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Tubelab Discussion and support of Tubelab products, prototypes and experiments

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Old 3rd October 2017, 09:12 PM   #11
colnago55 is offline colnago55  United States
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Join Date: Feb 2016
Location: New York City
Ok, so I completed the first step in my process of eliminating potential problems. I did calibrate the panel Ammeters so they read the same when given the same current. Per zxx222's suggestion I used a 1.5 volt battery and a 22 ohm resistor to generate 69 ma per ohm's law. When I measured with my cheap multi-testers I got a reading of about 62 to 64 ma.

I decided to ignore these results and set the meters to about 69ma with my current generator.

One panel meter read about 64ma and the other about 60ma, so they weren't too far off.

Next I will be disconnecting the aux cap and see if that makes a difference. I am now more concerned about the crackle at startup than in the drop in B+. I'm going to look at the connections for the power supply caps.

Am I correct that the voltage regulators and diodes are not part of the B+ chain?
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Old 3rd October 2017, 10:37 PM   #12
jdrouin is offline jdrouin  United States
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Join Date: Feb 2012
Location: Tulsa, OK
Originally Posted by zxx222 View Post
Are you sure about that? I made quick sim in PSUD, with 330-0-330V and 184mA total current for all tubes, B+ is 370V. If 300B's are biased to 100 mA each, then B+ drops to 360V.
This is right about what my TSE 300B was running with those same PT specs. At ~90mA bias, B+ was around 370 and change. At 74mA, B+ was in the 380V range and the amp was much happier.
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Old 8th October 2017, 05:57 PM   #13
colnago55 is offline colnago55  United States
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Join Date: Feb 2016
Location: New York City
Hi Guys,

Thanks for your help .

I replaced C4 with a 22uf capacitor and managed to get rid of the crackle. The two panel meters are now calibrated to each other.

I have the bias set to about 68ma and the B+ is 360 volts.

Would a different set of speakers cause the B+ to change?

It sounds great. The output transformers I'm using have multiple taps, I'm currently using the 5,000 tap and I'm tempted to try the 3,500 tap.

I wonder if I will hear a difference.

thanks again, Jacques
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