5150 mods... revealed w/ pictures

Dave, tried to email but I'm new here and got a 'don't have permission' message...must be on double secret probation or something. Just wondering if you or anyone thinks the resistor mod would quiet the amp any....play strats about 1/2 the time so didn't want to lose a lot of gain, some would be ok tho as the amp has a ton,
thanks!
 
JeffGT":tirjys7m said:
cool, thanks...which part of the mod do you think lowers the hiss the most?
Click to expand...

If by hiss you mean background noise and not part of the tone itself, my guess is that it would be to make the 39k resistor biasing the cold clipping stage (3rd I believe? someone correct me) smaller. But then it wouldn't really sound much like a 5150 then...
 
I havent tried this with my 5150 yet but my Mark III with extremely hissy/noisy. I swapped the filter caps and now its dead quiet
 
Dave, trying to piggyback 2nd resistor on r9 but there are 2 right next to each other and only looks like 1 on your board....if you have 2, is it the closest or farthest from the 6 pin connection for the ribbon cable?
thanks!
 
ah, so it's to the one farther from the 6 pins, but it can ground to either at the top right?

thanks!!! working on it now
 
Just got it done and fired it up for a bit until the wife came down to the basement and said 'what the f^&* are you doing??!!'....it's a little after midnite and the everyone was in bed I guess :no: I went with a 220k which I guess has less effect that the 120k. I like it but still will never use all the gain in the amp for what I do (I'm old school), so I may try the 120k, or maybe 150k and see if I can get the noise down a bit more. I also clipped the cap for the bass cut on the clean channel...really helps balance the two channels and still plenty of low end on the clean side. So far I am loving the changes and want to thank you a bunch for the help. It's sounding like I'd hoped it would sound way back when I bought it.
 
psychodave":3jdhhcuy said:
Mark said to use silver mica. Ceramic will work though... :rock:

Did you do the resistor mod?
Click to expand...
I tried all the mods and reversed all of them except the 10pf mod. That mod is a must IMO. :rock:
 
How many volts are the 10pf silver micas you guys are using? I've seen 1000, 500, and 300. I got a 500. Should that be good?
 
droptrd":1c3fnzod said:
that will work fine
Click to expand...
Cool thanks. I'm going to give the 10pf mod a try tomorrow. Is there anything I need to know before I do this, safety wise? I've already unplugged the amp. Is it just a matter of popping out the tubes, taking the chasis out, soldering the 10pf on, then putting it all back together?
 
Discharge the big filter caps. Its a good habit to form. Unplug the amp then turn the power switch to ON and the standby switch to PLAY then let the amp sit for a little bit.
 
I finished the mods a few days ago and like them a lot. Instead of the 120k resistor I tried a 220k and liked the sound, but it was still pretty noisy. Dropped it to a 150k and it reduced the noise pretty good and still has plenty of gain. I'd like to try something in between, like a 180k if they make it to see how much noise I get back. That part of the mod really has an effect on the noise floor. Thanks once again to Dave for the help on this.
 
Also just got my 5150 back from my buddy who did the mods Dave listed, and did a bias mod as well. Decided to go with pins 6/7 instead of 7/8, and a 120k for the R9 resistor.

The cleans are great. Like really great. I assume that's the bias mod doing most of that, but they're fantastic now instead of the thin lifeless and semi-distorted cleans that happened with the stock.

Noticeably a darker amp (obviously), but I like amps like that. It's lost a decent amount of the gain, but what's lost I'd rather pick up with a boost anyways.

The fizzy muck top-end is reduced a lot, noise floor seems greatly reduced, and the amp's a lot tighter.

I dig it a lot. It's lost that over-the-top ridiculousness that it had, but for me, the pros now outweigh the cons. :rock:
 
scorpion82":20mu9e51 said:
Can this same mod or one similar be done to the 5150II?? Thanks, Bob
Click to expand...

Assuming the cap mod, it can be done to any amp or any 12AX7 gain stage actually. All it does is increase the floor amount of stray capacitance from grid to cathode, smooths the sound just a hair.
 
You must log in or register to reply here.
Back
Top