Correct Bias Voltage for ST-70?

Postby nicole » Thu Mar 09, 2006 8:14 pm

vintage_dog wrote:
.... my recollection of the st70 being biased "correctly" (below 45ma), is that it looses a bit of dynamics. will try that tonight.


i biased my st70 down to about 1.35, and blah, didn't quite like it - slow and lacks dynamics, so it's back to 1.56 as recommended by the designers. luckily, the power transformers have been upgraded but they still get very hot...

yehey!!! :lol: 1.56V!!!!
User avatar
nicole
Citizen
Citizen
 
Posts: 637
Joined: Tue Sep 21, 2004 9:36 pm
Location: Da Nang City / Cavite

Correct Bias Voltage for ST-70?

Postby john » Fri Mar 10, 2006 7:40 am

Biasing to 1.35V or to 1.56V is in reality secondary to the sonic quality of the EL34 tubes being used in the amp. And also the overall sound quality of the audio chain where the ST-70 is linked with. And plus, the prefered acoustic perception of each individual owner.

I would prefer NOS EL34 tubes on an ultralinear connection versus Triode connected modern production EL34 tubes, because the later will never attain the sonics of a triode tube. And the former being to rare and very scarce to be configured on a triode connection.

On the stock biasing circuit of the St-70, One tube on each channel will surely be decomissioned in due time because the bias current is dependent on each other ( Pushing and Pulling). At a given time, the mismatch will take it's toll on the weaker tube. Independent biasing and regular monitoring of the bias settings will make the ST-70 sing longer than 3k to 5K hours.

ST-70 is a push-pull tube amplifier and we know that crossover distortion will always be an issue. No matter how small the percentage of distortion is, A distorting SET amp is much pleasurable to listen to.

John
User avatar
john
Citizen
Citizen
 
Posts: 159
Joined: Thu May 22, 2003 11:08 pm

Postby conspicuous » Wed Mar 22, 2006 7:10 pm

m_shoe_maker wrote:
hypertriode wrote:
m_shoe_maker wrote:Naku po :!: Nataranta na tong ST70 user. :shock:

Anyway, simple lang ang solution ko.........

Master Hyper, what reading from my volt meter will I bias my ST70 :?:

Simpleng tanong sa Tube God, and his answer will be my Gospel Truth. 8)


just my opinion fritz: i agree with john that NOS EL-34's can take the punishment inflicted by high or bias settings while new production ones can't. also take into account the stock stereo 70 transformer's size - it gets really HOT; reason why i overrate my stereo 70's trannies by at least 50% more. having done that, for me the stereo 70 sounds it best at 1.56v bias voltage or 50 ma per tube; set the bias to 1.4v or lower you lose a lot of dynamics (and dynamic-sounding isn't one of the stereo 70's traits to start with). i'd rather listen to a quad of EL-34's on a stereo 70 for one year at it's optimum (50 ma/tube) than spend two years (scrimping on tube replacement cost) with so-so sound...but this is just me :)


That's it :!: The Master has spoken. :D


AMEN! :D if need be i'll just work overtime to buy a new quad of el34 tubes as needed for as long as i get optimum sound :)
User avatar
conspicuous
Fanatic
Fanatic
 
Posts: 2257
Joined: Tue Oct 05, 2004 1:33 pm
Location: San Pedro, Laguna

Re: Correct Bias Voltage for ST-70?

Postby tony » Mon Jan 28, 2008 11:52 am

john wrote:Biasing to 1.35V or to 1.56V is in reality secondary to the sonic quality of the EL34 tubes being used in the amp. And also the overall sound quality of the audio chain where the ST-70 is linked with. And plus, the prefered acoustic perception of each individual owner.

I would prefer NOS EL34 tubes on an ultralinear connection versus Triode connected modern production EL34 tubes, because the later will never attain the sonics of a triode tube. And the former being to rare and very scarce to be configured on a triode connection.

On the stock biasing circuit of the St-70, One tube on each channel will surely be decomissioned in due time because the bias current is dependent on each other ( Pushing and Pulling). At a given time, the mismatch will take it's toll on the weaker tube. Independent biasing and regular monitoring of the bias settings will make the ST-70 sing longer than 3k to 5K hours.

ST-70 is a push-pull tube amplifier and we know that crossover distortion will always be an issue. No matter how small the percentage of distortion is, A distorting SET amp is much pleasurable to listen to.

John



very sensible post!
low biasing as in 1.35 volts decreases the classA window of the amp, compared to 1.56, that is why some does not like low bias.... :D

here is a link you may find usedfull: http://www.diyaudio.com/forums/showthread.php?s=&threadid=42111
User avatar
tony
Fanatic
Fanatic
 
Posts: 1882
Joined: Tue Jun 24, 2003 7:18 am
Location: Pasig City....

Previous

Return to DYNACO

Who is online

Users browsing this forum: No registered users and 1 guest