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New Build Complete -- odd voltages, but OK


 
11/5/2004 7:27 PM
Bob Arbogast New Build Complete -- odd voltages, but OK
I just finished a new 5E3 build. I used a Mercury Magnetics "lower B+" power transformer. I was told -- if I heard correctly -- that the voltage difference was about 30Vac. After I installed the PT and fired up the amp, I noticed quite low DC voltages: 295V on the 6V6 plates. Then I looked at the PT diagram: it's not 30Vac difference; more like 90V. D'oh! The amp was not very loud at all.  
 
Anyhow, I subbed in a GZ34 for the 5Y3, and now have 334V on the plates, 19.5V on the cathodes, and an idle dissipation of about 10.5W per bottle. The amp sounds really good. It's nice not to have to worry about burning up my old Webcor-branded blackplates. Too bad I just bought some spare 5Y3's.  
 
Bob Arbogast
 
11/6/2004 9:08 AM
tubegarden
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Hi Bob,  
I use these in my kits. I end up with 340 at pin 8 on the rectifier, with a NOS 5Y3... I wonder if you have a bad one for some reason....  
 
dan
 
 
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11/6/2004 9:47 AM
Bob Arbogast
Dan,  
 
I tried two different NOS 5Y3's, one a JAN, one an old production USA, with the same results. And, of course, the GZ34 yields 334V on the plates. Perhaps there is something else going on -- but the amp does sound great. What are you seeing for AC input to the rectifier?  
 
If there are no problems, then I'm just looking at an amp with three distinct options: 5Y3 for low power, GZ34 for medium power, and solid state plug-in for "high" power.  
 
Bob
 
11/7/2004 7:25 PM
tubegarden
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I don't have one in the shop to measure, Bob... sorry.. the things sell as fast as I can make them...  
 
dan
 
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