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RE: ... also a reminder bias is set with no signal. It goes up and down once signal applied. (nt)

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immatthewj

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In Reply to: RE: ... also a reminder bias is set with no signal. It goes up and down once signal applied. (nt) posted by Jonesy on July 28, 2020 at 15:01:40

Your previous explanation was great. thanks!
As far as input signal changing the bias, before I bought the Cary I had a pair of ARCs & they just had me spooked. For example, it wasn't uncommon for a grid resistor to go "POP!" shortly after I hit the power switch. I used to cross my fingers whenever I turned them on. & yes, I did notice that turning on the preamp made the bias do crazy things.
I didn't see that in the Cary. It never seemed to matter what I did with the preamp, the bias always stayed put.

Edits: 07/28/20 07/28/20

Follow Ups:

RE: ... also a reminder bias is set with no signal. It goes up and down once signal applied. (nt) - Jonesy 21:27:18 07/28/20 (6)
ARC was "infamous" for using those resistors as a protection circuit. That's how my old ARC D70 is designed. I've veer had any resisters blow over the years. Though I have had tubes go bad with destroying anything around them. Lucky I guess.

That's interesting about your bias not changing relative to the input signal. So I found an article that says if a certain impedance load is in place, bias will remain as set. Furthermore, if the impedance was too low (bad resistor), red plating can occur. I'm sure there's more to it than than just a resistor regarding the impedance circuit design. Either way, we're learning as we go!

Cheers!

Jonesy

"I know just enough to get into trouble. But not enough to get out of it."
- RE: ... also a reminder bias is set with no signal. It goes up and down once signal applied. (nt) - immatthewj 12:50:31 07/29/20 (5)
  My ARCs were the VTM 120s & I used to sincerely wish that a fuse would have blown instead of a resistor.
  Anyway, I am not ignoring your previous suggestions, but could I beat you up for one more favor? Could you paste a link to the cap tester that you bought from Amazon? I want to make sure that I get the one that will do what I need it to do. When I get back into it to check the caps, I'll inspect the tube sockets as you suggested.
  
  Edits: 07/29/20
  - Economic "in circuit" capacitor meter - Jonesy 14:50:59 07/29/20 (4)
    Yes, I remember you mentioning the ARC 120's. You have/had some nice amps.
    
    Here's a link to the "in-circuit" capacitor tester I use. Looks like a newer model and shipping direct from China.
    
    They also have an ESR meter that checks the health of a capacitor. I use them in tandem, but if I could only choose one, it would be that shown in the link.
    
    Sometimes you can get both as a set. Much cheaper that way. You may wish to check eBay or other sites as well.
    
    Cheers!
    
    Jonesy
    
    "I know just enough to get into trouble. But not enough to get out of it."
    - in circuit capacitor meter (Open in New Window)
    - RE: Economic "in circuit" capacitor meter - immatthewj 14:59:45 07/29/20 (3)
      Jonesy, I have said it before & I will say it again: you are the best!
      Thanks!
      - RE: Economic "in circuit" capacitor meter - Jonesy 15:11:12 07/29/20 (2)
        
        In Reply to: RE: Economic "in circuit" capacitor meter posted by immatthewj on July 29, 2020 at 14:59:45
        
        You're welcome.
        
        I'm just re-reading the online description. I don't see it saying "in circuit" anywhere, so check the manual that comes with it. Either way it's still the one to get.
        
        Jonesy
        
        "I know just enough to get into trouble. But not enough to get out of it."
        
        RE: Economic "in circuit" capacitor meter - immatthewj 15:24:56 07/29/20 (1)
        
        In Reply to: RE: Economic "in circuit" capacitor meter posted by Jonesy on July 29, 2020 at 15:11:12
        
        It has been ordered . . . .
        
        RE: Economic "in circuit" capacitor meter - immatthewj 16:26:12 08/05/20 (0)
        
        In Reply to: RE: Economic "in circuit" capacitor meter posted by immatthewj on July 29, 2020 at 15:24:56
        
        Thank you, Jonesy, for all the time & effort on & offline helping me solve this!

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