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.
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.
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
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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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
nice mix with the SITAMP
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An externally hosted image should be here but it was not working when we last tested it.
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
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
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.
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.
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
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
I'm not selling them at all. I was talking about my personal tube stash. These tubes aren't rare. I have quite a few NOS NIB ST 26s, and lots of "test as NOS", lightly used balloons that test as good as my NIB tubes.
Now I can understand a little premium for NIB balloon tubes, but it's easy to find these tubes testing 100% or better. I probably haven't spent $266 on all of the ones I have combined. My guess is this was a collector, not an end user, because a lightly used tube sounds just as good as a NIB.
Now I can understand a little premium for NIB balloon tubes, but it's easy to find these tubes testing 100% or better. I probably haven't spent $266 on all of the ones I have combined. My guess is this was a collector, not an end user, because a lightly used tube sounds just as good as a NIB.
For us living outside of the USA ebay is the only option to obtain the 26 but I agree that 266$ is too much.
Hello Magz,
Full disclosure here as I am the one who BOUGHT the tubes! I placed $275 as my max bid, and the rest was history. Steep? Yeah, I think so too. I made a bid and that's that.
I am constantly searching Ebay for NOS NIB (that can be verified) type 26 tubes. If I am in the mood, I will gladly pay the same premium for a pair that looks, smells, and test new( mica spacer is opaque in color and "powderly" not transparent) including the boxes and everything that comes with it. If I am not, then I will pass.
An externally hosted image should be here but it was not working when we last tested it.
Nahh, you did not offend me at all. We, in the audio world, have different degrees of craziness in each of us. It is probably time to display mine again
I too was surprised that it went up that high, but I already set my max bid for them so no turning back
Anyways, I will use them as soon as I receive and test them. Hopefully, it sound like its worth $266 That transformer is massive!
Abe