C+ is giving me problems..anyone??

[Stonge]

well today I fired my C+ up like I would any other time I play, except this time when I turnd it on...Almost all of the gain was gone on the lead channel.
I changed several preamp tubes to try and troubleshoot the problem. I have Mullards in there now, so they are very old tubes and probably were going to need to be changed someday. Anyways, I put basically brand new tubes in there that I originally bought for my Stiletto and the gain came back..just very weak, and I know mullards make a huge difference than the JJ gold pins/russian2s but even so, the gain should be smooth still. My gain is not smooth and it sounds very honky; like when a patch cable is shorting out on your guitar.(it's not the cable). I was wondering if anyone had any suggestions as to what may be causing this pproblem I am having. I know the previous owner had a couple caps already changed, but there are some original caps still in there. This thing just celebrated its 24th birthday and I am thinking that maybe some of the old caps that are left possibly need to be replaced. Does this sound like the problem? Thanks in advanced to all who respond. BTW the clean channel is still flawless and perfect. LDRs maybe??

 

[Blueracer]

There are a couple of things you can try to isolate the problem. To see if it is a tube problem swap V1 and V2 with V3 and V4. Note that V1 is the preamp tube closest to the guitar input, V2 is next closest and so on. V1 through V4 are all closest to the front of the amp. V1 and V2 should be good since your clean channel works. V3 and V4 are for the lead channel and the reverb. After trying the swap first try your clean channel. If it is good then your tubes should be fine. Just to make sure you still are having a problem try the lead channel. If the clean channel is fine you probably still have an issue with the lead channel.

If the clean channel is not good after the swap then it is a tube. Swap each tube back one pair at a time until you find the bad tube.

If it isn't one of the tubes then it could be one of the LDRs. If you are using a foot switch to change channels disconnect it and try changing channels with the lead pull. This is a bit of a long shot but worth a try. If this fixes the lead channel then there is a simple fix for the foot switch that involves changing a resitor.

Try these things and post back your results. We can go from there.

 

[Stonge]

well, I have definately tried all the tubes and that didnt really help much. The gain came back, but like I said before it was really weak and not smooth like the amp is known for.
Also, I have been trying to switch the channels without the footswitch by the pull lead and it is still the same, no result.
This really bums me out.

 

[Elpelotero]

I know you said you changed the tubes, but is that only the pre's or power as well? Also, going from prior experience with someone else on this board, it may be a screen grid resistor.

 

[phyrexia]

It has a loop, right? Did you check the loop jacks?

 

[Stonge]

come to think of it, it is reacting like a dirty effects loops kinda. Honestly, I haven't used the loop in months. I am not a pedal person..maybe dust has built up in there. I did not change the power amp tubes. I have some old siemens that I have been using for years. They tessted good on the tube tester. If it is the power tubes..It's those cheap *** Mesa 440s..I hate these things. It seems like I replace these in all my amps every 6months. If it is the screen grid resisters, I am pretty sure I can get that done by my friend. But I don't really want to go around changing ****, if it's not the problem ya know?? I am calling Mike on mon.

 

[JOEY B.]

I had an issue a while back with the lead channel of my '84 C+. It seemed like there was an issue with the Lead Master pot. When I had the Master on 4-5 and the Lead Master below 2, the sound was awful. When the Lead Master was turned above 2, everything sounded normal. I cleaned the pot, and thought that I had fixed it. But after a while it was back, with a fury. All the while the clean channel sounded fine. After a bunch of head scratching and cussing, I started swapping preamp tubes. I started with V3 and V4 because they are responsible for the lead channel. No luck :evil: . I then backed up to V2 and hit the jackpot. The GT-12AX7M was faulty, I guess. I had it happen again with a Tungsram 12AX7 after some experimenting. Changed the V2, and the problem was gone. I can't explain it, but I know where to look if this problem arises again.

Good luck!

 

[Stonge]

yeah I thought I had the gain back to normal after constant tube swapping..and I mean i completely retubed the amp. And boom back to fucking up. I honestly can't figure it out, and I really can't afford to send it to boogie right now. This really sucks right now. So...boogiebabies??? Where are you?? any suggestions before I call Mike??

 

[acorkos]

did you clean the effects loop jacks? try plugging in a guitar cable connecting the send to the return, and see if that helps. if not, at least you've ruled out the loop jacks as a possible problem

 

[Boogiebabies]

How is the V5 and does the reverb have the 1 wire mod ?

 

[Stonge]

I am not sure what the 1 wire mod is. It's an all original C+ except for the tube sockets that I had boogie replace about a year ago. V5 seems to be fine. I jammed out of it yesterday..I managed to get the gain back. But as soon as I changed the channels (manually by pulling the knob) and then went back to the lead, the gain was gone again. So I think it is either the knob or the LDRs maybe. I am going to mess with it more after work today. I tested all the tubes I pulled from the amp and all the "new" ones too. Every tube I have tested awesome.

 

[Blueracer]

Here is something else you can check. You will need a volt meter to do this. In the foot switch connection plug in a guitar cord. With the lead pull in the lead position measure the voltage of the guitar cord that is in the foot switch. One lead to the tip the other lead to the body. It should read about 12 to 13 volts. Now push in the lead pull to select the clean channel. The voltage should go to 0 volts. This is the voltage that controls the LDRs for selecting the lead or clean channels. If the voltage is significantly lower than 12 volts this would be a problem.

 

[Stonge]

after testing the amp as well as I possibly can; seeing as I am not an electronics buff. I have narrowed it down to the possibles:

-Abolutely no gain when footswitch is plugged in.
-gain is squirrelly when just switching manually.
-when gain drops out, it is not coming back until there is a complete power down.
-tested and switch ALL tubes. Power/pre
-switched ALL cables.

Please, please..if anyone can possibly come up w/ solutions before I have to send it to boogie; it is greatly appreciated. I don't want to send it if it ends up being a Pot or a simple Resistor swap. I am pretty sure it is not the pot though. Thank you all very much for your time.

 

[Blueracer]

-Abolutely no gain when footswitch is plugged in.
-gain is squirrelly when just switching manually.

These two items suggest that the contol voltage to your LDRs could be low. I gave you a procedure to check this in the post above your last post (two up unless someone gets a post in before me). If you don't have a volt meter borrow or buy one. If what I am suggesting isn't clear let me know and I can clarify. There is also the possiblility that one or more of your LDRs is faulty. This is not difficult to check but does require you to remove the chassis and jumper across the LDR with some clip leads. The question really is do you feel or even want to go this far with this. I can help you with this if you are willing. Check this thread out on the 2:90 I helped Stuart out with.

http://forum.grailtone.com/viewtopic.php?p=52508&highlight=#52508

As you will note there probably is not a single magic post that will solve this for you. Trouble shooting electronics is a divide and conquor strategy in which you try something and follow it if it tells you something about the fault or eliminate it if it doesn't. This is particularly true trying to do this from posting on a forum.