Marshall 2203 REEEEEEEEEEE-work

[PLX]

I think I see a new choke sitting alongside the LCR filter caps!!!!!!!!!!!!!

Yeah, I drilled out the rivets in the original choke and removed it from the chassis. New one's ready to go in.

I've replaced all the filter caps.

I'm going to re-do the heater wiring this evening.

[harddriver]

Maybe you should add 1 more filter 50/50 cap can to the chassis for the PI filter cap alone somewhere? Just a thought....

I feel 32uf is really low for the PI but give it a whirl and see if you like it.

I think 68 plexi's were 64uf if I remember correctly, if you look at the back of Ed's 12301 in the VHII pics that PI cap is a 50/50uf cap probably being run at 100uf. The 64u can caps were shorter and smaller in diameter. I did try the 64uf cap for a short while on my 68 and then went to a dual 50/50 for 100 uf. And never looked back...

[PLX]

Maybe you should add 1 more filter 50/50 cap can to the chassis for the PI filter cap alone somewhere? Just a thought....

I feel 32uf is really low for the PI but give it a whirl and see if you like it.

I think 68 plexi's were 64uf if I remember correctly, if you look at the back of Ed's 12301 in the VHII pics that PI cap is a 50/50uf cap probably being run at 100uf. The 64u can caps were shorter and smaller in diameter. I did try the 64uf cap for a short while on my 68 and then went to a dual 50/50 for 100 uf. And never looked back...

I was looking back at some of the earlier layouts I got from Steve (SDM) on this amp. One did have the 100µF on the PI. That one was entitled "2203 early filtering".

I had bought these filter caps a while back to try another filtering scheme and see how the amp feels.

I am going to order additional filter caps when I order new tubes here very soon. One possibility I see would be to get a 100µF/100µF cap for the type of filtering you're recommending.

The main filter supply follows the high voltage rectifiers, often on the Laney 100W AOR's (what this amp was originally) they used both halves of a dual 50uf can + half of another can 50uf can for 150uf total main filtering. Pretty stout filtering

A typical Marshall could have 50uf to 100uf total here (in 70's + amps anyway). Higher filtering generally means a stiffer overall B+ supply in general.

The screen filter supply follows the choke (or a resistor in the 100- 200 Ohm range in some amps instead), feeds the screens/screen resistors of all four power tubes. Again, the higher the capacitance, the stiffer the supply will be (and less ripple/hum results too). The screens really do the most to control the "feel" as most define it. As the amp is cranked, notes are struck, screen current changes a good bit. The more that current change can effect the supply voltage, the more of an effect you get. The more the screen voltage drops, the more compression and such. The drop and rebound of the voltage can make for some of that classic response older Marshalls had, the "touch sensitivity". Too little filtering here and you can encounter "ghost" notes, extra noise/ripple too. A trade off worth it to some, not to others.

The PI and preamp filter nodes are not really going to do much of anything in controlling the feel of an amp, really not an awful lot for the tone in standard value ranges either.

I could leave the filtering stock values for a JCM-800 and just add a resistor after the main diodes to mimic a tube rectifier. 25Ω ~ 50Ω resistor (25 watts) chassis mount/power resistor type.

[harddriver]

I couldn't remember what my 68 had for Mains and Screens it's been awhile since I opened that thing up. I try to open it up once a year and check the voltages, bias and current draw of the tubes. I am sure it 100% stock Mains Screens and Preamp.

So it's 100uf on each node of the mains, and 32uf on each node of the screens on a 68 then? I thought they were in series for some reason??

[PLX]

I couldn't remember what my 68 had for Mains and Screens it's been awhile since I opened that thing up. I try to open it up once a year and check the voltages, bias and current draw of the tubes. I am sure it 100% stock Mains Screens and Preamp.

So it's 100uf on each node of the mains, and 32uf on each node of the screens on a 68 then? I thought they were in series for some reason??

Looking at the way this amp was running until a couple weeks ago, I had two 50/50's in series for the PI (100µF), a single 50 on the screens, and 50 on the mains. And it was 32µF/32µF on the pre-amp.

All things REEEEEEEE-considered here, I think I'm gonna go to 100µF mains, 32µF/32µF screens/PI, and 50µF/50µF pre-amp nodes.

I might play with the "SAG" power resistor following the B+ bridge rectifier diodes.

[harddriver]

I hope you get it back to purrring like a kitten PLX! Sounds like you covered all the bases so the rebuild should go well with good results IMHO.

[PLX]

I hope you get it back to purrring like a kitten PLX! Sounds like you covered all the bases so the rebuild should go well with good results IMHO.

I think lowering the screen/PI filtering from 100µF down to 50µF (or even 32µF) should make a big difference in the feel of the amp.

[PLX]

REEEEEEEE-wired heaters with 22 gauge Teflon pre-tinned wire.
Ordered new filter caps - new filtering will be 100µF mains, 100µF PI, 50µF/50µF pre-amp filters, and a multi-section 32µF/32µF for the screens so I can either run the two sections in parallel at 64µF or 32µF by just adding or removing a jumper.
Ordered matched quad of EH 6CA7 power tubes.

[RockyStar]

Slap a Cameron mod of some sorts on it, (even if it's wrong) and sell it for $7K

[PLX]

Slap a Cameron mod of some sorts on it, (even if it's wrong) and sell it for $7K