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valve amp


ybl8te
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Hi - ok, recently aquired a fisher x 100 a, pair of klipsch f2.........have been playing vinyl. Have a old national TT which is place on 30kg of concrete for mass. (yes i know the TT has to be up graded hehe) Recently have noticed one power tube is fluctuating with high volume or heavy bass. Have rotated valve and sympton follows tube. Any idea if this is good ? or bad ? or a sign of something to happen.!!! thanks people

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Just saw your other note. If the filament is getting brighter/dimmer, then the tube should be replaced (actually, replace both tubes for that channel, and recheck the bias/balance). If you speak of the bluish glow, then that can be normal if the tube happens to have a bit more gas than the other.

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buggar - so why would the tube be doing this. only asking as these were new tubes(matched). or maybe the tube just decided to do it !

Bad filiment, possibly small loss of vacuum. Could have been damaged in shipping? Definately a bad tube.

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buggar - so why would the tube be doing this. only asking as these were new tubes(matched). or maybe the tube just decided to do it !

Over the years I've experienced many new tubes which were defective- in fact, a bad filament has been a common problem! Since they were matched, I would return the other one of that pair also so the replacement can be matched to the good one. Please post to advise after you get them replaced.

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cool - very new to valve amp, learning everyday, i have been told that the fisher x 100 a has 400v and use to run 7189, the person who worked on it put in el84 power tubes - are these right or will i need a higher grade tube for replacement.....thinking i will just buy another mached quad thou i WANT to get it RIGHT. I live in New Zealand and it seems hard to find people with valve amp knowledge and stockist of tubes

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cool - very new to valve amp, learning everyday, i have been told that the fisher x 100 a has 400v and use to run 7189, the person who worked on it put in el84 power tubes - are these right or will i need a higher grade tube for replacement.....thinking i will just buy another mached quad thou i WANT to get it RIGHT. I live in New Zealand and it seems hard to find people with valve amp knowledge and stockist of tubes

Well, it depends in part on what brand of EL84's you have (Mullards have a design max. rating of 550V on the plate). Also, EL84's have a slightly lower plate dissipation than 7189A's. Basically, you can't go wrong by using 7189A's. I'd have to pull out the schematic of the X100 to check the plate voltages used- that amp was available in a few different versions during the early sixties, and I think some used a tube rectifier and others a solid state rectifier; so, the plate voltages may be different depending on which version you have.

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well the tube fades/dulls when the music is above half or when heavy bass songs are on. No audible thump as of yet

Not likely I guess but you might make sure all the filament pins on the tube are clean by using something like a piece of emory cloth just in case.

mike tn

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well the tube fades/dulls when the music is above half or when heavy bass songs are on. No audible thump as of yet

Not likely I guess but you might make sure all the filament pins on the tube are clean by using something like a piece of emory cloth just in case.

mike tn

new tubes - quad matched - and changed the tube with one next to it, problem follows the tube, tube sockets have all been tightened also

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http://www.arrakis.es/~igapop/fishpart1.htm

http://www.arrakis.es/~igapop/fishpart2.htm

here are some diagrams i found - the tubes in are sovtek el84's - they do make the M for higher voltage, Would be nice to run 7189a's. Where would one look for some of these from New Zealand

You can get them from: www.vacuumtubes.net

They are reliable dealers and ship internationally.

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