Going to Build a 2204, Should I Mod?

Looking at the Marshall schematic it shows all 3 filter caps as 50u/50u. The Valvestorm layout shows a 33u/33u, a 50u/50u for the mains and a 32u/32u for the screens with 50u/50u in parenthesis. What effect would the different values have? Does it make any difference at all?
 
I'll repeat what others have said. Firstly, the output transformer you choose is important, & Chris Merren (Merren Audio) makes the best reproduction Marshall transformers available (you get what you pay for). Thing is, Chris had taken full time employment a while back, so I'm not sure if he's supplying transformers as yet. Best to shoot him an email, or ring him to find out. He's great to talk with & VERY knowledgeable. Next best quality is Brian Wallace at Marstran, with transformers being wound by Heyboer to his spec, obtained through tearing down original iron.
If you go with Heyboer from Mojotone, you want the Drake 784-139, not the Dagnall (trust me on this). Hammond make good transformers, but I believe most are wound on plastic bobbins rather than the paper former used in the original Marshall iron. Does this make a difference??? Definitely.
This brings us to the Power Transformer, you need a reproduction 1202-164, but (& this is a big but), you need to decide on & request the high voltage secondary's voltage, as through the years it varied, to give a B+1 of as high as around 465V, or as low as around 380~390V, & this greatly affects how the amp reacts. High voltage amps are great for chunky palm muted type rhythm stuff etc, low voltage amps are great for compressed lead type licks etc. If you say, went with a Marstran 1202-164 & didn't specify what HV secondary voltage you want when ordering, you'd get a low voltage type. Not sure about what HV secondary Chris Merren or Mojotone/Heyboer supply normally as I haven't ordered this type PT from them. Or, you could shoot for a B+1 of say, 430V for an amp that'll be good for just about everything.
The Ero/Vishay MKT1813 are great sounding caps, personally though I like the old Philips 341 "yellow block" type capacitors best for a 2203/2204 type amp. You'll find them on eBay (I'll shoot you a pm with a link).
Please, no silver mica caps for treble & treble peaking duties in a 2204, use ceramics (RS Lemco dogbones preferably).
I have tried the Vishay Dale metal films in a Marshall circuit & ripped them out. Carbon films please. If you want high quality, close tolerance types, use the 2% Takman 1 watt carbon films. Enjoy your build. Cheers
Edit:
I've got to agree with Mr 67plexi on the Green Hornet amp's transformer combination. I have a 50 watt (1987) type build using the JTM45's 1202-55 PT, 3 Henry choke & 784-139 OT. Fantastic amp. With solid state rectification the PT gives a B+1 of, IIRC, around 476V, but this PT has higher resistance than say, a 1202-118 or 1202-133 50 watt PT, so sags more under demand. Though Marshall never used this PT in anything other than the JTM45, it is a great combination with the 50 watt OT. Thanks for the tip on using JTM45/100 filtering Mr plexi, I'll look to that in my amp. Cheers
 
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Cadorman said:
Looking at the Marshall schematic it shows all 3 filter caps as 50u/50u. The Valvestorm layout shows a 33u/33u, a 50u/50u for the mains and a 32u/32u for the screens with 50u/50u in parenthesis. What effect would the different values have? Does it make any difference at all?
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Personally, for a 2204 I like 3 X 50uf/50uf (100uf main, 50uf screen, 50uf PI & 50uf each for V2 & V1), though some like 33uf for the screens, PI & V2/V1. There isn't a lot in it & you'll only notice a difference if you're pushing the amp HARD. Lower filtering makes the amp a little more pliant, or touch responsive whereas with the higher filtering it will be a little stiffer. Again, there isn't a lot of difference . Cheers
 
To add to what Ivan added regarding Chris Merren's transformers, I have the "JTM45 Marshall Audio Output Transformer:
Drake # 784-103 reproduction output transformer" and "Marshall JTM 45 Drake # 1202-55 Power Transformer" from his website. Together, they run at 465 volts B+ at 40 mA for KT66 tubes. It hits the sweet spot for that amp design. If his 784-139 50W transformer is anywhere near the quality as the one he made me, it's worth the extra cash. He is great to deal with. He answered a lot of questions for me, offered hand drawn sketches, and made sure I was a happy customer. Take Ivan's advice on the resisters, capacitors, etc. And accept any info that Steve will help you out with. You'll be glad you did. If it wasn't for their input (and Care Packages), my amp would not have come out as nice as it did.

Like anything else... If you need to put the project off a few weeks to get some better components that will make the build that much better, do it. Like any other tool, guitar, or amp, waiting the extra few weeks may make a big difference in the pay-off.

Hope it comes out awesome.
:cheers:
 
ivan H said:
Personally, for a 2204 I like 3 X 50uf/50uf (100uf main, 50uf screen, 50uf PI & 50uf each for V2 & V1), though some like 33uf for the screens, PI & V2/V1. There isn't a lot in it & you'll only notice a difference if you're pushing the amp HARD. Lower filtering makes the amp a little more pliant, or touch responsive whereas with the higher filtering it will be a little stiffer. Again, there isn't a lot of difference . Cheers
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I think Cadorman ordered the turret board and chassis that has the preamp filter cap located on the board. The only e-cap option here is the F&T 33/33 uF/450v e-cap... which will be fine too.n88gdawos4ujzk6vyviz.jpg
 
syscokid said:
I think Cadorman ordered the turret board and chassis that has the preamp filter cap located on the board. The only e-cap option here is the F&T 33/33 uF/450v e-cap... which will be fine too.View attachment 86534
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Ah yes, good catch sysco. Looking at the Valvestorm site, the chassis does not have the punch-out for a top mounted pre-amp filter cap either. Cheers
 
Clockworkmike said:
Isn't that why they kept the technical name Mk II on the JMP 2203/2204, because it just the next evolution of the previous amp? Someone told me that once anyways using that same logic with the 900 MKIII Master Volume ( though diode clipping became the next mod on that one) and the unofficial title of the SLX Master Volume: MkIV ( removed diode clipping added extra gain stage and preamp tube)
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Nobody really knows about exactly what the "MK" means, except maybe Ken Underwood who is the last living person who worked to build "MK I" the first original prototype amp.
Dudley Craven is the last person who would have known...

The 900 MV has a solid state preamp and 1 tube compression stage, tube power amp. The diode clipping for both clean and boost channels is the original factory design, not a mod.

The SLX is a tube preamp (they back pedaled) after making the solid state preamp for the 900 dual master volume....

However
there are "Transition Models" (that's what I call them):
It's a 2203/2204, but built on a JMP Plexi chassis, this proceeded the JCM 800.

You won't find many of these, they were only produced for a very short time.
1/2 plexi, and 1/2 800. The Chassis is stamped "JMP."
 
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Amp Mad Scientist said:
However
there are "Transition Models" (that's what I call them):
It's a 2203/2204, but built on a JMP Plexi chassis, this proceeded the JCM 800.

You won't find many of these, they were only produced for a very short time.
1/2 plexi, and 1/2 800. The Chassis is stamped "JMP."
Click to expand...
Yes, & this type 2204 MV amp is the rarest of all (schematic shown)
16655172620786946754376257513213.gif
Note that V1 is not cascaded, while the V2a voltage amplifier's plate load resistor's value is increased from 100k to 330k. Only the 50 watt master volume amps were done this way & only for a short time. Cheers
 
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