NOS-style JTM 45/100 on Metro chassis

[emmjaydubya]

's ok as I try to buy all the right angle ones that I see - the straight ones are no good live

BTW - really nice work. I have a similar project in kit form with one of Robert 7026 panels, Marstran chassis and trannies just waiting for time, I have all the NOS stuff (inc the RS 32uF caps and the Dickinson spec replaced caps and resistor types - how sad is that ?). Can't decide whether to relic the chassis and cap board too!

That will be a great build, by 'relic' I guess you mean taking a pair of rusty pliers to the power board? I really like the JTM50 you did. I plan on starting one of those after this one is finished ASAP and your thread will be a big help!

I made some progress today, started working on the boards. The paxolin I got from England is a lighter brown and more shiny than the stuff that Brian used for his boards. Really glad I have one of his as a reference for measuring as well as a high standard!



Printed a grid with 3/8" centers and very thin lines on paper as a drilling template, circled the holes to be drilled with a #38 drill bit, since I'm doing a solid pre board (the power board will be perfed):



After cutting and sanding the edges:



Commence drilling!





Made my own turret press, drilled an 1/8" hole in the end of a 1/4" steel stud and mounted it onto a 1/4" plate of aluminum so it could be clamped to a drill press. Then I ground one end of a 1/4" stainless steel stud to a point at about a 45* angle:



Commence pressing!





And inside the chassis for a test fit:



Tomorrow the power board!

[Strat78]

I noticed those preamp boards too on Amp Archives, but not before I had completely drilled out all my board material. Looks really great so far!

[emmjaydubya]

It seems like some of the later 7000 series amps and the early EL34 JTM100 amps had the solid boards, maybe early 10,000s? Most of the early 7000 serial #s on Amp Archives have fully perfed pre boards, except for the Dickenson. Also noticed many of the JTM50 black flags had solid boards too. I guess, like anything Marshall, it's a mixed bag.

[emmjaydubya]

Been working on the board, here's a sneak peek!



Finally got the OT, Marstran 1202-84 goes in this weekend!

[neikeel]

Looks very nice. Those mustards and pihers will sound good too

[emmjaydubya]

Thanks Neil, I'm still not sure what I'm doing for the pre filtering, or V1 for that matter. I have a 15uf Erie, but I also have a pair of 8uf Eries that I could split with another 10k there, I've read this lowers voltages in the preamp, but this might not be the right direction for a 45/100. Also I have a Radiospares 50uf for V1, I guess that would shave some subharmonics out, but again, might not be very '45/100'.

Another thing, what do you guys find works for the little bias resistor at the end of the board? I've seen 150k and 120k on all the Amp Archives JTMs, I have a 150k waiting...

[JimiJames]

Been working on the board, here's a sneak peek!

Looks great, man !

[Strat78]

I settled on 150k off the diode and 47k off the pot. Could be a little colder because I get the right bias with the pot around 8 o'clock vs. right in the middle at 6 o'clock.

[emmjaydubya]

Made some progress,finally got the PT and the choke from Marstran, they must really be doing the business.



Wired in the OT:



This time I thought I would try my hand at lacing the wiring instead of auto-piloting the zip ties. I'll never go back! Brian H.'s tutorial makes it easy.

http://forum.metroamp.com/viewtopic.php ... 33#p250730

After wiring in the switches, light, voltage selector and PT:





Finished up the power board:



I'm a little worried about the NOS Hunts snubber cap, I just noticed a slight crack along the seam in the rubberish coating, guess I'll find out if it's okay when I put the juice to it! Power board wired in:



Started wiring in the main board , getting close!!!

[neikeel]

[Strat78]

Beautiful work as usual, love the lacing. The lamp is bit awkeward to deal with, sticking out so far above the board, but yours looks cleanly done. The fuse dressings are cool!

[neikeel]

Beautiful work as usual, love the lacing. The lamp is bit awkeward to deal with, sticking out so far above the board, but yours looks cleanly done. The fuse dressings are cool!

You have to shorten the stand offs of the cap board to avoid that, making them longer does not work. An RS lamp is shorter as is the old style Marshall red square.

[emmjaydubya]

I've always used 3/4" threaded spacers (you can see them in the pics), instead of the 1/2" spacers which I believe is how Marshall did it. The lamp is clear of the turrets, do you think this might be a problem if they are that close?

[neikeel]

I've always used 3/4" threaded spacers (you can see them in the pics), instead of the 1/2" spacers which I believe is how Marshall did it. The lamp is clear of the turrets, do you think this might be a problem if they are that close?

Personally speaking - no. I did the same as you on my 45/100 when it went to a new owner (he wanted amber lamp instead of red. I had a little more room due to using spacers as per Marshall (I cut my own from tubing bought from a model shop).

[emmjaydubya]

Well I finished the pre board, everything wired in. Soldered a 100k forming resistor across the standby switch as instructed for the 45/100. Brought the voltage up slowly with the variac and monitored individual caps so as not to go beyond rated voltage, got it up to a comfortable 115v wall voltage. Measured across the 100k, NOTHING. Couldn't get a reading at all across the resistor, tried everything. Now I'm confused. I left it forming for about 45 minutes and I noticed a slight smell from the 15uf 450v Erie pre cap and could smell some heat coming off of it as well, which I figured was bad. I decided to shut it down and disconnect the pre cap to see if it was the culprit. Switched power back on with positive leg of the pre disconnected but still couldn't get a reading across the 100k for the PI, screens and mains. What do you guys think? I don't have a clue what to think right now...