69 Style JMP50 1987 Build

[M Fowler]

I like the components used in your build makes the amp look more original then what I build, great job.

[deeder]

05/31
Music in the workshop: Rival Sons - Head Down (’12)… Give a try to ‘Manifest Destiny’…

Thanks a lot for your support mates! Great info Firestorm that’s cool to share it. I’m about 37 hours working on it and I like that, it’s pretty addictive... Indeed!

It remains a soldering job to complete the whole board. And after that I’ll wire the PPIMV, I did it on my 2203 also. This 1987 will be a part of the stereo rig I love to use.

More later…

[deeder]

I like the components used in your build makes the amp look more original then what I build, great job.

Yes indeed it's something like a tribute to Jim, Ken and Dudley I had in my mind. That's said the other projects will be made with modern components ...

[deeder]

Nice amp good job

Thanks cbass, I spent one hour this morning to solder te bias pot, aarrgg...

[deeder]

I like your meter. Agilent makes some expensive kit!

Very usefull, I was lucky to grab it in a well known auctions site

[deeder]

06/01
Music in the workshop: The Jimi Hendrix Experience - Electric Ladyland (1968) & The Fabulous Thunderbirds - Walk That Walk (’91)

Well the build is completed , it’s a great day today even if it’s rainy (have a drink on me!^)

The big deal was to install the PPIMV, I did it for the second time and feel better with this job now.
Finally this build takes me almost 40 hours, but the best is yet to come with the reforming caps and testing procedure.

More later…

[deeder]

06/07
Music in the workshop: Me and my beloved 2203, hey…

Today was dedicated to the forming filter caps job since this 1987 is loaded with old can caps LCR 50+50 and Erie 32+32. That must be done before the first time firing up the amp.

Pulled out all the tubes, I clamp a 100k/1w resistor across the standby switch with two alligator cables to measure the voltage drop across the resistor with a DDM. From time to time I check the process of the voltage dropping. The caps will need several hours to form depending on the cap’s quality and age.

I hope to reach 2V to get a great result, otherwise 10V means its ok or 5V means good.

More later…

[deeder]

06/09

It’s done… He’s alive. I proud to announce you that a new JMP50 1969 species is born. It’s my first build and my first non MV amp. I had really thought to do this amp to hear what’s going on with a four holer. He has lots of gain, I can dial great cleans too.

The filter caps reforming process after 36 hours gave a good result about 7V, all the voltages are OK: B+ 466V.

Here is the tube selection: V1 Tungsram / V2 Siemens / V3 Brimar CV4004 / V4 & V5 Sed =C=

Cabs: 1960 Slant w/ G12M Greenbacks pair mixed with G12H Greenbacks pair, or 1936 w/ G12M Blackbacks (8 ohms series).

I discover that one of the great thrills of building amp is the build-up to that first moment of plugging in. The two channels Internally jumpered allow the amp to get a fat, searing, articulate lead tone and great sustain. After some tweaking, I decided to add a bright cap. With the volume 2, I can control the amount of ‘fat’ and even introduce a little bit more sag. The PPIMV works great far beyond my thoughts. I also use an attenuator for the moment.

Very fun amp to play, maintaining a bit of touch sensitivity/compression. Strat or LP are accepted without problem, depends on what you prefer to play but it’s just a personal taste. One thing I’m able to tell you now is that amp gives a very large register of tones from blues to hard rock as well.

So my new stereo rig set up is a very good one and probably the best I never had, this 1987 is in perfect line with my 2203 indeed. Delay and chorus effects respond themselves into these amps, enhance the guitar tones. It will be a real pleasure this summer to play it on stage… a nightmare for the sound engineer, ha ha ha…

I would thank all of the followers of this thread, as you know now I’m very happy with my brand new amp.

Rock on!

[deeder]

I’ve been away for a while. After a couple of year hiatus I did some improvements and modifications. So here is my take on my 2204ish (ex 1987):

In the first place I swapped all the NOS filter can caps with modern production F&T electrolytic. While working on the chassis I took the time to change some resistors for Iskra’s same values since I had them aside. Subjectively I hear better results with. I also removed the bright cap. The difference is pretty noticeable and enhance the overall sound of the amp.

Then I added a serial FX loop, the Metro Zero-Loss FX Loop Rev.4 and well took me to choose this one. This is a fine piece of engineering for sure.
The big deal was to drill the holes… Meh… But the result is at the ‘rendez-vous’. Such a good loop, I love it. The difficult thing about drilling holes on a small chassis is that you do have to mount the loop over the preamp tubes. That bothered me a little, but method is the key word.

The biggest modification was to convert this 1987 to 2204. At this time some problems came up because it was too bright with the stock version. To tame the brightness I added in parallel a .0022 over the 100k V2B cathode resistor. As every modifications interact with the whole preamp circuitry the amp became too bassy. Therefore I swapped the V1A .022 with a .0022, that was it for preamp mods since the Bass control was at 9.
Time to go further towards the power amp section. I pulled off .022 PI caps and installed in place .01 for more tight bass. The maths give .047* (see below). And installed a resonance filter (.0047//250k) after the 47k to the speaker jack. Excellent operation, the amp feel more airy and spongier meanwhile increasing the touch sensitivity.
Tube selection: I61 Mullard Preamp and PI (they last for ever), EL34 Sed =C=

I do not regret these improvements because the amp is more suitable to the use I have to have with. Not a high gain amp either, it wasn’t the goal. I do like attack the front end with some boosters to color a little my pallet of tones. I play the amp at 6 Gain, 6 Master, all the other controls are dialed at 6, except Mid at 4. Volume on the guitars stays most of the time between 5 and 7. The more distortion I can rid of, the bigger the guitar usually sounds. I like my guitars hot but just under that point of distortion, just on the edge of it or a little bit further no more.

I toured with it over 120 dates so far and no problem. The worry is that I have to take out the chassis to adjust the bias every time. This little big boy takes the Strats as well as the LPs.
The funny thing is that it’s still a four holler amp ;^)

*: (log10 (1/0.1) +log10 (1/0.022))/2 = (1+1.657577)/2=1.328788
C=1/10^ (1.328788) = 0.047 µF

[joeboo88]

Deeder: that's a beautiful build and some nice engineering indeed!

[deeder]

Thank you joeboo for yout king words.
And you know what I can nail the Brown Sugar tone with it like BG 'à l'époque'.

[67plexi]

The board material is killer great job.

Steve.

[martin manning]

Elle est belle!

I pulled off .022 PI caps and installed in place .01 for more tight bass. The maths give .047*

*: (log10 (1/0.1) +log10 (1/0.022))/2 = (1+1.657577)/2=1.328788 C=1/10^ (1.328788) = 0.047 µF

What is it you're trying to do here?

[deeder]

Thank you all!
At the beginning of this project my approach was to know how a real vintage 68 1987 sound does.
Using the best possible correct era electronic components. So I have managed to build this amp that sounds flawlessly good to me. That I have converted into MV thing. As the components started to drift toward each other the amp get quieter, smoother and more stable. I plug into it, hit the chord, I’m already there. It has clarity, speed, punch, transients and string definition on chords even with severe amount of boost.

Elle est belle!

I pulled off .022 PI caps and installed in place .01 for more tight bass. The maths give .047*

*: (log10 (1/0.1) +log10 (1/0.022))/2 = (1+1.657577)/2=1.328788 C=1/10^ (1.328788) = 0.047 µF

What is it you're trying to do here?

The conversion toward a 2204 model revealed a lack of Bass.
As is without PI caps mod, I had to set the bass control very high level. This leads me to believe that I may still be fine with 0.1uF output coupling caps. I have a slight hunch that one of the reasons Marshall went with .022 over 0.1 as output coupling caps was the change from Drake to Dagnall OTs. From what I've read about the Drake transformers, they seemed to handle the bass a little better whereas it quickly turns to mush with the Dagnalls. With the bass models, presumably this was less of a problem for bass players, hence the 0.1uF was still used in the Dagnall era bass amps.

Since the frequency rolloff is proportional to 1/capacitance, a 0.068 would be closer to a 0.1 frequency wise. In calculating the “tonal” midpoint, one would have to consider that one also perceives frequencies logarithmically (e.g. 1kHz is one octave up from 500 Hz, 2 kHz is one octave up from 1 kHz, so the “tonal” midpoint of 500 Hz and 2 kHz is 1 kHz not 1.25 kHz). Little trickier math with 0.1 and 0.022 caps. Basically take the log base 10 of the normalized frequencies, average them and then 10^x them.

it may be a little far-fetched, hum... period...

[Roe]

I'll help you to get rid of those LCR caps - they're dangerous and should only be sent to a marshall junkie like myself