Replacing a power tube (used as driver for mosfet car amp)...how to bias? - diyAudio
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Old 22nd June 2005, 02:25 PM   #1
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Default replacing power tube

Hi all,
I'm new here.I've seen there are many expert here,and i absolutely need your help.
I bought a used butler tube driver td1500 on ebay,but a power tube got broke during the shipment.
I just ordered a replacement,but i read that you need to adjust the bias on tube amp.How do i do that?
I phoned many car audio installer and they don't know how.
Music instrument store want to work only on home tube amplifier

Any help?Someone with that amp?
The amplifier is that :
http://cgi.ebay.com/ws/eBayISAPI.dll...MEWN%3AIT&rd=1

It is the original or the ppi version?I can only find the word phaze audio on it,no sign of butler and no sign of ppi
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Old 22nd June 2005, 02:46 PM   #2
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I don't know how it is biased...since you have to set it..it looks like fixed bias. In that case you should be able to find a little potentiometer with a track or wire leading to the grid of the tube in question.

What kind of tube is it? Looking at the specifications it looks like a pre or driver tube is being used and not a power tube. It is unlikely (with my limited knowledge) that the driver tube is fixed bias...leading me to think that you might stuff it into its socket and voila.
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Old 22nd June 2005, 03:19 PM   #3
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I don't know if that specifica amp has to be biased,i just read that the general rule for for replacing power tube amp is to bias them(have done some google search,but found only home amplifier topic).
The tube is that :
http://www.tubedepot.com/so-5881.html

I found a little screw near the 2 socket(there are 2 power tube) ,between the 2 of them, that could be a potentiometer ,but why there is only one if the tube are 2?
I will post some picture when i return home.
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Old 22nd June 2005, 03:32 PM   #4
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The photo would help I think..self bias is very inefficient..so it is likely that fixed bias was chosen..

here is the datasheet
http://www.retrovox.com.au/tsol5881.pdf

From this you can see that pin5 is grid one..ie that is where the bias needs to be set...to something -20VDC... so measuring between earth and pin 5 should give you around that voltage. The manufacturer however should have listed what the bias voltage needs to be.

NB...Your amp probably has lethal voltages inside. BE CAREFUL.

ps...since this thread concernes tubes..I'll move it to the tubes section...hopefully others with knowledge of this amp can chip in...besides in the tubes section there are more folks with the relevant knowhow..if you don't mind that is...
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Old 22nd June 2005, 03:49 PM   #5
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Thanks,you have been very clear.
Unluckily i didn't got any manual from the seller so i hope it is -20v,or you where referring to the manufacturer of the tube(sovtek)?
And i have 1 potentiometer only,does that mean i will change the bias of both?Is this possible?

Yes move the topic,thanks.
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Old 22nd June 2005, 03:51 PM   #6
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Hi Christian...


Quote:
And i have 1 potentiometer only,does that mean i will change the bias of both?Is this possible?
I've never used fixed bias myself...but I think that is very possible, but not so smart (I think)..as you cannot set the bias seperately for the 2 channels...????

Let's hope others chip in.


Quote:
Unluckily i didn't got any manual from the seller so i hope it is -20v,or you where referring to the manufacturer of the tube(sovtek)?
That is just a general figure I got from the datasheet.
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Old 22nd June 2005, 05:41 PM   #7
Giaime is offline Giaime  Italy
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I don't think that thing has power tubes in it, and the link that the guy provided was only to explain the bias thing, NOT meaning that there is a 5881 inside there (how would you fit it? ). Probably the guy doesn't know how to distinguish a pre tube form a power one. It will help if he posts any writing that's visibile on the damaged tube... I bet that's a 12AX7 or something.

Tell us, you tube looks like this
Click the image to open in full size.

or more like this
Click the image to open in full size.

What's the height of the tube? A pic or the model number would help...
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Old 22nd June 2005, 06:04 PM   #8
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No no,the tube is exactly that!
I know because i've checked the model number on the glass of the tube.Model 5881/6l6WGC sovtek.
Bytheway the amp is huge,something like 35x24x7,there is more than enough space for that.
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Old 22nd June 2005, 06:21 PM   #9
Giaime is offline Giaime  Italy
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Oh excuse me I didn't read carefully the whole thread.

How can only 2 5881 make a 150W amp???? I'd expect either class D (I don't think so) or a quad of those PER CHANNEL... so 8 tubes!!!

However it's possible that the power rates are inflated. Expect about a tenth of what is advertised. If the amp is really a SE of 5881, expect no more than 10-15W per channel. Btw, are even the output transformers inside the unit??? Can you provide a photo of the amp with the top cover removed??

It is quite important that we know the topology and the type of the amp in question before we can give any advice on tube replacing and biasing... because I think that's not a conventional topology!
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Old 22nd June 2005, 06:46 PM   #10
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Actually i just found googling that the amplifier is not a true vacuum tube amplifier.It just use tube for the input and mosfet for the output(haven't truly understood what that means ).
More info here :
http://groups.google.it/group/rec.au...c504c7510c96d+

What a pity,i didn't know that

BTW i got a reply from the butler technical stuff :

"The amp is self biasing as the tubes are run in class A.
No adjustments are necessary.
Butler Audio Staff"

So all i need is to replace them,but it is normal that they are soldered?
More shots coming.
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