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Post subject: 68 Custom Deluxe Reverb Bias Setting
Posted: Thu Jun 02, 2016 2:20 pm
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I have my bias set at 22ma with JJ 6V6 Tubes and the original GrooveTube 6V6 Tubes were also biased at 22 ma. This setting seemed to work good for me.

Recently I bought a matched pair of 6V6GT Electro-Harmonix tubes to try.
I cannot get the bias setting to go over about 19ma. The bias pot is maxed out. It sounds fair, but seems like I might need a little more oomph but have no more adjustment.

Why is the max bias setting lower with the EH tubes? I can get close to 30ma with the other tubes.
I use the Eurotubes single bias octal socket.


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Post subject: Re: 68 Custom Deluxe Reverb Bias Setting
Posted: Thu Jun 02, 2016 7:32 pm
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Assuming your plate volts are 420, then 19 ma is a good bias point.


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Post subject: Re: 68 Custom Deluxe Reverb Bias Setting
Posted: Fri Jun 03, 2016 2:35 am
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daver , bias millivolts with no plate voltage reading mean nothing. This may change on each homeé
Did you put 6V6 or 6V6 GT

68 Custom Deluxe Reveb schematic I have said 207 volts plates voltage. Bias could be 24 ma for 6V6GT and 20ma for 6V6
There is no bias pot on my schematic ! :o

Most Fender amp play very well at a colder bias


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Post subject: Re: 68 Custom Deluxe Reverb Bias Setting
Posted: Fri Jun 03, 2016 3:45 am
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stratele52 wrote:
daver , bias millivolts with no plate voltage reading mean nothing. This may change on each homeé
Did you put 6V6 or 6V6 GT

68 Custom Deluxe Reveb schematic I have said 207 volts plates voltage. Bias could be 24 ma for 6V6GT and 20ma for 6V6
There is no bias pot on my schematic ! :o
Most Fender amp play very well at a colder bias

The new tubes are Electro-Harmonix 6V6GT Tubes. I can only adjust bias pot to max 19ma for V7 tube and 19.5ma for V8 tube (measure with Eurotubes bias probe single octal socket)

My 68 Custom Deluxe Reverb schematic shows 407 volts and factory bias set at 24ma.
I am not sure how to measure the actual plate voltage.


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Post subject: Re: 68 Custom Deluxe Reverb Bias Setting
Posted: Fri Jun 03, 2016 3:58 am
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daver wrote:
stratele52 wrote:
daver , bias millivolts with no plate voltage reading mean nothing. This may change on each homeé
Did you put 6V6 or 6V6 GT

68 Custom Deluxe Reveb schematic I have said 207 volts plates voltage. Bias could be 24 ma for 6V6GT and 20ma for 6V6
There is no bias pot on my schematic ! :o
Most Fender amp play very well at a colder bias

The new tubes are Electro-Harmonix 6V6GT Tubes. I can only adjust bias pot to max 19ma for V7 tube and 19.5ma for V8 tube (measure with Eurotubes bias probe single octal socket)

My 68 Custom Deluxe Reverb schematic shows 407 volts and factory bias set at 24ma.
I am not sure how to measure the actual plate voltage.


I'm betting that your actual plate voltage is higher and your pair of tubes are colder running tubes.
That's why I purchased both a bias probe and a plate voltage probe.


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Post subject: Re: 68 Custom Deluxe Reverb Bias Setting
Posted: Fri Jun 03, 2016 4:07 am
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daver wrote:
I cannot get the bias setting to go over about 19ma. The bias pot is maxed out. It sounds fair, but seems like I might need a little more oomph but have no more adjustment.

Why is the max bias setting lower with the EH tubes? I can get close to 30ma with the other tubes.
I use the Eurotubes single bias octal socket.


If you can't get more than 19mA bias out of the EH, yet get almost 30mA on other sets/manufacter's 6V6GT on same amp --- the EH set are weak. If they are new I'd contact the seller for a refund or exchange.


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Post subject: Re: 68 Custom Deluxe Reverb Bias Setting
Posted: Fri Jun 03, 2016 4:10 am
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ckmckool wrote:
That's why I purchased both a bias probe and a plate voltage probe.



+1 , a great tool.


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Post subject: Re: 68 Custom Deluxe Reverb Bias Setting
Posted: Fri Jun 03, 2016 4:49 am
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BMW2002Ti wrote:
daver wrote:
I cannot get the bias setting to go over about 19ma. The bias pot is maxed out. It sounds fair, but seems like I might need a little more oomph but have no more adjustment.

Why is the max bias setting lower with the EH tubes? I can get close to 30ma with the other tubes.
I use the Eurotubes single bias octal socket.


If you can't get more than 19mA bias out of the EH, yet get almost 30mA on other sets/manufacter's 6V6GT on same amp --- the EH set are weak. If they are new I'd contact the seller for a refund or exchange.

This morning I checked EH tubes again with my multimeter set to ma, it goes to 21.2ma max. And, I dont know what I am actually reading when I set my multimeter to dc volts - it shows 415. It has to read pin 3 though. Last night the volts setting showed 396 and about 19.5ma.

I did contact the seller and they said their tubes are tested at 450volts at 90% is 19 (19 is the match number written on the boxes). I forget what he said the 19 number was - either amps or milliamps.

So thats exactly what I was thinking... that these EH tubes are actually just weak tubes. The supplier only said they not bad tubes. I'll buy another set elsewhere and try them.


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Post subject: Re: 68 Custom Deluxe Reverb Bias Setting
Posted: Fri Jun 03, 2016 4:56 am
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daver wrote:

I did contact the seller and they said their tubes are tested at 450volts at 90% is 19 (19 is the match number written on the boxes). I forget what he said the 19 number was - either amps or milliamps.

.


Milliamps

Electro Harmonix specs is 14 watts for 6V6GT

450 X 19ma = 8.55 watts

90% of 14 watts is 12.6 watts

If the seller check his tubes at 450 volts, it is not what your amp give you.

That is why we must always check bias with any new tubes.
With plate voltage reading.


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Post subject: Re: 68 Custom Deluxe Reverb Bias Setting
Posted: Fri Jun 03, 2016 10:25 am
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stratele52 wrote:
daver wrote:

I did contact the seller and they said their tubes are tested at 450volts at 90% is 19 (19 is the match number written on the boxes). I forget what he said the 19 number was - either amps or milliamps.

.


Milliamps

Electro Harmonix specs is 14 watts for 6V6GT

450 X 19ma = 8.55 watts

90% of 14 watts is 12.6 watts

If the seller check his tubes at 450 volts, it is not what your amp give you.

That is why we must always check bias with any new tubes.
With plate voltage reading.

So is this all telling me that the EH tubes I received are just a weak set. They do not sound right and are unusable for me. I reinstalled the JJ tubes and they sound good (and louder) bias trim pot set at 20ma. When I set multimeter to dc volts it says 400.


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Post subject: Re: 68 Custom Deluxe Reverb Bias Setting
Posted: Fri Jun 03, 2016 11:51 am
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For 400 vdc plate voltage you can go to 24.5 ma if amp sound better to your ears.

You'll see plate voltage will go down at 24.5 and you may have to do a new bias adjustma.
Each time you adust bias you must re-check plate voltage and do a new ajustment for ma if needed.

You can keep bias colder if you ears did not see a better tone. This make tubes last longer

http://www.tedweber.com/webervst/tubes1/calcbias.htm


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Post subject: Re: 68 Custom Deluxe Reverb Bias Setting
Posted: Fri Jun 03, 2016 12:42 pm
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stratele52 wrote:
For 400 vdc plate voltage you can go to 24.5 ma if amp sound better to your ears.

You'll see plate voltage will go down at 24.5 and you may have to do a new bias adjustma.
Each time you adust bias you must re-check plate voltage and do a new ajustment for ma if needed.

You can keep bias colder if you ears did not see a better tone. This make tubes last longer

http://www.tedweber.com/webervst/tubes1/calcbias.htm

I think you missed my point... I can adjust the bias trim pot and get close to 30ma with the JJ tubes. I can only get up to about 20-21ma with the EH tubes.


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Post subject: Re: 68 Custom Deluxe Reverb Bias Setting
Posted: Fri Jun 03, 2016 1:25 pm
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daver wrote:
stratele52 wrote:
For 400 vdc plate voltage you can go to 24.5 ma if amp sound better to your ears.

You'll see plate voltage will go down at 24.5 and you may have to do a new bias adjustma.
Each time you adust bias you must re-check plate voltage and do a new ajustment for ma if needed.

You can keep bias colder if you ears did not see a better tone. This make tubes last longer

http://www.tedweber.com/webervst/tubes1/calcbias.htm

I think you missed my point... I can adjust the bias trim pot and get close to 30ma with the JJ tubes. I can only get up to about 20-21ma with the EH tubes.


No I don't missed your point.

You write;
"I reinstalled the JJ tubes and they sound good (and louder) bias trim pot set at 20ma. When I set multimeter to dc volts it says 400. "

I give you some hints.


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Post subject: Re: 68 Custom Deluxe Reverb Bias Setting
Posted: Fri Jun 03, 2016 1:54 pm
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stratele52 wrote:
daver wrote:
stratele52 wrote:
For 400 vdc plate voltage you can go to 24.5 ma if amp sound better to your ears.

You'll see plate voltage will go down at 24.5 and you may have to do a new bias adjustma.
Each time you adust bias you must re-check plate voltage and do a new ajustment for ma if needed.

You can keep bias colder if you ears did not see a better tone. This make tubes last longer

http://www.tedweber.com/webervst/tubes1/calcbias.htm

I think you missed my point... I can adjust the bias trim pot and get close to 30ma with the JJ tubes. I can only get up to about 20-21ma with the EH tubes.


No I don't missed your point.

You write;
"I reinstalled the JJ tubes and they sound good (and louder) bias trim pot set at 20ma. When I set multimeter to dc volts it says 400. "

I give you some hints.

Ok.. Thanks
I guess I meant the other point - "So is this all telling me that the EH tubes I received are just a weak set" (since bias pot is maxed out at 20-21ma)


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Post subject: Re: 68 Custom Deluxe Reverb Bias Setting
Posted: Fri Jun 03, 2016 1:57 pm
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Yes EH are weak.

Where do you bought them ?


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