[tubesforever]

With the stock Hammond transformer and the kit specified H+ step down resistor I measured 5.86 VDC on initial power up.  This was 4 years ago!   I remembered that the unit sounded bass shy.  So I dropped the H+ step down resistor a 1/4 ohm in resistance and it hit 6.15 VDC and that is where I ran it for about a year. 

I also tried 6.0 and 6.35 VDC but the sound was thin at the lower heater voltage and  thick and syrupy at the 6.3 value.  The problem is that I did all this initial listening with a brand new build and components that had not broken in.  This was probably a mistake.

1 and 1/2 years ago I pulled out the Schottke diodes and ran HexFreds.  On my Cornet 2 all I could get was 6.0 V and no higher.    The Hex Freds have an insanely quiet noise floor.   However the limit of 6.0V and no higher has been a worry of mine. 

So this last week I pulled the HexFreds and went back to Schottke diodes.  I have my C2 running at 6.3 V on the heater circuit and the bass is a lot fuller and richer.  It is not a subtle change. 

So my question to the board is how many of you are running higher than 6.3VDC on the tube heaters.  Are any of you running 6.4 VDC or higher on the H+ lines?   Are you experiencing any issues? 

I decided to do this tweaking because last year I got a chance to hot rod a George Wright Signature Phono stage for a good friend and this unit has bass to die for.  It does not do midrange that nicely so don't go selling your Cornet 2's any time soon.  The Hagerman is a better sounding phono stage. 

George died last year, so I cannot ask him why, but he was running his unit at the equivalent of the C2 running at around 6.5 VDC at the heater.

So is it safe to try our C2's 12xx tubes at 6.5 VDC at the H+?  What does this mean for tube life?

[GRD]

6.5 volts is only 3% above 6.3 volts.  Spec is usually +/- 5%.  So 6.5 is OK.  There should be some shortening of tube life, but I doubt it would be much different than 6.3 volts.

[poty]

I also tried 6.0 and 6.35 VDC but the sound was thin at the lower heater voltage and  thick and syrupy at the 6.3 value.
...I have my C2 running at 6.3 V on the heater circuit and the bass is a lot fuller and richer...

Looking at the design I could say that you hear not the impact of higher voltage, but the impact of changing bias.

So my question to the board is how many of you are running higher than 6.3VDC on the tube heaters.  Are any of you running 6.4 VDC or higher on the H+ lines?   Are you experiencing any issues? ... So is it safe to try our C2's 12xx tubes at 6.5 VDC at the H+?  What does this mean for tube life?

I tried this on a tube tester for a double triode (Russian) and found that sometimes there are rather funny things like broken linearity and overheating at plate currents way lower than rated. I'm not have tube faults though, so I can't say it is shorten significantly tube lifes.

[GRD]

Tubes,

Only way to find out is to give it a try and you can't hurt anything.  Interesting in finding out what happens. 

Grant

[tubesforever]

Running the Clarinet heater voltage higher than 6.3 seems to muddle up the sound.  6.2 to 6.3 seems to deliver a nice frequency balance.

Poty is correct that the sound changes are most likely biasing based and not from the voltages themselves. 

On the Cornet 2 it seems to like 6.3 or 6.4.  I will try 6.5 when I get the chance.  I have been busy this spring!

[hagtech]

Indeed the heater voltage changes output plate bias.  You can see the effect very easily on a VacuTrace (I should post a movie sometime).  Transconductance is directly affected by cathode emission, hence, heater temperature, hence heater power (voltage & current).

It's not a lot, but in audio, everyone seems to prefer their own sweet spot.  And that's why DIY is such a great hobby!  We can each tune the flavor to our taste, whether rolling tubes or caps, or playing with biasing.

jh

[tubesforever]

Jim I think that is what I love the most about your designs.  Tube rolls are like going to a gigantic buffet. 

We each have different rooms, different speakers, and amps with different damping values.  A tube or H+ voltage in my system might not work in yours.  Its great to be able to dial in the sonics.

For those out there that feel their C2's are good but not perfect, then check your H+ voltage and try some different H+ drop down resistors at R223 for the Cornet 2 and R313 for the Clarinet.

I bought a variety of 12 watt Mills wire wounds for this chore.  I think I bought 0.25, 0.33, 0.5, 0.75, 1.0, 1.25, 1.50, 1.75. 2.0 and a few other values.  The idea was to have enough values to nail down the H+ to the exact voltage I wanted to try next.  You can buy these from PercyAudio.com (no affiliation other than I really like his service!)

For those willing to play a little with your heater voltages I believe you can achieve even more impressive sound. 

I mentioned here before that I take my gear on the road and show it to audio groups and with a tube roll or two I can nail the sound in most rooms in just a few minutes of listening.

Cheers!

[dangerbird]

I'm not to proud to ask,, where exactly do you measure the heater voltage at on the C II?

[WGH]

H+ is measured on both sides of R223. One side will be in 7v range, the other side you want between 6.2v - 6.3v.

You will probably want to read this entire thread for the calculations on how to adjust H+ for your favorite rectifier tube.
http://www.audiocircle.com/index.php?topic=41430.0

Wayne

[dangerbird]

Thank you sir.

[mucool]

Thanks guys,

Just curious whether, bumping up the voltages at heater drops the voltages across the other test points? As per Jim's suggestion I added resistors in parallel to R223, but that seems to be lowering the voltages at other test points. Right now they are a tad bit lower (155 is 151, 330 is 325, etc)

Just wondering whether I should keep upping the H+ without worrying too much about the other voltages.
Thanks,