JTM100 Black Flag vs. JMP100

[Elad E]

I'm contemplating building a 10,000 series amp and I'm intrigued by the Black Flag JTM100 in particular due to the impressive list of legendary live tones (Clapton, Hendrix at the Fillmore East and Paul Kossof) associated with the JTM100 over the short transitional period it was produced and due to the fact that it seems to sit right in the middle of the tonal spectrum I like (I already built a JTM45 and a '69 Superlead which I've since modified to 12,000 series Superbass specs).

What I would like to know is what tonal difference should I expect between a late '67 single rectifier 10,000 JMP (#6) and the dual rectifier Black Flag JTM100(#5C)?

Has a 67' single rectifier JMP featuring all 32uF filtering and a Drake 1202-80 PT ever existed?

[neikeel]

I have had originals of the BF type and JMP type and the preamp is the same, the power supply is very similar with both configurations. The single rectifier and a filter board with series 32+32 for 16uF on screens and series 100uF+100uF for 50uF mains and a 16+32 in parallel for 48uF PI is probably the best set up for this amp. Don't forget to get the 2" OT (either 1202-119 or 1202-132) that you must use with Drake 354-114 and the 1203-80 PT. All important parts of the jigsaw.

[Elad E]

Hey Neil, thanks for the swift reply!

So I take it that the Drake iron sets the tone (no pun intended) for the 67' amps. Doesn't the dual rectifier impart any tonal quality which sets these amps apart from later shared cathode amps (increased filtering non-withstanding)?

Also, what preamp filtering do you recommend for such a 67' JMP build?
Do you prefer 270 or 470 mixer resistors in these amps (mainly interested in Hendrix Fillmore East tones)?

[neikeel]

Dual 32 in the preamp is pretty stock.

I would go for the power section filtering I suggested

In my originals I like 270k but clones seem to need 470k to get the grind

[Roe]

I like 270k for mixer resistors. It makes a big difference whether you use 50uf or 33uf for mains filtering. In one of my amps I even made it (50/33uf) switchable. 33uf is perfect for cream, hendrix (67-68) and free. 50uf gives you that later jmp sound, heard on countless recordings. I use 16uf at the screens, although 23uf may also work. The phase inverter don't matter too much. I have 16uf in one amp and 32uf in another

[Elad E]

Tough choice...since I can't build both amps I may just build the later style '67 JMP (33+33uF screens, 100+100uF mains and a single rectifier) and order a spare set of 33uF electrolytics to swap in for the mains and a 16+16uF PI and use one side for the lower Black Flag PI filtering or bridged for a more JMP-ish filtering.

does that sound right or is the dual rectifier an essential part of the Black Flag magic?

[Roe]

I guess the filtering is more important than the dual rectifier

[neikeel]

I guess the filtering is more important than the dual rectifier

I think so. When I built my clone (with original sitting next to it) I ended up wiring the clone as a doubled up pair of bridges (so effectively single rectifier) also upped the mains filtering from x4 33uF to x4 47uF (so total 47uF) but left PI at 16 and screens at 16 with dual 32 in preamp as I felt it ghosted too much (they all do a little). Pesonally I think it is the low screens that give these amps their squishy feel to play.

[Roe]

For blues and psychedelica I even like the 33uf on the mains. It sounds beautiful for clean sounds and a little breakup, while collapsing when you really crank it for some cool blues solos with a lot of ripple and harmonics. For harder rock, ala AC/DC, 50uf on the mains is much better. On one of my 67 amps, I'm using the 100v/230v switch for switching between 33uf and 50uf. Just remember to add power resistors across the switch or you will blow fuses

[Elad E]

I've decided to stick with the Black Flag circuit, I'm afraid the late-'67 JMP has a power section that will give me too similar a feel to my '68 spec Superlead.
I'm basically hoping to find a middle ground between the spongey, bluesy feel of my JTM45 and the heft and push of my Superlead.

Can any of you guys who built a JTM100 Black Flag kindly provide or direct me to a wiring layout for the power board?

[neikeel]

I've decided to stick with the Black Flag circuit, I'm afraid the late-'67 JMP has a power section that will give me too similar a feel to my '68 spec Superlead.
I'm basically hoping to find a middle ground between the spongey, bluesy feel of my JTM45 and the heft and push of my Superlead.

Can any of you guys who built a JTM100 Black Flag kindly provide or direct me to a wiring layout for the power board?

What transformer have you got?

[Elad E]

I haven't got any yet.
planning on getting George's 1203-80 and 1202-132.

[neikeel]

The original 1203-80 has dual secondaries and twin rectifiers, I have a diagram somewhere

[Elad E]

The original 1203-80 has dual secondaries and twin rectifiers, I have a diagram somewhere

That's exactly the one I'm looking for - with the dual 95v secondaries.

[neikeel]

I do not know if the one George has is like that, but I do not think dual 95vac as that would be too low:

The Marstran one has the correct arrangement.

I was cloning my '67 45/100 block end which was -80 PT and -119OT but only had the single CT PT from George so built a dual rectifier board with the two rectifiers in parallel at all points, not like and original.

Look here:http://forum.marstran.com/viewtopic.php?f=2&t=415