SheDoesntDoIt4Me
New member
do I need a "probe for each tube or will doing one tube of a matched set be cool? What should i set it at for a e34l (yes they are a derivitaive of el34) on a marshall Jubillee? Thanks
Anyone bias their own amps????
- Thread starter SheDoesntDoIt4Me
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DeadSkinSlayer3
Guest
Re: Anyone bias their own amps????
My XXX has inputs in the back for a multimeter, and it measures the plate voltage. Can I bias it this way? Just return it to the stock 55V everytime I change tubes?
My XXX has inputs in the back for a multimeter, and it measures the plate voltage. Can I bias it this way? Just return it to the stock 55V everytime I change tubes?
aleclee
Major General GAS
Re: Anyone bias their own amps????
Personally, I use a probe for each tube. Some dealers "match" better than others and tubes can also drift over time. I prefer to know how each tube is doing.
As for what's the right bias current, 70% of max dissipation is considered typical. That's about 19W for the EL34 family. Your desired bias current is calculated by dividing 19W by your amp's plate voltage.
I use a Weber BiasRite with the VI option. The VI option lets you switch modes between bias current and plate voltage. It's a nifty piece of kit that's well worth the $$$ IMO.
Personally, I use a probe for each tube. Some dealers "match" better than others and tubes can also drift over time. I prefer to know how each tube is doing.
As for what's the right bias current, 70% of max dissipation is considered typical. That's about 19W for the EL34 family. Your desired bias current is calculated by dividing 19W by your amp's plate voltage.
I use a Weber BiasRite with the VI option. The VI option lets you switch modes between bias current and plate voltage. It's a nifty piece of kit that's well worth the $$$ IMO.
Burkwieser
New member
Re: Anyone bias their own amps????
I agree. This is a good subject that could be put in the vault. Maybe take some pics to better explain too. Pictures speak a thousand words. I had my VHT serviced and would really like to be able to do it myself. My RT has a built in self biasing feature, which is nice. Could someone snap some step by step pics? I think there are many on this forum that would benefit from it. Personally I have been on many sights that go into detail about the subject, but there are no pics. You can read all you want, but you kinda have to know what you are looking for. :smack:
Surgeon said:Just for the sake of it and to make things clear... Please explain how you'd do this...
I agree. This is a good subject that could be put in the vault. Maybe take some pics to better explain too. Pictures speak a thousand words. I had my VHT serviced and would really like to be able to do it myself. My RT has a built in self biasing feature, which is nice. Could someone snap some step by step pics? I think there are many on this forum that would benefit from it. Personally I have been on many sights that go into detail about the subject, but there are no pics. You can read all you want, but you kinda have to know what you are looking for. :smack:
Thames
Great White Malice
Re: Anyone bias their own amps????
You're talking about how to kill yourself when playing inside an amp right ? :laugh2:
Ok, YOU HAVE ALL BEEN AWARE THAT THIS IS A DANGEROUS TASK. DONT GET YOUR A.S.S. BURNED OFF IF YOU'RE NOT SURE OF WHAT YOURE DOING.
You have to take a reading of the PLATE DC VOLTAGE. It can be done this way :
1- solidly attach the BLACK probe of your DMM to the chassis (ground)
2- Set the DMM to DC High Voltage (youre gonna read 400-500 DC volts).
3- Turn on the amp, let it warm up for 30 sec, then engage standby switch.
4- Take a reading on both power tubes (but not at the same time!!), put you RED probe on PIN 3 and check the DMM. This is the PLATE DC VOLTAGE.
Ok, now you can go at http://www.webervst.com/tubes/calcbias.htm and calculate the bias current needed.
The only method I use to measure bias is to put a 1-ohm, 3 watts resistor across PIN 1-8 (tied together) to ground. Then you take the bias reading across this resistor. My BFDR is setup'd that way, and I modded my Laney for this too.
I DONT WANT TO SEE ANY OF YOU IN THE OBITUARIES SHORTLY, so dont be stupid! :evil:
Surgeon said:Just for the sake of it and to make things clear... Please explain how you'd do this...
You're talking about how to kill yourself when playing inside an amp right ? :laugh2:
Ok, YOU HAVE ALL BEEN AWARE THAT THIS IS A DANGEROUS TASK. DONT GET YOUR A.S.S. BURNED OFF IF YOU'RE NOT SURE OF WHAT YOURE DOING.
You have to take a reading of the PLATE DC VOLTAGE. It can be done this way :
1- solidly attach the BLACK probe of your DMM to the chassis (ground)
2- Set the DMM to DC High Voltage (youre gonna read 400-500 DC volts).
3- Turn on the amp, let it warm up for 30 sec, then engage standby switch.
4- Take a reading on both power tubes (but not at the same time!!), put you RED probe on PIN 3 and check the DMM. This is the PLATE DC VOLTAGE.
Ok, now you can go at http://www.webervst.com/tubes/calcbias.htm and calculate the bias current needed.
The only method I use to measure bias is to put a 1-ohm, 3 watts resistor across PIN 1-8 (tied together) to ground. Then you take the bias reading across this resistor. My BFDR is setup'd that way, and I modded my Laney for this too.
I DONT WANT TO SEE ANY OF YOU IN THE OBITUARIES SHORTLY, so dont be stupid! :evil:
