RM 50 baising problem need help badly

[Servantez]

I was biasing my amp, and for some reason both of my 5881 tubes won't get bais close to .038mA. If I bais 1 tube at .038mA the other will read 52. So I tried my new pair of el34 and try to bias them again and the same thing happen 1 will read 38 and the other 1 will read 52 if anyone knows what is wrong plz help me out.

 

[JKD]

#1 Make sure you are using the common (ground) + a test point when testing (obvious I know..but just checking)

#2 It's possible you have two bad/poorly matched sets of tubes but it would be quite a coincidence to get exactly 38/52 on both

#3 swap the pair of tubes round in the sockets and see if it follows the tube....if it does, then you have a bad tube..if not, I'm guessing a component has gone in the bias circuit.

 

[Soulinsane]

All of the above.

Also, have you tried to zero out the bias on all the tubes as low as they will go and bring them all up to bias in small increments. It takes longer to do it that way but it should get everything balanced and in range.

 

[Servantez]

yea the problem does follow the tube, so what would be your suggestion to fix this problem should I change both tubes or just the bad 1

 

[Soulinsane]

New pair of tubes. Keep the old pair to figure which one is in fact bad and you will have at least one backup tube for the future.

 

[Jaded Faith]

This sounds silly, but I swear I did it one night when it was VERY late and I was VERY tired......

....make sure your meter is set to voltage and not the amperage setting. :shock:

Sad but true, I did this one night and had the exact same problem. Once I set the meter correctly, they were right on about 3 mV's away from each other. :idea:

Worth checking out.

 

[Servantez]

Jade yea man I took your advice and checked my meter, and I found out that I have put my meter in Amps ha ha ha silly me, thx man that helped me a lot

 

[Jaded Faith]

Awesome news. Glad I could help! I just had a hunch that was your problem. It was the EXACT same thing I went through. Almost the same numbers too!