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Old 17th December 2009, 08:03 PM   #281
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Quote:
Originally Posted by coolzero View Post
Rod,

Thanks for the advice. BTW, can I use any N-channel MOSFET substitute for your schematic like IRF810/IRF740 (which I have already in my hand)? Also, can I substitute LM4041 with any other voltage reference?
Take care with those FETs! The specified ST part has very low threshold (about 1.7V) versus about 4V for IRFs - you'll have to add extra supply voltage (+4V) to make up for it!

the reference must be adjustable type with 1.2V reference pin - I don't know of any others...
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Old 18th December 2009, 01:51 AM   #282
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Originally Posted by Rod Coleman View Post
Take care with those FETs! The specified ST part has very low threshold (about 1.7V) versus about 4V for IRFs - you'll have to add extra supply voltage (+4V) to make up for it!

the reference must be adjustable type with 1.2V reference pin - I don't know of any others...
Thanks Rod. I'll try to find the same parts or otherwise try my luck with what I have already.
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Old 18th December 2009, 02:19 AM   #283
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Originally Posted by Rod Coleman View Post
Take care with those FETs! The specified ST part has very low threshold (about 1.7V) versus about 4V for IRFs - you'll have to add extra supply voltage (+4V) to make up for it!

the reference must be adjustable type with 1.2V reference pin - I don't know of any others...
Before any change of FET I would be turning the bias down to zero.

IRF in my experience usually need 7 volts bias, 3.5volts times two FETs.
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Old 19th December 2009, 06:11 AM   #284
disco is offline disco  Netherlands
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Originally Posted by Richard View Post
Disco, your pre looks sexy, great job. Can I ask what sort of output transformers and transformer volume control youíre using?
Hi Richard,
Thanks for the compliment. Volume controls are autoformers, made by Tribute. Plate chokes are made by Bartolucci.
Rgds, Jaap
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Old 19th December 2009, 10:24 AM   #285
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Extension rod?
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Old 20th December 2009, 07:53 AM   #286
disco is offline disco  Netherlands
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Originally Posted by nicoch46 View Post
Extension rod?
Between the Elma's there'll be an input selector with relais. In due time though, too cold at the attic right now
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Old 20th December 2009, 10:45 AM   #287
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here too !
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Old 20th December 2009, 11:42 AM   #288
Richard is offline Richard  Australia
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Disco,

Those tribute autoformers seem to be favoured, have you managed to compare to any others?

I like the fact that the Silk TVC allows some gain. Both seem to be receiving praises but I haven’t managed to find any comparisons between them on the web.

I hope you’re going to be using mercury wetted relays to complement the quality of the other parts .

Cheers,

Rich
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Last edited by Richard; 20th December 2009 at 11:55 AM.
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Old 20th December 2009, 11:44 AM   #289
Richard is offline Richard  Australia
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Salas, thank you for posting that schematic looks like I have a few Christmas projects.

Coolzero, my B+ power supply of fairly well filtered with chokes and finished off with VR tubes. Iím also planning to replace the series resistor before VR tubes with a ccs, just upgrading the filament supply for now.

Iím starting to put together Rods FET heater, should get my power supply chokes in a few days, Rod thanks for the updated schematic

Marty, good luck with the build. Are those chokes on a steel or ferrite core? The Hammond 60mH 2A is a cheap option, but not common mode. Here is a link to some test results for choke vs cap input.
RR#002 - DC Filament Supply Test

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Old 20th December 2009, 12:49 PM   #290
martyh is offline martyh  United States
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Hi Rich,
Thanks for the link.
Iím not positive on the core material (they are pulls) my guess would be ferrite though.
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