68 12,000 with 2" high impedance OT

[axeman]

You have the primaries wrong. The red and brown wires are twisted to gether and go to pin 3 the white wire is the bias wire.

[vh junkie]

You have the primaries wrong. The red and brown wires are twisted to gether and go to pin 3 the white wire is the bias wire.

Nah... the Marstran 132has the brown wire as the CT... these were initially sold as dual 2.2k/2.5k, they had the brown as the CT and a Red/Red w/stripe and a White/White w/Stripe... the striped wires (2.2k) were miswired inside the OT so are not used (and may have been removed) leaving the 2.5K wires... see the pic of the OT label where the 2.2k has been crossed out.

[emmjaydubya]

Yeah, I crossed it out to avoid future confusion. It came with the striped leads also for the bad 2.2k so I heat shrinked the leads and wrapped them up inside the bell cover. Brian also shipped an extra 2.2k transformer from Heyboer, so I have another OT. What a stand up guy he is, great company.

Pretty positive the brown is the CT, I measured all three. The resistance readings of brown & white + brown & red added up to the reading of red & white. Seems to me that brown would be the CT.

VH junkie, I was reading the Ben/2.2k thread in the VH section and saw that you had bad luck with squeal with this OT? I had planned on possibly sheilding the NFB wires, have you tried this? Could the impedance difference have anything to do with the NFB or are they unrelated?

[emmjaydubya]

Made some good progress and wired up the switches today, everything but the wires from the standby switch that go to the diodes:



Also routed all of the PT secondary wires with the grounds and the 120v input wires as well. Getting closer, it's almost time for the power board!!

[axeman]

Nice good job. It's coming along well.
Can you pitch me Marren's number, I need some transformers.

[vanhalen5150]

That looks pretty good.

[emmjaydubya]

Thanks guys! I ordered some NOS Erie 100uf mains caps AGAINST the advice of several guys here on the forum. I want to try the vintage ones since I've read that they sound better than the F&Ts, but some won't use NOS for filter caps. I've seen a bunch of builds on here with those mains caps, what do you think?

[vanhalen5150]

I've never tried them, just always used the F&T's. I have some I'm looking to try out. Not convinced they have any effect on the amps sound. I think a lot of guys use them from strickly a vintage look.

[emmjaydubya]

Yeah they sure do look good, that's for sure. I read in a thread somewhere that Larry (novosibir) never uses ARS caps for his builds but he never said why. If it has an effect on tone then its probably very subtle, maybe even a feel thing, both being very subjective.

On the other hand, YMI5150? says he possibly fried a trans because of a bad NOS cap that was leaking voltage, so thats the other side of it. I don't have the equipment to test them but I'll probably give it a shot anyway, 'cause I'm crazy like that...

[emmjaydubya]

Finished the power board tonight, ready to put it in! Against the good advice of several here on the forum, I went with the vintage Erie 100ufs. And yes they are untested. Had to remove the two bottom turrets to fit them in, and figured out a clean way to put them in without having to relocate the turrets, I just joined the two across the positive and negative with a yellow jumper! The yellow PT center tap wire will come straight up from underneath to the negative side.

I just hope they form properly, 'cause I like how they look!



Here is the altered Larry ground version on the backside for the Erie caps (with the PT center tap wire missing yet):

[Strat78]

Nice looking work as usual! To make forming the caps easier, you should have that little yellow wire going to the diodes come up through the board with a little extra length on top so you can temporarily attach the 100k resistor between that wire and the diode. Same with the yellow center tap. This way you don't have to lift the power board to get at these wires when you form the caps for the first time. I've yet to have a problem with those Erie cans, but I always use a variac while forming to keep the voltage from exceeding the maximum rating on the cans and cathode caps as well. Without any tubes in the amp the voltages are higher, so as the cans begin to form the voltages start climbing even higher, as much as 550v if you are running the amp directly from the wall, which is way beyond the 350v and 400v rating of the eries much less the mustards. Sorry for going on and on, you probably know all this anyway.

[emmjaydubya]

No! Actually thanks so much for bringing that up because I kinda spaced out on the temporary hookups for the forming. The yellow wire underneath that you mentioned is actually a red wire (crappy pic, it looks orangy-yellow). Maybe I can unsolder one end and tape it off under the board and just connect the 100k across the diode and positive cap turrets? Would that be okay? Seems like the same thing, above or below the board makes no difference, right? Reason is, the short red jumper is solid-core wire and lengthening it now would be close to impossible. As far as the yellow center tap, I'll run it through the board like I had planned on but I just won't hook it up till the forming is done.

You do bring up a good point about the Variac. I want one for daily use on this amp anyway, so I may as well get one sooner for the forming. Who'd have guessed, a Variac is useful for other things besides bitchin' sag.

[vanhalen5150]

Big blue fatties.

[emmjaydubya]

The power board is installed, big blue fatties and all!



I disconnected the red jumper underneath and put heat shrink on it and then temporarily soldered in the 100k forming resistor from the diode turret to the turret connected to the positive side of the mains cap for easy access. Is this okay? Seems right, just checking. The yellow wire sticking up is the PT CT which will connect to the negative side of the cap with the yellow jumper when forming is done:



Question about the mains fuse, have any of you ever put the line side of the 120 supply on the mains fuse, instead of the common coming from the PT? I've looked at lots of pics and I've seen it both ways. On my JTM45 I put the fuse on the line side because it seems safer, i.e. interupting line current instead of neutral. Just curious...

[julkke]

How is your build going? Looking really good, cant wait to hear clips!