Yup, Voltage doubler is the way to go as i will already have +_40v for the fet output stage. I should be able to get 140 to 150V out of it. I'm hopeing this will be more than enough for the valve gain stages. I have an example of this used in an RF amplifier i use and i've never had any trouble with it to date. Still cant understand why my triode CCS doesnt work tho....
Anyone any ideas??
Leigh
P.S the 'Tube sound' is exactly what i dont want. My aim is for absolute transparancy. I'm hoping the tubes can supply this as they seem rarther linear on paper.
Anyone any ideas??
Leigh
P.S the 'Tube sound' is exactly what i dont want. My aim is for absolute transparancy. I'm hoping the tubes can supply this as they seem rarther linear on paper.
nitrate said:
I did this scheme with a 2nd bridge to get some higher voltage at low current, in a CD player I was modifying for tubes:
The bottom bridge was an existing one in a CD player power supply. As you have +40 and -40 from a bridge supply (I'm guessing that you used a bridge), you could have +120V and if you return the tube circuit current to the -40V, it would be like 160V.
Good idea WA2ise, i have not considered tieing the two bridges together for a sneaky 80V advantage. As things are set up now that would give me about 240V ( +-40 + 80*2 ). Lol, maybe a bit much as i want to keep B+ to a minimum. Handy concept tho... Just don't like those caps linking the bridge.
Leigh
Leigh
hotbottle said:
That's essentially it. I did this to create some B+ to supply a few ma of current, in a CD player that I was adding a tube output buffer CF circuit into. Didn't feel like using a 2nd power transformer.
An externally hosted image should be here but it was not working when we last tested it.
http://pw2.netcom.com/~wa2ise/radios/tubedac.htm
for more CD players with added tubes.
Nice job WA2ise. Call me thick but on my 6922's there is a screen pin ( pin 9 ). Am i to belivethis is an internal sheild to help stop cross talk between the two triode sections? if this is the case is it wise/safe to connect this screen to ground??
Also has anyone had any problems with connecting two or more valve heaters in series? is this wise?
anybody got a good example of a valve CCS? as i still have problms with mine. It seems the valves are very sensitive to changes in anode voltage.
Leigh
Also has anyone had any problems with connecting two or more valve heaters in series? is this wise?
anybody got a good example of a valve CCS? as i still have problms with mine. It seems the valves are very sensitive to changes in anode voltage.
Leigh
Here is one used as a ccs tail in a long tailed pair phase inverter:
http://www.angelfire.com/electronic/funwithtubes/Amp-Phase.html
All of the tube CCSs that I have seen require substantial voltage to work correctly. A pentode may be much better suited for CCS duty than a triode.
I still like transistors as there is no need for an elevated heater supply and all that nonsense. You may not need this in your design, but I would for mine. Tubes are much more work in this position and won't work as well.
http://www.angelfire.com/electronic/funwithtubes/Amp-Phase.html
All of the tube CCSs that I have seen require substantial voltage to work correctly. A pentode may be much better suited for CCS duty than a triode.
I still like transistors as there is no need for an elevated heater supply and all that nonsense. You may not need this in your design, but I would for mine. Tubes are much more work in this position and won't work as well.
Actually, this is better:
http://www.angelfire.com/electronic/funwithtubes/Amp-DB_Heart.html
Notice the difference in negative supply voltages between the solid state CCS and the tube CCS.
http://www.angelfire.com/electronic/funwithtubes/Amp-DB_Heart.html
Notice the difference in negative supply voltages between the solid state CCS and the tube CCS.
That is an excellent site you posted wa2ise, it explains a lot about why my first play around with tubes seems to put the laws of physics into question. Seems toop and bottem of my problem is simply a plain lack of supply voltage. I'm gonna have to go higher if i want luxerys such as the tube CCS.
Leigh
P.S i might just take your advise and lob in a couple of tranny CCS's
Leigh
P.S i might just take your advise and lob in a couple of tranny CCS's
nitrate said:
Some of the nine pin dual triodes include a shield between sections. The 6BQ7A and the 6CG7 (amoung others) have this particular shield. If you decide to ground it, you must make certain that it isn't connected to any part of the circuit that is more positive than the cathodes. If it is more positive than the cathodes, it will act like a third anode. This will cause all sorts of problems with throwing off the design bias, and could lead to instability. In the project using the 6BQ7A, grounding it wasn't a problem since the cathodes were positive to ground.
If I used 6CG7s instead of 6FQ7s, then grounding the shield would have been a real problem since the cathodes are negative to ground. The 6FQ7 doesn't include that shield.
Miles Prower said:
This shouldn't be an issue, as the only source of electrons are the special coatings on the cathodes. And the parts of the cathode you see sticking past the mica spacers don't have this coating, and thus don't emit hardly any electrons. Thus the shield won't be able to draw any DC current, as the plates of both triodes get in the way of the only places where electrons are avaliable. The shield will draw a tiny bit of AC current, like a few picofarad cap would.
^^^^
Shouldn't be an issue, but it is. Forget about those simplified illustrations of electron flow in VTs. In reality, electron motion is quite chaotic, and plenty of electrons escape from the space charge between the anode and cathode. After all, these escapees are responsible for that blue glow you sometimes see in the glass if there's cobalt contamination.
Like the envelopes of metal VTs, those internal shields will conduct if they are more positive than the cathode(s).
Shouldn't be an issue, but it is. Forget about those simplified illustrations of electron flow in VTs. In reality, electron motion is quite chaotic, and plenty of electrons escape from the space charge between the anode and cathode. After all, these escapees are responsible for that blue glow you sometimes see in the glass if there's cobalt contamination.
Like the envelopes of metal VTs, those internal shields will conduct if they are more positive than the cathode(s).
In that case, then it would be best to connect the shield to the B- supply (like in a long tailed pair). That would give crosstalk shielding without drawing loose electrons. The shield may also redirect those loose electrons to their respective section's plate. A little like a supressor grid (G3) in a pentode.
This shield sounds pretty handicapped if it must be held very close to cathode potential. Perhaps thats why there is no mention of it in my data sheets. I think i'll just leave it floating untill i get some more experience of these glass wonders under my belt. Changing the subject slightly, does anyone here think that by making use of a transistor CCS instead of triode CCS will effect the signal in any way in a SE classA configuration?? Personally i think it will as the silicon's non linear current regulation over the wide voltage swings will be directly injected into the signal path via the triodes anode. I'm thinking of using silicon CCS in order to keep B+ requirements down as after experimentation and advise on here i've found it almost impossible to use a triode as a current source without throwing 100+ volts at it. My aim is for everything to work off an 80V supply.
Leigh
Leigh
http://www.freewebs.com/valvewizard/heater.html
Nice basic discussion on heater filaments
http://www.freewebs.com/valvewizard/ccs.html
And CCS
Nice basic discussion on heater filaments
http://www.freewebs.com/valvewizard/ccs.html
And CCS
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