#1
first off i'm pretty sure my tubes need replacing. its a jcm800 4104 combo 2x12...

well anyway if you plug into the low input it works fine but if i plug into the high input it crackles and fades in and out before finally stabalizing a few minutes later and then it'll cut in and out randomly. and it hums so loud you can hear it over the guitar almost. i know cranking a jcm800 is how to get that marshall distortion but even when i do crank it it sounds weak and doens't have any fullness. (still loud enough to make your ears bleed though).

as far as i know that means the tubes are bad...but which ones? since its just the high input is it the preamp tubes or the power tubes (el34's)...

pretty much i need a full breakdown on what to do to fix this problem...where to get tubes..who to install them...etc...or for all i know its not the tubes and something else is wrong.

also how much am i looking at in cost to get this thing working like it should.

thanks for any info.
Quote by deg0ey
The best pickups for emo are no pickups at all...


Gear:

1996 Les Paul Classic w/ Alnico II's
Marshall Jubilee 2550
Avatar 2x12..V30 and G12H
Vox V847 Wah
Assorted pedals
#2
from your descriptions, sounds like tubes, maybe even one of your preamp tubes in addition to power tubes getting old. Might as well get a whole kit, preamp tubes are cheap enough.

I've had pretty good luck buying complete kits, pre and power, from Bob at Eurotubes. He only sells JJ, but they are good tubes IME.

https://ssl.eurotubes.com/cart/index.php?page=view_products&category_id=9&sub_category_id=94

Installing them isn't hard, you just push thier pins into the sockets like Christmas tree lights. You won't have to bias preamp tubes, but you should have a shop bias your power tubes for best tone/lifespan. I've always biased my own, but I'm sure they can't charge too much just to bias it, I would assume under $50 if it's just a bias adjustment.
"The fool doth think he is wise, but the wiseman knows himself to be a fool." - W.S.
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#3
Quote by Erock503
from your descriptions, sounds like tubes, maybe even one of your preamp tubes in addition to power tubes getting old. Might as well get a whole kit, preamp tubes are cheap enough.

I've had pretty good luck buying complete kits, pre and power, from Bob at Eurotubes. He only sells JJ, but they are good tubes IME.

https://ssl.eurotubes.com/cart/index.php?page=view_products&category_id=9&sub_category_id=94

Installing them isn't hard, you just push thier pins into the sockets like Christmas tree lights. You won't have to bias preamp tubes, but you should have a shop bias your power tubes for best tone/lifespan. I've always biased my own, but I'm sure they can't charge too much just to bias it, I would assume under $50 if it's just a bias adjustment.


how do you bias your own?

and that link you gave me doesn't have the tubes for my amp...just the 2203/4103 models with 4 el34s in them...pretty sure mines the 2 power tube model.
Quote by deg0ey
The best pickups for emo are no pickups at all...


Gear:

1996 Les Paul Classic w/ Alnico II's
Marshall Jubilee 2550
Avatar 2x12..V30 and G12H
Vox V847 Wah
Assorted pedals
Last edited by bonchie1 at May 19, 2006,
#4
He can make a kit for you, email him, and he will pick you out some tubes, depending what you want from them. He's really good about helping you find what you need, he'll make up a kit for you. Email him: https://www.eurotubes.com/index.htm , there is a link on his site.

As far as biasing your own, one of my amps is a Mesa MarkIV, so it's a fixes bias. I only use Mesa tubes with it, so I don't have to worry about biasing. My Framus has test points at each power tube, and I used a DMM to measure the voltage from that test point to ground in mV. I then adjust the bias pot untill I have the desired values at the test points. It's obviously a lot easier if an amp has test points like that already. A tech would probably have a bias probe, so it would be easier for them even without the test points.
"The fool doth think he is wise, but the wiseman knows himself to be a fool." - W.S.
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amp vids
#5
so can this guy at eurotubes bias the tubes before he sends them to me just by knowing what kind of amp it is or is it a hands on deal where an amp tech has to tell how your amp is bias?
Quote by deg0ey
The best pickups for emo are no pickups at all...


Gear:

1996 Les Paul Classic w/ Alnico II's
Marshall Jubilee 2550
Avatar 2x12..V30 and G12H
Vox V847 Wah
Assorted pedals
#6
it's a hands on deal actually, it's the amp that needs to be biased for the tubes unfortunately. Tube quality and values can vary even from the same manufacturer, os you need to bias an amp each time you get tubes. Generally if they are the same brand and kind, you can get away without biasing, but it might not be running optimal for those tubes, which affects tone and tube life.
"The fool doth think he is wise, but the wiseman knows himself to be a fool." - W.S.
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amp vids
#7
^Not totally true..it's a good idea to check check the tube datasheets for the biasing voltages, if they're close enough to the origs, you won't need to rebias.
I'm not very active here on UG currently.
I'm a retired Supermod off to the greener pastures of the real world.
#8
problem with that though pink, tubes can vary even from the same batch, from the same manufacturer. You could get away with it if the datasheets are close, but that doesn't mean they are running optimal for that particular amps plate voltage, and those particular tubes. The reason Mesa can get away with it is because they throw out more tubes than they keep, after testing for that specific bias range of their amps.
"The fool doth think he is wise, but the wiseman knows himself to be a fool." - W.S.
amp clips
amp vids
#9
Quote by Erock503
problem with that though pink, tubes can vary even from the same batch, from the same manufacturer. You could get away with it if the datasheets are close, but that doesn't mean they are running optimal for that particular amps plate voltage, and those particular tubes. The reason Mesa can get away with it is because they throw out more tubes than they keep, after testing for that specific bias range of their amps.


shyea.

+1