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Marshall 2199 Master Lead Combo 30 Capacitor Replacement

Started by luke gibson, August 26, 2023, 05:30:26 PM

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luke gibson

Hello,

First post.  I recently purchased a 1979 2199 combo. I would like to replace some of the capacitors but having difficulty with the hand written Marshall schematic. Does anyone have a list of the correct value electrolytic capacitor values?

Thank you,
Luke G.     

Tassieviking

#1
I have never seen one of these amps, but I have looked at the schematic a few times and wondered if I should try making one for the fun off it.

The original schematic is fairly hard to read, but I gave it a go and re-drew it.
I have most likely made some mistakes,and I left some values off because I can not read them if wanted to.

When you replace the capacitors you only need to replace the electrolytic ones, they look like little cans.

They should be easy to check by just lifting the lid of the amp and having a look, please do not go by what I think the schematic says or even the original schematic as Marshall sometimes changed components to make the amps more reliable.

These changes did not always make it onto the schematic for years till they made a new revision of the schematic.

If you find any components I have marked wrong then please let me know and I will upgrade the schematic,
Cheers
Mick
There are no stupid questions.
There are only stupid mistakes.

luke gibson

Quote from: Tassieviking on August 27, 2023, 01:07:16 PMI have never seen one of these amps, but I have looked at the schematic a few times and wondered if I should try making one for the fun off it.

The original schematic is fairly hard to read, but I gave it a go and re-drew it.
I have most likely made some mistakes,and I left some values off because I can not read them if wanted to.

When you replace the capacitors you only need to replace the electrolytic ones, they look like little cans.

They should be easy to check by just lifting the lid of the amp and having a look, please do not go by what I think the schematic says or even the original schematic as Marshall sometimes changed components to make the amps more reliable.

These changes did not always make it onto the schematic for years till they made a new revision of the schematic.

If you find any components I have marked wrong then please let me know and I will upgrade the schematic,
Cheers
Mick

Thank you so much Mick! I will give you schematic a look. And, thank you for sharing!

Cheers,
Luke

phatt

Is there any particular reason why you want to replace the Capacitors?
If the Amp works fine don't mess with it.
Phil.

luke gibson

#4
Quote from: phatt on August 31, 2023, 06:58:21 AMIs there any particular reason why you want to replace the Capacitors?
If the Amp works fine don't mess with it.
Phil.

Hello Phil, I certainly agree with your statement. I don't think the amp sounds healthy, doesn't sound bad by any means. I owned a new 2199 in 1978 (my first Marshall amp) and it's been so long since I've owned one.  This one is lacking gain from memory. The "Normal Gain" and "Bright Gain" knobs only seem to work from 8-10 I don't remember my original amp being that way.  Maybe it was, It's been 40+ years ago and the memory is not what it once was.....

Also, the main 2 filter caps are not holding a charge.  As soon as I measure them with the power off they quickly drain to millivolts, they should hold a charge.  I appreciate your reply!

Luke

phatt

I would consider Main Caps draining in a few seconds Normal.
Likely some will take longer.
Valve Amps, Yes they can hold a charge for much longer.

Regards the pots position,, maybe the pots have been changed in a repair job. Lin to Log swap will make that happen.
Phil.

luke gibson

Quote from: Tassieviking on August 27, 2023, 01:07:16 PMI have never seen one of these amps, but I have looked at the schematic a few times and wondered if I should try making one for the fun off it.

The original schematic is fairly hard to read, but I gave it a go and re-drew it.
I have most likely made some mistakes,and I left some values off because I can not read them if wanted to.

When you replace the capacitors you only need to replace the electrolytic ones, they look like little cans.

They should be easy to check by just lifting the lid of the amp and having a look, please do not go by what I think the schematic says or even the original schematic as Marshall sometimes changed components to make the amps more reliable.

These changes did not always make it onto the schematic for years till they made a new revision of the schematic.

If you find any components I have marked wrong then please let me know and I will upgrade the schematic,
Cheers
Mick

Mick, excellent job on the 2199 schematic!

luke gibson

Mick, quick question: I noticed on the schematic Capacitors C3,C7, and C8 are marked 2u2 50V. I've never seen that nomenclature before; what is the actual value of these?

Thank You!
Luke

phatt

Yep this confused me years back, 2u2 would be 2.2uF

I did read somewhere that the point can be easy missed in drawings and after many photo copies and creases in the paper it may look like 22uF.
Same goes for R's 2k2 = 2.2k.
HTHelps, Phil.

luke gibson

Quote from: phatt on September 03, 2023, 06:45:16 AMYep this confused me years back, 2u2 would be 2.2uF

I did read somewhere that the point can be easy missed in drawings and after many photo copies and creases in the paper it may look like 22uF.
Same goes for R's 2k2 = 2.2k.
HTHelps, Phil.

That makes sense! I appreciate the reply, thank you!

Tassieviking

I started doing it that way because I had to search the net too many times  for photos of amps internals to confirm the values I could not read on the existing schematic, just looking at the Marshall 2199 schematic proves my point.
That's why I asked you to check the values in your amp before ordering any capacitors.
It's just so much easier once you understand it, and it goes for any values as well.
4n7 = 4.7nF  2k4 = 2.4 kilo ohms etc.
You will find it a lot on newer schematics.
Cheers
Mick
There are no stupid questions.
There are only stupid mistakes.

luke gibson

Mick and Crew,

Keeping with the "there are  no stupid questions":

How & where is the distortion produced in this amp? Looking at the schematic you shared (much thanks) it looks like the NORMAL GAIN & BRIGHT GAIN are just volume pots....?  I just don't understand how it produces the distortion.

I have been playing it quite a bit lately and rather enjoying using the MIX INPUT and running the normal and bright gains 8-9'ish. I bet this amp cuts well in a band context.

Thank you in advance!

Tassieviking

I have absolutely no idea myself where the distortion is produced, I would need to put a scope on the amp to work it out, but I don't have an amp.

I would guess the transistors are over-driven and possibly clipping the supply rails so the top of the sine-wave is squared off ?
It would be easy to simulate in a spice program but I have never used a spice program so I can't work that one out either.

Hopefully someone smarter then me will jump in with the answer.

The "there are no stupid questions, only stupid mistakes" was something I was told when I was an apprentice electrician by someone who got too close to 11,000v AC and had the left side of his face burnt with the ear melted off, that stuck with me ever after.
Stupid questions can be embarrassing, stupid mistakes can be deadly when playing with electricity.
There are no stupid questions.
There are only stupid mistakes.

luke gibson

#13
"I would guess the transistors are over-driven and possibly clipping the supply rails so the top of the sine-wave is squared off?"

Thank you for the reply!

Are you referring to the output transistors TR14 & TR15 mounted to the chassis?

Yikes, horrible way to get injured!!


Tassieviking

I would guess its in the first couple of transistors in the preamp, TR1 TR2 TR4 TR5 is the most likely in my opinion.

It would be easy to see if it is in the power amp or the preamp, if you turn the gain up all the way and leave the volume pot really low do you have distortion ?
If the amp distorts at low volumes  then it is being generated in the preamp, if you get a clean signal with full gain and low volume then its most likely distorting in the power amp section.

The preamp section goes up to the volume pot, and the power amp starts on the output of the volume pot, C18 is the first component in the power amp.

Cheers
Mick
There are no stupid questions.
There are only stupid mistakes.