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Post subject: Fender EC Tremolux Plate Voltage and Bias
Posted: Wed Jan 06, 2016 8:24 am
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There is a strange thing with my EC Tremolux what confuses myself.

The fixed bias was set to 30 mA (6V6 GT tubes). The plate current (pin 3/8) with the original JJ 5Y3 S (!) is 525 volts with a 5Y3 GT = 532 volts. Much higher than expected. If I calculate the bias with a plate voltage 500 Volts it should be around 15-17 mA. That is nearly 50% of the measured result. For the measurement I used a bias probe adapter.

I do not think that I have to devide by 2 because of two tubes.


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Post subject: Re: Fender EC Tremolux Plate Voltage and Bias
Posted: Wed Jan 06, 2016 12:14 pm
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A bias probe check bias current on one tube , you do not need to divide.

With 6V6 , 70 % = 18 ma at 525 Vdc.
30 ma is a way toooo hot if you are in AB class amp. Not for class A.
30 ma each tube ?

I'll set bias colder if tone is good. Maybe amp will be more quiet, less hum ?

Any EC Tremolux shematic ?


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Post subject: Re: Fender EC Tremolux Plate Voltage and Bias
Posted: Thu Jan 07, 2016 1:59 am
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Many thanks for your reply! I fully agree.

I tested with 16 mA. The sound was thin and swampy. Starting at 25 mA the sound was getting fine. The hum is changing with the bias setting from minimum to maximum. But not dramatically. Between 16 mA and 30 mA there is not a big difference. Currently I set the bias to 25.5 mA.

I was looking for a schematic but I found only one for the '57 Tweed Deluxe. Because of the cathode bias it should not be comparable. To be honest I do not know if the amp is really class A/B. But I assume.

I am worried about the 525/532 V because the capacitators are designed for 475 V.


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Post subject: Re: Fender EC Tremolux Plate Voltage and Bias
Posted: Thu Jan 07, 2016 2:23 am
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475 volts capacitors....... :(

As I know it is not very good for 6V6's to run at more than 425 volts

JJ's tube spec is max limit in pentode for plate ; 500 volts

https://www.tubesandmore.com/sites/defa ... nsheet.pdf

Does't mater for Eric Clapton, he have money for new tubes.


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Post subject: Re: Fender EC Tremolux Plate Voltage and Bias
Posted: Thu Jan 07, 2016 4:49 am
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Yes, strange thing. I already ordered some JJ 6V6 S. But this will not solve the root cause. :(


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Post subject: Re: Fender EC Tremolux Plate Voltage and Bias
Posted: Thu Jan 07, 2016 5:22 am
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tambu wrote:
Yes, strange thing. I already ordered some JJ 6V6 S. But this will not solve the root cause. :(



Sure is not. Bias reading tell tubes are matched.
Only a very mismatched output tube may hum.
A qualified tech may trouble shout and find why this amp hum.
The tech you see did not tell :(

After choice is to fix it or mod it


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Post subject: Re: Fender EC Tremolux Plate Voltage and Bias
Posted: Tue Jan 12, 2016 2:26 am
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I question the reading of 525+ VDC on the Plates. Something is not right about that, either wrong reading, or something up with the high voltage supply, I suspect the former. :idea:

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Post subject: Re: Fender EC Tremolux Plate Voltage and Bias
Posted: Tue Jan 12, 2016 2:42 am
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shimmilou wrote:
I question the reading of 525+ VDC on the Plates. Something is not right about that, either wrong reading, or something up with the high voltage supply, I suspect the former. :idea:


+1

That's the amount of plate voltage typically seen on something like an ultra-linear Twin Reverb or a Bassman 135.

Arjay

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Post subject: Re: Fender EC Tremolux Plate Voltage and Bias
Posted: Fri Jan 25, 2019 9:27 pm
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Got one on my bench the plate voltage is 374VDC


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