sudden change in tone

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Tone1026

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So is a sudden tone change, a major jump in high end, tube related? If so, power tube or preamp tube related. My 2 channel triple has el34 442's and i was unknowingly running it in diode mode at high volumes..
 
Well it actually kind of changes, say if i change channels, then change back sometimes it's better.. sounds good today.. when it changes it doesn't stay that way.
 
This is a guess, but sounds like there is drift on the DC supply, may be related to rectifier tube or drift on the cathode supply. Check for loose pins on the power tubes. It could even be oxidation on the preamp tubes too. How old are the preamp tubes? Something in the chain may be weak.
 
Don't know the history of the tubes. they are spax's so they are not stock, 5u4g, (and el 34 442not stock either) its a 97' 2 channel. There is also popping when swiching channels esp. when vintage to modern.. There is a scorch mark on one of the power tubes, and socket, corresponding to the underside of the socket aswell. That might have been caused by running it in diode mode w/ those el34's in there... not sure... seems thin today, and channel switching didn't change it today..
 
The socket may need replacement.

Popping noises are predominately caused by arcing. What you hear when switching modes is the circuit path is changing which results in the popping noise. That probably normal, I get similar issues with the MarkV when changing power settings, or other switches on the front panel. Actually all of my amps would make some sort of popping sound when swithing signal path that reqonfigures part of the amplifier sections. You should not get that when switching channels. As for the burn mark on the tube, socket, etc... High voltage found a circuit path that had less resistance than the tube itself. Did you install the tubes or were they already installed? Just curious of the burn mark was there or did it just occur.. If the base of the tube has similar marks on it, the residual debris will be carbon based and conductive. You may have to replace the tube socket.

The sockets themselves are inexpensive, replacing one mounted to a circuit board can be tricky, if you do not have the proper tools and experience using them, have it replaced by a tech qualified to service Mesa's.
 
ive got pics of the scorch...but cant upload them, have to get photo bucket or something. looks minor, but what do i know... ;)

they were installed..

i did have an incident when i layed papers on the amp vent and when i switched to bold, my tone oscilated hard.. I shut it down, saw and arc in one of the tubes, not one of the pair with the scorch... possibly related..

marks on the tube match the socket.
 
http://s1303.photobucket.com/user/Tone1026/media/2013-03-31_23-26-36_240_zps62ce12ed.jpg.html?sort=3&o=0#/user/Tone1026/media/2013-03-31_23-26-36_240_zps62ce12ed.jpg.html?sort=3&o=0&_suid=1365468518991013152108395435724

under chasis view, left socket
http://s1303.photobucket.com/user/Tone1026/media/2013-03-31_23-18-40_351_zps91e9c396.jpg.html?sort=3&o=1#/user/Tone1026/media/2013-03-31_23-18-40_351_zps91e9c396.jpg.html?sort=3&o=1&_suid=1365468597780016103868768701207
 
Looks like it might be ok, when you change settings from bold to spongy, or diode to tube rectifiers, it's a good idea to put your amp in standby to be safe.
 
Changes in power will also effect sound. If the voltage drops from the wall sound will change. Depending on the electrical load in your area your power company may be delivering a little less power to your house.
 
ned said:
Changes in power will also effect sound. If the voltage drops from the wall sound will change. Depending on the electrical load in your area your power company may be delivering a little less power to your house.

I have turned off my amp, set everything down untouched, come back two days later and it all sounds different.

I power can affect tone, but time on the amp getting your ears warmed up, or fatigued!

Interesting critter this elusive tone thing.
 
It looks like the arc was jumping pins 3 to 4. Caused by charge build up on the plate. Voltage spike may have originated in the output transformer due to sudden change in DC bias or load. The plates are directly coupled to the transformer, typically it should be center tapped, A/B circuit has A on one side and B on the other, one of the grids is connected close to the center tap potential probably with some windings to offset the bias. For a class A circuit, only half of the primary is used. Not sure if the B tube is operating as a dummy load or not. Arcing can ocurr across the active and or idle tube that is in parallel to it. If the holes in the socket appear clean you may be able to remove the carbon from the ceramic. Electrial parts cleaner or contact cleaner may do the trick, however, do not spray directly onto it. Spray it into a container and use a cotton rag to clean it, that stuff will damage wire insulation, eat your coverings on the amp. Not safe for most soft plastics. fine sand paper (600 grit) may help. Do not use steel wool. You may be better off replacing the socket. At least it is not connected to a PCB like the mark V. If you plan on replacing it, take many more pictures so you have reference as to what wire goes where.
 
bandit2013 said:
It looks like the arc was jumping pins 3 to 4. Caused by charge build up on the plate. Voltage spike may have originated in the output transformer due to sudden change in DC bias or load. The plates are directly coupled to the transformer, typically it should be center tapped, A/B circuit has A on one side and B on the other, one of the grids is connected close to the center tap potential probably with some windings to offset the bias. For a class A circuit, only half of the primary is used. Not sure if the B tube is operating as a dummy load or not. Arcing can ocurr across the active and or idle tube that is in parallel to it. If the holes in the socket appear clean you may be able to remove the carbon from the ceramic. Electrial parts cleaner or contact cleaner may do the trick, however, do not spray directly onto it. Spray it into a container and use a cotton rag to clean it, that stuff will damage wire insulation, eat your coverings on the amp. Not safe for most soft plastics. fine sand paper (600 grit) may help. Do not use steel wool. You may be better off replacing the socket. At least it is not connected to a PCB like the mark V. If you plan on replacing it, take many more pictures so you have reference as to what wire goes where.

I've heard from a couple sources that contact cleaner is good to spray on the pins before inserting new tubes. lightly spray pins only, insert, then reinsert? Should i do that to pre amp, rectifier, and power tubes?
 
The pins on tubes (unless they are gold plated) are plated with nickel. In some cases mfg may use a tin/silver or tin/copper alloy plating on the pins. If the tubes are China made, more than likely the pins are tin alloy than nickel due to ROHS initiative, as well as cost. Nickel plating is not Green or exactly ROHS compliant.

Contact cleaner will only remove carbon and organic compounds and will also disolve plastics of some types. If the pins appear shiney, cleaning is not required. If they are dark dull gray or black, contact cleaner will not clean metal oxides or sulfidation of silver terminals unless the chemical is acidic. If they are nickel, the tend to turn to dark gray due to oxidation, Silver will turn black (caused by sulfidation) and tin gray to white (caused by tin pest). Light abrasion is the only effective way to remove oxide layers. All that matters is the area that mates with the pin in the socket.
 
bandit2013 said:
The pins on tubes (unless they are gold plated) are plated with nickel. In some cases mfg may use a tin/silver or tin/copper alloy plating on the pins. If the tubes are China made, more than likely the pins are tin alloy than nickel due to ROHS initiative, as well as cost. Nickel plating is not Green or exactly ROHS compliant.

Contact cleaner will only remove carbon and organic compounds and will also disolve plastics of some types. If the pins appear shiney, cleaning is not required. If they are dark dull gray or black, contact cleaner will not clean metal oxides or sulfidation of silver terminals unless the chemical is acidic. If they are nickel, the tend to turn to dark gray due to oxidation, Silver will turn black (caused by sulfidation) and tin gray to white (caused by tin pest). Light abrasion is the only effective way to remove oxide layers. All that matters is the area that mates with the pin in the socket.

im talking about new tubes, so putting the contact cleaner would be to clean the contact point in the socket.
 
Hmm.. the 2nd pic shows some wires ( from bias select switch and leds) crossing the bottom of the socket. They look really close in the pic, any chance they are in contact with the socket?
If so, there may be a short happening if the wire coating has been worn away at any contacted point at the bottom of the socket.
 
Cleaning the socket pins may help. Also check them for fit. If the tube pins slide into the socket too easily, you may need to ajust the socket pin so there is more contact force. An ether based cleaner will work, just don't inhale too much.
Not sure if you can find non-synthetic pipe cleaners any more, if you can that may also help removing contaminants in the sockets.
 
The guy i talked to at eurotube says they serve no purpose but to scrath your tubes... unless of course the tubes are upside down, in which case he reccomended the spring ones.
 
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