Dear Sirs,
I would like to build a nice cathode-follower to buffer a passive pre using the very powerful 6H30P.
I intend to use it to drive a power amp with a low input impedance (about 10 kohm).
Unfortunately I have not been able to find a suitable schematic.
So I am here to ask for your very valuable help.
Are there any free schema in the web that you are aware of?
Thank you so much for your attention.
Kind regards,
beppe61
I would like to build a nice cathode-follower to buffer a passive pre using the very powerful 6H30P.
I intend to use it to drive a power amp with a low input impedance (about 10 kohm).
Unfortunately I have not been able to find a suitable schematic.
So I am here to ask for your very valuable help.
Are there any free schema in the web that you are aware of?
Thank you so much for your attention.
Kind regards,
beppe61
Hey-Hey!!!,
I would suggest that a pentode would make a better cathode follower than the 6H30. The parameter of use for a cathode follower is transconductance, and in second place, current capacity. The 6H30 is good in both. It is moderately expensive though, and 15 mA/V gm is easy to get for less than 3 USD per...
The critical parameter for good CF circuit performance is the load. This is the cathode load in parallel with the circuit you're plannig on driving. You said that this is 10k in the form of a SS amp. A good current source looks like the best idea from the chair I'm sitting in.
The circuit will depend on the means you choose todo it with. A negative supply would probably be a good idea, but may not be needed if the grid reference is at high voltage...
cheers,
Douglas
I would suggest that a pentode would make a better cathode follower than the 6H30. The parameter of use for a cathode follower is transconductance, and in second place, current capacity. The 6H30 is good in both. It is moderately expensive though, and 15 mA/V gm is easy to get for less than 3 USD per...
The critical parameter for good CF circuit performance is the load. This is the cathode load in parallel with the circuit you're plannig on driving. You said that this is 10k in the form of a SS amp. A good current source looks like the best idea from the chair I'm sitting in.
The circuit will depend on the means you choose todo it with. A negative supply would probably be a good idea, but may not be needed if the grid reference is at high voltage...
cheers,
Douglas
You don't need anything "powerful" to drive a 10K load. Anything that can swing half a milliamp AC will be more than adequate. My own preamp uses an ECC88 type tube to drive the 10K input Z of my power amp and it seems to work beautifully.
If you're just in love with the idea of using that tube (and that's OK, I've been there!), you might adapt the Heretical circuit. There's no reason that it won't work part-for-part with the 6H30 as long as you adjust the series resistor in the heater circuit.
If you're just in love with the idea of using that tube (and that's OK, I've been there!), you might adapt the Heretical circuit. There's no reason that it won't work part-for-part with the 6H30 as long as you adjust the series resistor in the heater circuit.
follower
Have a look at Allen Wright´s web site
www.vacuumstate.com
In the schematics section you find his Super Cathode Follower,
clever constant current, constant voltage design, near zero
distortion
You can build that with 6H30 or better use 6H6.
Reinhard
Have a look at Allen Wright´s web site
www.vacuumstate.com
In the schematics section you find his Super Cathode Follower,
clever constant current, constant voltage design, near zero
distortion
You can build that with 6H30 or better use 6H6.
Reinhard
Re: follower
Dear Mr. Reinhard,
thank you very much for the valuable link.
Actually I was thinking about something more basic, the school text-book CF, with just a resistor from the cathode to ground.
I have no claim of high-end performances.
I have on noticed that with digital source the simple introduction of a tube in the audio chain gives a "nice" flavour to the sound.
Maybe it indeed adds distorsion, but of a nice kind.
It makes the digital more human ?!
I would like very much to know your opinion on this.
Kind regards,
beppe61
reinhard said:
Dear Mr. Reinhard,
thank you very much for the valuable link.
Actually I was thinking about something more basic, the school text-book CF, with just a resistor from the cathode to ground.
I have no claim of high-end performances.
I have on noticed that with digital source the simple introduction of a tube in the audio chain gives a "nice" flavour to the sound.
Maybe it indeed adds distorsion, but of a nice kind.
It makes the digital more human ?!
I would like very much to know your opinion on this.
Kind regards,
beppe61
There are some real advantages to using a current source rather than the canonical resistor. You can get away with the resistor alone if either the tube is biased up with a high positive voltage on the grid (and a concommitantly large cathode resistor) or a large cathode resistor is returned to a negative supply. The simple resistor-to-ground is almost certain to give you poor performance.
Current sources are cheap and easy to build.
Current sources are cheap and easy to build.
using a transformer would be a better idea
A cathode follower is not going to like a 10k load, although a pentode can be made to like it more than a triode.
For best operation, a cathode follower should have the same AC load that it would use if it were being run plate-loaded.
If it were me, I would keep the 6H30Pi, and use a step down transformer, like the Lundahl LL1660S. That setup will give you a consistantly low output impedance that will laugh at a 10k load. You'll also have the added benefit isolated outputs breaking any ground current issues between the pre and power amps.
Joel
A cathode follower is not going to like a 10k load, although a pentode can be made to like it more than a triode.
For best operation, a cathode follower should have the same AC load that it would use if it were being run plate-loaded.
If it were me, I would keep the 6H30Pi, and use a step down transformer, like the Lundahl LL1660S. That setup will give you a consistantly low output impedance that will laugh at a 10k load. You'll also have the added benefit isolated outputs breaking any ground current issues between the pre and power amps.
Joel
Re: using a transformer would be a better idea
If you're going to go to that sort of expense and effort (Tx's over a cathode resistor) anode load it and get a Tx with a TR of 10+. With any decently configured 6H30 that's going to give a low output Z, roughly unity gain (depends on TR chosen), low distortion and will happily drive 10k. If you want to reduce the distortion more use an active load (CCS and parafeed) and use the 'mu' output to drive the Tx for lower output Z still though now you have an extra cap in the circuit.
I agree about the advantage of galvanic isolation.
A 6H30 has no particular problem with a 10k load. I've used them that way before and they sound fine and have a low THD with a predominantly low order profile, especially only swinging a volt or two.Joel said:
Then the circuit is running at under unity gain and I see no benefit at all to that over an anode loaded 6H30 in this instance.
If you're going to go to that sort of expense and effort (Tx's over a cathode resistor) anode load it and get a Tx with a TR of 10+. With any decently configured 6H30 that's going to give a low output Z, roughly unity gain (depends on TR chosen), low distortion and will happily drive 10k. If you want to reduce the distortion more use an active load (CCS and parafeed) and use the 'mu' output to drive the Tx for lower output Z still though now you have an extra cap in the circuit.
I agree about the advantage of galvanic isolation.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.