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Old 19th January 2013, 04:23 AM   #2311
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Ahh yes, you are right, thanks! I forgot to change it to GZ34. Lets assume its GZ34 from here on
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Old 19th January 2013, 07:54 AM   #2312
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AZ1 or any other mesh rectifier will sound better than GZ34. I have a variety of sockets in my PSU so I can try out different rectifiers. I couldn't tell any difference between the meshies, but they all sounded better than the plain ones like the 80/5Y3. Not night and day, since there's a lot of stuff after them, but enough to be audible and for me to have a preference.

You don't need to run the 26 so hot, but it's up to you. I use a 150v glow tube (0D3) instead of the voltage reg for instance. In that case the glow tube and both 26s would show a current of max 60mA but that's before the regulator not after it - after it would be max. 15mA depending where you run the 26s.

Agree on small first cap. Up to 1uf really.

For the filament supply I recommend pure choke input or small cap in range 100-660uF, which can be used to tune the output voltage. And using a choke something like a Hammond 159ZC. Then at least 20,000uF smoothing. Caps should be rated 1.5 times the expected output voltage of your raw filament supply to cope with the voltage off load. Rod has recommended JMS transformers, but that's in UK. you could find something similar in the USA.

http://www.jmsonline.co.uk/index.php...sort=2a&page=1

Last edited by andyjevans; 19th January 2013 at 08:01 AM.
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Old 19th January 2013, 08:51 AM   #2313
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Hi Andy,

Okay, let's see if I understand you correctly.

With the arrangement I posted, the Shunt Regulator will draw 20mA by itself and will drop 50V. If I operate the two 26 tubes at a total of say 15 mA, with 135V at the plate,the model that I should have as main PSU should only show 35 mA of load?

thanks!

Abe
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Old 19th January 2013, 09:38 AM   #2314
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Hi Abe,

Please connect the shunt regulator + to the dc supply + (ie, the top, or hot end of the LL1660 OT primary). Connect the shunt reg GND to 0V or GND. The shunt reg stabilises voltage by diverting current to GND.

The CCS should drop 25V to 35V minimum.

When you have a shunt regulator, the passive power components can be reduced to CLC - eg 1uF-2H-30uF. A good shunt regulator is VERY effective in removing ripple.
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Old 19th January 2013, 09:49 AM   #2315
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A 0D3 should draw about 22.5mA - that's what's recommended. Here's a draft version of a 26 preamp using the LL1660/5mA. You can play around with the cathode resistor size depending on how much you starve the 26 filaments, e.g. between 0.85A and 1A.
Attached Images
File Type: png 26FB+LL1660.png (72.1 KB, 324 views)

Last edited by andyjevans; 19th January 2013 at 09:57 AM.
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Old 19th January 2013, 09:54 AM   #2316
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See how the 0D3 fits into the same position as the shunt regulator. The gas tube is a shunt regulator!

Building the preamp this way, before trying the shunt regulator, is a good idea - and much simpler!
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Old 19th January 2013, 10:13 AM   #2317
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This is probably a slightly better version in terms of voltages, but different examples of 26 will give different results.
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File Type: png 26FB+LL1660.png (71.9 KB, 501 views)
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Old 19th January 2013, 07:01 PM   #2318
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Thank you Andy, and thank you Rod! I will try to build the preamp this way. I leaning towards battery bias, but it is good to learn about filament bias as well.

Rod, the CCS and Shunt Regulator on my schematic is the one from K&K and is already combined.

In the schematic that Andy posted, regarding the CCS, should I just aim for 150V raw DC supply or 200V is fine and just adjust the current as required?

Thanks!

Abe
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Old 19th January 2013, 07:39 PM   #2319
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Also, each channel has its own CCS(I have the K&K Cascode type) set to 32.5mA?

Thanks

Abe
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Old 20th January 2013, 12:06 AM   #2320
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Hello Andy, Rod,

Can you please take a look at these schematics. The 1st includes the main PSU and the second one is a schematic for the filament using Rod's Shunt Regulator.

All suggestions and corrections are most welcome! Thank you very much!

Abe

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