Trouble with my Caliber 50, any suggestions or similar exp?

[ke2]

I fired up the amp yesterday, and found a strange sound on the clean channel.


When plucking a string gently, the sound is clean (which it should be, the Caliber has a nice clean-sound with the preamp gain knob on 2-3)

However, when I strum a chord, I get some sort of distortion (not the nice kind). I even turned the volume down on the guitar, to get even less signal to the preamp section.

-The Calibers have an issue with the return jack of the fx loop, so I cleaned it with Contact cleaner, but no difference.

-I changed the output tubes to another pair I have lying around, but no difference.

-I changed a couple of preamp tubes, still the same (v1 and v2 were changed)

-I ran a Pod into the FX return, and it seemed to distort then as well. (So it seems like the problem isn`t in the first preamp tubes)

-I`m thinking PI tube, output transformer...? I`ll swap the PI when I get home from work today.
Does anyone have any other suggestions?

It`s not the mild overdrive you get from running the clean channel a little hot, this isn`t a nice overdrive.

 

[glpg80]

if it were an ohm issue mismatch with a transformer you would notice the OT being extremely hot to the touch. you would also hear the differences on the output, its not something thats immediate like you are describing.

OT issue would sound unpleasant but not note-sensitve to the point of distored crackling persay. it is more of a drift-type of volume decrease with lots of heat involved in shaping your tone differently.

if you have kept your ohm settings set correct or didnt recently install the OT, then there is no reason to believe its the OT or the OT is deffective.

you said you changed the P tubes? wierd dude.

it almost sounds like your bias has shifted drastically. but from what i hear all mesa's are fixed bias. thats what it sounds like to me. i'd say its either that, or you have a cold solder joint but it sounds more like a bias problem. i looked at a hand-drawn schematic and there isnt really anything complicated past that point - just the bare necessities. nothing that really stood out to catch my eye.

is it only a certain note? or all notes? what about the volume you are playing at? is it only at extremely low volumes or all volumes and amplified if turned up?

if it is only a certain note, you can almost guarantee its a cold solder somwhere since that is considered an intermident problem. best way to catch them is to go pencil tapping but its a but early to even be thinking about mentioning something like that.

hmm...im gonna think on this one.......

 

[ke2]

Thanks for reply

I`m using the same cab as always, (8 ohms), so I don`t think it is an ohms mismatch.

The OT is the original.

It is at any volume. When running the OD channel, there`s a lot of other noise so it`s difficult to say how much it is affected.
Clean channel, preamp at 2-3, and master at 2, shoud be fairly loud and clean, but it`s not, it happens at any volume

It`s not a particular note, it happens on finger picking and strumming all over the fretboard.

 

[glpg80]

from looking at the schems for it, its not the reverb circuit.

the effects loop is series and looks like the common easy fix but you said you cleaned both send/return and its still doing it. the next problem i see that could be to blame is the 280k volume pot.

you can try turning the volume pot clock-to-clock with the amplifier off and seeing if that is the issue. could be a dirty pot.

after that, it goes to the variable EQ, then finally to the power supply.

when was the last time you moved any of the 50k sliders? does it do it with the EQ out?

 

[ke2]

from looking at the schems for it, its not the reverb circuit.

the effects loop is series and looks like the common easy fix but you said you cleaned both send/return and its still doing it. the next problem i see that could be to blame is the 280k volume pot.

you can try turning the volume pot clock-to-clock with the amplifier off and seeing if that is the issue. could be a dirty pot.

after that, it goes to the variable EQ, then finally to the power supply.

when was the last time you moved any of the 50k sliders? does it do it with the EQ out?

Yes, EQ in or out makes no difference. I also ran a patch cable between send and return to see if the problem was there.

I cleaned the pots not too long ago, so I don`t really think so (Lots of contact cleaner, turned the pots from 1-10 several times etc...)

Could it be something as simple as a bad PI tube? I`m at work now, so I can`t check it, but I`ll try it out when I get home. Some of the symptoms of a bad tube sounded similar to what I`m experiencing.

 

[glpg80]

i was under the assumption you already checked all the tubes pre and post?

yeah of course. it could be anything from V3 onward, the reverb tank/circuit/tube and V2 and V1 are not at blame here as the effects loop is after all of these.

i would definately check the PI tube if you havent done so. i thought you already checked them all as well as the power tubes

my bad dude. yes - next thing i would check then is the PI tube. check it with a pencil and tap it when you get home. if it rings like a bell instead of a "thud" then its microphonic and drifted gassy which could be causing some of the issues you are hearing with internal electrons leaking across the grids or off of the plates from the vacume change.

 

[ke2]

i was under the assumption you already checked all the tubes pre and post?

yeah of course. it could be anything from V3 onward, the reverb tank/circuit/tube and V2 and V1 are not at blame here as the effects loop is after all of these.

i would definately check the PI tube if you havent done so. i thought you already checked them all as well as the power tubes

my bad dude. yes - next thing i would check then is the PI tube. check it with a pencil and tap it when you get home. if it rings like a bell instead of a "thud" then its microphonic and drifted gassy which could be causing some of the issues you are hearing with internal electrons leaking across the grids or off of the plates from the vacume change.

Aaah, sorry to waste yout time, man!!
I tried v1 and v2, but the little one was going to bed, so I had to keep it quiet after that.

Thanks for your help!!

 

[duesentrieb]

Besides the tubes (you know thats obvious in a tube amp) it could be either a capacitor or - as often in Boogies - a VTL (VTLs are switching channels, when they go south you either have no channel switching at all, or they simply start to f*ck with the sound before they quit their job completely)

I will look for a schem and come back, Knut . . .

 

[duesentrieb]

Are you familiar to use a multimeter, Knut?

here are the schems:
http://www.tubefreak.com/schema.htm#cal

 

[ke2]

Are you familiar to use a multimeter, Knut?

here are the schems:
http://www.tubefreak.com/schema.htm#cal

I have a multimeter, but I`ve mostly just measured the resistance in my cab, and the battery power wire of Ask`s toy car

Edit:
Olaf, would the switching relay(??) affect the sound of something running directly into the power amp (or at least the fx return) I`m thinking that the PI is after the fx return. It looks like it on the schem. If the VTL was the culprit, I should experience a fairly nice clean sound with a pod set to jazz chorus into the return, right?

 

[duesentrieb]

Your POD into return (if PI tube is healthy) indicates it's the poweramp, which can be a lot of things - powertubes, caps, resisitors, OT, . . .

Pull the powertubes and set your DMM to 1000 V DC.
Then make a chart for all PINs (black to chassis, red into the PIN) and post that here. Between 1 and 8 is that little cutout. Clockwise from it: 1,2,3,4,5,6,7,8

 

[duesentrieb]

You can read those from the top - no need to take it out of the chassis, Knut. It is safe, don't worry . . .

 

[ke2]

Your POD into return (if PI tube is healthy) indicates it's the poweramp, which can be a lot of things - powertubes, caps, resisitors, OT, . . .

Pull the powertubes and set your DMM to 1000 V DC.
Then make a chart for all PINs (black to chassis, red into the PIN) and post that here. Between 1 and 8 is that little cutout. Clockwise from it: 1,2,3,4,5,6,7,8

Thanks, Olaf

Just to see if I got this correct:

Pull 6L6s
Turn amp on? Standby or ON?
Measure with the red "pen" of the MM into each of the points in the tube socket, while the black "pen" is somewhere on the chassis?


Could I kill myself while doing this?

 

[duesentrieb]

Don't worry, vikings can handle a lot

Pull tubes
switch amp is if it is "playing"
black probe somewhere to a blank part of the chassis
red into the pins, ask your wife to write down the readings, then its a 3 minute job.

 

[ke2]

Don't worry, vikings can handle a lot

Pull tubes
switch amp is if it is "playing"
black probe somewhere to a blank part of the chassis
red into the pins, ask your wife to write down the readings, then its a 3 minute job.

Because as long as there`s no instrument connected, I won`t blow anything by running the amp without a load? I trust you Olaf, I just want to know that I understand correctly

 

[glpg80]

may i chime in and say, there is a VTL labeled "LDR4" that is located after the effects loop of the preamp circuit.

i wouldnt have thought those switches/relays could cause interference with the sound, i figured if one would go - it would go.

i have a better schematic for both of you to use, here is a direct link:

http://acapella.harmony-central.com/att ... 1240757619

a chart of the voltages would be helpful most definately.

yes, pull all the powertubes and dont worry about a load on the OT: turn the amplifier completely on (stanby is not activated - full playing on). go pin-to-pin from 1 to 8 and post the voltages here. as olaf said, with the "V" of the socket pointing upward and away from you looking from the bottom of the chassis you need to go clockwise 1, 2, 3, etc. and that will get what he needs

 

[ke2]

may i chime in and say, there is a VTL labeled "LDR4" that is located after the effects loop of the preamp circuit.

i wouldnt have thought those switches/relays could cause interference with the sound, i figured if one would go - it would go.

i have a better schematic for both of you to use, here is a direct link:

http://acapella.harmony-central.com/att ... 1240757619

a chart of the voltages would be helpful most definately.

yes, pull all the powertubes and dont worry about a load on the OT: turn the amplifier completely on (stanby is not activated - full playing on). go pin-to-pin from 1 to 8 and post the voltages here. as olaf said, with the "V" of the socket pointing upward and away from you looking from the bottom of the chassis you need to go clockwise 1, 2, 3, etc. and that will get what he needs

Thanks again, man!

It seems that this might be the EL84 version, since there are 4 power tubes, but the preamp section might be the same, right?

 

[glpg80]

yes i posted that schematic for the preamp to be read a little more clearly.

dont go by that poweramp drawing. your 50 watter runs two valves with their own grids so of course they are different from that preamp circuit-onward.

if you dont want to use that PDF you dont have to , just alot easier to read that part of the schematic than the hand-drawn sketch stuff.

 

[ke2]

yes i posted that schematic for the preamp to be read a little more clearly.

dont go by that poweramp drawing. your 50 watter runs two valves with their own grids so of course they are different from that preamp circuit-onward.

if you dont want to use that PDF you dont have to, just alot easier to read that part of the schematic than the hand-drawn sketch stuff.

Most definitely!
I can`t imagine why they let the person with the worst handwriting in the company to draw the schem

 

[glpg80]

yes i posted that schematic for the preamp to be read a little more clearly.

dont go by that poweramp drawing. your 50 watter runs two valves with their own grids so of course they are different from that preamp circuit-onward.

if you dont want to use that PDF you dont have to, just alot easier to read that part of the schematic than the hand-drawn sketch stuff.

Most definitely!
I can`t imagine why they let the person with the worst handwriting in the company to draw the schem

i know right?!

early in my engineering degree we were taught to hand draw only with utenciles (sp?), otherwise just use the computer

freehand was a big no-no. at least that will give everyone a clear view of the relays. thats all i posted it for