Hi there,
I just finished my first tube project, building a Single Ended Triode amplifier based off a kit. It sounds wonderful, but I have a feeling I'm loving the time I put into the design of the amp rather than the resulting sound (I'm not an audiophile in any way).
When I picked up the amp, I was also offered an 832A tube. I immediately grabbed it for it's aesthetic value, but looking further into it, I noticed people have made amps based off of it! All these amps are Push Pull type amps, but I was wondering if it would be possible to make a "single ended tetrode" (got the terminology from wikipedia) type amplifier using only this tube. I wouldn't mind having only a mono output (would this tube being a double tetrode mean it can possibly have two inputs and two outputs?), and sound quality is not a large concern. Would this be possible?
Thanks,
Sonik
I just finished my first tube project, building a Single Ended Triode amplifier based off a kit. It sounds wonderful, but I have a feeling I'm loving the time I put into the design of the amp rather than the resulting sound (I'm not an audiophile in any way).
When I picked up the amp, I was also offered an 832A tube. I immediately grabbed it for it's aesthetic value, but looking further into it, I noticed people have made amps based off of it! All these amps are Push Pull type amps, but I was wondering if it would be possible to make a "single ended tetrode" (got the terminology from wikipedia) type amplifier using only this tube. I wouldn't mind having only a mono output (would this tube being a double tetrode mean it can possibly have two inputs and two outputs?), and sound quality is not a large concern. Would this be possible?
Thanks,
Sonik
Last edited:
The only tetrode I would like to listen is a GMI-11 wired as Triode:
http://www.gstube.com/photo/2969.jpg
This jet radar tube works since 1200V on plate;
The socket is cheap and hi quality stuff:
''GSTube.com''. Tubes, sockets etc. Tube sockets of this type.
http://www.gstube.com/photo/2969.jpg
This jet radar tube works since 1200V on plate;
The socket is cheap and hi quality stuff:
''GSTube.com''. Tubes, sockets etc. Tube sockets of this type.
You can make a stereo SE amp with one of these since there are indeed 2 inputs and outputs available. Use fixed bias, -22 volts on the grids, 250 volts on plate and screens, and 5k transformers as a starting point and tweek from there.
I tried my hand at making a schematic, based off of existing 832A amps and my SET amp. Could anyone advise me on what is missing and suggest parts I should grab?
jerluwoo, I'm not sure what you meant by -22 Volts on the grids, could you explain that part?
jerluwoo, I'm not sure what you meant by -22 Volts on the grids, could you explain that part?
Pano: Are the resistors I added in this schematic appropriate for this tube?
I created another schematic to add in what I believe to be the appropriate application of bias voltage. I am, admittedly, just referencing others' schematics and adapting them to this design. I have a few questions though which may be helpful for understanding these components and deriving the most appropriate values. I would greatly appreciate anyone taking the time to answer them:
Is the value for the bleeder resistor R5 appropriate? Should there be any more bleeders throughout the circuit? Is R1 a bleeder?
What is the purpose of C1 and R1? Some circuits have pin four going directly to ground, while others have a resistor, a polarized capacitor and an unpolarized one!
Is the input stage overkill for an RCA signal? Or would the biasing stage assist in the signal getting through?
Should there be some sort of filtering between the plates and the HV supply (currently the signal goes straight through the transformers into HV) so that the signals from both the left and right side don't mix when they go back into pin 3? Currently there is only a resistor R2 there...
Thanks is advance for all your help in helping me understand the principles behind these wonderful technologies!
I created another schematic to add in what I believe to be the appropriate application of bias voltage. I am, admittedly, just referencing others' schematics and adapting them to this design. I have a few questions though which may be helpful for understanding these components and deriving the most appropriate values. I would greatly appreciate anyone taking the time to answer them:
Is the value for the bleeder resistor R5 appropriate? Should there be any more bleeders throughout the circuit? Is R1 a bleeder?
What is the purpose of C1 and R1? Some circuits have pin four going directly to ground, while others have a resistor, a polarized capacitor and an unpolarized one!
Is the input stage overkill for an RCA signal? Or would the biasing stage assist in the signal getting through?
Should there be some sort of filtering between the plates and the HV supply (currently the signal goes straight through the transformers into HV) so that the signals from both the left and right side don't mix when they go back into pin 3? Currently there is only a resistor R2 there...
Thanks is advance for all your help in helping me understand the principles behind these wonderful technologies!
Interesting Do you want to operate in tetrode mode or strap it as a triode?
It's something of a high voltage tube. Are you okay working with high voltage B+ power supply? Pretty easy to kill oneself with that kind of potential. Just sayin... It might be better to do this one on paper.
Either way, you will need about 20 volts pp to swing this tube so you will need an input stage.
It looks like a -10 volt bias to me. It's not clear to me why you can't just use cathode bias. Perhaps Jerluwoo can answer that.
Operating point could be in the neighborhood of 400v, 100ma, -10v with an 800v B+ and a 5k OT, assuming tetrode mode. LOAD LINES. (Ignore the lower line)
I couldn't find any data on triode connected operation.
Data sheet LINK
It's something of a high voltage tube. Are you okay working with high voltage B+ power supply? Pretty easy to kill oneself with that kind of potential. Just sayin... It might be better to do this one on paper.
Either way, you will need about 20 volts pp to swing this tube so you will need an input stage.
It looks like a -10 volt bias to me. It's not clear to me why you can't just use cathode bias. Perhaps Jerluwoo can answer that.
Operating point could be in the neighborhood of 400v, 100ma, -10v with an 800v B+ and a 5k OT, assuming tetrode mode. LOAD LINES. (Ignore the lower line)
I couldn't find any data on triode connected operation.
Data sheet LINK
An externally hosted image should be here but it was not working when we last tested it.
Last edited:
Never mind the high voltage comments. The B+ in this application will be just ten volts or so higher than the OP given the transformer load.
Too much wine.
Captn Dave: Completely understandable, it's been a long new years 🙂 that said, I am comfortable safely working around 300-400V Tube Amps, and have constructed, tested, and measured capacitor diode voltage multipliers in a lab for learning purposes.
Is there a way to create an input stage to swing the input 20Vpp from a typical stereo without using another tube? I cannot find a reliable source for RCA input specifications, but assuming it's 1Vpp at 0db, the gain would have to be 20 to make this tube start singing? I'll try building it as is in this schematic, and if this isn't enough, I'll try a simple CMOY or even transistor amp hardwired to give me a gain of 20?
I modified the schematic to incorporate the power supply I brought up in a separate thread so that I can use the same transformer from a different tube amp project I built.
My calculations show that the negative bias from this supply will be around -15 V, would this be enough?
Is there a way to create an input stage to swing the input 20Vpp from a typical stereo without using another tube? I cannot find a reliable source for RCA input specifications, but assuming it's 1Vpp at 0db, the gain would have to be 20 to make this tube start singing? I'll try building it as is in this schematic, and if this isn't enough, I'll try a simple CMOY or even transistor amp hardwired to give me a gain of 20?
I modified the schematic to incorporate the power supply I brought up in a separate thread so that I can use the same transformer from a different tube amp project I built.
My calculations show that the negative bias from this supply will be around -15 V, would this be enough?
Here is a LINK for you. You can search for data sheets on just about any tube. I'd look at 6dj8 first. Its a twin triode so one will do both stereo channels. You could probably swing the power triode with a 1v pp signal. Print out the curves and draw the load lines to see.
Read about unbypassed cathode resistors. The negative feedback inherent to this mode will reduce your gain by 20% or so and make it about perfect.
Read about unbypassed cathode resistors. The negative feedback inherent to this mode will reduce your gain by 20% or so and make it about perfect.
Can this tube be connected in triode mode? The G2 are tied together.
R1/C1 are the bias circuit. If you use a negative bias voltage (fixed bias) then they should not be needed.
As Dave stated, this tube does not have huge gain, so you'll need an input stage.
R1/C1 are the bias circuit. If you use a negative bias voltage (fixed bias) then they should not be needed.
As Dave stated, this tube does not have huge gain, so you'll need an input stage.
In post 6 you pose some questions. R1 and c1 are the bypassed cathode resistor, the point of which is to raise the dc potential of the cathode above the grid so that the grid is more negative. C1 eliminates negative feedback so you get more gain. This is one way to bias a tube.
R4 is feeding your negative bias from a transformer winding. This is another way to bias a tube. You don't need to bias both ways. Do one or the other.
If you decide to use cathode bias, you look at the load line and operating point to determine the operating conditions. I think I suggested 100 ma and -10v bias. Ohms law is used to calculate the resistor value (100R). Your 270R is a bit off if my suggestion of operating point were to be used. You will want to have a good look at that for yourself, obviously. I notice that Pete Millet operates his at a -22 volt bias so my suggested operating point is very much in question.
Morgan Jones "vacuum tube amplifiers" is good reading on these subjects and much more.
R4 is feeding your negative bias from a transformer winding. This is another way to bias a tube. You don't need to bias both ways. Do one or the other.
If you decide to use cathode bias, you look at the load line and operating point to determine the operating conditions. I think I suggested 100 ma and -10v bias. Ohms law is used to calculate the resistor value (100R). Your 270R is a bit off if my suggestion of operating point were to be used. You will want to have a good look at that for yourself, obviously. I notice that Pete Millet operates his at a -22 volt bias so my suggested operating point is very much in question.
Morgan Jones "vacuum tube amplifiers" is good reading on these subjects and much more.
Last edited:
I have been researching 632A amp projects...I really want to do an elegant, simple stereo project. This one seemed to be close to a build. Was it ever built? Was a working schematic ever finalized? I'm intrigued by the simplicity and of course by the tube...which are still very modest in cost....
The two tetrodes inside the glass share common screen and cathode, so not when using each tetrode separately. They only have their own grid and plate.
Just a little history, as I understand / misunderstand it:
The Tetrode has only 2 grids, and no beam forming element.
The 832A is a Beam Power Tube. It has 2 grids, and a beam forming element.
The Beam Power Tube was a great invention that allowed RCA to get around the Patented Pentode tubes.
Pentode tubes have 3 grids.
I use them all (and Triodes too)
I never new why the Beam Power tube was ever called a Tetrode.
Perhaps it was because the Beam Power tube only has 2 grids.
The Tetrode has only 2 grids, and no beam forming element.
The 832A is a Beam Power Tube. It has 2 grids, and a beam forming element.
The Beam Power Tube was a great invention that allowed RCA to get around the Patented Pentode tubes.
Pentode tubes have 3 grids.
I use them all (and Triodes too)
I never new why the Beam Power tube was ever called a Tetrode.
Perhaps it was because the Beam Power tube only has 2 grids.
odontojeter,
The 832A is a neat looking tube. I believe you meant 832A, not 632.
As discussed earlier in this thread, this amp would need another tube, a dual triode would be simplest.
The 832A Beam Power mode will have high output impedance, not a very good damping factor.
With a 12AT7 dual triode, you could use plate to plate feedback to fix the damping factor.
Take a look at the RH807 amps.
The problem is that the 807 plate can dissipate 25 Watts, the 832A plates can only dissipate 11 Watts. It would take re-engineering to make the 832A to work within its rated specifications.
The 807 is another neat looking tube, so you might duplicate the RH807 Amp.
Depending on your experience, you might select another amp project, a good kit (there are lots of not so good kits out there; lots have poor documentation, lots of poor quality parts, or designs that stress tubes to the limits).
The 832A is a neat looking tube. I believe you meant 832A, not 632.
As discussed earlier in this thread, this amp would need another tube, a dual triode would be simplest.
The 832A Beam Power mode will have high output impedance, not a very good damping factor.
With a 12AT7 dual triode, you could use plate to plate feedback to fix the damping factor.
Take a look at the RH807 amps.
The problem is that the 807 plate can dissipate 25 Watts, the 832A plates can only dissipate 11 Watts. It would take re-engineering to make the 832A to work within its rated specifications.
The 807 is another neat looking tube, so you might duplicate the RH807 Amp.
Depending on your experience, you might select another amp project, a good kit (there are lots of not so good kits out there; lots have poor documentation, lots of poor quality parts, or designs that stress tubes to the limits).
Isn't that why they made the 829B? It's 40 watts / plate IIRC. 5894 is in between the two.
Win W5JAG
w5jag
Those are great tubes!
But with the common cathodes, I can not use individual self bias, which is what I prefer for push pull. I would have to use plate sense resistor(s) and adjustable fixed grid bias
(I like to make sure there is less than 1mA DC imbalance in the output transformer primary).
I have considered using the two 5894 tubes I have in a pair of Parallel Single Ended Amplifiers.
Those are great tubes!
But with the common cathodes, I can not use individual self bias, which is what I prefer for push pull. I would have to use plate sense resistor(s) and adjustable fixed grid bias
(I like to make sure there is less than 1mA DC imbalance in the output transformer primary).
I have considered using the two 5894 tubes I have in a pair of Parallel Single Ended Amplifiers.
thanks
These are all good comments and helped answer my original question.
I have built a few amps from the ground up but I do my projects because I enjoy the build process and then the subesquent tweaking that we do. I am not strong on running the numbers and usually depend on others (like you, this forum) to get a working schematic.
Back to the 832a project, there are a couple of other designs aligning to what was just described...including the 12AT7 as a driver...I am enamored with the funky design of the 832 and have a couple that need to produce music....If anyone reading these threads is aware of a proven, simple musical design, please comment!! Again Thanks!
These are all good comments and helped answer my original question.
I have built a few amps from the ground up but I do my projects because I enjoy the build process and then the subesquent tweaking that we do. I am not strong on running the numbers and usually depend on others (like you, this forum) to get a working schematic.
Back to the 832a project, there are a couple of other designs aligning to what was just described...including the 12AT7 as a driver...I am enamored with the funky design of the 832 and have a couple that need to produce music....If anyone reading these threads is aware of a proven, simple musical design, please comment!! Again Thanks!
Tee hee hee.... It all depends what you're pushing and pulling, doesn't it? Back in the HAM days, it was a 40 meter ( 300 Mm/s ÷ 40 m = 7.5 MHz ) continuous-wave (Morse Code) transmitter circuit. The core material of the output transformer was … air … so imbalances in the pair of tube sections wasn't a problem. LOL. Having the pair of anode-pins so conveniently “on the top” of the dual-tetrode was great: short path to the output transformer, made from a bit of ³/₁₆ inch bare copper tubing. 16 total turns, 6 inch diameter. 21.7 μH, 41.5 pF capacitor tank tuning capacitor.
Simple power NPN “grid quenching” keying (gating) shunt plus inverter attached to the Morse key. Safe, too. Maybe only 20 volts involved. The “Q” of the circuit was high (in the thousands with high quality capacitor), and a vernier (20:1) knob controlled the output frequency. Oh… it was sensitive to the temperature, of course. But a 20 MHz frequency counter eliminated the lookup tables. Just “dial it in” and watch it.
About 100 watts for the rig. Plate input watts.
Around the world with a great antenna. It was - in the end - all about the antenna, both for receiving and directionalizing transmission. BIG "yagi" antenna.
GoatGuy
- Status
- Not open for further replies.