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Old 15th May 2013, 05:38 AM   #3161
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Hi,

Me too! I only have one Shunt Regulator and I am very happy with the sound!

Cheers!
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Old 15th May 2013, 05:40 AM   #3162
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Quote:
Originally Posted by Magz View Post
I put one on each channel, for what it's worth. Was it necessary? I don't know, but it doesn't hurt!
Beautiful Preamp you got there!
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Old 16th May 2013, 07:14 PM   #3163
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thanks to all , my 26 tube DAC is now working , first i don't" recommend Tentalb filament regulator with filament bias... the cheap 10V caps have burned so i give up with those craps and bought a pair of Rod coleman reg with my own filter 159hammond choke and 33000uf nichikon 50V with
100uf and 1uf decoupling the input of the reg.

LCLCLC with one VR CCS regulated 150V B+
CCS Mu output with 127V on plate and 4ma on the 26 ,,, so far so good, very smooth sound , little more refined than my previous 6Ah4 output stage ( thanks to thomas mayer) .. and very silent thanks to andy , and rod...

pics to come.
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Old 17th May 2013, 02:10 AM   #3164
Magz is offline Magz  United States
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Quote:
Originally Posted by juanitox View Post
thanks to all , my 26 tube DAC is now working , first i don't" recommend Tentalb filament regulator with filament bias... the cheap 10V caps have burned so i give up with those craps and bought a pair of Rod coleman reg with my own filter 159hammond choke and 33000uf nichikon 50V with
100uf and 1uf decoupling the input of the reg.

LCLCLC with one VR CCS regulated 150V B+
CCS Mu output with 127V on plate and 4ma on the 26 ,,, so far so good, very smooth sound , little more refined than my previous 6Ah4 output stage ( thanks to thomas mayer) .. and very silent thanks to andy , and rod...

pics to come.
IMO, 150V is a little low for B+ when you have 127V on the plate. CCS like to have some headroom in order to minimize the capacitances of the chips, and to allow enough signal swing. If you start with 127V, add the peak signal voltage possible (peak voltage * mu of the tube), then add the chip headroom to get an absolute minimum, then I'd add some to that to account for tube aging, which will require higher anode voltage to get the same anode current. So, for example if the max signal is 2V rms, that's 127V+2V*1.414*8+10Vminimum CCS headroom+20V for aging = about 180V. That's why I use a VR150 +VR75 get 225V B+, so I know I'll always have plenty of voltage. My own personal preference is to have 90-100V headroom when using a CCS, but at least have enough to cover the above calculation.

By the way, I also have found that the 26 sounds better with anode current in the 6-7mA range, which would require even more voltage in your case, if 127V gives only 4mA.


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Last edited by Magz; 17th May 2013 at 02:16 AM.
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Old 17th May 2013, 05:14 AM   #3165
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Magsz , i have 1V input on the 26 and with 5ma on the CCS i have big distortions on the sound ,you are damn right i am in the limit of my CCS . with 4ma it sounds good but i will try to give more air to the CCS adding another VR tube, thanks for the help
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Last edited by juanitox; 17th May 2013 at 05:27 AM.
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Old 17th May 2013, 01:58 PM   #3166
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magz you are the man ,,, so this is my TOTALDAC 26 line stage with your update . so i have now 225V on my CCS 145V B+ at 6ma on the 26.

nice mix with the SITAMP

Click the image to open in full size.
Click the image to open in full size.
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Old 17th May 2013, 02:33 PM   #3167
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Awesome! Glad to be of assistance.
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Old 20th June 2013, 03:06 AM   #3168
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I've picked up a few 26s and have been testing them, measuring Mu (Current Source driven) and Gm (clamped anode voltage with a 10R sense resistor), and ran into one that is a bit strange.

I am using a Pyramid Phase III (13.6V, 10A) power supply with a series of droppig resistors to provide the filament supply.

Most of the tubes are real close with the setting I was using and were at 1.5V +/- .05V.

However one tube ran 2.25V across the filaments with this resistor setting and I had to increase the variable resistor considerably to compensate. When I got to 1.5V across the filament, it did not glow bright enough to see with the lights off, and emission was zilch!

The tube is definatly marked 26 and is a Philco tube.

The readings I got with the tubes were:

GM Mu MFG
960 - 8.38 - Wards (same construction as the Philco)
930 - 8.36 - Philco with weird filaement run at 2.25V on the filaments
1120 - 8.07 - Philco
1150 - 8.32 - Philco
1160 - 8.14 - TungSol
1040 - 8.26 - RCA (Balloon)
980 - 8.41 - Sonatron X226 (looks like a Cunningham/RCA)

Another thing that surprised me was how narrow the spread of Gm and Mu are, considering the wide range in claimed test readings that the sellers were listing.

Any thoughts?

tks
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Old 24th June 2013, 12:46 PM   #3169
TheGimp is offline TheGimp  United States
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This weekend I was working with the Philco that has the strange filament voltage.

I was seeing the same requirement for 2.25V to get the filament hot enough when I noticed the voltage fluxuating. I shut off the B+, and then the heater supply and pulled the tube and found one pin hot.

I removed the solder from the pin, cleaned it and re-soldered it.

Once powered up again the filament voltage was rock solid at 1.5V!

The problem was a poor solder joint.
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Old 3rd July 2013, 11:28 PM   #3170
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HOLY CRAP!

I was watching this auction on e**y, for a nice looking pair of CX-326 tubes; not sure why I was watching as I have dozens of them. In any case this pair sold for $266.00!!!

I routinely buy these tubes for $5-10 at hamfests/antique radio shows, testing at 100% or better!

What's up with that!

A Pair of Cunningham CX 326 Globe Tubes NIB | eBay
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