Tube Amps / Music Electronics
For current discussions, please visit Music Electronics Forum.

ampage archive

Vintage threads from the first ten years

Search for:  Mode:  

Re: AC30 TB low/high Power Switch

5/31/1999 4:44 AM
Steve A.

Re: AC30 TB low/high Power Switch
    If the output section of the AC30 is wired up with a single 50 ohm cathode resistor for all 4 tubes (as on the schematics I have) I guess you'd rewire it with 2 or 4 cathode resistors if you were going to cut out 2 tubesó right? Correct my math if its wrong, but for the same bias current you'd want to use 100 ohms for a pair of EL84's or 200 ohms for a single EL84. BTW what value cathode resistors do you think work best with the Vox EL84 amps? Do you prefer a single resistor, two resistors or four resistors (for an AC30)?  
Steve Ahola
And now, a word from our sponsors:

5/31/1999 9:08 AM
Bob S

Boy what a dope I was. I completely forgot about the cathode resistor. Absolutely you need to change the cathode value or you'll burn up those bad boys. My guess would be more like 120 -130 ohm. My two EL-84 amps have these in them. But just get the ma @ 40-45 per tube and what ever value it takes to get it there. Depending on the load factor of your tubes you could go from 100-150 ohms. I leave the single resistor in there. I haven't really messed with going multiples. I've had real good luck with the Sovtek EL-84's and when I order them I order nothing above 100 value in there matching system. This allows me to keep the 47-0hm resistor in place, but I've used up to a 62 ohm resistor to maintain the ma. load I prefer. Steve thanks for jogging my memory on the cathode, wouldn't what to screw anybody up!!!  
Bob S.
5/31/1999 11:22 AM

How's it going? My vintage 30 should be here tommorrow so I'll let you know how that amp sings with that (this is currently my favorite amp). Can't wait!  
6/1/1999 8:54 AM
Bob S

Pickin up another V30 myself. If you get a chance try it with two twelves!!! It will knock your socks off.  
Bob S.
5/30/1999 9:48 PM
Re: Suggestions
Is that the same as the one posted in the schem section here?  

<<First Page<PrevPage 2 of 2