My official JTM45 kit build thread. Pics & CLIPS ADDED

mushmouth · Post by **mushmouth** » Wed Aug 29, 2007 6:28 pm

EDIT: I found the missing 270K allen bradley. So the only one I'm missing, unless George says otherwise, is the one 100k allen bradley. SA-WEET.

Also, was going to swap out the 470s on the output tubes with the sweet old-school W22's George sent me, however I just looked and I have one 470 and one 1k...

So I replace ONE of them, will do the other one when I get it.

mushmouth · Post by **mushmouth** » Wed Aug 29, 2007 9:20 pm

Ok, the circuit board is now soldered! Step 14 complete.

God that flux in the solder is a real bear when dealing with these turrets. It really seems excessive...

Pics:

Ok, looking ahead, when are you supposed to install the bias adjustment kit? I don't see anywhere in the last step, or in the testing steps where you're instructed to install it. What am I missing here?

SDM · Post by **SDM** » Wed Aug 29, 2007 10:33 pm

You've got a 470K resistor where a 470 ohm resistor ought to be in the PI. Follow the wire from pins 3 and 8 of v3 to resistor in question. Very common mistake.

mushmouth · Post by **mushmouth** » Wed Aug 29, 2007 11:22 pm

SDM wrote:You've got a 470K resistor where a 470 ohm resistor ought to be in the PI. Follow the wire from pins 3 and 8 of v3 to resistor in question. Very common mistake.

Ah, thanks! Good catch.

Fixed.

toner · Post by **toner** » Thu Aug 30, 2007 12:06 am

mushmouth wrote:
SDM wrote:You've got a 470K resistor where a 470 ohm resistor ought to be in the PI. Follow the wire from pins 3 and 8 of v3 to resistor in question. Very common mistake.
Ah, thanks! Good catch.

Fixed.

Sorry I missed that earlier.

mushmouth · Post by **mushmouth** » Thu Aug 30, 2007 12:24 am

No prob, toner. I had missed it too. *shrug*

Step 15 is done. Installing power cable and 500pf cap across pins 1 and 2 of high treble volume pot.

Pics, including a shot of the W22 on the second output tube socket:

Now I have the testing stage, which scares the living sh*t out of me. Who wants to volunteer for phone tech support as I do it so I don't die? lol

I need to go through the various other build notes and find what people found "missing" in the instructions and meld those into the instructions so I know what I'm doing. I notice sometimes it'd say "get a reading of pin x and pin x and pin x and I'm wondering "where's the other lead? Grounded to the chassis? In my rectum? Where? So I need to get that straight as a total reading-taker-newbie first. If anyone has any advice on this section of the build, now would be the time to speak up. If not, and you never hear from me again, you'll know why.

*knock wood*

franc · Post by **franc** » Thu Aug 30, 2007 1:20 am

For most readings, stick the common probe somewhere in the chassis, like a mounting hole or something. Keep one hand in your backpocket and take measurements with the other probe. You can take readings of everything, although I find it easier to measure the filament with both probes on the tube socket (takes a steady hand) and of course in AC mode on your DMM.

mushmouth · Post by **mushmouth** » Thu Aug 30, 2007 1:21 am

TESTING PART 1:

First I tested the white wire on fuse holder and black wire on power switch. Got 118.9v AC coming in from the wall. So far so good.

I flipped the power on, the light lit up. Sweet.

Here were my test results for voltage testing at the requested spots:
(*NOTE: on rectifier pins 2 and 8, I put one lead on 2 and one on 8, as others have corrected on here, rather than putting one on ground and testing each.)

Rectifier Tube Socket:
Pins 2 and 8: 4.9v
Pins 4: 318.9v
Pin 6: 318.6v

Output Tube Sockets 1 (furthest from transformer):
Pin 2: 3.436v
Pin 7: 3.431v

Output Tube Socket 2 (nearest transformer):
Pin 2: 3.434v
Pin 7: 3.431v

Preamp Tube Socket 1 (furthest from transformer):
Pin 4: 3.44v
Pin 5: 3.44v
Pin 9: 3.44v

Preamp Tube Socket 2:
Pin 4: 3.445v
Pin 5: 3.445v
Pin 9: 3.443v

Preamp Tube Socket 3:
Pin 4: 3.443v
Pin 5: 3.443v
Pin 9: 3.443v

Before I move on, how do these numbers look?

EDIT: According to my math those are all within 9%, so we should be good.

franc · Post by **franc** » Thu Aug 30, 2007 1:24 am

Wow, you're either up late, or up very early and on my side of the ocean

Numbers look okay at first glance, but don't just trust me, it's early for me and I haven't had my first cup oo coffee yet

mushmouth · Post by **mushmouth** » Thu Aug 30, 2007 1:28 am

franc wrote:Wow, you're either up late, or up very early and on my side of the ocean

Numbers look okay at first glance, but don't just trust me, it's early for me and I haven't had my first cup oo coffee yet

It's midnight my time. Central US time.

So it's not CRAZY late here.

mushmouth · Post by **mushmouth** » Thu Aug 30, 2007 1:48 am

Looks like I'm done for the night. I need a U-frame now. I've gotten away with building this with it sitting on it's transformers, but that won't be possible with the power tubes in, so I have to figure something out to hold it up. Stay tuned...

mushmouth · Post by **mushmouth** » Thu Aug 30, 2007 2:32 am

Christ, this is a sickness. I found a way to jury rig a 3 rack CD stand to work as a perfect amp holder for testing. lol Necessity is the mother of invention.

OK. TESTING PART 2:

Rectifier Pin 8 with Rectifier tube in: 316.4. Should read 340. Within the 20% variance allowable.

PREAMP TUBES.
V1 READINGS:
Pin 1: 204.7
Pin 3: 1.726
Pin 6: 192.2
Pin 8: 1.722

V2 READINGS:
Pin 1: 173.7
Pin 3: 1.182
Pin 6: 310.5
Pin 8: 176

V3 READINGS:
Pin 1: 231.7
Pin 3: 44.4
Pin 6: 233.7
Pin 8: 44.4

Unless I miscalculated somewhere, all appear to be within the 20% allowable as well. Lemme know if I'm wrong, otherwise so far so good. NOW I'm going to bed.

Testing part 3 is tomorrow night!

NY Chief · Post by **NY Chief** » Thu Aug 30, 2007 10:07 am

mushmouth wrote:Christ, this is a sickness.

Sure is. Welcome to the club!

George, 'nother one on the hook!

jimapr · Post by **jimapr** » Thu Aug 30, 2007 4:34 pm

Tomorrow my JTM45 Clone is also finish. I will post then my Voltages. If its okay for you, mushmouth

mushmouth · Post by **mushmouth** » Thu Aug 30, 2007 5:37 pm

jimapr wrote:Tomorrow my JTM45 Clone is also finish. I will post then my Voltages. If its okay for you, mushmouth

THREAD JUMPER!!!!!!!!!!!!

Seriously, I think you should do this in your own thread just to avoid confusion about who is talking about who's readings.