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 Post subject: Ronan Regulator for DHT
PostPosted: October 8th, 2021, 5:49 pm 
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Just a question out to the group if anyone has experience with using the Ronan Current regulators for DHTs. I am working on a rebuild of a PP 2A3/300B amplifier and trying to fit it into a preexisting chassis. The Ronan regulator was the DIY rage back before the TentLabs and Coleman DHT filament regs became available. I use the Coleman regs in my GM70 amp, which have been running reliability for several years, so no complaints But that has more substantial demands on the raw power supply, and between the transformers, power supply and regulator, and start to run out of real estate with two regulators in the amp (each tube needs their own).

The neat thing about the Ronan regs are they use 3 terminal regulators (LT1085 LDOs) for a voltage regulator feeding a current regulator. The voltage regulator is used for noise and voltage stabilization, it is the current regulator that feeds the filament. I have attached a schematic of the concept, though I would use a 2 stage rather 3 stage regulator as shown in the upper view. Both the current and input voltage requirements are lower for the Ronan-style regulators that for the Coleman regs.

I already have AC heating with with 2A3s, and with a 10 turn WW hum pot on the filament of one tube (and a pair of matched resistors to a virtual CT on the other tube, I can null out the hum to inaudibility. But if I want to try 300B tubes I need 5V heaters and then hum and IMD becomes an issue. I am presently using JJ 2A3-40s at 300B op point, so locked in to a single tube, it would be nice to have the flexibility.

Anyway, any thoughts?

(BTW click the image below to view the schematic clearly)


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PostPosted: October 8th, 2021, 6:08 pm 
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Another possibility is the LT1085 version of the D-Noizator. See post 1985.

https://www.diyaudio.com/forums/power-supplies/331491-noizator-magic-active-noise-canceller-retrofit-upgrade-317-based-reg.html

ray


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PostPosted: October 8th, 2021, 6:54 pm 
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Ray,

Thanks for the suggestion, but I am not sure how this can apply to a DHT filament CURRENT regulator providing 5VDC/1.5A for 300B. It could potentially apply to the voltage pre-regulator to help clean it up before going to the current regulator, but any circuit would have to be sensitive to the fact there is substantial current being supplied. I have to say, if I wanted that level of complexity, I would just give Rod Coleman the business and figure out a way to make it all fit.

Just trying to keep it simple, small and good enough.

I know ultrasonic AC with hum balance pot is another way as well.

David


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PostPosted: October 8th, 2021, 10:19 pm 
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If you are open to the high frequency AC solution, read Alex Kitic's methodology in his RH813 amp. I used it in my GK71 amp adding extra turns to obtain 20 VAC. For 6.3 VAC, you would need to reduce the number of turns. It seemed to work for me and it did not require a hum pot. By the way, for 115 volts, I used a 560 uf 200 volt cap to get rid of the buzz. Also note that after powering off, the caps do not discharge.

http://rh-amps.blogspot.com/2014/06/rh813-flagship-project.html

I am currently rebuilding my GK71 amp since I had to disassemble it for the trip to Oz.

ray


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PostPosted: October 10th, 2021, 11:26 pm 
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Aside from proper balanced heating of the tube and freedom from hum, high-frequency ac heating does not cause the electromigration issues that dc heating can.


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PostPosted: October 11th, 2021, 10:41 am 
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dberning wrote:
Aside from proper balanced heating of the tube and freedom from hum, high-frequency ac heating does not cause the electromigration issues that dc heating can.

In the interest of clarity, David -- could you explain "electromigration?"

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PostPosted: October 11th, 2021, 11:16 am 
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As I understand it, a DC current can cause molecules of the filament metal to migrate over time. It is similar to a plating process where metal molecules move to a charged metal plate. Different process but a similar result. It causes thinning in part of the filament which then has greater dissipation and earlier failure.


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PostPosted: October 11th, 2021, 2:53 pm 
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tomp wrote:
As I understand it, a DC current can cause molecules of the filament metal to migrate over time. It is similar to a plating process where metal molecules move to a charged metal plate. Different process but a similar result. It causes thinning in part of the filament which then has greater dissipation and earlier failure.

Does this only apply to direct-heated triodes where the filament serves as the cathode as opposed to the filament heating a separate metal cathode?

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PostPosted: October 11th, 2021, 3:02 pm 
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SoundMods wrote:
tomp wrote:
As I understand it, a DC current can cause molecules of the filament metal to migrate over time. It is similar to a plating process where metal molecules move to a charged metal plate. Different process but a similar result. It causes thinning in part of the filament which then has greater dissipation and earlier failure.

Does this only apply to direct-heated triodes where the filament serves as the cathode as opposed to the filament heating a separate metal cathode?


Yes. Except for the triodes part ;)

Roscoe

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PostPosted: October 11th, 2021, 3:42 pm 
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It applies to any metal through which the DC current flows. If it is a direct heated cathode, it will be affected. If it is an indirect heated cathode only the filament wire will be affected, but if it fails the tube is toast anyway.


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