Can't bias tubes to 40mvdc

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I went to re-bias my Rebel 20 for the first time since I bought it and found the bias way cold at 18.6 mvdc on the el84 side and 19.9 mvdc on the 6v6 side.

I tried to re-bias hotter and the highest that I can get with the pots all the way is 25.8 mvdc on the el84 side and 30.6 mvdc on the 6v6 side.

These are the stock tubes. Anyone know whats going on here? Do the resistors need to be modded to give more power to the tube? Higher rated tubes?

Thanks for any advice.
 
get diffrent tubes with higher ratings no biggie
 
Thanks just42dave

I'm new to tube amps and wasn't sure what was going on here. I have done some searching on the web and seen several people with this problem but no definitive answers.

I would have thought that the amp with the stock tubes would have been able to have been biased within Egnater's specs?
 
central":o937vvrz said:
Thanks just42dave

I'm new to tube amps and wasn't sure what was going on here. I have done some searching on the web and seen several people with this problem but no definitive answers.

I would have thought that the amp with the stock tubes would have been able to have been biased within Egnater's specs?
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I think you could have made a "mistake".For exemple,some people use probe-meters and measure one tube at a time.In that case,your original numbers would be just right.You wouldn't be the first to do that.
 
you are using bias points right?? I think my mod 50 and renegade measured as a pair so read the manual to see if its per tube or not..Pretty sure its for the pair.
 
I re read the post and get an milliamp reading though volts is ok Im sure he uses ma on his bias quotes..
 
Verify your meter is set for DC millivolts, not milliamps. This Mostar happens quite often. Is there any way to confirm your meter is working properly? FYI, if you had a dead tube in each pair, you might get this sort of symptom. Can you get another pair of either tube type to test? Since you are not really a repair per, troubleshooting yourself may not be a feasible option.
 
Bruce,

I have tubes ordered and am waiting on them but i did put a set of el84's from another amp in this one and had the same problem with the low bias. I am sure the meter is working properly and is set properly. As I am waiting on the tubes, this is what I have done.

Measuring pin 5 of the 6v6 sides without the tubes in I get -28vdc to -42vdc for both sockets at the far ranges of the bias adjustment pot. Measuring pin 3 I get 395vdc on both sockets.

For the el84, measuring pin 2 I get -16vdc to -22vdc for both sockets at the far ranges of the bias adjustment pot. Measuring pin 7I get 332vdc.

Is there any way that I am just getting the bias from one side from the bias check points and not the pairs?

Sorry if i am off here. I am not new to electronics. Just tube amps.
 
Your readings are all about right. Do this:
Remove on of each tube type and measure the bias on each. Remove those two tubes and put the other ones into their original sockets. Measure the bias. Report back.
 
Thanks Bruce.

Here is what I get when I do what you requested.

For the 6v6's I removed the left tube and I measure 19.8mvdc on the right tube. Remove the right tube and put the left tube back in and I measure 20.2mvdc on the left tube.

I done the same for the el84's and I measured 15.9mvdc for the right tube and 15.4mvdc for the left tube.

(These numbers are the highest bias numbers that I can get with the adjustment pots)

What do you think Bruce? Am I right in thinking that since my earlier numbers looked o.k. (I'm guessing these numbers I just posted are a little low since the bias number that we are looking for is the combination of the pair of tubes---correct me if I am wrong please), that my problem boils down to just needing warmer grade tubes???

Thank you very much for the help. It is very much appreciated. It is not just everyday that a user can talk with and get help from the designer of the product in question. Thank you.
 
My mistake, your readings are not correct. There is really no way you can get a different reading on Pin 3 of the 6V6 and pin 7 of the EL84. They are physically connected together in parallel. Please reconfirm that. Also, I believe you understand the bias readings the test points are the sum of the pair of tubes. It is also strange that you get the same reading regardless of whether you have one tube or two tubes installed. Please email me directly at begnater@aol.com so I can resolve this quicker for you.
 
Update. With the great help of Mr. Bruce Egnater, this problem has been solved.
 
central":2vab0rei said:
Update. With the great help of Mr. Bruce Egnater, this problem has been solved.
Click to expand...

If you happen to check back here, could you quickly summarize what your issue was and how it was resolved? I noticed that my bias readings were a little cold, as well.

Thanks!
 
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