I am about to order a matched quartet of el34's but the company I am ordering them from, the tubestore.com, needs to now the bias of the tubes that are in my amp. And because I never asked about my amps bias after I had It serviced about two years ago in the famous Hollywood CA, the quickest thing for me to do is mail the tubes that are in my amp to the company so they can match them. My question is, can I simply pull the old tubes out of their sockets without damaging myself or my amp? I've read that there are parts inside tube amps that carry a very powerful electric shock even with the power off. Once they are taken out I can put in new tubes that are matched to my old ones without re-biasing my amp right?
I'm not sure if I am going to break my amp.
I am a proud owner of a marshall JCM2000 dual super lead, 100-watt, ect...
I am about to order a matched quartet of el34's but the company I am ordering them from, the tubestore.com, needs to now the bias of the tubes that are in my amp. And because I never asked about my amps bias after I had It serviced about two years ago in the famous Hollywood CA, the quickest thing for me to do is mail the tubes that are in my amp to the company so they can match them. My question is, can I simply pull the old tubes out of their sockets without damaging myself or my amp? I've read that there are parts inside tube amps that carry a very powerful electric shock even with the power off. Once they are taken out I can put in new tubes that are matched to my old ones without re-biasing my amp right?
I am about to order a matched quartet of el34's but the company I am ordering them from, the tubestore.com, needs to now the bias of the tubes that are in my amp. And because I never asked about my amps bias after I had It serviced about two years ago in the famous Hollywood CA, the quickest thing for me to do is mail the tubes that are in my amp to the company so they can match them. My question is, can I simply pull the old tubes out of their sockets without damaging myself or my amp? I've read that there are parts inside tube amps that carry a very powerful electric shock even with the power off. Once they are taken out I can put in new tubes that are matched to my old ones without re-biasing my amp right?
# 1
Yes. You should be able to replace the old tubes with new tubes if the new ones are the same type of tubes without re-biasing the amp. I dont know about parts inside the amp carrying an electric charge though.. someone else will have to answer that question !
By virtue of their electrical properties, tubes generate a special waveform when they're saturated, which is why tube engineering has tremendous tonal advantages over solid state or DSP solutions, particularly for crunch and lead sounds. Tubes enter the saturation zone gradually or softly, which lends tube-driven tone its trademark yet totally unique character.
# 2
The biasing voltages of tubes can go over 600v .... The capacitors inside your amp can carry those lethal charges for hours or even days after you switch off the amp .
I've never heard of someone who died while fixing his amp , but you should take care while doing yours ... Just wear heavy gloves (like those in your kitchen) , discharge those caps one way or another.
I've never heard of someone who died while fixing his amp , but you should take care while doing yours ... Just wear heavy gloves (like those in your kitchen) , discharge those caps one way or another.
# 3
Wasn't 600v a bit much? It lies between 55 and 30 volts, and can be measured pretty easy. You ca but a 1ohm, 2w resistor between pin 8 on the tube socket and ground, and measure milliamperes over it. U=R x I, so 1ohm times the amount of milliamperes will be the exact same amount of volt. On Marshall-amps you can find BIAS trimpots for each tube I think, if not one for all the tubes. So, find a chart which tells you how much BIAS you want, measure the BIAS, and turn the trimpot until you have the right numbers. Then you can put the tubes in it.
I don't think you can burn the amp, but you can burn tubes pretty easy. If overbiased, they are running hot, real hot, if they are underBIAS'ed, they will stay cold, and sound, bad...
I don't think you can burn the amp, but you can burn tubes pretty easy. If overbiased, they are running hot, real hot, if they are underBIAS'ed, they will stay cold, and sound, bad...
# 4
I've been told to leave the stanby switch on and turn the power switch off, that this will discharge it. I've done it this way many times to check my tubes, and I've never been shocked.......
Or unplug the amp, and then turn both the power switch and standby switch on....
Or unplug the amp, and then turn both the power switch and standby switch on....
Check out my band:
Havoc Din
Havoc Din
# 5
Dont' hold me responsible if you do get shocked though. I'm not an electrician............
Check out my band:
Havoc Din
Havoc Din
# 6
Never thought of that, sounds correct. Couse you will then stop loading the caps but still have a connection to the ground, which discharges the tubes.
And, after the power is gone, the filter caps are the only "threat". It can take days for these to charge out, and can knock you flat if you touch them.
And, after the power is gone, the filter caps are the only "threat". It can take days for these to charge out, and can knock you flat if you touch them.
# 7
Pulling the tubes out of their sockets should not put you in any danger because you will be pulling on the glass part without prying up under the tube socket with a screwdriver or something conductive that might touch the pins.
There are usually resistors wired in parallel with the large caps to discharge them - at least after a couple of minutes after being turned off.
The standby switch may or may not take power off the capacitors, depending upon how the amp is wired. That switch does not even have to take power off the tubes either but usually does.
The bias issue has two ramifications - not burning up the tubes in the case of to little bias (ie. less negative) and not sounding good (ie. bias too negative/too much).
The bottom line is replace the tubes, if they get overy hot or they don't sound good clean, get the bias checked..
Have a great day, Eric Pritchard, Pritchard Amps
There are usually resistors wired in parallel with the large caps to discharge them - at least after a couple of minutes after being turned off.
The standby switch may or may not take power off the capacitors, depending upon how the amp is wired. That switch does not even have to take power off the tubes either but usually does.
The bias issue has two ramifications - not burning up the tubes in the case of to little bias (ie. less negative) and not sounding good (ie. bias too negative/too much).
The bottom line is replace the tubes, if they get overy hot or they don't sound good clean, get the bias checked..
Have a great day, Eric Pritchard, Pritchard Amps
# 8