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previous: Nick I have an old '64 Vox AC-50 head. I... -- 10/16/2004 12:22 AM View Thread

Re: VOx AC-50...component drift, and mojo factor...???

10/16/2004 1:59 PM
loudthud
Re: VOx AC-50...component drift, and mojo factor...???
Many people will disagree about this subject so let the Bar-B-Que begin.  
 
It's been my experience that carbon comp's usually drift to the high side. One can assume that the more heat a resistor receives the higher and faster the drift. All the NOS parts I have obtained over the last couple of years have meeaured higher than nominal value, most out of spec.  
 
Those Sprague caps can pass a phenomenal amount of current. I used them on a project to tune a 133KHZ antenna and they were passing 10 amps P-P. Most other caps I put in that circuit burned out. They tend to sound a little harsh.  
 
I have tried 100K 1/2w CC's for plate loads and they subjectively add a little sweetness. I've also tried 1/4W 330K's in the second stage ( with appropriate cathode resistor ) and they sounded as good if not better. Operating them beyond their voltage rating makes a sweet sound.  
 
I suggest replacing those 716's and the plate loads first. If you're not there yet, replace the rest of the resistors in the signal path. Check the resistors in the B+ decoupling. They may have reduced the B+ some and that could also affect the sound. As to what component went where, I'd put the high ones in the plates but I don't think that's as important as the type of part.  
 
I hope you will report you results here for us all to see.

 
Replies:
Nick Thanks for the reply. Here'... -- 10/16/2004 2:49 PM