Difference in a 12000 Series and 69' Spec SLP

[marshallkiller91]

So I'm getting ready to build a Marshall kit and something of interest came up.

What's the difference between the two specs? Is it different resistor/cap values at different points?

I know 12000 series' had the caps under the board and the 69' had top mounted filter caps.

Forgive my ignorance.

Thanks!

[bill bokey]

You'll find tons of useful info on Roe's page : http://folk.ntnu.no/roef/JTM100.html" onclick="window.open(this.href);return false;

The main differences between 68 and 69 are stiffer filtering (up to 50µF) and V1b cathode resistor (2k7).

[neikeel]

Pretty much as above.

You can build either spec in either format (caps up or on board) so you are not constrained by the overall layout. You probably have more choice of cap values with cans (up top style) but for some reason I prefer the 12 series type (and the balance of laydown PT)

[bill bokey]

Neil, what do you mean by the balance of laydown PT ?

[marshallkiller91]

Thanks for the info guys.

I'm looking to buy a kit from valve storm later next year and build a stock Plexi. Probably just gonna use a Lar/Mar PPIMV to keep things tame.

[neikeel]

Neil, what do you mean by the balance of laydown PT ?

The laydown C of G is lower so that when you carry it it does not flop around so much, or need special brackets to stop the feet breaking. The really early JTM45/100s are a bit lopsided too

[shakti]

You'll find tons of useful info on Roe's page : http://folk.ntnu.no/roef/JTM100.html" onclick="window.open(this.href);return false;

The main differences between 68 and 69 are stiffer filtering (up to 50µF) and V1b cathode resistor (2k7).

There's been some debate on the v1b cathode resistor. Some say 820R all the way through the plexi panel era. I've certainly seen '69 amps with 820R, but there may have been some overlap.

As for the original question - I don't yet have a '69 build, but have a '68/12 series build and am going to do a '69 in the very near future. Based on my experience with early 70s Super Leads, I think it's safe to say...

12-series: Plate voltage typically 460ish, negative feedback 47k/8ohm, very low screens filtering at 16uF and preamp at 32+32. Due to this they sound more on the brown, compressed and middy sound. The "feel" of these amps is spectacular, but they don't exactly excel at clean IMHO. To be fair, I don't have a volume bright cap, which would probably help the clean sounds and maybe cut through a little better. But at what it does best, there's nothing else that sounds quite like it.

'69: Plate voltage 490-500, negative feedback 47k @ speaker jack, screens filtering 50uF, preamp 50+50uF. V1b cathode possibly 2k7. All these combine to make it a little tighter and punchier, and somewhat cleaner. Not quite as middy, better cleans, but a little stiffer and not the same feel as a 12-series.

Feel free to disagree.

[bill bokey]

Neil, what do you mean by the balance of laydown PT ?

The laydown C of G is lower so that when you carry it it does not flop around so much, or need special brackets to stop the feet breaking. The really early JTM45/100s are a bit lopsided too

I thought you meant some kind of eletrical balance ! Silly me !


Shakti : you may well be right but I thought the HT went up to around 500V with the metal panels. But did it start with the stand up transformer ?

[neikeel]

Oh and I have a 2k7 on V1b in my original '68 SL (ie I put it there as I prefer it!)