Bias adjustment Herbert

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Ampaddict

Ampaddict

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According to the site 6L6's and EL34's should be Biased at around 65mA, is this correct?
 
It would be helpful to know the plate voltage that the amp is running at so that you could calculate the max dissipation. That would let you know what ma to adjust to.


Anyone know how much plate voltage puts out?
 
The manual says 35mA while the website says 60-70mA. Which is it? :la:
 
thanks pete for the quick info!

I love my new herbert!
 
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Ampaddict":52dbb said:
The manual says 35mA while the website says 60-70mA. Which is it? :la:
Click to expand...

Remember that the 60-70 reading is for the pair not the single tube :wink:
 
Oh Oh....I followed the sticky on this site from duesentrieb that said bias for EL34 is 60 to 70 mA ....Is this higher number based on it being a set?? I followed his instructions exactly and set at 65ma .

I just put in the new tubes a week ago. If the bias current is only supposed to be 32ma I hope I have not fried them or anything else. Can anybody confirm this ?
Thanks
 
Hi Chief,
I see you posted the answer just as I posted the question ! Thanks for the clarification.
 
I'm talking a new bias adjust Herbert here. 3 bias pots, 6 tubes. I think that 1 bias pot is for two tubes.... so each should be read in the 60's????????? :? (see below) Or do I divide it in half????

3 total readings each of around 65mA for 6L6 and 34's.... right?

Recommended bias currrent for one pair (thats what you read with your DMM)

5881: 50 mA
6L6: 60 to 70 mA
EL34 60 to 70 mA
6550, KT66, KT88: 80 mA

Here is a pic:
http://www.diezelamplification.com/close/biaseinstein.jpg

http://www.diezelamplification.com/html/tech.htm
 
i guess it is for the pair and your 65 should be right on the money

32ma x 2 = 64 for el34
36 x 2 = 72 for 6l6 if summed for pairs I guess.
 
the picture shows it as 65 so thats my thinking too. the manual says the lower number so I can see where confusion arrives. :?
 
Let your ears decide, at 475/480V there is a safe area, where just your ears decide:

6L6.gif


Keep in mind that in the pic its for single tubes, while the recommendations are for PAIRS. Also in the pic you see tubes with a max. plate dissipation of 25 AND 30 Watts. 6L6GCs have 30 Watts.
30*550/475 = 35 mA (single tube), so up to 70mA for a pair.

If you prefer 60mA or 70mA for a pair - let your ears decide.
 
>|<>QBB<
duesentrieb":98ea6 said:
Let your ears decide, at 475/480V there is a safe area, where just your ears decide:

6L6.gif


Keep in mind that in the pic its for single tubes, while the recommendations are for PAIRS. Also in the pic you see tubes with a max. plate dissipation of 25 AND 30 Watts. 6L6GCs have 30 Watts.
30*550/475 = 35 mA (single tube), so up to 70mA for a pair.

If you prefer 60mA or 70mA for a pair - let your ears decide.
Click to expand...

Thanks much, I did it correctly- just wanted to be certain.
 
What if you don't have the external bias adjustment feature on the herbert? How do you adjust?
Thanks,
Rick
 
Each pair has a fuse on the board (pots facing you upper right corner). Pull one fuse, hook a DMM with crocos to each side of the fuse holder set to 200mA DC and read current after switching it on (be careful!). Adjust bias (trimmer on the left). After adjustment put fuse back into holder and repeat for other fuses/pairs.
 
Could you use one of the Weber bias tools or the compubias in lieu of the process described? I will look at the board...hopefully it's obvious as described.
thanks,
Rick
 
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