8233, 8116 & 6BZ6 valves - what are they good for?
I have recently come across a huge stock of 8233, 8116 & 6BZ6 valves and would like to know if anyone knows of a DIY tube amp, pre-amp of headphone amp that uses any of them.
If so, please direct.
Thanks
Jack
I have recently come across a huge stock of 8233, 8116 & 6BZ6 valves and would like to know if anyone knows of a DIY tube amp, pre-amp of headphone amp that uses any of them.
If so, please direct.
Thanks
Jack
You are very lucky to have found 8116s. They are listed (when they can be found) at stupid prices.
This is truly a super valve; 60W Pa, only 11W to light it up, anode resistance a mere 650 ohms, very linear, a choice of 13 or 26v heaters. Lovely things
The only problem is the exposed anode pins, but a little adventure is no bad thing in todays "nanny" environment!
7N7
This is truly a super valve; 60W Pa, only 11W to light it up, anode resistance a mere 650 ohms, very linear, a choice of 13 or 26v heaters. Lovely things
The only problem is the exposed anode pins, but a little adventure is no bad thing in todays "nanny" environment!
7N7
By the way, I was recently very kindly given a pair of YL 1150s; this one's a cracker too and usually a horrible price. (the "0" at the end or the type number implies that the type is a prototype)
One day I might even have time to do something with them.
It's a beam tetrode. 75W pa. According to Mullard data, with 600V on the anodes and 300V on G2 a pair will give 200W in AB1 at 2% THD.
Another excellent example of the direction that valves were going before they were scuppered by a lot of cheap and often dubious silicon!
Imagine if the valve makers' research departments had survived for a few more years.
7N7
One day I might even have time to do something with them.
It's a beam tetrode. 75W pa. According to Mullard data, with 600V on the anodes and 300V on G2 a pair will give 200W in AB1 at 2% THD.
Another excellent example of the direction that valves were going before they were scuppered by a lot of cheap and often dubious silicon!
Imagine if the valve makers' research departments had survived for a few more years.
7N7
7N7, Welcome back after a one year hiatus! 
The 8233 is no slouch either. It's one of those gold-pin special quality pentodes with a high transconductance (~50mA/V). As a triode it has m»30, and rp»600ohms, and is far too linear than it has right to be. (Triode-mode data attached).
I was dreaming last night that I found this stash....
Jack,
I don't know of any designs out there on the web (or anywhere else for that matter) which uses these valves. It's probably because they're not all that well known.
I noticed from your profile that you are an EE, so you probably don't need our help designing something with these valves, but if you do, just ask.
But if you're willing to sell them to a guy here in Melbourne... 😉
I do every day.
Jason (still dreaming of 8233s and 8116s...)
EDIT: When I said "a guy in Melbourne" I didn't mean Circlotron 😉
The 8233 is no slouch either. It's one of those gold-pin special quality pentodes with a high transconductance (~50mA/V). As a triode it has m»30, and rp»600ohms, and is far too linear than it has right to be. (Triode-mode data attached).
I was dreaming last night that I found this stash....
Jack,
I don't know of any designs out there on the web (or anywhere else for that matter) which uses these valves. It's probably because they're not all that well known.
I noticed from your profile that you are an EE, so you probably don't need our help designing something with these valves, but if you do, just ask.
But if you're willing to sell them to a guy here in Melbourne... 😉
7N7 said:
I do every day.
Jason (still dreaming of 8233s and 8116s...)
EDIT: When I said "a guy in Melbourne" I didn't mean Circlotron 😉
Attachments
Yeah, 6BZ6. mmm...
First-generation Astor TV sets circa 1956 used four in the video IF strip and two in the sound IF. 20 or 21 tubes in all IIRC. Must have been good to work in that design lab where the mandate was to design something to work properly, not just barely good enough.
First-generation Astor TV sets circa 1956 used four in the video IF strip and two in the sound IF. 20 or 21 tubes in all IIRC. Must have been good to work in that design lab where the mandate was to design something to work properly, not just barely good enough.
8233
Thanks for the friendly greeting audiousername.
Ha - my fading memory; of course 8233 = E55L;
I used to have a few of these but I flogged them off to a fellow enthusiast.
My friend EC8010 and I have discussed E55L and have never managed to find a use for them. The problem is the very low anode voltage limit; and following tests where I very easily blew one up, the makers obviously meant it - with some types you can get away, if not with murder, certainly a little "GBH".
If you want to run a linear triode-strapped pentode with medium mu and decent gm, have a look at E282F. Mu is 25 and gm about 30 (therefore ra = 800 ohms)and you do not have to run 50mA through them; pa is about 5W.
7N7
audiousername said:7N7, Welcome back after a one year hiatus!
The 8233 is no slouch either. It's one of those gold-pin special quality pentodes with a high transconductance (~50mA/V). As a triode it has m»30, and rp»600ohms, and is far too linear than it has right to be. (Triode-mode data attached).
I]
Thanks for the friendly greeting audiousername.
Ha - my fading memory; of course 8233 = E55L;
I used to have a few of these but I flogged them off to a fellow enthusiast.
My friend EC8010 and I have discussed E55L and have never managed to find a use for them. The problem is the very low anode voltage limit; and following tests where I very easily blew one up, the makers obviously meant it - with some types you can get away, if not with murder, certainly a little "GBH".
If you want to run a linear triode-strapped pentode with medium mu and decent gm, have a look at E282F. Mu is 25 and gm about 30 (therefore ra = 800 ohms)and you do not have to run 50mA through them; pa is about 5W.
7N7
6BZ6
I took the opportunity to have a look at 6BZ6.
I cannot see any audio application for this one; it's just a little variable-mu pentode.
The only possible use given its reasonable Ra (about 250k) and gm - about 8, would be as a small pentode current sink.
However there are far better pentodes for this purpose - 6AU6 with its Ra of between 500k and 1M is far better and it is beautifully linear - makes quite a nice triode too and there are probably millions of them!
7N7
I took the opportunity to have a look at 6BZ6.
I cannot see any audio application for this one; it's just a little variable-mu pentode.
The only possible use given its reasonable Ra (about 250k) and gm - about 8, would be as a small pentode current sink.
However there are far better pentodes for this purpose - 6AU6 with its Ra of between 500k and 1M is far better and it is beautifully linear - makes quite a nice triode too and there are probably millions of them!
7N7
Re: 8233
I saw the pentode-strapped distortion spectrum in Valve Amplifiers. I bet distortion up to 12th harmonic would sound mighty ugly!
What I was thinking is perhaps a single-stage SE amplifier with the E55L in triode mode. With its 10W Pa rating, you'd probably be getting 2W or so, though choosing a loadline that doesn't stray much above 200V might reduce this a little. Maybe for an office or bedroom amp, or an alternative to 45s (though I somehow doubt the DHT only gang will accept this...).
Jason
EDIT: Is that a YL1150 in your avatar? I can't find a datasheet so I don't know. By the way, they can be had round here for around ₤17, but then you have to ship them halfway round the world.
7N7 said:My friend EC8010 and I have discussed E55L and have never managed to find a use for them. The problem is the very low anode voltage limit; and following tests where I very easily blew one up, the makers obviously meant it - with some types you can get away, if not with murder, certainly a little "GBH".
I saw the pentode-strapped distortion spectrum in Valve Amplifiers. I bet distortion up to 12th harmonic would sound mighty ugly!
What I was thinking is perhaps a single-stage SE amplifier with the E55L in triode mode. With its 10W Pa rating, you'd probably be getting 2W or so, though choosing a loadline that doesn't stray much above 200V might reduce this a little. Maybe for an office or bedroom amp, or an alternative to 45s (though I somehow doubt the DHT only gang will accept this...).
Jason
EDIT: Is that a YL1150 in your avatar? I can't find a datasheet so I don't know. By the way, they can be had round here for around ₤17, but then you have to ship them halfway round the world.
Re: Re: 8233
Hello.
Ha-ha! I cannot see the DHT advocates being impressed by an indirectly heated triode - let alone an indirectly-heated, triode-strapped MODERN pentode😀
Seriously I think that you are right: ulimately you have to swing some volts to get the power and E55L/8233 is reluctant to let you do that. However since it is so easy to drive, why not have a go?
I'm a bit rusty, but with its low anode resistance might not it be suitable for a small p-p amplifier using a toroidal mains transformer as the output transformer? And in p-p you'll cancel even order distortion (well most of it anyway!).
The new avatar shows a Mullard TY4-400. This is a 400W directly-heated (Hurrah😉!! )Class B RF Industrial heating valve. Filament is 5V @ 14A and they can run at up to about 3kV (they are similar to TB3-750) I had a pair of these and having a very large transformer, thought about a really silly amplifier. I did build a test rig to make some curves and ran it up about 1.2kV - with its 5V filament, an old computer PSU was perfect to light it up. Of course it was all nonsense so I sold them.
I would be willing to buy a few YL1150s if they can be sourced; perhaps I'll build a rig and do some triode curves; I'll bet it would be excellent
Best
7N7
EDIT
The data for YL1150 are on Frank's; I was wrong about the g2 voltage for 200W: it is 250V. Pa is 75W. Of course with a maximum g2 limit of 300V UL is out - at least for big power - but I imagine that it would be safe up to 400V as a triode (like 6146) or there's the possibility of beam tetrode operation with a bit of feedback if you're a mathematician and can do the physics
audiousername said:
Hello.
Ha-ha! I cannot see the DHT advocates being impressed by an indirectly heated triode - let alone an indirectly-heated, triode-strapped MODERN pentode😀
Seriously I think that you are right: ulimately you have to swing some volts to get the power and E55L/8233 is reluctant to let you do that. However since it is so easy to drive, why not have a go?
I'm a bit rusty, but with its low anode resistance might not it be suitable for a small p-p amplifier using a toroidal mains transformer as the output transformer? And in p-p you'll cancel even order distortion (well most of it anyway!).
The new avatar shows a Mullard TY4-400. This is a 400W directly-heated (Hurrah😉!! )Class B RF Industrial heating valve. Filament is 5V @ 14A and they can run at up to about 3kV (they are similar to TB3-750) I had a pair of these and having a very large transformer, thought about a really silly amplifier. I did build a test rig to make some curves and ran it up about 1.2kV - with its 5V filament, an old computer PSU was perfect to light it up. Of course it was all nonsense so I sold them.
I would be willing to buy a few YL1150s if they can be sourced; perhaps I'll build a rig and do some triode curves; I'll bet it would be excellent
Best
7N7
EDIT
The data for YL1150 are on Frank's; I was wrong about the g2 voltage for 200W: it is 250V. Pa is 75W. Of course with a maximum g2 limit of 300V UL is out - at least for big power - but I imagine that it would be safe up to 400V as a triode (like 6146) or there's the possibility of beam tetrode operation with a bit of feedback if you're a mathematician and can do the physics
audiousername - want some 8116s and 8233s ?
Jason,
Although I am an EE, I have NO experiance with valves at all, and I would like to get some. I know the theory behind how they work, but thats it.
My first step was to build something already proven by someone else, and work through it step by step, fiddle, change, measure, test, to see how the sound is affected, etc, etc.
If you have something suitable I can copy (or can knock one up or modify one), I would be happy to part with some 8116s and 8233s for you to to experiment with or use.
How many do you need? (be realistic - I have a couple of dozen to part with, but not commercial quantities). I'll leave it up to you to make a decision on what is a reasonable payment, as I have no idea how much they are worth. But I'm prepared to let them go cheap, as I dont know my level of interest in the valve phenomenon yet, or how long that interest will last.
You can contact me direct at carpetsnakeaudio@hotmail.com, and we can exchange phone numbers if your interested.
Shane (Jack) Daniel
Jason,
Although I am an EE, I have NO experiance with valves at all, and I would like to get some. I know the theory behind how they work, but thats it.
My first step was to build something already proven by someone else, and work through it step by step, fiddle, change, measure, test, to see how the sound is affected, etc, etc.
If you have something suitable I can copy (or can knock one up or modify one), I would be happy to part with some 8116s and 8233s for you to to experiment with or use.
How many do you need? (be realistic - I have a couple of dozen to part with, but not commercial quantities). I'll leave it up to you to make a decision on what is a reasonable payment, as I have no idea how much they are worth. But I'm prepared to let them go cheap, as I dont know my level of interest in the valve phenomenon yet, or how long that interest will last.
You can contact me direct at carpetsnakeaudio@hotmail.com, and we can exchange phone numbers if your interested.
Shane (Jack) Daniel
Hi Shane,
Yes, I can easily draw something up, maybe later today - though I'm not an EE.
I'll post it publicly here... just in case I make a mess of it, so others can hopefully give it a bit of a check.
Yes, I can easily draw something up, maybe later today - though I'm not an EE.
I'll post it publicly here... just in case I make a mess of it, so others can hopefully give it a bit of a check.
8116/YL1071 Single Ended
As promised, something simple, and suitable for fiddling, modifying and general stuffing around with. And maybe capable of making pleasing noises as well 😀
A single ended amplifier using both sections of the 8116 paralleled in triode mode good for around 13W. This is necessary when using triode mode since the screen grid is wound around the entire cathode and thus is shared between both sections.
WARNING For those of you allergic to devices with a tendancy to being silicon, do not download the schematic! It will likely cause a severe reaction!
A quick circuit description - though this is basically a circuit which would probably have put engineers to 😴 in the 1930s.
The input/driver section in half of a 7N7 (or half a 6SN7 or a 6J5 etc etc...) biased by two cheap red LEDs in series used as a cheap, relatively low noise voltage reference, and loaded by an 8mA CCS. The CCS can be replaced by a suitably sized anode load resistor, but the distortion performance of the input/driver stage will be worse, and gain will drop a little. Actually, it might be a good idea to ditch the LEDs for more common R||C bias when using an ordinary plate load resistor since the slope resistance of the LEDs is a little non-linear with current and may result in distortion if there is significant current swing through them.
The input/driver stage is RC coupled to the paralleled sections of the 8116 in cathode bias. I haven't been able to find anything telling me the maximum grid leak resistance, so I drew in a 200K grid leak resistor. This may have to be tweaked if there is a DC voltage appearing across the grid leak resistor when the amp is on and doing nothing (a sign of grid current) - I'd hate for any of these beautiful valves to be destoyed by runaway. Gridstoppers are basically a must, since the 8116 was designed VHF valve and probably won't mind going back to its roots without asking your permission first. The output stage sees a 2.5K load reflected by the OPT which has to be capable of withstanding 110mA of DC.
Eagle-eyed readers will notice that the 8116 is run short of maximum conditions - it is rated at 60W Pa max, and it is run at around 44W Pa. These things aren't physically very large and it is warned in the datasheet that they may need forced air cooling to maintain the max bulb and seal temperature of 250ºC at max dissipation. The (inevitably) improvised anode pin connectors of course will have to be able to withstand quite a bit of heat. Also, the screen grids are at 400V (triode mode) while Vg2 max is 300V. Exceeding Vg2 max has been done many times before when using triode-strapped output valves but still makes me very nervous.
A few suggestions for modifications:
The PSRR of the output stage is low, so it needs a quiet power supply. There are quite a few clever ways to improve it, and a read of a few articles at the TubeCad Journal might yield some ideas to help it along - try the "Lowering the SE Amp's Output Noise" parts 1 and 2 (back from April and May 1999) as a start.
The pdf has the additional schematic for a fixed bias version and does away with the cathode resistors in the first iteration that dissipate around 5W continuous, and the cathode bypass capacitor at the expense of the requirement of a negative supply rail (at almost zero current).
Modifying it to a fixed-screen (pentode-mode) output stage will probably increase output power, and local feedback around the output stage can do away with many of its disadvantages, so a read of John Broskie's Partial Feedback Amplifiers article would be a good idea for those interested in this.
The CCS for the input stage is quite crude and will probably self-destruct with a heart-stopping bang if the 7N7 somehow shorts itself out (Vce max = 300V for the MJE350). You can do much better. Have a look at Gary Pimm's webpage for some nicer CCSs.
To avoid blocking distortion, we should avoid using RC coupling to any stage which can be overloaded, so we really shouldn't use RC coupling to the output stage if we are concerned about blocking distortion. A direct coupled cathode follower would alleviate this, at the expense of the booing and hissing from those who denounce cathode followers.
This is it for now (I'll post a PP amp next), more suggestions always welcome - just remember this was never intended to be the best amp in the world, just a starting point which will hopefully work 😀 and be suitable for modifications and general experimentation.
A big thank you to Paul Leclercq for sharing the triode-mode anode characteristics he produced for the 8116/YL1071!
As promised, something simple, and suitable for fiddling, modifying and general stuffing around with. And maybe capable of making pleasing noises as well 😀
A single ended amplifier using both sections of the 8116 paralleled in triode mode good for around 13W. This is necessary when using triode mode since the screen grid is wound around the entire cathode and thus is shared between both sections.
WARNING For those of you allergic to devices with a tendancy to being silicon, do not download the schematic! It will likely cause a severe reaction!A quick circuit description - though this is basically a circuit which would probably have put engineers to 😴 in the 1930s.
The input/driver section in half of a 7N7 (or half a 6SN7 or a 6J5 etc etc...) biased by two cheap red LEDs in series used as a cheap, relatively low noise voltage reference, and loaded by an 8mA CCS. The CCS can be replaced by a suitably sized anode load resistor, but the distortion performance of the input/driver stage will be worse, and gain will drop a little. Actually, it might be a good idea to ditch the LEDs for more common R||C bias when using an ordinary plate load resistor since the slope resistance of the LEDs is a little non-linear with current and may result in distortion if there is significant current swing through them.
The input/driver stage is RC coupled to the paralleled sections of the 8116 in cathode bias. I haven't been able to find anything telling me the maximum grid leak resistance, so I drew in a 200K grid leak resistor. This may have to be tweaked if there is a DC voltage appearing across the grid leak resistor when the amp is on and doing nothing (a sign of grid current) - I'd hate for any of these beautiful valves to be destoyed by runaway. Gridstoppers are basically a must, since the 8116 was designed VHF valve and probably won't mind going back to its roots without asking your permission first. The output stage sees a 2.5K load reflected by the OPT which has to be capable of withstanding 110mA of DC.
Eagle-eyed readers will notice that the 8116 is run short of maximum conditions - it is rated at 60W Pa max, and it is run at around 44W Pa. These things aren't physically very large and it is warned in the datasheet that they may need forced air cooling to maintain the max bulb and seal temperature of 250ºC at max dissipation. The (inevitably) improvised anode pin connectors of course will have to be able to withstand quite a bit of heat. Also, the screen grids are at 400V (triode mode) while Vg2 max is 300V. Exceeding Vg2 max has been done many times before when using triode-strapped output valves but still makes me very nervous.
A few suggestions for modifications:
The PSRR of the output stage is low, so it needs a quiet power supply. There are quite a few clever ways to improve it, and a read of a few articles at the TubeCad Journal might yield some ideas to help it along - try the "Lowering the SE Amp's Output Noise" parts 1 and 2 (back from April and May 1999) as a start.
The pdf has the additional schematic for a fixed bias version and does away with the cathode resistors in the first iteration that dissipate around 5W continuous, and the cathode bypass capacitor at the expense of the requirement of a negative supply rail (at almost zero current).
Modifying it to a fixed-screen (pentode-mode) output stage will probably increase output power, and local feedback around the output stage can do away with many of its disadvantages, so a read of John Broskie's Partial Feedback Amplifiers article would be a good idea for those interested in this.
The CCS for the input stage is quite crude and will probably self-destruct with a heart-stopping bang if the 7N7 somehow shorts itself out (Vce max = 300V for the MJE350). You can do much better. Have a look at Gary Pimm's webpage for some nicer CCSs.
To avoid blocking distortion, we should avoid using RC coupling to any stage which can be overloaded, so we really shouldn't use RC coupling to the output stage if we are concerned about blocking distortion. A direct coupled cathode follower would alleviate this, at the expense of the booing and hissing from those who denounce cathode followers.
This is it for now (I'll post a PP amp next), more suggestions always welcome - just remember this was never intended to be the best amp in the world, just a starting point which will hopefully work 😀 and be suitable for modifications and general experimentation.
A big thank you to Paul Leclercq for sharing the triode-mode anode characteristics he produced for the 8116/YL1071!
Well done Jason on preparing the circuit for 8116/YL1071.
I would just like to add a couple of comments.
I would think that I would opt for a higher output transformer value - say 4k . Of course this will reduce output power most likely, but distortion will probably be better. Of course ultimately this is best done by building and measuring. As an example, on my 6528A push-pull amplifier I have an output transformer that has 4k, 6k and 8k primaries. One would think that 4k would be more than enough for 6528, but in fact distortion improved with 6k with minor effect on power
On the subject of output valve grid leak resistors, I would not be quite so brave. Call me a poltroon if you like, but I generally opt for 47k where there are no maker's data. On 813 one is limited to 30k in fact.
Also I would opt for slightly more gain. As I mentioned I have an amplifier that uses QQVO7-50s which are a close relative of YL1071 (in fact I have run it with YL1071s and 829Bs too). Originally I used 6EW7s and there was insufficient gain even though the amplifier was driven from a 6BL7 line stage. 6EW7 for those who do not know the type is a dissimilar double triode; the higher-gain section's mu is about the same as that of 7N7 (I used the low gain section as a cathode follower). For the SE amplifier I would select something with a bit more mu and lower anode resistance - say a paralleled E88CC; this would probably suit.
[EDIT: I should add that the 7N7 with active load as shown would have a high output resistance and given the Ca-g of the paralleled YL1071 may be too high to drive it nicely]
You are quite right about the cooling aspect; this family of valves does get very hot. However a tiny computer fan vaguely directed at the 7-50s seems to be adequate and those output valves are fine after nearly two years' use. They are running at 45W (375V and 120mA) each and are rated at 50W. The best solution I have come across is mentioned in Morgan Jones's "Valve Amplifiers" Vol III where, in the "Scrapbox Challenge" 6528 amplifier, a fan is installed underneath the valve base. At the very least a series of holes drilled around the valve base and free air-flow from underneath the chassis would be essential.
Regarding anode connectors, this was a problem. For my QQVO3-20 tweeter amplifier I even went to the trouble of making some special nylon plugs with inserted brass connectors epoxied into them. Hopeless results - a nasty melted mess. The solution, albeit rather dangerous in terms of exposed high voltage, is the Fahnstock clip. I bought a box of these from AES in America. They work perfectly. On this subject I have one beautiful original 829B anode connector machined from aluminium that is finned to help with cooling. I doubt I could ever find any more! The beauty of the Fahnstock clips is that they can accomodate various sizes of anode pin thus allowing experimentation with different types.
I should be interested to hear how this project sounds .
best wishes
7N7
I would just like to add a couple of comments.
I would think that I would opt for a higher output transformer value - say 4k . Of course this will reduce output power most likely, but distortion will probably be better. Of course ultimately this is best done by building and measuring. As an example, on my 6528A push-pull amplifier I have an output transformer that has 4k, 6k and 8k primaries. One would think that 4k would be more than enough for 6528, but in fact distortion improved with 6k with minor effect on power
On the subject of output valve grid leak resistors, I would not be quite so brave. Call me a poltroon if you like, but I generally opt for 47k where there are no maker's data. On 813 one is limited to 30k in fact.
Also I would opt for slightly more gain. As I mentioned I have an amplifier that uses QQVO7-50s which are a close relative of YL1071 (in fact I have run it with YL1071s and 829Bs too). Originally I used 6EW7s and there was insufficient gain even though the amplifier was driven from a 6BL7 line stage. 6EW7 for those who do not know the type is a dissimilar double triode; the higher-gain section's mu is about the same as that of 7N7 (I used the low gain section as a cathode follower). For the SE amplifier I would select something with a bit more mu and lower anode resistance - say a paralleled E88CC; this would probably suit.
[EDIT: I should add that the 7N7 with active load as shown would have a high output resistance and given the Ca-g of the paralleled YL1071 may be too high to drive it nicely]
You are quite right about the cooling aspect; this family of valves does get very hot. However a tiny computer fan vaguely directed at the 7-50s seems to be adequate and those output valves are fine after nearly two years' use. They are running at 45W (375V and 120mA) each and are rated at 50W. The best solution I have come across is mentioned in Morgan Jones's "Valve Amplifiers" Vol III where, in the "Scrapbox Challenge" 6528 amplifier, a fan is installed underneath the valve base. At the very least a series of holes drilled around the valve base and free air-flow from underneath the chassis would be essential.
Regarding anode connectors, this was a problem. For my QQVO3-20 tweeter amplifier I even went to the trouble of making some special nylon plugs with inserted brass connectors epoxied into them. Hopeless results - a nasty melted mess. The solution, albeit rather dangerous in terms of exposed high voltage, is the Fahnstock clip. I bought a box of these from AES in America. They work perfectly. On this subject I have one beautiful original 829B anode connector machined from aluminium that is finned to help with cooling. I doubt I could ever find any more! The beauty of the Fahnstock clips is that they can accomodate various sizes of anode pin thus allowing experimentation with different types.
I should be interested to hear how this project sounds .
best wishes
7N7
Yes, higher load Z would be nice, but that screen grid thing still gives me the nerves, and using a higher load Z will mean that you'll be swinging more volts on the screen. The lower distortion would of course be nice. I suppose it's something that needs to be tried to see how much one can get away with...
47K should be a safe value for a grid leak 😀... but if I built this particular version there would be a direct coupled cathode follower between the driver and output valve. The output Z of the 7N7 (around 8K) will cause -3dB to occur around 132kHz (assuming a total of 150pF miller capacitance, perhaps bringing it a little lower with strays) - which ought not to be too much of a problem. The possibility of blocking distortion reducing the transient overload recovery of the amp is, in my opinion, more insidious and the reason why I'd put a CF there. The schematic was supposed to be simple, and avoid controversy - for some reason some people hate cathode followers even though they can do some wonderful things. Hmm.. it also solves the grid leak resistor problem because we now can get rid of it altogether. Plus, it allows more glass in the amp, which is pleasing to the eye 🙂
On the issue of gain, I think the YL1071 would only need around 45V peak for full output (90V p-p), and with the gain of 20 from the 7N7 that would give an input sensitivity of around 1.6Vrms for full output, which should be adequate.
With cooling - the idea of mounting the valve base into a fan guard seems great for convection, and allows easy installation of a fan later if forced air is required. It's one of those "why didn't I think of that" moments...
What is a Fahnestock clip.. is it something like this?
Gee, safety conscious types had better not visit your house!
For those who haven't seen it, here's 7N7's Instock Amplifier (6528 PP) from about a year ago.
47K should be a safe value for a grid leak 😀... but if I built this particular version there would be a direct coupled cathode follower between the driver and output valve. The output Z of the 7N7 (around 8K) will cause -3dB to occur around 132kHz (assuming a total of 150pF miller capacitance, perhaps bringing it a little lower with strays) - which ought not to be too much of a problem. The possibility of blocking distortion reducing the transient overload recovery of the amp is, in my opinion, more insidious and the reason why I'd put a CF there. The schematic was supposed to be simple, and avoid controversy - for some reason some people hate cathode followers even though they can do some wonderful things. Hmm.. it also solves the grid leak resistor problem because we now can get rid of it altogether. Plus, it allows more glass in the amp, which is pleasing to the eye 🙂
On the issue of gain, I think the YL1071 would only need around 45V peak for full output (90V p-p), and with the gain of 20 from the 7N7 that would give an input sensitivity of around 1.6Vrms for full output, which should be adequate.
With cooling - the idea of mounting the valve base into a fan guard seems great for convection, and allows easy installation of a fan later if forced air is required. It's one of those "why didn't I think of that" moments...
What is a Fahnestock clip.. is it something like this?
An externally hosted image should be here but it was not working when we last tested it.
Gee, safety conscious types had better not visit your house!
For those who haven't seen it, here's 7N7's Instock Amplifier (6528 PP) from about a year ago.
8116 Push Pull
Much more interesting than that boring SE stage that I posted yesteday. So interesting in fact that I don't actually know if it will work!
I was looking over Paul's Instock amplifier, and noticed its actively loaded differential pair, and the pentode cathode followers. Now, the pentode cathode followers have a gain of rougly unity, so I was thinking... why not try to combine two stages into one?
Since the pentode CF has roughly unity gain, we can tap the signal off a triode, sit the pentode on top of it and use it to bootstrap a resistor to make it look like a CCS. This is essentially what a mu-follower/mu-stage is. Furthermore, I am in a direct coupling mood, so why not try that as well... There are some safety concerns with the DC coupling, but this can be worked out later.
I haven't worked out any component values yet. I see no obvious reason why this will not work, but it's probably best that I ask. Of particular concern is the possible instability of the bias for the output stage...
Comments and suggestions very welcome.
Much more interesting than that boring SE stage that I posted yesteday. So interesting in fact that I don't actually know if it will work!
I was looking over Paul's Instock amplifier, and noticed its actively loaded differential pair, and the pentode cathode followers. Now, the pentode cathode followers have a gain of rougly unity, so I was thinking... why not try to combine two stages into one?
Since the pentode CF has roughly unity gain, we can tap the signal off a triode, sit the pentode on top of it and use it to bootstrap a resistor to make it look like a CCS. This is essentially what a mu-follower/mu-stage is. Furthermore, I am in a direct coupling mood, so why not try that as well... There are some safety concerns with the DC coupling, but this can be worked out later.
I haven't worked out any component values yet. I see no obvious reason why this will not work, but it's probably best that I ask. Of particular concern is the possible instability of the bias for the output stage...
Comments and suggestions very welcome.
Naughty Jason - posting a picture of the Instock lash-up!
Mind you it is completely reliable and has I am proud to say, PENTODE CATHODE FOLLOWERS (D3As).
I love cathode followers and more glass is a very good thing as far as I am concerned. Pentodes have so much gain and as I understand it, all this gain (100% feedback) goes to reducing distortion in the stage although unfortunately not elsewhere!
Yes the picture you show is a Fahnstock clip.
My view on all this is if you don't want a shock, then don't touch anything when it's switched on or at least keep one hand in your pocket.
Note: I might give the impression that I am flippant about safety - I assure you that I treat electricity with great respect and trepidation too when testing and strongly recommend that others do too
I shall have to think about your suggestions in your second post - I am a bit rusty you know!
7N7
Mind you it is completely reliable and has I am proud to say, PENTODE CATHODE FOLLOWERS (D3As).
I love cathode followers and more glass is a very good thing as far as I am concerned. Pentodes have so much gain and as I understand it, all this gain (100% feedback) goes to reducing distortion in the stage although unfortunately not elsewhere!
Yes the picture you show is a Fahnstock clip.
My view on all this is if you don't want a shock, then don't touch anything when it's switched on or at least keep one hand in your pocket.
Note: I might give the impression that I am flippant about safety - I assure you that I treat electricity with great respect and trepidation too when testing and strongly recommend that others do too
I shall have to think about your suggestions in your second post - I am a bit rusty you know!
7N7
7N7 said:
Muhahaha
Cathode followers are great, pentode cathode followers are even better - if it's only to mess with the common cathode only direct heated only mob!
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