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AB165 Bassman @ 499V B+


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3/6/2000 7:31 PM
Ted
 AB165 Bassman @ 499V B+
Hi I have a 66 Bassman which I have modded mostly back to AA864 (left the extra gain stage the same as in the AB165 though). I have noticed that it seems to distort fairly early @ 3-4 Volume setting.  
 
It seems to have quite high voltages compared to the schematics. I measure 499V on the 6L6 plates vs. the schematic 425V. The preamp tubes have correspondingly high plate voltages as well when compared with the schematic. This is while idling.  
 
It is a CSA tested PT (has a ink stamp CSA tested). I wonder if its a different PT than typical Bassmans?  
 
Can this higher voltage be causing some pre-amp distortion? Should I attempt to remedy the pre-amp plate volatages somehow?  
 
Thanks.  
Ted.
  
3/6/2000 8:26 PM
Corwin
Ted: what is the voltage coming from your wall? I have 125V coming in from mine and the Bassman was made when common household voltages were 117V, so unless you have a variac or make RG Keen's "Vintage voltage adapter", the voltages will be higher than the schematic. I've still yet to measure the voltages in my Bassman, but I'm sure they're probably aruond 500V on the 6L6s  
 
Corwin
  
3/6/2000 9:49 PM
Ted
Yea, forgot about that. I'll check.  
 
(Actually I need a new meter. I accidentally grounded out the screen resistor with the needle probe when checking the plate V recently and it hasn't worked since. It was cheap anyway. Time for a good one!)  
 
Thanks.
  
3/6/2000 10:21 PM
M/J
I converted my ab165 bassman to aa864. It has plate voltages of 423v. Mine breaks up at around 5 and sings at 7.  
 
M/J
  
3/7/2000 3:46 AM
Max
Hi guys!  
 
I have 370V on the plate of mine(aa 165),with a tube rectifier i aded.My wall ac suply is 220V and i have a stepdown transformer,which gives me 106V,that's why.  
 
I think i gonna mod mine toAA864 too,even with the BFSR norm chanel,i'd say that i need a creamier nsound and bluesier.  
 
Best regards.  
Max.
  

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