plate resistor, input lead

vlljpior · 23rd January 2005, 02:09 AM

Hi, i found when i place my plate resistor wire close to my grid resistor my hiss problem come off. But i have a little squeal problem. What can cause this problem ? If anybody have a idea, i be happy...
:-)

SY · 23rd January 2005, 02:11 AM

Oscillation from stray coupling, more than likely.

Sch3mat1c · 23rd January 2005, 02:37 AM

Ya. And hiss stops because the amplifier is overcome by the stronger high frequency oscillation.

Hiss is fixed by NOT using carbon composition resistors, or switching to lower noise figure tubes (may require redesign of the circuit).

Tim

vlljpior · 23rd January 2005, 03:25 AM

Yes, i'm using carbon composition resistors, so i have to switch to what type...

Sch3mat1c · 23rd January 2005, 03:51 AM

Anything. Carbon or metal film are popular.

Tim

SY · 23rd January 2005, 04:24 AM

For the plate resistor, wirewound. Grid stopper should be carbon comp (you ARE using a grid stopper, aren't you?). Grid leak can be metal or carbon film.

Sch3mat1c · 23rd January 2005, 06:03 AM

Quote:

Originally posted by SY
For the plate resistor, wirewound.

If it needs to handle a few watts. Metal oxide is also possible, though may give more noise. Most of the time, 1/2W will suffice. Ohm's law and P = V*I if in doubt.

Quote:

Grid stopper should be carbon comp (you ARE using a grid stopper, aren't you?).

Resistance is resistance AFAIK. At least at the typical <100MHz parasitic frequencies. Whatever's on hand or cheapest or easiest to get will work...

Tim

SY · 23rd January 2005, 11:06 AM

Carbon comps as grid stoppers are more effective at RF suppression, though this is admittedly gilding the lily. Resistance IS resistance, but reactance and Q are reactance, too. Real resistors do have reactive elements.

Wirewound plate resistors are much quieter than metal films and that's no gilding, it's the whole flower. Additionally, they have a lower deltaR/deltaV than other types, significant at the large deltaV seen at plates.

23rd January 2005, 02:09 AM	#1
vlljpior diyAudio Member Join Date: Jul 2004 Location: laval	plate resistor, input lead Hi, i found when i place my plate resistor wire close to my grid resistor my hiss problem come off. But i have a little squeal problem. What can cause this problem ? If anybody have a idea, i be happy... :-)

23rd January 2005, 02:11 AM	#2
SY diyAudio Moderator Join Date: Oct 2002 Location: Austin, TX Blog Entries: 1	Oscillation from stray coupling, more than likely. __________________ “Listening to records is like ****ing a picture of Brigitte Bardot.” - Sergiu Celibidache

23rd January 2005, 02:37 AM	#3
Sch3mat1c diyAudio Member Join Date: Jan 2003 Location: Milwaukee, WI	Ya. And hiss stops because the amplifier is overcome by the stronger high frequency oscillation. Hiss is fixed by NOT using carbon composition resistors, or switching to lower noise figure tubes (may require redesign of the circuit). Tim __________________ See my Electronics webpage -- the home of Vacuum Tube Drag Racing. The key to being a successful Audiophile: "I reject your reality and substitute my own!"

23rd January 2005, 03:51 AM	#5
Sch3mat1c diyAudio Member Join Date: Jan 2003 Location: Milwaukee, WI	Anything. Carbon or metal film are popular. Tim __________________ See my Electronics webpage -- the home of Vacuum Tube Drag Racing. The key to being a successful Audiophile: "I reject your reality and substitute my own!"

23rd January 2005, 04:24 AM	#6
SY diyAudio Moderator Join Date: Oct 2002 Location: Austin, TX Blog Entries: 1	For the plate resistor, wirewound. Grid stopper should be carbon comp (you ARE using a grid stopper, aren't you?). Grid leak can be metal or carbon film. __________________ “Listening to records is like ****ing a picture of Brigitte Bardot.” - Sergiu Celibidache

23rd January 2005, 03:25 AM	#4
vlljpior diyAudio Member Join Date: Jul 2004 Location: laval	Yes, i'm using carbon composition resistors, so i have to switch to what type...

23rd January 2005, 11:06 AM	#8
SY diyAudio Moderator Join Date: Oct 2002 Location: Austin, TX Blog Entries: 1	Carbon comps as grid stoppers are more effective at RF suppression, though this is admittedly gilding the lily. Resistance IS resistance, but reactance and Q are reactance, too. Real resistors do have reactive elements. Wirewound plate resistors are much quieter than metal films and that's no gilding, it's the whole flower. Additionally, they have a lower deltaR/deltaV than other types, significant at the large deltaV seen at plates. __________________ “Listening to records is like ****ing a picture of Brigitte Bardot.” - Sergiu Celibidache

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