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CATHODE CURRENT

D

donemad

Active Member
Jun 21, 2008
104
1
26
can anyone help me to set the cathode current on 8950 tubes? This is 1 preamp driver and 2 drivers driving 6. Looks like all are jumped from pin 2 and pin 6. But has the adjustment just under the preamp driver, white square looking with a metal flathead screw....thanks for any help.
 

That white thing is a ceramic variable capacitor. If you did not touch it then it is already set at the factory.

If you google that tubes data it will give the data you need to set the bias.
 
ElectronTubesRule said:
That white thing is a ceramic variable capacitor. If you did not touch it then it is already set at the factory.

If you google that tubes data it will give the data you need to set the bias.
Click to expand...
Yeah... thats just it. It was turned buy the pre-owner, now I just need the steps to correct it.........thanks for any help.
 
I guess I am not following your problem. If you have the specifications for the tube and you have the ability to measure the current current and the capacitance setting of the variable cap on the back of the socket then what is your problem???? I know run on sentence!!Do you need to know how to use a multimeter or how to read the spec. chart for the tube??? I do not get what it is you are not getting....I am truly wanting to help but do not understand what it is you do not understand?
 
Electron, I think the confusion here is that this cap is not a bias adjustment. It's part of a tuned RF circuit between two stages of this amp. Donemad has discussed this topic in another tread and I think he understands how to adjust it now.
 
Shockwave said:
Electron, I think the confusion here is that this cap is not a bias adjustment. It's part of a tuned RF circuit between two stages of this amp. Donemad has discussed this topic in another tread and I think he understands how to adjust it now.
Click to expand...
OK, I,am back with what I see! Shockwave & Electron, this is no way a adj. for SWR, my mistake, I should explane more clearly. I took a second look @ it & I see that it is connected to my hi/lo switch & is connected to some ceramic caps & a wire wound coil. It has two legs on it with one leg to ground. Looks like it goes to the top of (cap) the 8950 pre-driver. I,am thinking it maybe the plate adjustment. That may explane why the 8950 was no good on these drivers. The pre-driver was dead & the other two 8950,s no good. Thanks for any help....
 
donemad said:
OK, I,am back with what I see! Shockwave & Electron, this is no way a adj. for SWR, my mistake, I should explane more clearly. I took a second look @ it & I see that it is connected to my hi/lo switch & is connected to some ceramic caps & a wire wound coil. It has two legs on it with one leg to ground. Looks like it goes to the top of (cap) the 8950 pre-driver. I,am thinking it maybe the plate adjustment. That may explane why the 8950 was no good on these drivers. The pre-driver was dead & the other two 8950,s no good. Thanks for any help....
Click to expand...

It's exactly what I thought it was. The tuned circuit between the first driver stages. Adjust it for maximum output power.
 
Shockwave said:
It's exactly what I thought it was. The tuned circuit between the first driver stages. Adjust it for maximum output power.
Click to expand...
OK, I guess it would mean on high switch side of the hi/lo switch! Sorry for all the confusoin. I will try this & let you know how it goes. Thanks so much...
 

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