If the amp provides less than good sonics, the 811A best be kept to high voltage RF or modulator service. Radio Daze in NY sells the available 812 for $42 each. AES has the 812 available from China, Russia & NOS US manufacture. A heavy duty version was manufactured with a 572B type carbon plate called the 812H. Now, that is a rare tube.
Re: It lives !!!
Great! I'm very interested. I happen to have these tubes on hand.
Would you please share some more about how it sounds?
About the grid voltage, I believe, at +16V (with 300V on anode), it's just awakened.
I tried marking that point on the plate curves, I saw only around 40mA. It's indeed in the far left/bottom region of the chart.
On Shishido's design, it runs the tube at 440V / +30V / 100mA with 3.5k load. FYR
john 807 said:
Great! I'm very interested. I happen to have these tubes on hand.
Would you please share some more about how it sounds?
About the grid voltage, I believe, at +16V (with 300V on anode), it's just awakened.
I tried marking that point on the plate curves, I saw only around 40mA. It's indeed in the far left/bottom region of the chart.
On Shishido's design, it runs the tube at 440V / +30V / 100mA with 3.5k load. FYR
I am Glad you have taken an interest
HI
Well, I am only 14 but I had the valve in my collection and I had a output transformer needs to be within the region of 3.5 to 5k at about 15watts rated the 811-A runs about +300v on the plate witch is cathode driven you can use some of the circuits on this thread. it draws the minimiun of about 100ma
that some kind people have offered to share with us. it is driven using the 6V6G and as a pre gain stage you will need a 6j7 or some over kind of pentode of your choice i used the 6J7 because it looks cool next to the 811 coke-bottle style but you
can use any style of pentode to use as the pre amp there is not a circuit for that i made it up if you need help with it i will give you them in a seperate thread
Warning - High voltages are present !!!
And you can have problems with the hum i didnt cause i used a big meaty capacitor (22000 uf +22000 uf 62v dc wrk) with a 2mh choke needs to be heavy or it will over heat as i had problems with i used a battery chager transformer for the heater and it worked very well gets warm
experements - it works very well the bass is so well held the high freq 's need to be held down with a bit of negitive feedback
NFB but overall a very good reasult
this amp is certanly one of the most fun to experement with a used my transmitter power supply to run the 811 on about 800+v
made the valve work a bit harder for a few more watts but that was only for experement i run it only on about 300 The rectifire is a GZ34 it gives the best voltage boost A 5U4 saggs the B+ down a lot a coventional choke needs to be used for HT smmothing at a bout 10H minimium
I will get some pics soon!!!
Jonathan Kelly
MW3KGQ
HI
Well, I am only 14 but I had the valve in my collection and I had a output transformer needs to be within the region of 3.5 to 5k at about 15watts rated the 811-A runs about +300v on the plate witch is cathode driven you can use some of the circuits on this thread. it draws the minimiun of about 100ma
that some kind people have offered to share with us. it is driven using the 6V6G and as a pre gain stage you will need a 6j7 or some over kind of pentode of your choice i used the 6J7 because it looks cool next to the 811 coke-bottle style but you
can use any style of pentode to use as the pre amp there is not a circuit for that i made it up if you need help with it i will give you them in a seperate thread
Warning - High voltages are present !!!
And you can have problems with the hum i didnt cause i used a big meaty capacitor (22000 uf +22000 uf 62v dc wrk) with a 2mh choke needs to be heavy or it will over heat as i had problems with i used a battery chager transformer for the heater and it worked very well gets warm
experements - it works very well the bass is so well held the high freq 's need to be held down with a bit of negitive feedback
NFB but overall a very good reasult
this amp is certanly one of the most fun to experement with a used my transmitter power supply to run the 811 on about 800+v
made the valve work a bit harder for a few more watts but that was only for experement i run it only on about 300 The rectifire is a GZ34 it gives the best voltage boost A 5U4 saggs the B+ down a lot a coventional choke needs to be used for HT smmothing at a bout 10H minimium
I will get some pics soon!!!
Jonathan Kelly
MW3KGQ
BIAS
HI All
sorry the last one was quick has a few mistakes in it,
anyway the bias improves the sound quality a lot and power
output ( PD )
it is worth checking the data sheets and reading the graphs to understand the bias points to run the 811-a at you can do it very easily by ploting your H.T Volts by your H.T Current and you get a result I will test it tommrow seen as it will wake every-one up and i will be popular 
73,s
MW3KGQ
HI All
sorry the last one was quick has a few mistakes in it,
anyway the bias improves the sound quality a lot and power
output ( PD )
it is worth checking the data sheets and reading the graphs to understand the bias points to run the 811-a at you can do it very easily by ploting your H.T Volts by your H.T Current and you get a result I will test it tommrow seen as it will wake every-one up and i will be popular 73,s
MW3KGQ
Good for you, Jonathan !
How I wish I could be like you in my youth.
Back to the circuit, I supposed there're both driver's Ia + 811's Ia on the Rk of 811.
So if you measured the voltage across the Rk of 811, you couldn't see the Ia of 811 alone, and there's also grid current in it.
Correct me if I'm wrong.
How I wish I could be like you in my youth.
Back to the circuit, I supposed there're both driver's Ia + 811's Ia on the Rk of 811.
So if you measured the voltage across the Rk of 811, you couldn't see the Ia of 811 alone, and there's also grid current in it.
Correct me if I'm wrong.
Right you are
Yes,
you get the reading of the bias of the driver valve which is controleing the 811 so the bias is infact controlled by the driver in my case 6v6 I must admit i have a problem with it i am getting something called ( cross-over-distortion ) and not enough out-put
(PD) it is becomeing difficult to sort my dad is having a think about it should be resolved.
Grid curent - nope thers no current draw it is voltage swing the circuit is very strange to most valve-amp-constructors because it uses + bias the idea of using such a powerfull driver is so that it can swing the volaage 80+ and back down to 80- again you need a very big valve to do this with triodes it is the same with the 300b and other valves alike. the 6v6 can give 5w to 10w depending on the plate voltage. now this is a usefull trick I am going to tell you if you havent enough b+ to drive the 6v6 to maximum output you can use a 6Y6 or an other one in the family is the 6F6 saves a lot of time and confussion they can be pluged into the same pin connections as well also if your after a bit more power you can use the 6L6 best of building the amp around the 6v6 and then experement later
so , are you going to give it ago ???
I am very tired today after last night tinkering to one in the morning so i haven't done much with it i hate it when i am tired it really annoys me
Best wishes
Jonathan kelly
MW3KGQ
Yes,
you get the reading of the bias of the driver valve which is controleing the 811 so the bias is infact controlled by the driver in my case 6v6 I must admit i have a problem with it i am getting something called ( cross-over-distortion ) and not enough out-put
(PD) it is becomeing difficult to sort my dad is having a think about it should be resolved.
Grid curent - nope thers no current draw it is voltage swing the circuit is very strange to most valve-amp-constructors because it uses + bias the idea of using such a powerfull driver is so that it can swing the volaage 80+ and back down to 80- again you need a very big valve to do this with triodes it is the same with the 300b and other valves alike. the 6v6 can give 5w to 10w depending on the plate voltage. now this is a usefull trick I am going to tell you if you havent enough b+ to drive the 6v6 to maximum output you can use a 6Y6 or an other one in the family is the 6F6 saves a lot of time and confussion they can be pluged into the same pin connections as well also if your after a bit more power you can use the 6L6 best of building the amp around the 6v6 and then experement later
so , are you going to give it ago ???
I am very tired today after last night tinkering to one in the morning so i haven't done much with it i hate it when i am tired it really annoys me
Best wishes
Jonathan kelly
MW3KGQ
How about installing a 'grid stopper' for 811?
A small one like 10R~100R would be sufficient I guess. With this resistor in place, you can monitor the actual current through 6V6. (and that is also the grid current of 811)
PS. I'll build such an amp for sure, but it takes time. For a 'middleager' like me, free time is the most luxurious thing.
A small one like 10R~100R would be sufficient I guess. With this resistor in place, you can monitor the actual current through 6V6. (and that is also the grid current of 811)
PS. I'll build such an amp for sure, but it takes time. For a 'middleager' like me, free time is the most luxurious thing.
same problem as my father
Dad has the same problem it is the holidays for me but not for him he gets only a few hours a night and thats pushing it i dont blame you for not having enough time it is very unfortunate
i fixed the problem i had set the wrong plate impedence on the the output transformer that is helped a lot also my choke is dragging the output stage voltage down so i have by-passed it
this morning i am now going to play with the feed back to see if i can make that beter.
if you need any help with parts e.t.c or circuit problems i am willing to help you I find it very interesting that someone has given the same project some interest.
I have made a few audio amps before hand when I was 12 I built a 807 push-pull amplifier brilliant thing is that puts out about 100w with about 700v on the plate from a sowter transformer
oww!! that was fun my dad has built a superb HI-FI amp using 4 6v6-g's and using quad spekers 12L
jonathan
Dad has the same problem it is the holidays for me but not for him he gets only a few hours a night and thats pushing it i dont blame you for not having enough time it is very unfortunate
i fixed the problem i had set the wrong plate impedence on the the output transformer that is helped a lot also my choke is dragging the output stage voltage down so i have by-passed it
this morning i am now going to play with the feed back to see if i can make that beter.
if you need any help with parts e.t.c or circuit problems i am willing to help you I find it very interesting that someone has given the same project some interest.
I have made a few audio amps before hand when I was 12 I built a 807 push-pull amplifier brilliant thing is that puts out about 100w with about 700v on the plate from a sowter transformer
oww!! that was fun my dad has built a superb HI-FI amp using 4 6v6-g's and using quad spekers 12L
jonathan
sorry grid stopper!
Hi All
I havent found a problem with osc but the bias on the 6v6 needs to be fiddeled with because the 811 draggs it into a higher bias
of about 20+ when you want it at about 12 to 13+ the 6v6 needs about a 300k on the grid to ground as a stopper and the in series with the cathode of the 6v6 and grid of the 811 a 220 ohem resistor and then take a 300k resistor from the grid of the 6v6 and take it to the 811's grid this is to get 6v6 in the right bias voltage this is my own little mod it helps to give more drive from the 6v6 and results in better response power output
Thanks
Jonathan
Hi All
I havent found a problem with osc but the bias on the 6v6 needs to be fiddeled with because the 811 draggs it into a higher bias
of about 20+ when you want it at about 12 to 13+ the 6v6 needs about a 300k on the grid to ground as a stopper and the in series with the cathode of the 6v6 and grid of the 811 a 220 ohem resistor and then take a 300k resistor from the grid of the 6v6 and take it to the 811's grid this is to get 6v6 in the right bias voltage this is my own little mod it helps to give more drive from the 6v6 and results in better response power output
Thanks
Jonathan
811a
Been looking at making an amp based around the 811A for a while. Ive built a 6c33c single-ended, with home-wound output Tx's but fancy something a little different!
I would be quite interested in a fellow Welshmans schematic and findings Johnathan!--How is it coming along? I was thinking of using something like a KT66 as driver, as I have some around, but Ill probably use my Nuvistor Mu-Stage for the input/gain stage, as I found this works great with the 6c33 project.
What have you found is the optimum 811A output Tx impedance? I was planning around 350-400V Vp for the 811.
Been looking at making an amp based around the 811A for a while. Ive built a 6c33c single-ended, with home-wound output Tx's but fancy something a little different!
I would be quite interested in a fellow Welshmans schematic and findings Johnathan!--How is it coming along? I was thinking of using something like a KT66 as driver, as I have some around, but Ill probably use my Nuvistor Mu-Stage for the input/gain stage, as I found this works great with the 6c33 project.
What have you found is the optimum 811A output Tx impedance? I was planning around 350-400V Vp for the 811.
Hi all!!
The driver arrangement in this circuit is crucial to how it works and probably the bigger, high mu example you can use the better. The quiescent current through the driver effectively sets the operating point of the 811 so a valve that allows a big current to pass at this point when it is operating ideally in class A will give a higher positive grid bias to the 811
One of the main issues also with this is to get as big a voltage output swing out of the driver as possible whilst keeping it working in class A. If a 6V6 is used as per the schematic with its grid resistor to ground and a direct connection between its cathode and the grid of the 811, the grid to cathode voltage of the 6V6 is about -21V with the anode/cathode voltage approx 200. The 811 grid is then at about +14. The only way to get this bias up to something more reasonable is to increase the current through the 6V6 (or decrease its effective resistance if you like.) To do this and also get the 6V6 to something like a reasonable operating point it needs the insertion of a resistor of around 100 ohms between the cathode of the 6V6 and the grid of the 811 with the grid resistor of the 6V6 connected to the 811 side instead of ground. This effecively provides a cathode bias for the 6V6 and gets its grid to cathode voltage down to around 12 volts ie more or less were it is needed. With other pentodes or big beam tetrodes that run in class A with a grid bias of -20V or so this is probably not neccesary. We've found that both arrangements work similarly well ie with the 6V6 or a 6BG6 without the resistor.
The sound quality achieved so far has been reasonable, but our ouput transformer is not at all up to the mark, becoming saturated with the DC that the 811 is drawing (120ma with about +24 bias on the 811.) Accordingly the power output is a bit 'strained' and feeble, but the voltage swings on the 'scope look pretty good and clearly there is a lot more potential with a properly specified transformer designed for a single ended use. This has to be the next thing to sort out and I will be interested to see what everyone else has been trying. By using a few odds and ends that we have, the impedance doesn't seem to be that critical, but we're going to look on the basis that about 5K is going to be about right.
Phil MW3KGP (Jonathan's Dad and another valve nut ) and Jonathan
The driver arrangement in this circuit is crucial to how it works and probably the bigger, high mu example you can use the better. The quiescent current through the driver effectively sets the operating point of the 811 so a valve that allows a big current to pass at this point when it is operating ideally in class A will give a higher positive grid bias to the 811
One of the main issues also with this is to get as big a voltage output swing out of the driver as possible whilst keeping it working in class A. If a 6V6 is used as per the schematic with its grid resistor to ground and a direct connection between its cathode and the grid of the 811, the grid to cathode voltage of the 6V6 is about -21V with the anode/cathode voltage approx 200. The 811 grid is then at about +14. The only way to get this bias up to something more reasonable is to increase the current through the 6V6 (or decrease its effective resistance if you like.) To do this and also get the 6V6 to something like a reasonable operating point it needs the insertion of a resistor of around 100 ohms between the cathode of the 6V6 and the grid of the 811 with the grid resistor of the 6V6 connected to the 811 side instead of ground. This effecively provides a cathode bias for the 6V6 and gets its grid to cathode voltage down to around 12 volts ie more or less were it is needed. With other pentodes or big beam tetrodes that run in class A with a grid bias of -20V or so this is probably not neccesary. We've found that both arrangements work similarly well ie with the 6V6 or a 6BG6 without the resistor.
The sound quality achieved so far has been reasonable, but our ouput transformer is not at all up to the mark, becoming saturated with the DC that the 811 is drawing (120ma with about +24 bias on the 811.) Accordingly the power output is a bit 'strained' and feeble, but the voltage swings on the 'scope look pretty good and clearly there is a lot more potential with a properly specified transformer designed for a single ended use. This has to be the next thing to sort out and I will be interested to see what everyone else has been trying. By using a few odds and ends that we have, the impedance doesn't seem to be that critical, but we're going to look on the basis that about 5K is going to be about right.
Phil MW3KGP (Jonathan's Dad and another valve nut ) and Jonathan
Last week I finished building a prototype monoblock 811SE mainly due to the fact that I had the necessary ironware ready for a timepass project.
The circuit itself could not have been any simpler. Right now I’m using SRPP 6SN7 input RC to a triode strapped KT66 (discard from a QUADII). The Cathode directly feeds the grid of the 811. OPT is 3.5k with the 4r tap connected to an 8r load for a higher reflected load. 811 plate is at around 400 volts.
I have all AC filaments and I am getting away with just about audible hum. It is certainly not bothering me and I intend to continue with this arrangement wich will save major parts costs.
Lots of experimentations ahead. There is the pentode input (EF86/5693) option and perhaps power MOSFETs to replace the driver. I suspect that would a major improvement. And no…a MOSFET will not hurt my pride at all : )
Listening impressions are very good. I have made a ‘Stereo’ arrangement by a restored QUADII as the other channel. With my 88dB ‘guinea pig’ speakers the comparison is stark. 811 sounds very open and the dynamics are very extended compared to the QUAD. I had always admired the QUAD, but the 811 just leaves it far behind. I am also finding that the 811 likes a little feedback. I am experimenting with feedback ranging from 6dB to 20dB. That is taking care of a subtle brightness.
This is also the first time that I am using oil cans for the PSU. With a minimalist GZ32 rectified 4uf-10Hy-4ufs scheme the speed and transparency in amazing. I am hoping they will become even better as we go along. The caps are ex military in original packing.
At this point my OPT, which was originally bought for EL34/6L6 SE project is the limiting factor. I think with +25volts at the grid and 385-400volts on the cap, the 811 is running around 135mA which much beyond rating of the OPT. I would ideally like an OPT rated at around 5k5/150mA/20watts.
It helps that NOS RCA 811 is locally available for a song.
Measurements shall be taken this weekend and posted here.
The circuit itself could not have been any simpler. Right now I’m using SRPP 6SN7 input RC to a triode strapped KT66 (discard from a QUADII). The Cathode directly feeds the grid of the 811. OPT is 3.5k with the 4r tap connected to an 8r load for a higher reflected load. 811 plate is at around 400 volts.
I have all AC filaments and I am getting away with just about audible hum. It is certainly not bothering me and I intend to continue with this arrangement wich will save major parts costs.
Lots of experimentations ahead. There is the pentode input (EF86/5693) option and perhaps power MOSFETs to replace the driver. I suspect that would a major improvement. And no…a MOSFET will not hurt my pride at all : )
Listening impressions are very good. I have made a ‘Stereo’ arrangement by a restored QUADII as the other channel. With my 88dB ‘guinea pig’ speakers the comparison is stark. 811 sounds very open and the dynamics are very extended compared to the QUAD. I had always admired the QUAD, but the 811 just leaves it far behind. I am also finding that the 811 likes a little feedback. I am experimenting with feedback ranging from 6dB to 20dB. That is taking care of a subtle brightness.
This is also the first time that I am using oil cans for the PSU. With a minimalist GZ32 rectified 4uf-10Hy-4ufs scheme the speed and transparency in amazing. I am hoping they will become even better as we go along. The caps are ex military in original packing.
At this point my OPT, which was originally bought for EL34/6L6 SE project is the limiting factor. I think with +25volts at the grid and 385-400volts on the cap, the 811 is running around 135mA which much beyond rating of the OPT. I would ideally like an OPT rated at around 5k5/150mA/20watts.
It helps that NOS RCA 811 is locally available for a song.
Measurements shall be taken this weekend and posted here.
It's funny that all the 811A people are in India, the UK and Europe.
I have a prototype Parafeed 811A up and running. I'm using
the stacked raw 6V6/6W6/6Y6 driver ontop of the 811A
and it sounds excellent! I'm using an unloaded Hammond
1628SE as the plate load choke, and a Magnequest RF PF
nickle/M6 pinstriped parafeed tranny (5K to 8 ohms)
They key is to use a tube with a high enough gm so that the
cathode follower resistance is 100 ohms or less. This gets
the distortion down. Any tube with a cathode bias point of
20V or so passing 20mA or so will work.
430V is a great operating point since the grid current is less
than, say, 320V. If you run the 811A lower, you need an even
stiffer driver for the grid!
I got away with AC filaments and a hum bucking potentiometer. However, on the spectrum analyzer, you can clearly see all the
60Hz intermodulation products. i.e. a 1kHz sine wave gives
stuff at 1060Hz and 940Hz on the FFT.
It sounds awesome though! I think what I'm hearing is the detail of the nickel parafeed transformer.
-- Jim
I have a prototype Parafeed 811A up and running. I'm using
the stacked raw 6V6/6W6/6Y6 driver ontop of the 811A
and it sounds excellent! I'm using an unloaded Hammond
1628SE as the plate load choke, and a Magnequest RF PF
nickle/M6 pinstriped parafeed tranny (5K to 8 ohms)
They key is to use a tube with a high enough gm so that the
cathode follower resistance is 100 ohms or less. This gets
the distortion down. Any tube with a cathode bias point of
20V or so passing 20mA or so will work.
430V is a great operating point since the grid current is less
than, say, 320V. If you run the 811A lower, you need an even
stiffer driver for the grid!
I got away with AC filaments and a hum bucking potentiometer. However, on the spectrum analyzer, you can clearly see all the
60Hz intermodulation products. i.e. a 1kHz sine wave gives
stuff at 1060Hz and 940Hz on the FFT.
It sounds awesome though! I think what I'm hearing is the detail of the nickel parafeed transformer.
-- Jim
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