Problem with normal channel cutting out on Bluesbreaker?

McGoogle McDougal · Post by **McGoogle McDougal** » Mon Feb 21, 2005 12:54 pm

I've been in the process of getting my Bluesbreaker broken in and have developed a problem in the normal channel. When I play the amp at about 6 or higher on the volume and hit any of the low strings the amp makes a sound like it is cutting out. It seems to take a few minutes before it starts. I seem to be able to play the bright channel all the way up without the amp doing this. I can't tell if this means it is just a problem with circuitry/wiring specific to the normal channel, or it is maybe caused by vibration and the bright channel doesn't produce enough bass to make it happen.

I tried swapping out the preamp tubes one by one with a known good one from another amp and the problem did not go away. I inspected (and tested continuity with my meter) all of the wiring from the normal channel up through to the mixer resistors and found no problem.

The fact that it seems to take a few minutes to occur after starting up the amp cold makes me think that it's a connection that gets iffy once it gets heated up. This makes me wonder if it's a problem with one of the tube sockets (maybe the normal channel side of the V1 socket?). I didn't notice anything weird while watching the tubes when I was playing.

I'm trying to figure out what my next step should be - maybe fire the amp up on the bench (let it warm up for a few) and try the chopstick/pencil method to test out all the connections and the terminals of the preamp sockets? Any ideas?

Eamon

Flames1950 · Post by **Flames1950** » Mon Feb 21, 2005 3:02 pm

If you think there's a possibility of heat and vibration causing the problem together nyour idea of bench testing with the chopstick may be a good start. Run some kind of signal into the Normal channel and have at it. Is it a total cut out of sound or just a drop in volume?

Guest · Post by **Guest** » Mon Feb 21, 2005 4:30 pm

Hi Flames,
It sounds a little like when a guitar cord is bad, if you know what I mean. It's kind of an ugly stuttering distortion. Like I said, I can only get it to do it on the normal channel (don't know if that's just because maybe the bright channel doesn't produce enough bass to make a big enough vibration to make it happen). If it really is exclusive to the normal channel then there can't be many things responsible for it.

I was reading R.G. Keen's tube amp debugging page and found this under the section for "ugly sounding distortion":
"Sound cuts out or squawks on loud notes"

One of the things he says could cause this is a failing coupling capacitor (on a preamp of output tube). Since it only seems to happen on the normal channel, then I suppose it could be the first to second stage coupling cap for the normal channel. I ought to be able to test this with my meter, right? Correct me if my thinking is wrong here, but if this cap is leaking then I ought to see voltage on pin 2 of V1, right?

thanks,
Eamon

McGoogle McDougal · Post by **McGoogle McDougal** » Mon Feb 21, 2005 4:33 pm

Oops, that last "guest" was me, thought I was logged in...

Eamon

Flames1950 · Post by **Flames1950** » Mon Feb 21, 2005 5:10 pm

One of the things he says could cause this is a failing coupling capacitor (on a preamp of output tube). Since it only seems to happen on the normal channel, then I suppose it could be the first to second stage coupling cap for the normal channel. I ought to be able to test this with my meter, right? Correct me if my thinking is wrong here, but if this cap is leaking then I ought to see voltage on pin 2 of V1, right?

It's a possibility, I'd have thought your caps were fresh enough not to die yet but maybe there's an occasional dud in the batch. You shouldn't see voltage on the grid, at least not much. Or you could swap the two coupling caps in the first stage and see if your problem moves too.
Dead couplers usually sound like a blown speaker to me, a lot of fizz on the signal peaks and a general lack of volume. I'll confess I've never heard a bad one in a guitar amp, only in my 1930's tube radios.

McGoogle McDougal · Post by **McGoogle McDougal** » Mon Feb 21, 2005 5:29 pm

Yeah, I agree that a bad cap seems very unlikely, as they're new. I'll double check with the meter to be sure. The fact that it doesn't seem to happen until the amps been on and played through for a few minutes makes me think it might be a bad connection that occurs once it gets hot enough. Seems to me like the most likely place would be at the V1 socket... Maybe the socket got messed up (inside where it's not too visible?) when I desoldered the old wires and then wired up the new board.

thanks,
Eamon

Flames1950 · Post by **Flames1950** » Mon Feb 21, 2005 9:19 pm

Does it make the noise whether you're playing or not? If it makes it no matter what you could let it heat up then get some of that icy-spray stuff at the electronics store and see what stops the noise when it gets cool.

McGoogle McDougal · Post by **McGoogle McDougal** » Mon Feb 21, 2005 10:35 pm

No, it only happens when I push the normal channel hard - like hit a low "E" string hard with the amp volume about 6 or higher. That's what makes me think it's a combination of heat and vibration. I suppose once I put the amp on the bench and fire it up it's not going to experience vibration like it does in the combo cab...

Eamon

Dax · Post by **Dax** » Wed Feb 23, 2005 1:46 am

I had the same noise and it was bad filter caps. Just a thought.

dirtydeeds22 · Post by **dirtydeeds22** » Wed Feb 23, 2005 6:47 pm

I had a similar problem a few months ago. play for a few minutes then get the sputtering in and out sound. for me it was the treble pot. I had an extra one and replaced it. No more cutting in and out. Try checking your pots, they may need to be cleaned.

Jeff

McGoogle McDougal · Post by **McGoogle McDougal** » Fri Feb 25, 2005 3:20 am

Well I put the chassis on the bench, cleaned all the pots and jacks, fired it up and cranked away for a while. I played the normal channel with the volume up in the 7-10 range for almost 20 minutes. No problems at all (also tried the bright channel and it was OK).

So, I put it back in the combo cab, made sure it was securely tightened down, and fired it up again. Right away it started stuttering and cutting out again. I don't have retainers on my preamp tubes and thought maybe it's vibration there causing the problem. I grabbed some retainers off another amp and tried it - nope, same problem still.

When I had the chassis on the bench I poked around with a pencil while strumming a low "E" note trying to find signs of a loose connection, but it was quiet everywhere. I'm baffled... Maybe this chassis doesn't want to be a combo anymore!

Eamon

Flames1950 · Post by **Flames1950** » Fri Feb 25, 2005 8:28 am

Do these combos use anything like rubber washers or something to try and isolate the chassis from some amount of vibration, or just let 'em shake?
What about input jack contacts? Would they need to be cleaned or re-tensioned? Vibration may be shaking the actual input jack contacts on the Normal channel.

McGoogle McDougal · Post by **McGoogle McDougal** » Fri Feb 25, 2005 7:32 pm

Nope, no rubber between the the cab and the chassis mounting board. I'll take another look to see if there is anything that seems loose on the input jack or anywhere else (output tube sockets, speaker jack, transformers, choke, etc). It sure does seem like it must be vibration related....

I wonder if the KT66's can't take the vibration. Anyone every had a vibration problem that was tube specific?

Eamon

Flames1950 · Post by **Flames1950** » Fri Feb 25, 2005 9:40 pm

McGoogle McDougal wrote:Nope, no rubber between the the cab and the chassis mounting board. I'll take another look to see if there is anything that seems loose on the input jack or anywhere else (output tube sockets, speaker jack, transformers, choke, etc). It sure does seem like it must be vibration related....

I wonder if the KT66's can't take the vibration. Anyone every had a vibration problem that was tube specific?

Eamon

More than just seeing if something's loose I'd try cleaning the jacks themselves, even if all you can do right now is work the cable in and out until you're blue in the face. Actually, bluesbreaker59 (Jason) had a crackling noise problem very similar to yours that was taken care of this way. Wish I'd thought of that sooner to check.

Flames1950 · Post by **Flames1950** » Fri Feb 25, 2005 9:42 pm

Were your KT66's the GT's or Valve Arts? We all know how well the GT's worked out for George's customers in the end.......