"Black Flag" JTM100 - the build has begun!

[Roe]

I've been using the 240v primary and the 490v seconary of the 1202-43, resulting in 485v with winged Cs and 495v with RFTs

[shakti]

Good news - this build is sounding tighter and better with every time I plug it in. Hope to have my RIFAs today though.

[shakti]

F&Ts replaced with RIFAs. Whereas the F&Ts all measured 31-32uF, the RIFAs were all between 34-35uF, and formed all the way down to 1.1V at the lowest, with less than 1 hr of forming.

Whether the difference in measured capacitance made the difference I don't know, but (predictably?) I'm hearing a distinct difference. I'd say it's subtle, but definitely noticeable. Amp sounds tighter, warmer, sweeter, more "relaxed". Clean sounds are especially improved - it sounds "cleaner" but in a good way. Bass is definitely improved, and is no longer a problem at all. I need more time on it, but I'm very, very close to what I had been hoping for all along. Now I just need to select the right tubes for it. Maybe I'll throw in an NOS Hunts 16+16 in the preamp just for kicks, or maybe get an Erie 32+32. A shame RIFA doesn't make a dual 33, as I really like what I heard with these caps.

[Roe]

I need to try the rifas too. I just too delivery of 30 bc 33uf today btw. personally, I like the bc 22uf in the preamp. I use two in my 67.

the BCs sound dirtier than the F&Ts

[shakti]

Interestingly, I'd say my immediate impression of the RIFAs was that they sounded cleaner than the F&Ts, but I need to give it more time. The F&Ts sounded looser and more ragged, with a hint of shrillness due to the looseness, particularly in the highs. But I really like that cleanliness - I can just turn it up if I want it dirty!

[shakti]

Amp is still breaking in ever so slightly. I am really, really pleased with the sound of it by now.

After some experimentation, I've ended up with these tubes in the preamp:

V1: Amperex
V2: Mullard
V3: Tesla E83CC

A Tungsram also sounded great in V1, but the Amperex was really leaps and bounds better than anything I've tried in that position, and *really* made things fall into place! A Mullard in V1 made things a little too sluggish and almost muffled (typically I've come to prefer Mullards in V2 more than any other position in a Marshall circuit). The Tungsram was better, a little "faster", very sweet, but also a little mushy when dimed. The Amperex just sounds perfect for this amp - it holds its composure all the way up to ten, tight as a [insert sex-charged description here], fast response, not a shrill note in sight, and superb clean-up. Finally, the Tesla E83CC delivers the goods in the PI, always!

[shakti]

Here's another great photo of Hendrix with a Black Flag amp. I'm not certain about the date, I think I saw this photo connected to a European fall '67 date, does anyone know? He's got a JTM45/100 by the side.

Also, I can't make out whether the amp has got a square or round indicator light. What do you think?

[yladrd61]

Yeah, definitely a tone roll-off on the bridge, but then it starts to sound super-sweet! I don't have T-tops in my LP, which is what Clapton probably had, but the Throbak SLE101+ Ltds aren't doing too badly either...

The amp is really starting to fall into place, sound-wise. I get much, much less artifacts and fart-outs now. I've been really abusing it and running everything at 10 for long periods, just to see how it stands up. Not a hitch so far, except for the bias oscillation. Fortunately it doesn't seem to happen under "normal" playing circumstances. It's a little unstable right after switching standby, but settles if I turn up the bass (which I would do anyway). I can't make it happen by playing at normal tone settings (i.e. bass turned up to at least 2). If I turn bass and treble on 0 and mids to 10, it will sometimes happen. Playing some more (without touching tone controls) will usually stabilize it though.
I do notice that it doesn't make my attenuator quite as hot as my JTM45/100 for some reason. I found that strange, but it may be because...
1) The amp needs more break-in
2) I'm running GECs @ 560V in the 45/100, biased to almost 70%, and RFTs @ 460V in the black flag, biased at 60% currently (until it burns in)

BTW, I measured the plate voltage under load, and it sags quite nicely down to 380V or even less at peaks. I like that!

If I can't find a solution I may just have to live with it, but I would love to find out if nothing else than for the learning experience. My multimeter just died, so I'm going to have to leave it until tomorrow anyway. That's a good excuse to get a new one that measures capacitance as well.

BTW: I have video of EC playing Crossroads { maybe at Fillmore West } on the Gibson Firebird with 1 mini humbucker and 2 or 3 full stacks not sure if 45/100 or black flag maybe both I will have to watch it again

[brujo]

Hey! A friend of mine has one of these, really really rocks! #10266

[yladrd61]

Nice work on your build I hope your neighbors like it

[shakti]

My neighbor loves it!

I live on a small farm, the amp resides with the full pinstripe stack in a barn. There's only one close neighbor, and they don't mind at all...in fact, he's an ex-drummer!

[elronhoover]

My neighbor loves it!

I live on a small farm, the amp resides with the full pinstripe stack in a barn. There's only one close neighbor, and they don't mind at all...in fact, he's an ex-drummer!

Those barn-dwelling critters must be enjoying some tinnitus ;^)

And you gotta make that ex-drummer neighbor back into a drummer!

Dave

[shakti]

I'm working on it... The rodents are probably digging it...my cat really does too! Mind you, if his paws start ripping on that pinstripe cloth he's gonna get it...

[shakti]

Update: this past weekend, I had the great pleasure of comparing my clone side by side with my friend's original Black Flag JTM100, serial # 10277. Photos here: http://forum.vintagegitar.no/index.php? ... rt=0&rid=0" onclick="window.open(this.href);return false;

Before we set them up to compare, we played my clone for a little while, and both thought it sounded really good. The original had developed some "issues", which we put down to failing filter caps. So I swapped them all for RIFAs, except the preamp filter cap which was kept. I also swapped the bias supply caps, biased it and checked out that everything else was in shape. It was set up with a quad of Siemens (probably RFT) EL34s, and a trio of Mullards in the preamp. Mine had 80s/early 90s Tesla black eagles, Amperex in V1, RFT in V2 and Tesla E83CC in V3.

After the tune-up, the original was very quiet. In fact, we were both quite amazed that the original was quieter, and quite simply sounded better in every way - tighter, yet warmer, more complex, with an almost fuzzy and very musical midrange that was evident right from very low volume settings. Mind you, the clone still sounded great, but the original had *something* which the clone simply didn't match. The clone was also louder, brighter, and had more hiss (while still being a quiet amp).

I couldn't get it out of my head, as I was really quite amazed at the difference - one could clearly hear that they were the "same" amp, but those little differences still stuck out. I had initially thought they were the same exact circuit, as I hadn't looked at the photos of his original for a long time, and didn't think to look things over again while I was working on it. However, tracing back, I see there were some key differences:

- the original had the negative feedback at 16 ohm, not 8. In fact, I've gone over photos at the Amp Archives now, and the few amps where I can accurately trace it in photos, it seems like all the amps with a 1202-119 OT has the feedback at 16 ohm. I had erroneously thought it was at 8 ohm because it was wired to the middle lug of the impedance selector. However, the 1202-119 had only 100v, 8 and 16 ohm terminations, and the 16 ohm is actually in the middle on the switch! So it looks like a Black Flag JTM100 should actually have the feedback at 16 ohm. I wired mine to 16 ohm, and it does of course make a difference, in a positive direction IMO. The bass is tighter, the amp is overall a touch cleaner and not so ragged, more touch sensitive and "tidier" sounding for lack of a better word. It also cuts the output volume ever so slightly.

- I also discovered that I had mine at the 230V primary tap (wired for the wall voltage where I lived before). When I set it to a more appropriate 240V, I got a plate voltage of about 480V, vs 477 when I tested the original. Dropping the voltages slightly like that really did make the clone sound more "relaxed" and warm, and cut the output volume a little. It's a lesson I've come to learn again and again...IMHO EL34s don't sound very good pushing 500V. They tend to sing better in the 420-480V region.

- and probably most importantly - I had forgotten that the original has no mixer bypass cap!! Doh!! It's in fact set up like a PA spec amp, but with a small bright cap on Volume 1. Mine has a 560pF RS silver mica, which will of course make the amp a little more strident and spikier on channel 1, and give it a little more hiss.

- I also swapped the F&T preamp can for a NOS Erie 32+32. That was also a bump in the right direction - I think it made the midrange a little warmer and more musical.

- there are other minute differences; 470k mixer resistors in the original vs 270k in mine; the clone has some modern carbon film resistors in certain spots where the original has either Piher or Iskra, but these differences should be very, very minor. However, in the eternal chase for perfect tone, I am still searching for those last missing pieces. I have some 100k Iskras and may have found some other values which will go in there. I'll report on that later.


Bottom line, however: No matter how much I tweak the amp, I suspect there's still something about that original that it will never match. The old one simply had a milky, buttery, complex, warm, musical, organic FLOW that the clone still doesn't. I suspect no amount of tweaking, tube changes and whatnot will change that. However, with all the small differences I mentioned above, I need to get these two amps side by side again to make another comparison on an even more level playing ground. My friend also has an original JTM45 Bluesbreaker chassis that needs some TLC and he wants me to go over. Bring it on.

Bottom line #2: If you have a Black Flag clone, try the negative feedback at 16 ohm - that looks like the stock value!

[VintageCharlie]

Shakti, thanks for the fantastic report - very interesting read! Looking forward to future comparisons, if you get the chance. Clips maybe?