build with ABs down on tape for posterity. We'll see what those mustards do

These are recorded with the Hotplate at the -12 setting. Amp settings: Presence: 3.75, Bass: 2, Mid: 10, Treble: 5, Volume: 6

(Cold shot is neck position. Other two are bridge pickup.)

http://www.mushmouth.com/metrobuild/jtm_highway_dry.mp3

http://www.mushmouth.com/metrobuild/jtm_ColdShotdry.mp3

http://www.mushmouth.com/metrobuild/jtm_funk49dry.mp3

RECORDING NOTES:
Gibson Custom Shop Historic '57 Goldtop Les Paul.
Metro kit JTM45 w/Allen Bradleys.
Metro 4x12 with 25watt Celestion Heritage Speakers.
Mic: SM57, about 4 inches back, (pointed too close to cone center, adding a little too much... harsh).
Recorded in Logic.
Bone dry.