69 Style JMP50 1987 Build

[deeder]

Hi all! I build my first 50-watter guitar amp: JMP 1987 ‘69 species. The purpose of that build is to add this one to my 2203 since I play a stereo rig, to replace the Deliverance 60W (KT88) I’m currently using.
I have spent a lot of time to get all the parts and hardware for it, and already initiated my building; here is a photograph of the chassis inside.

After a bit of research, I pay attention for a 1987 and see what’s going on with the 2203. If it’s not convincing:
Plan A: add a PPIMV
Plan B: internally jumpered inputs
Plan C: conversion to 2204

I prefer playing than building, some would say I’m lazy. The reason why I want to post some steps here on the board. Actually the three pieces band I’m involved with needs a lot of time to rehearsal, doing the management things, etc.

I count on you gents to kick my ass to get it over with! For those who don’t know me yet, here is my introduction: https://tubeamparchive.com/viewtopic.ph ... ht=#297201

I can imagine that one the great thrills of building an amp is the build-up to that moment of plugging in. The second best is unveiling it here, I wish it will be settle for May…
Thanks for your attention.

[stump]

Nice heater wiring. My first complete amp build was a 1968 spec, 1987, a Metro kit actually. The Metro site is down, but if you'd like a copy of their build instructions I'd be happy to get them to you, they're in PDF format. It covers everything you need to know, including initial testing and measuring voltages before plugging into a cabinet and letting it rip.

My 1987 has a few changes from stock. I added a Post Phase Inverter Master Volume( LAR/Mar type) and a Zero Loss effect loop. I run it in stereo with my 1983 JCM 800 4104 combo. Tone of the gods and plenty loud.

[deeder]

Thanks stump, fortunately I got this build instructions just before the forum was down. Nevertheless I like to study old pictures of this amp to determine the right orientation of coupling caps for instance since I'm going to use some old parts.

[deeder]

05/04
Music in the workshop: Pat Travers - Putting It Straight (’77) & Doobie Brothers - Stampede (’75)

Et voilà, at last! PT and OT transformers are wired.

Finally I go for an alternate grounding with 6 local ground nodes (the individual circuit grounds connected to each node is selected so that one node doesn’t interfere with another and, in theory, remain quiet. Thus, the ground currents are localized to their part of the circuit.
That scheme can be viewed here: https://tubeamparchive.com/viewtopic.ph ... 0caa022586
Essential that the input ground is dedicated to chassis, also the heater centre tap is tied to the guitar input jack ground. About the 1 ohm resistors the best is to ground those at ground point 5 (mains filtering, etc.).

To come back to the PT wiring, and specifically to the pilot light, I choose a 120V so the wiring was different because of European 230VAC. So I studied the PT primary according the winding schematic (I have made a Visio if interested).

Fuse holders ‘made in England’ came from Poland, and they are identical to those fitted into my 2203 from the seventies.
Not so easy to solder screen grid resistors on power tube sockets, la vache! I measured the resistors wilt the DMM: 1.001 kΩ each one, not bad.

Of course, I double check all solder points for the continuity and always verify that I’m clear with the layout (SDM). Better to take the time at each step than debug something wrong at the end. Well it’s my very first build and I’m not an expert, hum…

I’m off until the end of next week, so I go on doing the job… more later…

[deeder]

My 1987 has a few changes from stock. I added a Post Phase Inverter Master Volume( LAR/Mar type) and a Zero Loss effect loop. I run it in stereo with my 1983 JCM 800 4104 combo. Tone of the gods and plenty loud.

I'm wondering how you manage them since they are different, do you add an OD or disto in front of the 1987 for instance?
I ask you that to be sure that I take the right way with the stereo rig I want to have.

[martin manning]

Looking good, deeder!

[deeder]

Your support is very welcome Martin
About alternate grounding schematics, yours and the one I use, both have the similar interest to delete the bus wire to ground all nodes. That is pretty cool when some modifications must be made.
Going back to... the workbench !^)

[deeder]

05/09
Music in the workshop: Robin Trower - A Tale Untold (years ’73-’76) & Dream Theater - Awake (’94)

At this point I have spent almost 25 hours on this build and like it far beyond I supposed. At times I’m thinking about Bletchley Jim’s facility in the ’60, the tube amp guitar golden age back then. Well…

So I decided to go for internal jumpered inputs. I find out that the 68K grid stopper resistors must be changed for 34K. The way the input setup is designed to work on Marshalls four inputs, when the two channels are bridged then the amp is seeing 1M load to ground and a series resistance of 34K.
I really don’t know what I’ll get with this internal wiring but I guess it would be interesting.

Wiring the board needs to make attention to details and precision. That is Ken Fischer wrote in Vintage Guitar about Marshall’s lead dress: “To reduce hum and buzz press all preamp tube wires to the chassis except lift all green control grid wires up into the air”. That’s what I did.

More I’m going forward, more I have to take decisions. Reason why the 5.6K input grid resistors are soldered to pin 5 of each output socket but not connected yet to the feed from the PI. I’m going to wire a PPIMV pot in place of the second output jack. These grid resistors will be connected when the board will be populated.

More later…

[deeder]

05/23
Music in the workshop: The Who - Quadrophenia (’73), Jeff Beck - Blow by Blow (’75) & Tchaïkovski symphony n° 6 (‘93)

I triple checked all the connections, the lead dress has to be very clean. All the jumpers are located underneath the board. At this point every things are going fine, will see tomorrow populating the board.

More later…

[Reeltarded]

Excellent work! It's beautiful.

[deeder]

05/30
Music in the workshop: Heaven and Hell - Live at the Radio City Music Hall (’07) & Rainbow - Rising (’76)

Merci Reeltarded! I try to do my best for this first build even if my knowledge isn’t first hand. And more that’s true I’m learning a lot.
I must confess that my RS Imperial’s wrenches save my life since all the bolts and nuts aren’t metric. Actually I’m trying to adopt the British way of life during this build !^)

I spend a lot of time to select the component parts, and measuring all resistors and capacitors to be closer to the right values. Here is the species for that build:

V1A Cathode Combo: 220mF/820R
Is there a difference in tone between the 220mF and 330mF in V1A position? For all intents and purposes the difference is mathematical. This particular capacitor (along with the resistor) sets which frequencies will be boosted. The bigger the value of the cap, the lower the frequencies it boosts will be. The difference between them is well below the human hearing range. In fact, both boost everything down to below 2Hz. Even if you could hear that (nobody can), our speakers aren't designed for such a thing.

V1B Cathode Combo: 680nF/2k7
The 1987 ’69 species according to all the pictures I’ve seen seems to have 820 ohms cathode resistors on both 680nF cathode caps. I’m not sure when (if ever?) the 50 watters went to 2K7.

V1B Plate Bypass Cap: 2.2nF
V2A Cathode Combo: 680nF/820R
Inputs Resistors: 33k since this 1987 is internally jumpered
TS: 560pF/33k - 22nF/22nF
Mixer: 470k/470k/560pF
PI Caps: 100nF/22nF/22nF
NFB: 47k/8ohms Tap - 100nF Presence Pot
No bright cap
Filtering: 100mF Mains / 50mF Screens / 50mF PI / 32+32mF Preamp (as that is correct for a ’69)
Choke 3H: C1999
PT: 1202-118 (Drake clone)
OT: 784-139

Some NOS parts, not all, were sourced from military surplus like the 22nF mustard's for instance which they have the same date code ‘060H’.

More later, tomorrow…

[martin manning]

Interesting to see this great project coming together. Looks like you'll soon be making your own music in the shop!

[Firestorm]

V1B Cathode Combo: 680nF/2k7
The 1987 ’69 species according to all the pictures I’ve seen seems to have 820 ohms cathode resistors on both 680nF cathode caps. I’m not sure when (if ever?) the 50 watters went to 2K7.

According to Greg Germino (who knows these things) the 100W 1959 models got the 2K7 in May or June of 1969. If I had to guess, the 1987 did at roughly the same time. It more or less coincides with transition from Plexi to metal faces.

[xtian]

I like your meter. Agilent makes some expensive kit!

[cbass]

Nice amp good job