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Old 12th December 2020, 01:10 AM   #911
itsikhefez is offline itsikhefez  United States
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After a 14 year run, the TSE must DIE!
Can anyone provide insight into the use of 4700uF (C3) after the MIC29502WT regulator?
The datasheet calls for 10uF.
I've seen many designs oversize this to 100-1000uF, but not more.
Curious about this as I need to make a similar decision on another amp
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Old 12th December 2020, 10:54 AM   #912
Bas Horneman is offline Bas Horneman  Netherlands
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Quote:
The datasheet calls for 10uF.
The datasheet is written bij engineers. The 10uF I think is minimal needed to prevent issues. This 10uF makes the bean counters happy because it is cheaper then 1000uF. But for you and me this is less a consideration (I think). And so most would choose a nice fat cap there to reduce any possible ripple a little more. Whether that is a good idea or sounds better in a filament supply is up for debate ( I don't know the answer)
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Old 12th December 2020, 12:53 PM   #913
Tubelab_com is offline Tubelab_com  United States
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The 4700 uF cap is a carry over from the original TSE. All of these IC voltage regulators use a high gain feedback loop to compare the output voltage to a known reference and adjust it as needed.

There have been continuous debates about the audibility of these "feedback" systems, whether CC or CV is best.......

The Sharp regulator used in the original TSE had the lowest dropout voltage of any regulator I have ever tested. It however was an old design and was never updated before it went extinct.

No output impedance VS frequency specs were given for the Sharp part. The Microchip part has a graph showing a low output impedance at 100 or 120 Hz, but this rises to nearly half an ohm at 20 KHz.

The chip is driving a load of about half an ohm when feeding a pair of 2A3's so it is quite possible that any audio voltage developed across the filament in the output tubes will be present in the regulators feedback loop.

The output impedance of the regulator also rises as the regulator gets near dropout and can become nonlinear.

Testing in the original TSE did show some remnants of the audio signal across the filament supply when the amp was driven to clipping. 300B's were worse case. The big fat cap (4700 uF) reduced it to below detectability with an amplifier on my scope input.

As predicted in the data sheet the Microchip part goes crazy with no output cap, generating bursts of HF energy at a 120 Hz rate. 22 uF across the output stops the craziness. No instability was seen with 22,000 uF so I left the 4700 uF cap in place.

The data sheet cautions against using a super low ESR part, as this may add a "zero" in the feedback loop. I did not see anything unusual with a 10 uf ceramic SMD part across the 4700 uf electrolytic, but I would not put one in my amp.

As with anything like this, circuit layout and operating conditions make a difference, so feel free to experiment, but I would stay away from extremes (ceramics, less than 22 uF, or more than 22,000 uF).
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Old 19th December 2020, 11:34 PM   #914
sgtnoah is offline sgtnoah
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After a 14 year run, the TSE must DIE!
Getting parts together for a TSE-II build. I have a 660v trans for the power supply and a 5H choke with 58 ohms DC resistance. Thinking that the B+ will be a bit high. Thought about using a 5U4 to get the voltage down, but prefer the slow start of a GZ34. Would putting a 5W (of yet to be determined value) resistor in series with the choke be the best way to get the B+ down? My PT has a 200ma secondary, so I think there is a bit of room to make a bit of heat.

Am I on the best path? Thanks in advance!
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Old 26th December 2020, 03:49 AM   #915
Maryanta is offline Maryanta
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Quote:
Originally Posted by sgtnoah View Post
Getting parts together for a TSE-II build. I have a 660v trans for the power supply and a 5H choke with 58 ohms DC resistance. Thinking that the B+ will be a bit high. Thought about using a 5U4 to get the voltage down, but prefer the slow start of a GZ34. Would putting a 5W (of yet to be determined value) resistor in series with the choke be the best way to get the B+ down? My PT has a 200ma secondary, so I think there is a bit of room to make a bit of heat.

Am I on the best path? Thanks in advance!
Adding resistor will drop the voltage. Before adding resistor, Please consider to add inrush current limiter similar like CL-60. In my experiment, it will help reduce the input main voltage 1.5 VAC for each CL-60 (my line voltage is 230 Volts 50 Hz). If you still need to drop the voltage, resistor may be added after the Choke to have LCRC filter. Please note however that if you use the same PT for Power supply and heater, adding Inrush current limiter will also drop the output voltage to Heater. I also learn from building of TSE-II that different PT will have different voltage drop under loaded conditions. I think the best way is to try first and then make adjustment from there to aim the target operating point.
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Old 31st December 2020, 08:49 PM   #916
kstolleis is offline kstolleis  United States
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I used a 10H choke and 660V trans and the B+ was not alarming. I would try setting it up and checking what B+ is before going to extremes. It seems like there are a number of variables and trying to predict exact B+ in advance is not easy. Maybe there are folks smarter than with the math that me...
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