|
Audio Asylum Thread Printer Get a view of an entire thread on one page |
For Sale Ads |
175.38.139.66
Thank you....
First question:
based upon GE 211 spec sheet.....
CLASS A Amplifier
DC plate voltage 1000
DC Grid voltage -61
DC plate current 53ma
CLASS B
DC plate voltage 1000
DC Grid voltage -72
DC plate current 20ma
In broad layman terms does that mean the higher plate current and lower - grid voltage drives it further into Class A or another answer ...??
Second Question:
based upon the picture should the amp meter go before the resistor or after the resistor or across the 1 ohm 2W resistor and what differences will be shown in the readings
again, many thanks
Follow Ups:
Thank you Tre'
to confirm: ...Current meter, in line, either before or after the cathode resistor will give the same correct reading.
Do not place it across the cathode resistor. That would give a false reading.
.....that is an answer I was chasing......
Thanks Palustris
....the present pot is a quality 100 5w wire wound, I have not seen a 50 after a quick search .....can I still use the 100 and the suggested 15 resistors or do I need different value resistors......as you suggested or would the fact that the existing is a quality ww be ok and no need for the alteration
....if the bias currant is a suggested 70ma reading at the bottom of the existing circuit [after the 1 ohm resistor] with the existing circuit will your alteration affect this reading and by how much ......
Thanks everyone so far
Palustris.......thanks for your input
my intention is to put a switch in to switch in/out [while of] between an analogue amp meter [100ma] in circuit for bias adjust when tube rolling etc.
thus the question of where to put....before, over or after the resistor and what will be the differences in the readings
I will implement your resistor and pot network when doing the meter input......and thanks re the simulator.....does not appear to have the 211 valveTriode King......thanks for your input.....
amps are VAL MP-211 [mono blocks] based upon an original Kondo design.....can provide schematic [via email] for your perusal and opinion .......Chips647......thanks for your input.....
Tre'.....thanks for your input.....
your volt meter is good ......I was thinking in line of an amp-meter and wether to put it before, after or across the resistor and what the difference would be in the current readingsagain thanks all so far ....looking forward to more info
Edits: 07/07/15
Current meter, in line, either before or after the cathode resistor will give the same correct reading.
Do not place it across the cathode resistor. That would give a false reading.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
I would put test points for a volt meter in parallel with a 1r or 10r resistor in the cathode of the 211. You can put an amp meter in series with the cathode, but it will always be in the circuit and could be prone to failure.
One problem with the part of the schematic that you show is that the entire plate current for the 211 tube is going through the wiper of a pot. That will generate noise and hum and the pot is subject to failure. A far better solution would be to use a 50ohm 2W pot and parallel the two legs to the wiper with 10r or 15r resistors. Most of the current will go through the resistors and you will still have the hum nulling function.
You can determine the operating points for the 211 yourself using the Triode / Pentode Loadline Simulator.
To get the most from the 211 in A1, you'll want to operate it at roughly 80W anode dissipation. My 211s run at +1,050V and 70-75mA. That operating point occurs with -52V at the grid.
Incidentally, what's the source of that schematic? There's a lot of junk floating around the Internet, much of it apparently published by persons who don't know whether it works and have never actually built it. I say that because a direct-coupled follower wouldn't normally be used to drive a SET unless Class A2 is desired. In that case, a 6SN7 isn't the right tube for the job. Maybe the designer had a different goal in mind...
--------------------------
Buy Chinese. Bury freedom.
A single ended amp is "Class A" by definition. Class A1 means that the grid voltage is always more negative than the cathode voltage. Class A2 means that the grid voltage is more positive than the grid voltage at least some of the time.
The more idle current you bias a single ended tube, the more potential power you can get, up to the point where the tube will not produce more power. At that point you just get increased distortion. "Deeper" Class A is a push-pull amp construct. As Tre said, if you want to change operating points you need to really understand the tube plate curves and also understand what it does to the plate impedance.
The "Class B" rating is for push-pull operation.
"In broad layman terms does that mean the higher plate current and lower - grid voltage drives it further into Class A or another answer ...??"With 1000vdc on the plate, a grid voltage of -61vdc will cause the tube to draw 53ma. of plate current.
With 1000vdc on the plate, a grid voltage of -72 will cause the tube to draw 20ma. of plate current.
Class A1 is when the tube draws 1/2 of the maximum plate current (plate current at the intersection of the load line and 0 grid voltage) at idle (no music signal present) determined by looking at the load line (plate load impedance, AKA the impedance of the output transformer) used.
"based upon the picture should the amp meter go before the resistor or after the resistor or across the 1 ohm 2W resistor and what differences will be shown in the readings"
Just measure the voltage across the 1 ohm resistor and use Ohm's Law to calculate the current.
Current = voltage / resistance.
P.S. the load line is not shown on the data sheet. You have to learn to draw your own.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Edits: 07/06/15
Post a Followup:
FAQ |
Post a Message! |
Forgot Password? |
|
||||||||||||||
|
This post is made possible by the generous support of people like you and our sponsors: