Who/Where do you buy amp tubes from? And how do you determine which ones are shot?

[edgarbc1]

my tube amp (Marshall 1974x) is sounding muddier
esp. on the rhythm/neck pickup of my guitar. I am surmising
that some/all of the tubes may need replacement.

I am curious to hear your input on where to get tubes..
and how to determine which ones need replacement, if any
currently im looking at Groove Tubes website. (There are several
variants of the 12AX7 for example)

This will be my first change out of the tubes since i purchased
the unit

Preamp = 3 ECC83 (12AX7)
Rectifier = 1 EZ81
Power Amp = 2 EL84

thanks in advance
Edgar

[sbag]

have you tried checking with your local music equipment store >
they usually offer repairs from a authorized repairer >
you stated that your on the manufactor site > do they have that info on there > some form of repairs > http://duc.digidesign.com/images/smilies/confused.gif

[sunburst79]

I grew up in a hollowstate household....One of your best tools are your ears. if something doesn't sound right than chances are somethings changed. Often several tube of the same model and batch will sound different so you can and should swap them about to see if any particular combination sounds better. And the quickest way to troubleshoot a bad tube is to substitute a known good one.

If you own more than one amp its a good idea to pick up a simple vacuam tube checker. Best place for one of these are the local classifieds and Ham Radio swapmeets.

Also find a good local or regional tube amp repairman.

I have always had GREAT luck will Groove Tubes, I suspect that the 6CA7 Quad in my HIWATT are just starting to go. They were in the amp when I bought it 15+ years ago.

A lot of choices as far as new tubes, JJ's, Winged C etc, Electro Harmonics, Groovetubes to name a few.

One name that always seems to come up in tube supplier discussions is a guy named "Lord Valve" in Colorado.

Thats the handwired 20wt? how do you like it?

[guitardom]

contact eurotubes.com the guys are great and are marshall lovers!!

[DrFord]

A thread I posted a while back when I was begining to upgrade by tubes

http://duc.digidesign.com/showthread.php?t=232842

[edgarbc1]

Originally Posted by sunburst79

Thats the handwired 20wt? how do you like it?

yes it is...
it was like butta set at about 6-7 on the gain knob...
but now its muddy.. i hope to get that sweet sound back again

[sunburst79]

Originally Posted by edgarbc1

yes it is...
it was like butta set at about 6-7 on the gain knob...
but now its muddy.. i hope to get that sweet sound back again

It really could be anything, Preamp tube, Phase inverter or Power tubes. Since those are a non master volume amps I would lean towards the power tubes since they get a good workout or possibly the phase inverter. It will be interesting to see which it is. I have no idea what tubes are the current favorites in those but you have places like 20watt.com and other bunch of community resources that you can lean on.

Almost bought one myself and I will almost certainly kit one sometime in the future.

[Amin7b5]

Generally speaking, power tubes gradually lose tone over time, and preamp tubes just die. Preamp tube failure is usually easier to diagnose because the effects are obvious (squeeling, microphonics, no sound, no gain). Power tubes can simply wear with age.

I will concur that Bob at eurotubes.com knows his stuff, and I have had good success with the JJ tubes he usually recommends.

Keep in mind if you change your power tubes you will have to have the amp biased by a qualified tech.

Happy tube shopping! Try as many as you can afford.

[M.Brane]

Tube testers are pretty much useless for audio tubes since all they will really tell you is if the tube is functional. If the amp still works you already knew that.

Generally changing power tubes in modern amps won't require a bias adjustment, but it is something to watch for. More so for older amps as they can have other problems lurking like bad caps/resistors.

Tubes wear out directly proportional to how hard they are driven/handled. An amp that gets cranked, and bounced around a lot will need to be re-tubed much sooner than one that sits or rarely gets cranked-up.

The sound of the different varieties of tubes available is a very subjective thing. You could blow a lot money trying different variations for very little real-world return on your investment. If you have the time/money knock yourself out. Just be aware that there are only a handful of tube manufacturers left, and many of the so-called "quality" tubes out there are simply re-badged from the same factories. There are also fake NOS re-badged tubes. Know exactly what you are buying before paying premium prices for mediocre product.

[edgarbc1]

Originally Posted by M.Brane

Tube testers are pretty much useless for audio tubes since all they will really tell you is if the tube is functional. If the amp still works you already knew that.

Generally changing power tubes in modern amps won't require a bias adjustment, but it is something to watch for. More so for older amps as they can have other problems lurking like bad caps/resistors.

Tubes wear out directly proportional to how hard they are driven/handled. An amp that gets cranked, and bounced around a lot will need to be re-tubed much sooner than one that sits or rarely gets cranked-up.

The sound of the different varieties of tubes available is a very subjective thing. You could blow a lot money trying different variations for very little real-world return on your investment. If you have the time/money knock yourself out. Just be aware that there are only a handful of tube manufacturers left, and many of the so-called "quality" tubes out there are simply re-badged from the same factories. There are also fake NOS re-badged tubes. Know exactly what you are buying before paying premium prices for mediocre product.

thanks M.Brane and Others!
yes the amp still works, its just muddier sounding.. i posted on Gearslutz
as well and some were suggesting probably the rectifier and power tubes
would require changing... im going to attempt to post at 18watt too, but
had troubles yesterday from my work PC.

As for biasing.. this amp is supposed to be a Class A amp circuit. So I
was under the impression that this requires no biasing.

I cannot be certain of this, but the schematic is at 18watt and here
http://gallery.mac.com/edgarbc1#gallery
and i cant tell if the variable resistors in this schematic are biasing
resistors but they are grouped by the ECC83 preamp tubes and not
the power amp tubes EL84. My meager knowledge is that the power
amp signals need the biasing for the top and bottom halves of the
output waveform for class AB circuits... but i could be wrong.... :)

Edgar