Hello I need a little help with my final checkout. Specifically the part that says
"Connect a load to the amp, speakers or resistor. It is wise not to use your good speakers during initial testing. Finally, clip voltmeter leads across the 10 ohm resistors in the plate supply of each output tube (R18 and R29), put in the output tubes, and power the amp on. The tubes should draw no (or very little) current. " etc....
Everything up to this point has been fine but I'm not sure what my meter should be set for.
Should it be set for dcv or dca? I tried both, dca gives me zero and pots do nothing, dcv start at zero but the pots do increase when turned but only up to about 0.60 when on the 20v scale.
Can someone clarify what I should be doing to set bias correctly, this is my first intermediate project and I think i have done pretty well so far but I have never set a bias before. I don't want to try playing the amp until I've completed the checkout, so any help will be greatly appreciated.
"Connect a load to the amp, speakers or resistor. It is wise not to use your good speakers during initial testing. Finally, clip voltmeter leads across the 10 ohm resistors in the plate supply of each output tube (R18 and R29), put in the output tubes, and power the amp on. The tubes should draw no (or very little) current. " etc....
Everything up to this point has been fine but I'm not sure what my meter should be set for.
Should it be set for dcv or dca? I tried both, dca gives me zero and pots do nothing, dcv start at zero but the pots do increase when turned but only up to about 0.60 when on the 20v scale.
Can someone clarify what I should be doing to set bias correctly, this is my first intermediate project and I think i have done pretty well so far but I have never set a bias before. I don't want to try playing the amp until I've completed the checkout, so any help will be greatly appreciated.
You want to measure the voltage drop across the 10R resistors. The plate current is then V/10 amps.
If you want for example 50mA (0.05A), set the bias control for a voltage drop of 0.050A x 10R = 0.50V.
Use the most sensitive scale of the meter that still allows a reading. Turn up each control slowly and
don't exceed the specified current. Also be careful of the high voltage present in the circuit.
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Yes, that's right. Use the meter scale setting that gives a reading nearest the meter's limit.
This will be the most accurate. For example, use 2V full scale instead of 20V full scale.
Suggested Bias for SE with 45 tubes?
I got 27ma from a thread on here but I'm not sure if that is a good bias for my setup.
My specs are
B+=320v
B-= -225v
Grids= -125v during checkout
5842 plate= 175v
Bias= 27ma currently
amp works great but volume is on the low side but very listenable. I'm wondering if raising the bias will increase volume and if its recommended.
Any suggestions for a good bias point for my amp?
I got 27ma from a thread on here but I'm not sure if that is a good bias for my setup.
My specs are
B+=320v
B-= -225v
Grids= -125v during checkout
5842 plate= 175v
Bias= 27ma currently
amp works great but volume is on the low side but very listenable. I'm wondering if raising the bias will increase volume and if its recommended.
Any suggestions for a good bias point for my amp?
The volume (gain) is not affected by the bias setting. This has a single voltage gain stage,
so amp gain is on the low side. How much gain does your preamp have?
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I do not have a pre-amp currently, i installed a 100k volume pot on the board.
but i also had a cell phone hooked up as a source, afer some thought i changed it out for a cd player and the volume is much better now.
My question still applies though, even if it does not efect the volume, what IS a good bias to set on this amp? I have read threads with values all over the spectrum. Is there a rule of thumb or a spec to look up that will give me a nice safe bias setting. one not to hard on the tubes but not completely light weight? I forgot to mention in my 1st post that im running 45 tubes.
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Depends on the tubes, power supply voltage, and how much dissipation is acceptable.
Subtract a safety margin (if desired) from the rated power. Calculate the bias current
from that power divided by the plate voltage, and don't exceed that level of bias current.
The power supply voltage may vary with the bias current setting, though.
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Per George's instructions I set my 45's around 27ma. See the Tubes and Applications page from the Tube Lab site. Tubes and Applications | Tubelab
I have a Sonos or a cd-player as my input source and I find I can get enough volume with my Monitor Audio speakers rated at 91db.
Good luck and enjoy!
I have a Sonos or a cd-player as my input source and I find I can get enough volume with my Monitor Audio speakers rated at 91db.
Good luck and enjoy!
27 mA is a good spot for 45 tubes. The maximum plate dissipation rating is not specified in some books, and 10 watts in others. That gives a maximum current of 31 mA with 320 volts on the plate.
I set mine at 33 mA quite some time ago and haven't checked it in a long time. My tubes are actually NX-483's which are a 45 with a 5 volt heater. The tubes were dated 1929 and they are still going strong after almost 90 years!
I set mine at 33 mA quite some time ago and haven't checked it in a long time. My tubes are actually NX-483's which are a 45 with a 5 volt heater. The tubes were dated 1929 and they are still going strong after almost 90 years!
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