NEW AMP DAY, PART 2! PROBLEM SOLVED!!!! :) last page.

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guitarslingerans

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FJA Modded 5150II.

It sounds bad ass........but something is wrong with it. Oblivion, I sent you a PM. I'm not sure what, but it was working fine for about 10-15 minutes, then suddenly the volume dropped, like almost to half. Basically, I had to turn it up to 5 to equal the regular 5150 I have on 3, when just before, I had it on 3 as well and it was fine. Jerry, any ideas? Anyone else?


Please help me out.


-Ans-
 
More preamp or power tubes?


BTW, I'm going to the post office tomorrow to send you some.
 
You think it's the V1 slot that's messed up? I think I have an extra tungsol to chunk in there.


Let me go try it.

-Ans-
 
Have you tried spraying some contact cleaner in the effect loop? That's always a problem on 5150's, and always causes volume drops.
 
No I haven't, I would assume that isn't what it is though, just because of how it happened, but I guess anything is possible. Hmm.

-Ans-
 
2 things I can think of that are worth trying.

1. Are they jj 6l6 tubes if so pull them out and put them back in. I had the newer jj's in mine and they kept wiggling loose. Something about the pin sizes with them.

2. put a straight cable from the loop out to the loop in with out anything else in there and see if that makes a difference.
 
Tried all the suggestions so far, no change.

:(

-Ans-
 
Did you plug a cable in and out of the effect jacks after you sprayed the cleaner inside?
 
:|::QBB:
strungup":ce61f said:
2 things I can think of that are worth trying.

1. Are they jj 6l6 tubes if so pull them out and put them back in. I had the newer jj's in mine and they kept wiggling loose. Something about the pin sizes with them.

2. put a straight cable from the loop out to the loop in with out anything else in there and see if that makes a difference.
Click to expand...

JerryP has mentioned several times that the 5150 has problems with the JJ tubes fitting inside, but nobody ever seems to listen to him. :doh:
 
:|::QBB:
Megadeth7684":5541e said:
:|::QBB:

JerryP has mentioned several times that the 5150 has problems with the JJ tubes fitting inside, but nobody ever seems to listen to him. :doh:
Click to expand...

the 5150 I had came with them. The problem sucked.
 
Well I took them out and stuck them back in, no change. I took all the preamp tubes out and reseated them, no change. I took a cable and ran out of the FX into the FX and there was no change, and I replaced V1 and there has been no change. I don't have any contact cleaner here, so I guess I'll wait for Jerry or Oblivion to respond and give me some suggestions. :( This sucks though, it was sounding bad ass before it messed up.

-Ans-
 
Jerry has mentioned that there's a large blue resistor inside that tends to mess things up sometimes. Mine was like that (not soldered in) but it wasn't a fix. You might wanna check that too.
 
Do you know how to measure the bias test points on that amp? See if both sides are about the same. Try some different tubes if you have some around. I'd guess a tube couldn't handle the vibrations of shipping. Hard to really do anything but guess without the amp in front of me. If you can check the bias shoot me an email with the results.
Jerry
 
How do I go about measuring the bias? I've never done it before, so could you guide me through how to do so?

Thanks in advance,

-Ansley-
 
Dude fucking shit man! I just got home from my girlfriend's place and I got your message.
I sent you a PM with some suggestions. I don't know what to tell you. I've got a spare set of JJ 6L6 tubes on my desk right now and I'll send them out to you if that's what you need. Make sure the bias hasn't drifted into a too hot setting and cooked a tube. When it left my place it was set for 74 mA a side (37 mA/tube) and it was sounding pretty good.
The JJ's that people complain about are some of the newer ones because they changed the thickness of their pins. Doug assured me that these are old stock JJ's that he ordered a long time ago before they changed the pin thickness, so there shouldn't be any problem with that.

You might want to shoot Jerry an email and see if he has any suggestions for you. Keep me up to speed on what's going on and let me know if I can do anything to help.
Really sorry about this man.
 
I'm gonna need like a list of stuff to get so that I can check the bias and rebias the amp when I get hoem tomorrow if it's needed.

I'm assuming that since I inserted a cable into the FX loop in/out and there was no change that the problem if after the pre-amp, right? Or is that not a safe assumtion?

-Ans-
 
What you do is fire up your multimeter and click over to DC volts.
Turn all the knobs on the amp to 0 and unplug the guitar cord from the amp input.
Put it on Standby and let it warm up for a few minutes.
Unscrew the rear grill and look for the bias adjustment pot on the left side of the amp (left when you're standing behind it).
You'll see a black socket and two red sockets in the back of the amp - those are the test points you use to check the bias.
Take it off of Standby.
Plug the black probe into the black socket and the red probe into one of the red sockets.
You should be getting a reading of 72-74 mA.
That is the combined reading for two of the tubes on one side.
This means that I set each tube to idle at 36-37 mA.
If it's not where I left it, try adjusting the bias knob so that the reading on the Multimeter changes.
Pull the red probe out and put it in to the other red socket.
You should see that the numbers are already either the same or at most one or two numbers off.

That's all there is to it.
 
You can get a multimeter at Radio Shack for 25 or 35 dollars. That's all you need to do the job.
 
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