think I've bought the wrong transformers for my JTM45/100

[HTH]

ok, so I got some transformers from Marstran maybe 18 months ago (might even be longer than that). Anyway, I've got a 1203-80 PT (2.5" stack, laydown, dual HT windings) and a 1202-119 OT (2" stack, EL34s, ???k primary).

I got the Metroamps JTM45/100 chassis, boards and cab separately and it seems that the filter cap board isn't geared towards the 1203-80 PT as it needs the twin bridge rectifiers.

Also, I was planning on using KT66s, so the OT is wrong too (argh!!!). what is the primary on the '119 OT btw? anyone? Bueller?

I'm contemplating two options:

(1) keep the '119, run EL34s and get the correct PT (not sure which one IS the correct PT though)
(2) sell both transformers and get the correct '84 OT and '43 PT

Opinions?

The amp will be my main gigging amp used for 70s rock essentially. I'll be setting it for a crunch tone then using my valve OD pedal for extra gain. Should I just go with option(1) and make it a '67 JTM along the lines of the EVH amp or make it a real-deal JTM45/100?

[VelvetGeorge]

IMO your best option with those trannys is to build an EL34 version. And you will need the voltage doubling type of power supply.

The 119 OT should be 1.75k primary.

george

[HTH]

cheers George,

btw, what is the difference between the 119 and 132? - they've both got 1.75k primaries. It is just the stack size? (2" versus 1.5"). What are the tonal differences?

as for the voltage doubler power supply, instead of running each winding with a diode bridge and running them in series, could I just use one diode bridge and link the windings on the PT?

[VelvetGeorge]

The 199 OT had 8, 16 and 100V line secondaries. The 132 had the more ubiquitous 4,8 and 16 ohm secondaries.


That circuit will work so long as your Marstran has dual HT secondaries.

george

[Wayne]

I just ordered the exact transformers you have from brian for a 67 JTM100 build. I asked brian what the difference between the 119 & 132 OT's was and this is an exact quote from an email he sent me.

"The 1202-119 came in around early 67, the 1202-132 came in around mid 67 and the C1998 came in around late 67. So you have a choice here. The difference between the 119 and the 132 would have to be the 100V winding. The 132 is missing this winding and will have less bass to it and a bit of a high boost but not brittle due to it's size"

Both his 119 & 132 OT's have 4, 8 & 16 ohm taps for EL34's.


I am about 2 hours away from testing the build - so i do not know what it sounds like.
I got boards from Brian & repro turret boards and built mine with a single rectifier - looks like the 10000 series inside the chassis.

Wayne.

[HTH]

Thanks for the clarification guys. I'm hoping that this amp will sound like my old '67 plexi, that was an amazing amp. The term 'dripping with tone' is way overused, but my old '67 was just that and didn't have the problem some old Marshalls do where they sound a bit limp at lower volumes. On '4' this thing was in Jimmy Page territory.

Think I'll wire the PT up with the low-Vac option for around 490v B+ rather than the high-Vac (around 560v). It'll make for earlier breakup, easier on the EL34s and therefore a more reliable amp (this will be my main gigging amp).

I know it's probably considered sacrilege on this BBS, but I'll probably end up with a Jose Master volume in it to have more control over the stage volume.

[Roe]

I just ordered the exact transformers you have from brian for a 67 JTM100 build. I asked brian what the difference between the 119 & 132 OT's was and this is an exact quote from an email he sent me.

"The 1202-119 came in around early 67, the 1202-132 came in around mid 67 and the C1998 came in around late 67. So you have a choice here. The difference between the 119 and the 132 would have to be the 100V winding. The 132 is missing this winding and will have less bass to it and a bit of a high boost but not brittle due to it's size"

Both his 119 & 132 OT's have 4, 8 & 16 ohm taps for EL34's.


I am about 2 hours away from testing the build - so i do not know what it sounds like.
I got boards from Brian & repro turret boards and built mine with a single rectifier - looks like the 10000 series inside the chassis.

Wayne.

I just wanted to add that I do not think marstran's 119 is overly bassy or dark in a jtm/bass circuit

[Wayne]

Haven't tested yet - tomorrow maybe - but i think the 80 PT should give you around 440 on the LV taps and 490 to 500 on th HV taps.

I'll post what i get when i have finished.

Wayne

[Wayne]

Just finished my 67 build with the 80 PT & 19 OT.
Heres the pics.

http://forum.metroamp.com/viewtopic.php?f=7&t=27468" onclick="window.open(this.href);return false;

Just did the voltage readings - all good with B+ under 440v using the LV taps.
I'll post the chart if anyone is interested.
I'll be running it in over the next few days - but it sounds FANTASTIC already !!!

Wayne

[HTH]

440v with the LV taps, hmm... bet thats nice and fat.

[neikeel]

Interesting because I got 400v on LV and 490v on HV taps on my '67 Black Flag style amp.

I used the Marstran -132 on mine:

http://s76.photobucket.com/albums/j2/ne ... ck%20Flag/

It looks like the dual rectifiers but I simply used two bridges and put them in parallel.

I used NOS Mullards throughout. To be honest I found little difference in tone between the HV and LV taps on this amp. The difference is much more marked on a 12 series.

[HTH]

I'm decided on using the LV option on the HT tap for reliability reasons and also so that I get quicker breakup. With 400v on the plates the EL34s (or even 6L6s) won't break a sweat. Could even run 6V6s (JJ ones anyway) with those voltages.

[MacGaden]

I know it's probably considered sacrilege on this BBS, but I'll probably end up with a Jose Master volume in it to have more control over the stage volume.

Nothing is sacrilegious on the Metro forum as long as your are looking for Tone.. I´d look into ther Lar/Mar Master instead. It´s better: http://metroamp.com/wiki/index.php/Lar/Mar_PPI-MV Way better...