Marshall 2199 Master Lead Combo 30 Capacitor Replacement

[luke gibson]

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 ?

I like how you laid out the schematic, very easy to follow!
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

Mick, it does distort at low volume (sorta fizzy distortion) so it is generated in the preamp. Which makes total sense, similar to a tube amp which Marshall was trying to replicate with Solid State devices.   

I like how you laid out the schematic, you made it very easy to follow.

[luke gibson]

Opened her up today to replace the power supply filter caps and found that my amp was a little different from the schematic. On my amp C18 is a .047uf yellow square capacitor from the factory. Not sure how different it sounds from the 25uf cap shown in the schematics.

I appreciate the help you have  given me, thank you!

[Tassieviking]

It might be you have a different style of PCB, possibly an earlier or later version of the same amplifier.
Marshall would release the same model but with several different layouts but basically the same circuit, they did however completely renumber all the components with several new revisions.

If you have the same circuit you should have 2 47nF capacitors in there, C14 and C15.
Can you find 2 47nF capacitors in there ?
Can you find a 25uF capacitor on the PCB ?, there should only be one.

If you can take some pictures of the top and bottom of the PCB I will see if I can trace your version out for you properly, the more pictures the better.
If I can see the top and the bottom and then compare where the traces go to what component it's fairly easy to do.

Cheers
Mick

[luke gibson]

It might be you have a different style of PCB, possibly an earlier or later version of the same amplifier.
Marshall would release the same model but with several different layouts but basically the same circuit, they did however completely renumber all the components with several new revisions.

If you have the same circuit you should have 2 47nF capacitors in there, C14 and C15.
Can you find 2 47nF capacitors in there ?
Can you find a 25uF capacitor on the PCB ?, there should only be one.

If you can take some pictures of the top and bottom of the PCB I will see if I can trace your version out for you properly, the more pictures the better.
If I can see the top and the bottom and then compare where the traces go to what component it's fairly easy to do.

Cheers
Mick

There are 2 47nf caps remaining. I traced it using the schematics and when I removed the cap it had C18 screen printed under it.  I have it buttoned up, next time I remove the chassis I will take a picture. Also noticed someone had replaced Q6 (2N3819) at some point with a different transistor.

[GeorgA]

Hi together,

my first post in this community:
After opening up my new and still stock 2199 from 1979, I can share the info, that all the 25k pots in the schematic are 22k in my amp. I read the A on it and checked the taper, it is still linear. Maybe something to add to the excellent redrawn schematic! It could be relevant to others due to the fact that 25k Lin with the offset center PC leg are unable to source.

Greetings from Germany, Georg

[J M Fahey]

Thamks for the update.

Don´t worry, pots are the same and will work fine.

In the old days, component values often followed the "2-5-1" scale, so you would find 10 - 25 - 50 100 k pots and so on. .02 .05 .1uF caps, etc.

Today a more evenly distributed "exponential" scale is used, similar to the one used in resistors, 10 - 22 - 47 - 100 k pots and so on.

Pots actually have wide tolerasnce, think 20-30%, yet amps work fine.

[GeorgA]

Thanks for your reply and the kind words. Just for the record: the pots are the first ones, factory installed, not changed before. That's why I shared the information. Mine is June 1979. 

Greetings George