# YCV40 bias reading help



## venn (Mar 11, 2015)

Before I swap tubes in my YCV40 (previous thread http://www.guitarscanada.com/showthread.php?69746-Swap-tubes-in-YCV40-to-EL34 ) I took a reading from r91 and r92 with the old tubes. I tried the 200mv setting and it just gave me the 1 reading so I tried 2V setting. The readings are 0.394 and 0.402V! According to the manual they should be set at 75mv(not 394!). This is my first time at this but something is not right here. Yes I checked the connections and took several readings. I also checked the multimeter on a AAA battery and it reads 1.47V.


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## jb welder (Sep 14, 2010)

You are measuring across each resistor? One probe to each end of R91, then repeat for R92.
Amp idling with no signal, meter set on DC volts?
If this is an accurate reading, are tubes red-plating? Does amp sound normal? With power off, check resistance of R91 & R92. Should read very low resistance, approx. 2 ohms each.


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## venn (Mar 11, 2015)

Yes, one probe to each end of R91 AND R92. Meter was set to 200mv but couldn't get a reading so I set it to 2V, not a fluke but not a harbor freight meter either (ideal brand). Amp is turned on and not in standby mode. I have pulled the chassis from the amp-so no speaker is connected (or reverb for that matter). Tubes are glowing orangeish I would say. This is how this amp has been since the day I bought it a little over a year ago (I have moderately used it-cant say I ever pushed it more than half volume). When I bought it the po said tubes were replaced with tung-sol 6l6gc-str, had receipts from a reputable local shop.

- - - Updated - - -

Spoke with Traynor this morning. They said there is no way that is what the reading is. I can't count how many times I checked and verified the readings. I put in the el34's just to see if there was something up with the 6l6's. They were reading about 112mv. But what is up with the stock readings? If tubes are going bad, would it cause this?


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## dtsaudio (Apr 15, 2009)

Traynor is notorious for not providing accurate schematics, or making changes that are documented.
Check the values of the two cathode resistors. I have seen them a 10 ohm as opposed to the schematics 2 ohm. This would explain the difference.
BTW - do your testing with a speaker or dummy load connected. It is not good practice to run a tube amp without a load.


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## venn (Mar 11, 2015)

dtsaudio said:


> Traynor is notorious for not providing accurate schematics, or making changes that are documented.
> Check the values of the two cathode resistors. I have seen them a 10 ohm as opposed to the schematics 2 ohm.


R91 and R92?




dtsaudio said:


> BTW - do your testing with a speaker or dummy load connected. It is not good practice to run a tube amp without a load.


Thank you! I'll take all the tips and pointers I can.


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## jb welder (Sep 14, 2010)

Dan has sorted it out for you. The earlier versions used 10ohm resistors there so the factory bias setting would be 350mV.
The older schematics I have show the 10ohm resistors and state the 350mV target voltage.
Their online manuals will always be the latest versions.


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## venn (Mar 11, 2015)

jb welder said:


> Dan has sorted it out for you. The earlier versions used 10ohm resistors there so the factory bias setting would be 350mV.
> The older schematics I have show the 10ohm resistors and state the 350mV target voltage.
> Their online manuals will always be the latest versions.


Hmmm, well according to the traynor tech, my model number is the latest version of the board.


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## venn (Mar 11, 2015)

I just verified that the R91 and R92 are indeed 10 ohm resistors. Now I need to figure what the bias should be for EL34's


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## jb welder (Sep 14, 2010)

Factory bias setting for the EL34's is the same, 350mV. Now you will get to find out if you need to change R78 or not.


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## Ti-Ron (Mar 21, 2007)

Wrong thread, sorry.


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## dtsaudio (Apr 15, 2009)

> Hmmm, well according to the traynor tech, my model number is the latest version of the board


I've talked to a couple of guys at Traynor, they don't seem to either keep very good records or really don't know what's going on with their products.

I'm glad you found the issue though.


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## venn (Mar 11, 2015)

jb welder said:


> Factory bias setting for the EL34's is the same, 350mV. Now you will get to find out if you need to change R78 or not.


Yep, gonna have to. Max bias I can get is 250. I also checked the R78, it is 27K. I know the schematic doesn't show it, but it does list it under the board version changes. If I did my figuring correctly(which I probably didn't so don't laugh), I need atleast 37K resistance, correct? Is the trim pot (10K I believe) in series or parallel? I didn't figure that into it.


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## venn (Mar 11, 2015)

dtsaudio said:


> I've talked to a couple of guys at Traynor, they don't seem to either keep very good records or really don't know what's going on with their products.
> 
> I'm glad you found the issue though.


R78 needs to be changed from 27K to 18K. Thanks for the help!


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## jb welder (Sep 14, 2010)

Good that you were able to get the correct info. If it is easier to do a "short cut" from the component side of the board, you can just tack a 56K across the existing 27K. That will give a resistance of 18K.


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## venn (Mar 11, 2015)

Success! Not too much of a pain to get to. Thanks to all who helped!


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## greco (Jul 15, 2007)

Interesting thread!

Wonderful, dedicated and generous tech assistance here.

Cheers

Dave


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## Church-Audio (Sep 27, 2014)

venn said:


> Yes, one probe to each end of R91 AND R92. Meter was set to 200mv but couldn't get a reading so I set it to 2V, not a fluke but not a harbor freight meter either (ideal brand). Amp is turned on and not in standby mode. I have pulled the chassis from the amp-so no speaker is connected (or reverb for that matter). Tubes are glowing orangeish I would say. This is how this amp has been since the day I bought it a little over a year ago (I have moderately used it-cant say I ever pushed it more than half volume). When I bought it the po said tubes were replaced with tung-sol 6l6gc-str, had receipts from a reputable local shop.
> 
> - - - Updated - - -
> 
> Spoke with Traynor this morning. They said there is no way that is what the reading is. I can't count how many times I checked and verified the readings. I put in the el34's just to see if there was something up with the 6l6's. They were reading about 112mv. But what is up with the stock readings? If tubes are going bad, would it cause this?


Um no speaker??? That's a no no. Make sure you always have a load or you will be replacing more than just tubes.


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## venn (Mar 11, 2015)

greco said:


> Interesting thread!
> 
> Wonderful, dedicated and generous tech assistance here.
> 
> ...


Yes I was impressed with everyone I came into contact with there.

- - - Updated - - -



Church-Audio said:


> Um no speaker??? That's a no no. Make sure you always have a load or you will be replacing more than just tubes.


That's already been covered or you just wanted to add your 2 cents?


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## Church-Audio (Sep 27, 2014)

venn said:


> Yes I was impressed with everyone I came into contact with there.
> 
> - - - Updated - - -
> 
> ...


Sorry I did not see that btw lots of people pay more than two cents for my advice. Just trying to help!


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## venn (Mar 11, 2015)

Church-Audio said:


> Sorry I did not see that


No problem. 



Church-Audio said:


> btw lots of people pay more than two cents for my advice. Just trying to help!


No doubt, I probably would too! Trying to learn this stuff. Thanks!


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