1986 Marshall 2205

[shampoch]

Does anyone recognize this repair? The amp sounds fantastic and very quiet.

[Enzo]

Recognize? Looks like a couple of diodes blew up and were replaced. They blew some soot on the cap next door.

Those two provide the power supply for the channel switching circuits. So if that works, then it must have been fixed properly.

[shampoch]

Yeah switch works and amps sounds great! What about the picture of the POT scuffed up - is that related you think?

[Enzo]

No. The black wire is just a ground wire. The finish on the back of the pots gets in the way of solder adhesion, so to solder to it, you need to buff up the surface to expose clean metal.

[shampoch]

No. The black wire is just a ground wire. The finish on the back of the pots gets in the way of solder adhesion, so to solder to it, you need to buff up the surface to expose clean metal.

thanks for your input. any idea why that pot is stacked up?

[Robert M. Martinelli]

Hi,
the master volume pot in the 2205 ( and in its combo counterpart, the 4210 ) is placed after the phase inverter stage , so it needs to be "dual gang"

Hope this helps

Best regards

Bob

[Pedro Vecino]

There are two versions of Split channel. The first (only produced for two years aprox.) had pre-drive eq, four clipping diodes in lead channel and post phase inverter master volume. Very crude amp
Second had post drive eq, a bridge rectifier in lead channel and pre phase inverter master. In the second version there are variations in the switching circuit (transistors/IC). The amp in the photo belongs to the most modern (with IC) and the dual pot controls the gain of the lead channel (two steps at a time).
Regards

[Robert M. Martinelli]

Hi all,
Pedro's right, I'd like to mend my previous statement.
Cheers
Bob

[shampoch]

There are two versions of Split channel. The first (only produced for two years aprox.) had pre-drive eq, four clipping diodes in lead channel and post phase inverter master volume. Very crude amp
Second had post drive eq, a bridge rectifier in lead channel and pre phase inverter master. In the second version there are variations in the switching circuit (transistors/IC). The amp in the photo belongs to the most modern (with IC) and the dual pot controls the gain of the lead channel (two steps at a time).
Regards

Great info Pedro! The amp is really quiet and sounds really good with the gain on 7. I know some of these 2205's had channel bleeding complaints and if I run the lead channel gain on 10 the clean channel doesn't sound quite as pure. what ever! lol.

[Pedro Vecino]

http://www.bymcomunicacion.com/pvecino/john/2210_1.jpg
In this scheme there are marked the capacitors of the switching circuit. Habitually they are small ceramic multilayer that go below the board, though it depends of the unit (if you does not see them, they are below). They have a value of 220n (.22uF) and the solution for the poor fitering of low frequencies between chanels is to replace them with 1uF or 1.5uF.
Merry Christmas

[dtaw]

Good looking 2205, nice and clean inside besides that small miss hap with the diodes. I am a huge fan of the Split Channel Reverb amps of the 1980's. I just finished a 1988 year diy project incorporating a ppiv-mv because I need and like the extra drive it creates. Check it out, see the link in my sig.

I am also looking for feedback on ways to improve this amp, I notice that my ppiv-mv is a bit different than the one used on the earlier versions pre 1988, then when they re-designed it in latter years they took the ppiv-mv out, any ideas why?

[Enzo]

Hell of a lot cheaper to use a single pot a stage earlier instead of that double stacked pot. If Marshall can save a dollar or two per amp making just that one change, they make 10,000 amps, they save $10,000. And really, which side of the PI they put the MV on doesn;t matter a whit to most players.

[Gtr_tech]

The guy who repaired it coulda cleaned the carbon off the board......jeez....

[scole]

are those pec pots?

[Pedro Vecino]

They are standard Alpha. Currently there is an identical Bourns version with split shaft
I've never seen PEC pots in a Marshall (very expensive)