Heater Filament Center Tap or Artificial Center Tap?

[RickyLee]

My two 100R 2W resistors measure the same on my Fluke but that is a basic measurement and these are only 5% tolerance resistors. I am wondering if anyone makes precision 100R resistors? Maybe that would help quiet my amp a bit more? I am figuring to test that theory, I would have to hook up a hum balance pot to test?

Another question: Is the cathodyne phase inverter possibly inducing a bit more noise in this amp? As in, is the cathodyne PI noisier than the long tail pair PI?

 

[RickyLee]

One more idea.

I am wondering if the lamp socket could be part of this problem? Would it be worth the hassle to remove the lamp from the circuit then try running the CT again?

 

[mickeydg5]

If the filament secondary center tap has an internal short that is bad. Being so, an internal short may be causing the noise internally. You have to think about that. No amount of balancing on the filament circuit will remedy that.

Two 5% resistors that read 101 ohm each will work no better than two 1% resistors that read the same 101 ohm for all practical reasons. One set is better for quaility and holding tolerance. You can try in an attempt to figure which set on hand works best.

 

[RickyLee]

UPDATE: I removed the lamp socket from the chassis and also pulled the lamp. Hooked up the CT wire with my amp meter. Problem is gone. I put the lamp back in and also put the socket against the chassis and still no issues.

So I am thinking that one of the lamp socket terminals where the heater wires also terminate could possibly have been touching the lamp housing. But if that was the case, how would that have not surfaced when the two 100R were used and only with the CT wire was used?

 

[mickeydg5]

Maybe something moved or made intermittent connection. Start moving stuff again to see if anything happens. You definitley do not want a meltdown one day while playing.

 

[RickyLee]

One of the lamp socket terminals is very close to the socket. But if that was touching would it not also have acted up while the 100R's were in circuit? Very odd.

I am going to try AB'ing noise differences between using the CT and the 100R's. And like you said about future issues, I was already thinking about wiring in an inline fuse on that CT wire if I go with that.

I am also interested in the schematics posted in this thread:

Elevated Heaters/DC heaters How? - Hoffman Ampifiers Guitar Tube amp forum

 

[RickyLee]

The amp has less noise now for sure. It is the same using the CT or the 100R's. Very odd as I did not move anything around to fix it except for pulling that lamp socket out. But I did just try wiggling wires to see if I could make it act up, and it did not. But that CT wire problem is in the back of my mind for sure. I would rather go the easier less parts route and just solder down that CT wire. I am thinking about fusing it in case it draws that huge current again.

 

[Guitar-Rocker]

My two 100R 2W resistors measure the same on my Fluke but that is a basic measurement and these are only 5% tolerance resistors. I am wondering if anyone makes precision 100R resistors? Maybe that would help quiet my amp a bit more? I am figuring to test that theory, I would have to hook up a hum balance pot to test?

Another question: Is the cathodyne phase inverter possibly inducing a bit more noise in this amp? As in, is the cathodyne PI noisier than the long tail pair PI?

I've seen the artificial ground use resistors as low as 64R on some older organ amps, so I doubt they need to be too close in tolerance.

 

[mickeydg5]

One of the lamp socket terminals is very close to the socket. But if that was touching would it not also have acted up while the 100R's were in circuit? Very odd.

I am going to try AB'ing noise differences between using the CT and the 100R's. And like you said about future issues, I was already thinking about wiring in an inline fuse on that CT wire if I go with that.

I am also interested in the schematics posted in this thread:

Elevated Heaters/DC heaters How? - Hoffman Ampifiers Guitar Tube amp forum

That is what Alabama was mentioning in the his post, elevating the heaters.

The short may have been something you did not notice, a fluke. Let us hope so. Just double check everything.