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Old 21st January 2013, 12:09 AM   #2341
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Quote:
Originally Posted by Rod Coleman View Post
Hi Abe,

The preamp circuit looks about ready to build, I'd say.

For the Filament's raw dc, please aim for about 6.7Vdc.
Hello Rod,

Here's the model I come up with with your suggestions in mind.

Click the image to open in full size.

Thanks!

Abe
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Old 21st January 2013, 06:44 AM   #2342
euro21 is offline euro21  Hungary
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Originally Posted by amandarae View Post
One more question, for the AZ1 filament, can I just use 5VCT tap(eg. power transformer) and calculate the dropping resistor to drop 1V at the rectifier current draw? What do you use for your AZ1 filament?
I use AZ1 mesh from 5.6V (220V transformer at 230V), with 1R and 0.5R dropping resistors.

AZ1 filament current varies 1A-1.15A, depends of the manufacturer.
Try 0.5R (5W) on both sides of 5VCT (about 2*0.5V drop), but current must be measured.

Last edited by euro21; 21st January 2013 at 06:46 AM.
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Old 21st January 2013, 08:18 AM   #2343
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Originally Posted by euro21 View Post
I use AZ1 mesh from 5.6V (220V transformer at 230V), with 1R and 0.5R dropping resistors.

AZ1 filament current varies 1A-1.15A, depends of the manufacturer.
Try 0.5R (5W) on both sides of 5VCT (about 2*0.5V drop), but current must be measured.
Thanks much!

Abe
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Old 21st January 2013, 08:23 AM   #2344
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As euro21 says - you can use a 5v winding with two equal resistors on each leg. Start with Ohms Law for measuring the resistor values and then try it out and make whatever changes you need to get exactly 4v. Make sure the resistors are large enough in wattage (again Ohms Law) by sizing them for 3x what they pass. You probably need to parallel a couple of resistors on each leg to get the exact value.
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Old 21st January 2013, 08:30 AM   #2345
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Oh - I should add that if your mains transformer doesn't have a centre tap you need to use a hybrid or Graetz bridge. Diodes can be UF4007 or whatever you fancy.
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Last edited by andyjevans; 21st January 2013 at 08:35 AM.
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Old 21st January 2013, 09:04 AM   #2346
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Originally Posted by andyjevans View Post
Oh - I should add that if your mains transformer doesn't have a centre tap you need to use a hybrid or Graetz bridge. Diodes can be UF4007 or whatever you fancy.
Excellent. Thanks much Andy!
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Old 21st January 2013, 09:49 AM   #2347
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Default My #26 is undergoing

Just received these beauties, more photos of the construction will be posted afterwards.

Thanks Thomas for the Iron (Vinyl Savor)
Thanks Campbell Barker for the custom made Morgan Jones capacitors (Supression Devices UK)
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Last edited by rclourenco; 21st January 2013 at 09:52 AM.
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Old 22nd January 2013, 10:32 AM   #2348
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Work in progress
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Old 22nd January 2013, 11:29 AM   #2349
iko is offline iko  Canada
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Very nice!
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Old 22nd January 2013, 11:55 AM   #2350
12B4A is offline 12B4A  United States
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It looks like you made a crucial design change in the mechanical orientation of the filament resistors.
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