Consider restoring my ’77 2203, the last crusade…

Info for maintaining and tweaking your amp to perfection.

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Did J
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Consider restoring my ’77 2203, the last crusade…

Post by Did J » Sun Feb 27, 2011 8:44 am

Few times ago I’ve bought in Geneva a brand ol’ 2203 MV vertical inputs (SL/A 0XXXXJ) in a pretty good shape. The only part missing was the impedance plug, since I’ve find one. The amp sounds very good meanwhile is very loud too… but sounds very good…

34 years after it was built, I believe it’s time for him to do some restoration and upgrades. So I’m tuning at your side folks to get some advices.

First step of this story is taking numerous pictures of it, and studying, identifying parts. The PCB is well populated; the coupling caps are sort of green beans, only one dijon (0.68mF).

The chassis inside seems to be very dead stock, except for V1. As you can note, the two green wires were cut off, and we can see: pin2 one 39k resistor (orange/white/orange) in place of 68k, and pin7 another 39k resistor, both with shielded wire coming from the input jacks.

For the moment I haven’t do any measurement. No scratch with pots, even they aren’t in good shape for my taste. Do I have to change them? There is the bright cap still soldered on the gain pot. I’ve just dusted off the whole thing that’s it.

As for upgrade I want to install the Larry/Mark MV in place of the second output jack rear the chassis, it would be an interesting thing to manage pre and post MV. I would plan to switch the PCB to a PTP board, but honestly I’m not prepared yet to do that, in the future maybe. Anyway I think to play it stock first to hear how it sounds once restored.

I’ve noted that the power rocker switch is illuminated directly when the amp is plugged in the wall… Do I have to buy a new one, or it’s a malfunction of the PSU ?

Enough words, now here are the pics. If some of you can deliver the expertise it’ll be great for the following work I’ll have to with my 2203. According to me the big business will be to change PSU caps, forming them, and perhaps the bias caps too… (Writing this text listening Foreigner, Mick Jones is an excellent guitarist!) Thousands thanks!

Did J
PCB Populated.JPG
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V1.JPG
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V1 Green Wires.JPG
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neikeel
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Re: Consider restoring my ’77 2203, the last crusade…

Post by neikeel » Mon Feb 28, 2011 5:15 am

The amp looks basically original from the limited pictures that I can see, the green bean caps date it to late '76/early '77 and a lot of people like the way that they sound.

A previous owner has presumably had issues with parasitic oscillation/noise and has bypassed the grid resistor on V1 (the 68k on the board) with a 30k soldered directly onto the V1 socket, that is quite common although it is more unusual to put one on the other half of V1 (the cold biased 10k) unless you are planning on decreasing that down to 8k2 or 5k6 or even 4k7 for more gain (a neat way of adding more gain is to bypass the 10k with a 0.1uF cap in the empty slot next to the 10k (see the long AFD/SIR thread in the Marshall section).

You may find that if the amp has not been used for a while that the large filter can caps have dried out which manifests itself as a hum. You would need to replace those cans with some new ones (F&T are probably the best ones currently available in Europe).

Suggest you post a tone report and some more photographs 8)
Neil

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Did J
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Re: Consider restoring my ’77 2203, the last crusade…

Post by Did J » Mon Feb 28, 2011 2:13 pm

Hi Neikeel, thanks for coming in this thread :wink:

About tone, I play it straight in with a Strat loaded with single coils (Irish Tour, Bare Knuckle), 16 ohms 412 cab and 16 feet guitar cable.
It’s a crunchy amp (master= 4, pre=8 for instance) and well… that’s very loud but it seems breathy with a lot of headroom. The setting is P=4/B=2/M=4/T=5 for the moment to test it. IMO I get good tonal response with it, the EQ pots are accurate, no particular hum.
I switched pre tubes Groove Tube for V1=Brimar CV4004, V2=Brimar CV4004 Box Plate and V3=Telefunken Smooth Plate, not a definitive choice. Power tubes are EL34 Groove Tube. With this arrangement the amp is less rough, I mean is more playable to my taste.

Here some picture of it:
Front Chassis.JPG
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Bright Cap.JPG
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Presence Cap.JPG
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Did J

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Re: Consider restoring my ’77 2203, the last crusade…

Post by Did J » Mon Feb 28, 2011 2:53 pm

... and more photographs
Rear Chassis.JPG
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ssis.JPG[/attachment]
PSU Lead Dress.JPG
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Did J
Attachments
Rectifier Diodes.JPG
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rockstah
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Re: Consider restoring my ’77 2203, the last crusade…

Post by rockstah » Mon Feb 28, 2011 4:06 pm

leave that amp alone!

install your lar/mar master and see what you have.

don't worry about PTP. yes its easier to work if you wanted to tweak but thats the only benefit over PTP.

leave the big caps as they are unless you have issues. they don't make those anymore and nothing sounds quite like them.

the only other tweak i might do is change the first gain stages coupling cap from the .022u to a .0022u unless you like a somewhat fatter sound than the .0022u would provide.

also i might change one of the 10k dropping resistors to 8k if teh amp didn't sound open enough. raising the preamp voltages make it not so congested. ( closer to earlier amp spec)

i have a 79 stock PCB that i went form PTP back to stock using the PCB and it kills.

Mark

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Re: Consider restoring my ’77 2203, the last crusade…

Post by demonufo » Mon Feb 28, 2011 6:49 pm

Is it just me, or do the transformers look like replacements?

As for the rocker switch light, it may either be bad, or a replacement that is wired up wrong. Show us a close up of the power switch please. :D
So I like purple, okay!!!!!!

83.7% of all statistics are made up on the spot!

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Re: Consider restoring my ’77 2203, the last crusade…

Post by neikeel » Tue Mar 01, 2011 5:44 am

They look like original Dagnalls to me............

Yes most likely incorrectly wired switch, which begs the question why (so maybe you are right about the power transformer :wink: )
Neil

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Re: Consider restoring my ’77 2203, the last crusade…

Post by Did J » Tue Mar 01, 2011 5:41 pm

… Here some more photographs:
Choke.JPG
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PSU Wiring.JPG
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Choke.JPG
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Switch IO STB.JPG
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Did J
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Re: Consider restoring my ’77 2203, the last crusade…

Post by Did J » Wed Mar 02, 2011 9:42 am

Thanks a lot to help me :wink:

So what I have to do:

Neikeel: combo 10k/0.1µF option

Rockstah: first gain stage coupling caps .022 -> .0022µF, no PTP, lowering 10k dropping resistor to 8k option.

Have a good time boys! :toast:

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Re: Consider restoring my ’77 2203, the last crusade…

Post by rockstah » Wed Mar 02, 2011 9:55 am

Did J wrote:Thanks a lot to help me :wink:

So what I have to do:

Neikeel: combo 10k/0.1µF option

Rockstah: first gain stage coupling caps .022 -> .0022µF, no PTP, lowering 10k dropping resistor to 8k option.

Have a good time boys! :toast:
like i said, leave the amp alone and add your PPIMV (lar/mar version) and see what you get. ;)

Mark

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Did J
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Re: Consider restoring my ’77 2203, the last crusade…

Post by Did J » Wed Mar 02, 2011 10:37 am

... Roger Red Leader One... :thumbsup:

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Re: Consider restoring my ’77 2203, the last crusade…

Post by rockstah » Wed Mar 02, 2011 10:48 am

what can i say? i'm passionate about what i believe. ;)
Mark

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Re: Consider restoring my ’77 2203, the last crusade…

Post by neikeel » Wed Mar 02, 2011 11:30 am

I think that is right.

Always try it out first and tweak according to your ears.

The Lar mar might allow you to crank the master volume (where these amps sound their best, IMO).

I have however found that the inbetween settings (PPIMV at 12 o'clock and the PreMV at 12 o'clock) the amp was strngely flat and lifeless.

See what you find :wink:

The mods suggested were to give the amp a bit more brightness and lead like tones (the 0.0022uF first coupler will remove some lows) decreasing the second stage cathode resistor will give more gain an adding a bypass cap will also effectively give you more gain across the spectrum.

Let us know how you get on 8)
Neil

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Did J
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Re: Consider restoring my ’77 2203, the last crusade…

Post by Did J » Wed Mar 02, 2011 12:59 pm

rockstah wrote:what can i say? i'm passionate about what i believe. ;)
Mark
That's the way it is Mark. I've spend 17 years running the world with my nikons, one thing I've learned is without passion nothing is possible... Today I put all my mind in music, guitars and amps and that's very kewl :D

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Re: Consider restoring my ’77 2203, the last crusade…

Post by rockstah » Wed Mar 02, 2011 1:00 pm

Good deal man! ;)

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