Metropoulos Forum

I've been testing my jtm45 superlead lately. this amp has the same circuit as the black flags but use an aluminum chassis not steel.

I've experimented with filtering, ended up preferring the stock filtering, although around 44uf on the mains didn't sound bad. Upping the screens filtering sounded terrible, 32uf at PI also sounded a bit hard.
Also, I tried several chokes, preferring the classictone 352-114 3h 250ma choke.
I tried adjusting the preamp voltage a little, settled on 260 on PI and 220ish on V1.
Also, I tried 470k mixer resistors, but ended up preferring the 270ks. it just gave more clarity and definition - the 470k sounded too fat and muddy in this particular amp (shakti prefers 470ks). Finally I added a 220k 2w over the standby switch for safety.

How does it sound? its one of the best blues amps I've ever tried with the low filtering. higher filtering or higher choke values changes the whole character so that is sounds more modern and feels stiffer. Mine ghosts slightly at when cranked but its manageble. I think the main reason for this lies in the larry grounding and larry filter cap forming procedure, although good tubes, caps and choke also helps.

I'm getting some convincing jimi, EJ, kossoff and EC tons with this amps. Its very easy to play with the low filtering. Its a keeper for sure. However, before its was broken in and fine tuned it sounded nasty, partially in a cool way, partially in a not so cool way.

Any comments from those of you who have experience with this circuit. I've heard it can be a pain in the ass but appears to have been lucky sofar

pic: https://www.facebook.com/photo.php?fbid ... tif_t=like

Nice, were did you get the chassi and tranies?

Its a marstran chassis with blank backside (I choose to drill it myself for use with a superlead backplate). 1203-80 and 1202-119 are both marstran, the 352-114 is classictone. filter caps are BC 33uf, expect preamp that is 22uf. Signal caps are real mustards and one RS gray cap. Resistors are piher, iskra, AB CC and a few new carbon film resistor

Can't see the photos from here, but I'm sure it looks nice.

As Roe says, I ended up preferring 470k. I had 270k in mine from the start. When I compared it to my friend's original, his sounded fuller, fatter, warmer and had more sustain all over. I never even thought to change the 270k resistors, as I didn't think they made much of a difference. It turns out my friend's amp has 470ks, so I changed mine to 470k as well. I prefer that overall - it does give the whole amp more body, particularly in the low mids, and it brings up the gain just a tiny notch, so it appears fuller and with more sustain. Admittedly, 270ks sound more snappy and probably works better for clean sounds, but for the classic Marshall full-bodied EL34 grind I think 470ks are the ticket.

In the lineage of 100-watters, 470k is a feature that appeared sometime in mid-late '67. Clapton "Crossroads" tone is very easy to get with this amp. It also helps differentiate this circuit (JTM45-style preamp, EL34 output stage, dual rectifiers) from the preceding JTM45/100 amps and the later split cathode lead amps.

I'm also getting close to the crossroads tone, although my amp sounds slightly more nasty than EC's. I did a/b tests with 270ks and 470ks, using a 500pf mixer bypass cap (on brilliant ch only) and testing both the normal and brilliant channels separately. on my amp, the 470ks sounded a little to dark - the bright cap gives the brilliant channel more low mids (than with 270k) but it also removes mids from the normal channel. I got a better woman tone with the 270k

BTW: For those who are bothered with ghosting: Here's a method for getting rid of it w/o getting a stiff amp: Just install a massive choke (CLC filter) after the rectifier and before the OT (cf. 5e8a, 5e1 and 1959f ac15s).

http://forum.metroamp.com/viewtopic.php ... rlead+pics

I have to echo Roe's opinion. The clone I built:

http://s76.photobucket.com/albums/j2/ne ... %20JTM100/
As you can see the basic compnents are identical (apart from the transformers - Marstran OT, Metro PT).

On the clone I went for 470k mixers and 47uF mains filtering. A bigger choke was disastrous for me and a Drake -114 clone restored the tone. The Black Flag went to Canada and the only mod I did was to change the PI tail resistor to 22k and decrease the bright cap on volume 1 to 100pF instead of 5000pF to stop redplating when caned (new owner wanted to use the high voltage taps) but keep it sweet at lower volumes. The new owner is very pleased with the amp.
The BF sounded slightly more modern with a humbucker guitar but still had that percussive vintage you know who tone with a strat. Cream era Clapton was kind of a default tone

Sorry even though the exact pics have been posted on the forum before at the same sizing for some reason it will not accept direct links of those pictures now???

Another thing: mine sags quite a lot. b+ voltage is around 470 at idle but drops easily to 410-420v when playing (when running flat out it can even drop slightly below 400v). I'll experiment a little with higher voltages and see how that sounds.

edit: am running slightly higher voltages now

Update, I've been breaking in and fine tuning my three 67 100w amps. I had a small shootout yesterday w/LP, SG, strats, Gretsch, Jr.

Amps were (A) early 67 super 100 w/el34/1202-119, (B) mid 67 dual rectifier, and (C) late 67 ala 10000 series/Fillmore classic. I also referenced a 66 kt66 amps (and an original superbass)

For Disraeli Gears, both A and B sounded right on "strange brew." However, B sounded closer to "SWLBR" than A, but both were good. "Sunshine" sounded like the 66 amp probably. For "Crossroads" live at Winterland ("Fillmore") its B, probably with 270k mixer resistors. EC's amp - a very early superlead - could either had a jtm45 faceplate and an aluminum chassis or a jmp faceplate and a steel chassis. a black flag faceplate is also possible, but not plausible, since pics of cream show jtm45 and jmp faceplates only. the 270k mixer resistors suggests its a jtm rather than a jmp.

For early-mid period kossoff it's B, although A also excel at this.

For Axis: Bold as Love, its B, although A is close. For "Catfish Blues" on Blues, its B probably, A is close though. For "Voodoo child" and "Voodoo child blues" I got slightly closer with A than B.

For AC/DC (Mal), A and B were equally good. C also very close. C may also be better at superbass tones and at Doyle Bramhall 2 as well as some heavy riffin'.

In conclusion, the amps are very similar. However, B has a little more character than the others but also more ghosting. B can give you both the best and the worst tones, depending on ghosting largely. A has tighter bass and a slightly smoother lead tone than B. For some blues solos and punchy riffs I preferred it slightly to B. For big cleanish riffs both A and B excel. C gives you more of the later superbass tone. My general preference is for B, possibly A. However, others seem to prefer C. Germino, for instance, changed the Fillmore model - probably named after EC/Crossroads - from B to C, probably to remove ghosting.

I'm bumping this since I find the cream, hendrix and kossoff tone important