500 series Gyraf G9

[peter purpose]

With my slow start 12v regulator installed and the series heaters seeing 12v only, I'm pulling 95mA from the plus 16v rail for both tubes.
What are the consequences of underheating?

 

[Kingston]

unreliable and unstable tubes that are not working up to the specification set in datasheets. And perhaps an early death due to B+ hitting the plates full force while filaments are not providing the heat which allows the electrons to move.

 

[peter purpose]

haha..... better do it right then... cheers.

 

[peterc]

I did.... 12v into 4.. out of 5 to the other 4, 5 to ground.

What I was thinking of was to put the heaters between the + & - 16v rails with a dropping resistor (1.8R 5W) in series  to bring the voltage down to 24v across the 2 valves.

http://twin-x.com/groupdiy/displayimage.php?album=random&cat=10096&pos=-4638

 

[peter purpose]

Eeeenteresting.... cheers Peter.

 

[emrr]

unreliable and unstable tubes that are not working up to the specification set in datasheets. And perhaps an early death due to B+ hitting the plates full force while filaments are not providing the heat which allows the electrons to move.

Unfounded rumors.

Depends on tube type, application, and B+ being far far higher than those of us in audio ever experience.  Cathode stripping seems to be reality for transmitters at multi-K DC, and myth at audio voltages.  Been discussed here before.  I have plenty of 6.3 type tubes running at 5VDC, for years on end.  Sound and work as well as brethren running at 6.3.    Look at the bottom of the heater spec range, and try it to see what current looks like. 

Source of filament may be tricky, in that inrush current is huge with filaments.  Could cause PSU problems if not thought out clearly, especially if hung off a single rail.   

 

[gemini86]

maybe current regulated filaments are needed. Tube warm up will be longer, but in a 500 rack, who cares.

 

[Kingston]

I have plenty of 6.3 type tubes running at 5VDC

20% deviation is within acceptable range of most tubes, looking at their datasheets. A non-issue.

Give that 6.3 filament just 3 volts for "years on end", which is roughly what happens with two 12V filaments in series getting only 12V total. Tube-breaking-unknown territory.

 

[emrr]

well, yeah, a rectifier tube will hardly pass voltage at 50%, but shoots up a lot at 60%.

 

[peterc]

I do not know WHERE I got 1R8 from..... 

Should be 53R, so try a 56R 5W resistor

with a dropping resistor (1.8R 5W) in series  to bring the voltage down to 24v across the 2 valves.

 

[peter purpose]

I thought you said a lb of raspberries.

 

[okgb]

Hey Pete , what happened to the variable impedance pre ?

 

[peter purpose]

Hey Pete , what happened to the variable impedance pre ?

Nothing to do with me Greg.

 

[deuc224]

Thinking of ptownkid. I'm still interested in it as well. But will build these if Peter gets jakobs blessing

 

[bkbirge]

I'll take 4 kits. Haha, love this. And no I'm not really kidding about the kits, get to it! You guys are geniuses.

 

[gemini86]

Where does Jakob stand in all this? This is his design, after all.

 

[pacemaker]

yeah ,
if jacob's is agree with it,i would like to build , i don't know,
at least 4  !!!
amazing work pete !!
regards,
francois

 

[gyraf]

Jakob is definitely OK with this, as long as it's kept open and free (as in software, not beer)

That said, I ran the calculations several times, and couldn't find power enough in the 500-system to support a "standard" G9 channel.

Going with ECC86 and lower voltages may be a solution?

(attached a schemo for a low-voltage mic preamp)

Jakob E.

 

[peter purpose]

Jakob is definitely OK with this, as long as it's kept open and free (as in software, not beer)
That said, I ran the calculations several times, and couldn't find power enough in the 500-system to support a "standard" G9 channel.
Going with ECC86 and lower voltages may be a solution?
Jakob E.

That's mighty good of you Jakob, but I'm going to let someone else run with this.
Being within the power specs was never a concern for me.
Besides, I have a problem I can't nail down.....
After powering up for 15 seconds I start an 80V voltage drop, so I hunt for heat and find none... v.strange.
It's not my booster, as I get the same with an independent power supply.
I'll get back to it when I've got more time.

peter

 

[gyraf]

Power-up plus 15sec is about the time the tubes start conducting.

Try finding the tube that takes too much current

Bad tube? Excessive current drain from some wrong resistor?



Jakob E.