John Suhr Provided Details Regarding the SL68 (JMP SL clone)

[bmf5150]

Any idea on filtering???

[vanhalen5150]

Any idea on filtering???

Pete Thorn:

If I could add my .02:

Marshall type amps, while being simple, can vary widely, with just a part change here or there (the bright cap, for example). Everything affects everything else. So each of these amps will have a combo of parts/features that the builder feels is the "optimum" for whatever they were trying to achieve.

With the SL68, John made a plexi spec amp that's pretty magic, because it has that ability to do 60's to 80's tones with relative ease. We worked on the bright cap and the filtering together a bit- dialing in the cap so the amp works across the whole range of the volume control beautifully. It's got low filtering but not super super low, for a great combo of feel, tightness, and just the right sag.

[julkke]

Low but not super low might be something like mains 50 screens 32 PI 64 and preamp dual 32.. Someone know someone who owns one of these? Ask for pics from the outside, especially the cans.

[vanhalen5150]

Also keep in mind this is all dialed in for a PPIMV. (Sniffs Xmas wine cork)

[mixn4him]

So are we all in agreement before I start ordering parts that :

820/220
820/.68
.022-.0022
820/.68/220
10k
470/470-500pf mixers
33k/500pf Tonestack
.022 PI couplers with what looks like a 47pf
Any Ideas on the Presence value??

By the way I LOVE this forum!! Thanks!

[julkke]

So are we all in agreement before I start ordering parts that :

820/220
820/.68
.022-.0022
820/.68/220
10k
470/470-500pf mixers
33k/500pf Tonestack
.022 PI couplers with what looks like a 47pf
Any Ideas on the Presence value??

By the way I LOVE this forum!! Thanks!

Yes thats the spec I guess, though the mixer and tone stack caps can be 560pf too.

[bmf5150]

I have to say,John suhr is one of the nicest guys in the amp bussiness...

[johnnybgoood]

So are we all in agreement before I start ordering parts that :

The 10k doesn't belong.

Here's a link to the specs provided by Friedman (aka RackSystems) on a thread generated a while ago.
http://forum.metroamp.com/viewtopic.php ... &start=616" onclick="window.open(this.href);return false;

The "low but not that low" probably refers to the 100uf PI filter cap. That looks like the top-mounted chassis cap in the far corner (50+50uf??)

There are terminal strips to mount the PPIMV resistors on pin 5 of the power tubes.

[julkke]

There are terminal strips to mount the PPIMV resistors on pin 5 of the power tubes.

Cool idea actually, I always hated "flying" swamp resistors.. Gotta use that for my next build.

[mixn4him]

So are we all in agreement before I start ordering parts that :

The 10k doesn't belong.

Here's a link to the specs provided by Friedman (aka RackSystems) on a thread generated a while ago.
http://forum.metroamp.com/viewtopic.php ... &start=616" onclick="window.open(this.href);return false;

The "low but not that low" probably refers to the 100uf PI filter cap. That looks like the top-mounted chassis cap in the far corner (50+50uf??)

There are terminal strips to mount the PPIMV resistors on pin 5 of the power tubes.

Thanks! Sorry I meant the 100k that feeds into the tonestack...

[Maverick]

components mounted off the board and on the tube sockets or controls is a good thing

[bmf5150]

It's a great sounding amp, and it sure dont hurt that Pete thorn demo it!!

[mixn4him]

Hey did anyone else notice on the picture that the purple NFC seems tied to the speaker terminal and the IMP selector common..Is that right or even possible?

[julkke]

Yes I noticed that. The nfb resistor value is 47k, standard plexi.

[motrock]

I can confirm that Dave drops the voltage to the whole amp. Thats why I had the Variac inside my Variplex removed and a regular power cord installed. That way I could plug directly in to a Variac and lower the WHOLE amp. Dave did stress that the heater voltage being dropped was part of the equation!