Stock White legos vs. Sozo Mustards question re: swapout

Necrovore · Post by **Necrovore** » Fri Jul 16, 2004 9:57 pm

Ok one mod down, one more to go.
I am wanting to swap out all the Lego type caps on my JCM800 board.
Everyone has been ranting about the Sozo's and I would like to see what all the hoopla is about.

My question is George sells several caps that are the same uf ratings as whats in my amp but voltage ratings are different. If I change the old for new what would the difference be and would the amp still work right?

.022uf 400v I need 7 of these and Sozo's make these, easy swapout.

C3 is .68uf 100v Sozo makes .68uf 160v Difference would be?
C13 and C15 are .1uf 250v Sozo's equivalent are .1uf 400v Difference would be?

Would changing the .68uf and .1uf benefit my sound or be detrimental?

Flames1950 · Post by **Flames1950** » Sat Jul 17, 2004 3:13 am

As long as the new caps are rated for higher voltage you're fine. These voltage ratings are the same values that we all have used and rave about; you'll be very happy with the sound after the caps break in.
You'll want to change all the caps. The originals are cheapo crap and as long as you're going as far as changing some, there's no point in not changing them all -- your tone will only improve!
FWIW a guy over at PlexiPalace changed all the box caps/white polyester caps out of his MV amp (a late 70's JMP or early JCM800, can't remember which) and really thought that amp came to life with smoother ballsier sound.

Guest · Post by **Guest** » Sat Jul 17, 2004 10:33 am

Thanks Flames, Ill definately take your suggestion.
Do you have any suggestion as far as how to get a bit more grindy gain from this amp(superlead). Its almost getting the amount of gain Ide like to hear.
The style of music I play is extreme metal but the tone Im after is something more in the way of a early/mid era Judas Priest to Randy Rhoads tone.
Right now my amp sounds a bit woofy, even without jumping channels. Ide like to get my tone controls a great deal more responsive without getting too radical from the original circuit.
Keep in mind that I have a JCM800 era Super Lead that has one of those floating boards that is held in place by the volume/tone pots and input jacks. I dont want to get a P2P board for it because I do not want to drill holes in the chassis to hold its potential resale value if I ever decide to sell it.
Thanks in advance for any suggestions guys, you all are a great help.

Necrovore · Post by **Necrovore** » Sat Jul 17, 2004 10:38 am

Soory above post was mine

Flames1950 · Post by **Flames1950** » Sat Jul 17, 2004 11:08 am

The common way to add gain (as a starting point) is to add another .68uF cap across V2a's cathode resistor, which bumps your gain up in the upper nids and highs. Earlier amps had this, but it got phased out around the time a feedback loop change was made. May also help counteract the woofiness, but that may also have to do with speaker choice. What speakers were you running? Tube choice could affect this as well; making feedback loop adjustments may help too.

Guest · Post by **Guest** » Sat Jul 17, 2004 9:49 pm

Im using Celestion 65 watt speakers that were stock in the anniversary white cabinets. not sure what model as I haven't taken the back off in some time. Tubes Im using JJ El34L's as well as JJ ecc83s'

Ok when you mention the .68uf cap across V2a's cathode resistor, you are talking on V2's tube socket? Please bear with me as I am still green.

How does one make feedback loop adjustments? Where in the circuit would I see this on the schematic?

5150loveeddie · Post by **5150loveeddie** » Sat Jul 17, 2004 11:01 pm

Should try those 30watts Celestion (the heavy duty Greenbacks.....) as they are great Rock and Roll speakers, unless you can find yourseft some pre-Rola Greenbacks in good condition. But be ready to pay lots of do for those............JF

Flames1950 · Post by **Flames1950** » Sun Jul 18, 2004 9:50 am

Ok when you mention the .68uf cap across V2a's cathode resistor, you are talking on V2's tube socket? Please bear with me as I am still green.

How does one make feedback loop adjustments? Where in the circuit would I see this on the schematic?

No, the V2a's cathode resistor will be on the board, you'll just tack the cap across it. I don't have a pic of a board made that late, although I can doctor up some directions from a pic of a late-70's board I've got here if it will help.
Changing the feedback resistor (probably a 100K on your amp) could help tighten up the feel some, you can just add another 100
k across it to increase the feedback stabilizing your power amp section. Changing the tap on the impedance selector that the feedback comes from can also get you more feedback (it's usually a purple wire goin to the back of the selector.) Adding feedback reduces the power amp's gain some and may make the .68uF cap above a must to keep the overall gain up.
Lemme know if pics of my earlier board would help, or if you can post pics of your board I can draw in where you want to be looking. I'll look for a schematic to know what the parts would be labelled on your board as well.

Country Boy Shane · Post by **Country Boy Shane** » Sun Jul 18, 2004 11:59 am

Lego's are meant to build kiddie space stations in a fancy box-set

Believe the hoopla when we say that SoZo's are absolutely out of this world. Once they start to break in, they just sound better and better everyday!

Necrovore · Post by **Necrovore** » Sun Jul 18, 2004 1:02 pm

Right now Im using the poweramp/PSU section of the schematic on the upper half of page 218 in the Marshall History book. I also have been told to use the SLP schematic and at times use the schematic from '70. Sort of confusing as it seems like the 800 series Super Leads were an "in-between" evolution of the amp when talking documentation. I will try to take some not so fuzzy closeups of the board in the next few days. As far as the layout of the board is concerned, it is set up like the R1-whatever; C1 -whatever style instead of how the old P2P boards are set up(everything goes from left to right instead of how they appear in sections in the circuit like on older boards)

Flames1950 · Post by **Flames1950** » Sun Jul 18, 2004 4:21 pm

I guess I would stick with the schematics in the Doyle book. I'm looking at the power amp schem on 218, and the 1987 preamp schem on 219 (should be identical as yours, same PCB.)
On the power amp schem (and hopefully the board) the feedback resistor is the 100K at R24. You'd solder another 100K across it (for a total of 50K resistance) if you want to try more feedback to tighten things up.
On the preamp schem the cathode resistor for V2a is R12, an 820 ohm. That's the one you would solder a .68uF cap across.
The SLP was based off a specific amp they copied, I don't think I would rely on the values on that schematic as an example.

Necrovore · Post by **Necrovore** » Thu Sep 16, 2004 10:10 pm

Bringing this topic back up. Flames thanks again for your help. Somewhere during this topics initial life I emailed Marshall for the actual schematic for the JCM800 Super Lead. If anyone needs a copy pm me and I will email it to you.

I am sending off for th Sozo caps tonight. My fretsaw that I wanted will have to wait. I wanted to know a bit about burning the caps in. I understand that they need about 100 hours to properly form but does this include playing time or can I just turn the amp on at night and let it run overnight. If I can let it run all night I am assuming that this is power on/standby off or on?

Flames I will take your advice on changing out all the caps. I want to do the main lego style caps first. And while I am doing this I guess changing out the 5%+/- resistors to 1%+/- wouldnt hurt either.

Flames1950 · Post by **Flames1950** » Thu Sep 16, 2004 10:45 pm

I think Gnugear said that you could burn them in by taking out your power tubes and letting the amp run for a few hours at a time.
I also think you'll be very happy with the sound of the new caps after you've broken them in. I re-capped my original JMP printed circuit board with SoZo's, converting it to the non-master Lead circuit, and tried it out back in the '78 head. It sounded KILLER, honestly as good as the PTP conversion sounded.
I actually made a mistake putting the board together and put in an extra 10K resistor in the preamp B+ line (50 watt amps should just have a link in that spot on the board ,I assume due to the JMP's already decreasing plate voltages.) Sounded great, so I left it in.

Necrovore · Post by **Necrovore** » Fri Sep 17, 2004 6:30 pm

My only fear right now is that I wont have enough room to put the Sozo's in. I know how to get around this (standing the caps). I have seen the PCB's in the JMP's and they are usually way way larger than the pcb Im working with.

Flames1950 · Post by **Flames1950** » Fri Sep 17, 2004 11:30 pm

I don't think the JMP's really have as much room as you're giving them credit for. On most of the caps I had to bend the leads straight down at the ends, then under the cap, then bend down again to fit in the PCB holes, all so that they could stay as tight to the board as possible. I don't like the thought of them standing up where they could vibrate, and if you're careful bending the leads under the cap you can get them down nice and reasonably tight. I didn't think to take pics because I figured I'd be branded a heretic for life for putting the PCB back in the amp (it was sitting on the bench crying to me....) but if I have it open again soon I can snap a shot, it came out very clean.