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152.132.10.193
http://www.diyparadiso.com/proj/maison300b.htm
I'm talking about after the coupling capacitor there is no resistor to ground.
What would happen if one removes this resistor?
Follow Ups:
Usually only used with small signal tubes. Not recommended for power tubes and not very reliable as tubes age.
"It is better to remain silent and thought a fool, then speak and remove all doubt." A. Lincoln
"...If the grid has high enough resistance to ground it can develop a small negative potential (excess electron charge) of a few volts. Suitable resistances are in the order of several megohms."
Contact bias requires a DC reference to ground. Without a grid resistor, it's not contact bias. It's a misprint.
"This is a very unreliable source of bias. Contact potential bias is useful only in very small low voltage tubes..."
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
.
Have Fun and Enjoy the Music
"Still Working the Problem"
It would have to be a misprint and with no potential on G1,it would runaway just as Jim said.
"If it measures good and sounds bad, it is bad; if it measures bad and sounds good, you have measured the wrong thing."
- Daniel R. von Recklinghausen
What would happen? The cathode biased 300B would like run away into over-current either immediately or at sometime in the future.
On another thread where the built amp actually worked. If you provide enough phantom resistance, and remember it only has to be a few megohms, it will work. A dirty old tube socket may be just enough.Certainly not advised but this may be how people get amps to still work this flaw in place.
Edits: 02/25/15
Here is a Stromberg Carlson ASR-444 integrated amp with that setup.They sound very good but I still put a grid stopper in. Why do you think SC did this?
"If it measures good and sounds bad, it is bad; if it measures bad and sounds good, you have measured the wrong thing."
- Daniel R. von Recklinghausen
He's talking about the grid leak, not grid stopper. There is no resistor to ground after the cap coupling the 300B. A big error on the schematic.
Dan Santoni
Wow!
I just looked at that circuit and how can that amp operate with no potential on G1? It if were direct coupled to a cathode follower that may work but I don't see where the 300b would be stable at all if it did work.
"If it measures good and sounds bad, it is bad; if it measures bad and sounds good, you have measured the wrong thing."
- Daniel R. von Recklinghausen
Grid stopper or Grid resistor?
dave
Grid stopper,the one that goes to the control grid.It basically acts as a high frequency low pass filter to help keep RF out causing parasitic oscillation.
"If it measures good and sounds bad, it is bad; if it measures bad and sounds good, you have measured the wrong thing."
- Daniel R. von Recklinghausen
The typically 1K series resistor to the grids of PP output tubes was not historically there to prevent oscillation but to prevent blocking distortion from periodic overload. Crowhurst covers this in the link below.
The grid stopper is very often optional.The grid leak is typically not optional.
Edits: 02/25/15
Yes
I see that now..I just noticed it had no grid stopper and it also has no grid leak which is far more important.
"If it measures good and sounds bad, it is bad; if it measures bad and sounds good, you have measured the wrong thing."
- Daniel R. von Recklinghausen
nada aqui
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