Newbie - How do I learn? Please respond.

playwell · Post by **playwell** » Thu Jul 14, 2005 12:29 pm

AWESOME. Thanks HEAPS, cats...

Heaps and heaps of thanks shall be thrust upon your souls for your replies.

Ya know what the biggest freakin' drag of all time is? Radio Shack. Sure they have small stuff, but when you need a big capactior, or anything other than basic stuff for a HAM Radio project - they have NADA. Meaning, 4 or 5 day wait for a Mouser order - brutal. =(

The output tranny on this amp is the original Drake 789-87. This is a BAD tranny?! I've read some guys talking about Merc. Mag. and Heyboer etc etc.

The 2 big blue filter caps (is that what they are?) are labeled L C F and are 50uF a piece. Would replacing those make a difference??

myker · Post by **myker** » Thu Jul 14, 2005 1:30 pm

The output tranny on this amp is the original Drake 789-87. This is a BAD tranny?! I've read some guys talking about Merc. Mag. and Heyboer etc etc.

The 2 big blue filter caps (is that what they are?) are labeled L C F and are 50uF a piece. Would replacing those make a difference??

the drake is a frail sounding OT, they started doing that in the 800 series amplifiers... they have the crunch, but no low end balls whatsoever. id say purchasing a mercury magnetics or oei or heyboer would be a major inprovement. some people say that this is all the 900 series needs is a better output transformer. the heyboer plexi-clones george has might just do the trick. or try used ones on ebay to experiment. the output transformer is the heart of the amplifiers tone.
mike

myker · Post by **myker** » Thu Jul 14, 2005 1:32 pm

upping the first 50x50 cap to 100x100 tightens up the lows a bit. tightens up the whole amp actually. would make a difference.
mike

Billy Batz · Post by **Billy Batz** » Thu Jul 14, 2005 1:39 pm

I agree with Mike. I didnt want to get into that, and my mods are easy and only a few dollars to do, but if your serious, an OT upgrade will greatly improve the tone. The rtrannys marshall has been using the last 20 years are junk. Hell the trannys Marshall used in 68 were junk but junk was different then.

playwell · Post by **playwell** » Thu Jul 14, 2005 1:45 pm

Thank you guys. Your souls will slowly begin to reap the rewards of your kindness. LOL.

Let's say I were to replace this Drake... What type of cost are we talking about here? Is it a direct drop in replacement for the Drake size-wise?

PS - I would not want to buy a "used" OT - would not feel comfy with that.

As for the replacement and install it seems like it would be very straight forward. 4 connections in the back, 5 in the front.

Would the color codes remain the same? In other words, just make note of where the various wires are attached now, pop in the new tranny, and connect back up as normal?

Thank you, kind gentz - this type of info is INVALUABLE to me!!!

myker · Post by **myker** » Thu Jul 14, 2005 5:39 pm

your looking at upwards of 120.00 for a new tranny, and they will not fit into your existing hole. but maybe the guys over at heyboer can make one to fit your hole. the guys at heyboer are super easy to deal with.
otherwise, you can fabricate a metal plate to cover the hole, and drill some holes in it to slip the wires through. that way you can mount anything in there.
do i talk about hole too much???
mike

NY Chief · Post by **NY Chief** » Thu Jul 14, 2005 6:21 pm

myker wrote:do i talk about hole too much???
mike

that's a band, innit?

Billy Batz · Post by **Billy Batz** » Thu Jul 14, 2005 6:27 pm

people dont talk about hole enough

paco · Post by **paco** » Fri Jul 15, 2005 12:25 am

What's the deal with the 220K Bass pot on the SLX? Why didn't they use the standard 1Meg? What would changing it to 1 Meg do?
Also: -the output coupling caps are. 047 not the standard .022.
-the nfb is 27K (I changed to a 100K and removed c13 across it).
-what's with the 91K P.I. plate? (I changed to 100K).
-what's the cap across the 82K P.I.? (c14-mine is now gone).
-P.I. R18-15K (now a 10K) and R19-1K (now a 470).
-What were they thinking with the bias circuit? On the 100W, they put
the second set of tubes 1.5K grid resistors in series after the other set of tubes 1.5K grid resistors. Wouldn't that lower the bias at the second set? No wonder I lost a tube 1 week out of the box! I re-wired mine so that they are all parallel to the 150K bias supply resistors, and changed them from 1.5K to 5.6K.
These changes got rid of that harsh treble and added more of the Marshall "Roar", but now it seems like there's to much pre- gain (is that possisble

). If you turn the 2 pre-gains down to about half, it sounds crappy, no balls. I guess changing the pre plates to 100k would help. Oh yeah! That's another thing! Why is the plate on V2a 27K?

The chips that they use for the dual masters and effects loop can be bypassed with a 1 Meg volume pot, snip at the treble pot(remove R27), and lift c7 from the board (on the side leading from the chip), insert one side of pot to wiper of treble pot, other side to ground, wiper to c7. Probably get more headroom, sound less like a rack pre-amp(ADA), but probably get more noise (I think noise was a problem and they use chip as a buffer, or they are just cheaper than a relay

).
I guess a choke can replace R35.
The transformer is one of them small wimpy ones that the new Marshalls use, yet the blue anniversary 6100 has the same one as the 2203 ( I knew I should have bought that Blue Full Stack instead of the SLX/900 Full Stack

)
Maybe one day I'll take it out of the closet ( it's been in there since 1995

), and experiment some more on it. After all, it's supposed to be a hot rodded/hair metal 2203...come to think about it, I think that suitcase next to it is full of hairspray, spandex, fingerless gloves, wristbands, bandanas, studed leather belts, eyeliner, multicolored shirts with zippers and chineese emblems.

(Closes door and walks away).

Sorry for rambling...
Frank

Billy Batz · Post by **Billy Batz** » Fri Jul 15, 2005 7:23 am

What's the deal with the 220K Bass pot on the SLX? Why didn't they use the standard 1Meg? What would changing it to 1 Meg do?

If its linear then it makes very little difference at most settings. It seesm to only cut some of the really low frequencies.

-what's with the 91K P.I. plate? (I changed to 100K).

Its probably best kept at 91k. Its offset to make sure the pair of tubes match btter. If theres no problem in that aspect then theres no reason to change to 100k. I doubt it will cause any problems either way.

-what's the cap across the 82K P.I.? (c14-mine is now gone).

Hmmm... Value? More info?

-P.I. R18-15K (now a 10K) and R19-1K (now a 470).

What you have done will make the amp thinner and more trebly. In that amp I would probably prefer the thicker darker values they had. Bright amps always increase those values to make the PI thicker and bassier.

-What were they thinking with the bias circuit? On the 100W, they put
the second set of tubes 1.5K grid resistors in series after the other set of tubes 1.5K grid resistors. Wouldn't that lower the bias at the second set?

No. I actually do that myslef.

No wonder I lost a tube 1 week out of the box! I re-wired mine so that they are all parallel to the 150K bias supply resistors, and changed them from 1.5K to 5.6K.

If the 1.5k worked fine in the circuit theres no need to go up to 5.6k. Those resistors you only want to go as high as you need to. Again if it works fine all your loosing is treble but I think its cut and detail you loose but its very subtle.

These changes got rid of that harsh treble and added more of the Marshall "Roar", but now it seems like there's to much pre- gain (is that possisble ). If you turn the 2 pre-gains down to about half, it sounds crappy, no balls. I guess changing the pre plates to 100k would help. Oh yeah! That's another thing! Why is the plate on V2a 27K?

Hmmm... Strange value.

Its weird your mods made a large difference in that amp. I wouldnt think it would. Marshall had a good idea by making an amp with all the mods, they just have absolutely no idea of taste. A stock modded amp doesnt mean diodes and ICs everywhere. Oh well.

paco · Post by **paco** » Fri Jul 15, 2005 3:49 pm

I think back then they had a real hard time finding reliable EL34's, so they messed with the power amp section. I took the 2203 schematic and the DSL/TSL schematic and compared what they used to do, did for the SLX/bad tubes, and then went back to in the DSL/TSL. It looks like they went back to 100K pre plates (mostly), the 82K/100K P.I., the 5.6K bias grids, 1Meg Bass,.....
I think maybe by using all those 220K plates they over did it, and then changed the Bass pot to loose some mud, and used the 27K NFB to tighten it up a bit ( I think the Dsl's use 47K). The 100K NFB probably made the bigest change in the harshness , but now its too distorted/muddy. I'm guessing 100K pre plates will tame it and sound beefier.
It looks like the whole amp was set up like a rack system, tons of pre amp into a tight sounding power section. I guess it should have been a 2203 with an extra tube, but they blew it.

Opps.. wife's yelling got to go........

Billy Batz · Post by **Billy Batz** » Fri Jul 15, 2005 7:11 pm

paco wrote:I think maybe by using all those 220K plates they over did it, and then changed the Bass pot to loose some mud, and used the 27K NFB to tighten it up a bit ( I think the Dsl's use 47K). The 100K NFB probably made the bigest change in the harshness , but now its too distorted/muddy. I'm guessing 100K pre plates will tame it and sound beefier.
It looks like the whole amp was set up like a rack system, tons of pre amp into a tight sounding power section. I guess it should have been a 2203 with an extra tube, but they blew it.

Opps.. wife's yelling got to go........

I thought the only 220k plate was on the first stage? I have little doubt mot of those changes were compensation. Why else would you raise the PI cathode and tail resistor? Thats a compensation tactic. And 27k in an amp like that? Either they wanted a real clean output section or like you say they want to get rid of some flabbyness in the low end. I dont think the 900s are complete garbage like many people but I dont think theyre great amps. Certainly not well designed from a standpoinmt of people who know tone. Looks like you said, a lot of mods squeezed in the preamp then a lot of bandaids to make it work.

playwell · Post by **playwell** » Fri Jul 15, 2005 8:14 pm

BillyBatz - What would you recommend as a real easy mod to smooth out the treble response of my SLX?

I've noticed that the MID adds a LOT of treble.... I find myself needing mid on 2 and treble on 1, with presence on about 4. Above that it just gets REAL high endy/slightly piercy... Thanx.

Also need help with how to bias - I have never done it before and do not want to explode my heart or launch my body 50 feet across the room.