A friend of mine is a HAM operator and needed to replace this tube in his transmitter. He asked if it could be used in a home stereo amp. In his application it runs 3600VDC on the plate, and around 700ma plate current. I simply don't know.
https://www.tube-data.com/sheets/140/8/8877.pdf
https://www.tube-data.com/sheets/140/8/8877.pdf
It may be easier to work with than an 833. Have two for stereo?
It may not be as putry as an 833 and will need some forced air depending on how much power you want.
Each needs 50Watts of hater than can be AC though it will need a 90 second delay before applying plate voltage.
Really I am stuck between el-34 and 4x-150s for a new build. I really do not need as much power though I may go a little farther so the kids can blast.
It may not be as putry as an 833 and will need some forced air depending on how much power you want.
Each needs 50Watts of hater than can be AC though it will need a 90 second delay before applying plate voltage.
Really I am stuck between el-34 and 4x-150s for a new build. I really do not need as much power though I may go a little farther so the kids can blast.
Years ago, a 19 inch wide, 6 foot tall equipment rack, was used to house a pair of 200 Watt single ended power amplifiers.
It used Eimac's 1500 Watt Linear Triode that was designed for VHF TV.
The designer wound his own 200 Watt output transformers.
Can high voltage, high power RF tubes be used for Audio?
Yes.
Just prepare yourself for the expense and the work that has to be done.
A dive off the 10 meter platform, with degree of difficulty 4.5, is easier than building that amplifier.
It used Eimac's 1500 Watt Linear Triode that was designed for VHF TV.
The designer wound his own 200 Watt output transformers.
Can high voltage, high power RF tubes be used for Audio?
Yes.
Just prepare yourself for the expense and the work that has to be done.
A dive off the 10 meter platform, with degree of difficulty 4.5, is easier than building that amplifier.
That’s the tube in my Henry floor model amateur amp. I have a spare. Cooling system is noisy. I have a spare Peter Dahl power transformer also. I’d love to see your output transformer 🙃
The 833C transmitter tube makes a great set of SET mono amps. Took me a year to complete and $10K+ about 10 years ago. Still making beautiful music. Plate voltage 2300V, plate current 160mA, power about 200WPC, The first 40W in Class A1, the rest in A2.
I don't think I'd try it with a metal tube, though...I like the light show too much.
I don't think I'd try it with a metal tube, though...I like the light show too much.
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Well not necessarily simple, and definitely not cheap.
Here's the DUMM BLONDE's clip lead version of an 833A SE, it did do about 200 watts on 1500 volts at 270 mA, and survived several days of my lousy guitar playing. NO, DON'T TRY THIS AT HOME. Note the 1/4 inch thick Lexan blast shield between me and the "test circuit." This "rest" only existed for one week back in 2003.
The metal cased 3CX1500A7 poses more mechanical mounting and cooling challenges since the case of the tube is the heat sink for the plate and is electrically connected to it. It also requires a considerable amount of forced air cooling, though that can be reduced considerably if operated at power levels similar to the 833A, which was 400 watts of idle dissipation in my test amp. More current did not produce any more power, and I didn't have any more voltage to apply.
The 3CX1500A7 has a Mu of 200 which will impart a pretty high plate resistance, requiring a pretty high impedance OPT. The real purpose of my clip lead monster was to test a one off custom OPT that was built for me by Transcendar. The OPT as received would have needed a bit of feedback to get HiFi like specs, so the project died 20 years ago and the tubes, OPT and power transformer still sleep in a box on the shelf. The Mu of the 833A is 35, quite a bit lower than the 3CX1500A7. I would say that a HiFi spec OPT for the 3CX1500A7 at a sane (around 250 watts) power level would either be impossible, or cost as much as a Corvette!
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oof, I was just going by the lower heater power requirements and no need for filtered DC on a filament.
Now the suspense is killing me. I need to see how you calculate plate resistance from constant current curves.
Now the suspense is killing me. I need to see how you calculate plate resistance from constant current curves.
From the datasheet: mu = 200 and gm = 55000 @ 1 Amp
mu = gm rp so rp = mu/gm
rp = 3636 Ohm @ 1 Amp
practical gm variation proportional to SQRT (Ip) so rp variation 1/SQRT (Ip)
so 250 mA gives rp of 7272 Ohms
3X to 5X rp for triode load
OT: NASA contract, Krell metal laminations
You could parallel a few tubes to bring the OT impedance down. But they might oscillate at 200 Mhz.
mu = gm rp so rp = mu/gm
rp = 3636 Ohm @ 1 Amp
practical gm variation proportional to SQRT (Ip) so rp variation 1/SQRT (Ip)
so 250 mA gives rp of 7272 Ohms
3X to 5X rp for triode load
OT: NASA contract, Krell metal laminations
You could parallel a few tubes to bring the OT impedance down. But they might oscillate at 200 Mhz.
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The beam regulator triodes like the 6JH5 and 6HV5A work like this on a much smaller scale. The Gm is in the 55,000 to 65,000 range with a Mu of 300. I have seen a few schematics that show these being used as a high gain driver for a bigger tube like an 845, but never saw one used as an output tube. I have made a few half hearted attempts to tame these beasts without success. 20+ years later there is still a box full on the shelf.
Anything that was breadboarded with lead lengths longer than microscopic oscillated over a wide range of frequencies at switch on. A stable idle current could not be reached.
I did make a successful (OK it amplified and didn't oscillate) small amp using the 6JD5 with the grid - cathode fed directly from the headphone jack in a Sony Discman with an OPT in serries with a power supply connected from cathode to plate. This was definitely the lowest component count circuit ever seen in any audio amp. I turned the power supply up until I got some plate current (over 600 Volts) and hit play on the Sony. It did make sound, sound much like the basser kid's car across the street without the license plate rattle.
I still have a box full of these things. I plan to try them in the UNSET topology someday as the direct plate to grid negative feedback might create a much lower effective working Mu.
Anything that was breadboarded with lead lengths longer than microscopic oscillated over a wide range of frequencies at switch on. A stable idle current could not be reached.
I did make a successful (OK it amplified and didn't oscillate) small amp using the 6JD5 with the grid - cathode fed directly from the headphone jack in a Sony Discman with an OPT in serries with a power supply connected from cathode to plate. This was definitely the lowest component count circuit ever seen in any audio amp. I turned the power supply up until I got some plate current (over 600 Volts) and hit play on the Sony. It did make sound, sound much like the basser kid's car across the street without the license plate rattle.
I still have a box full of these things. I plan to try them in the UNSET topology someday as the direct plate to grid negative feedback might create a much lower effective working Mu.
There is someone out there who will attempt to do the most difficult of tasks.
I have no desire to climb Mt. Everest.
There are thousands who have attempted, and many who have suceeded.
Want to try an unusual and difficult climb?
Climb K2, the Second highest mountain.
(It is a much more difficult climb than Mt. Everest).
There are RF tubes that can do 100,000 watts or more.
Push Pull, anybody?
If you want to use a pair of them, check with your local power company.
You might need to upgrade your mains from the power pole, and need a new power panel in your house, just to light up the filaments.
I have no desire to climb Mt. Everest.
There are thousands who have attempted, and many who have suceeded.
Want to try an unusual and difficult climb?
Climb K2, the Second highest mountain.
(It is a much more difficult climb than Mt. Everest).
There are RF tubes that can do 100,000 watts or more.
Push Pull, anybody?
If you want to use a pair of them, check with your local power company.
You might need to upgrade your mains from the power pole, and need a new power panel in your house, just to light up the filaments.
I am currently investigating using pair of DA42 triodes in pp
I intend to limit plate voltage to 500V by practical reasons, the existing documentation does not have decent
plate curves. Thus i made them myself as a start.
One issue is that grid has to be positive in the range 5 - 30 volt as i see it so far.
Any interest i can post my findings so far.
I intend to limit plate voltage to 500V by practical reasons, the existing documentation does not have decent
plate curves. Thus i made them myself as a start.
One issue is that grid has to be positive in the range 5 - 30 volt as i see it so far.
Any interest i can post my findings so far.
Page 65 has a design using the DA42, although it's class B. https://pearl-hifi.com/06_Lit_Archive/15_Mfrs_Publications/GEC_UK/GEC-UK_AF_Amplifier_Design.pdf
DA42 15K Zout
Hope you have a bunch of them to parallel.
6HZ5 Beam triode, like George mentioned. 100V/div. Horiz., 20 mA/div Vert., 0.5 V steps, 4th curve from bottom is 0 Vg1, about 5000 Ohm Zout.
gm 55000, mu 300.
The curve tracer has a string of ferrite beads on the grid1 lead to trace this. Could use paralleled tubes in P-P with an 8K OT. This tube (1st tracer pic) is one of the uncommon beam triodes with actual flat plates. 2nd pic is the more usual beam triode type with the Barkhausen type plate (vertical box in plate edge, it's actually missing the Barkhausen plate inside the vertical box.) Needs more plate V.
3rd pic. My kind of output triode tube. 7241/7242 Zout 67/82 Ohms !!! Low plate V, Amperes output. Kinda expensive compared to the big sweep tubes though.
Hope you have a bunch of them to parallel.
6HZ5 Beam triode, like George mentioned. 100V/div. Horiz., 20 mA/div Vert., 0.5 V steps, 4th curve from bottom is 0 Vg1, about 5000 Ohm Zout.
gm 55000, mu 300.
The curve tracer has a string of ferrite beads on the grid1 lead to trace this. Could use paralleled tubes in P-P with an 8K OT. This tube (1st tracer pic) is one of the uncommon beam triodes with actual flat plates. 2nd pic is the more usual beam triode type with the Barkhausen type plate (vertical box in plate edge, it's actually missing the Barkhausen plate inside the vertical box.) Needs more plate V.
3rd pic. My kind of output triode tube. 7241/7242 Zout 67/82 Ohms !!! Low plate V, Amperes output. Kinda expensive compared to the big sweep tubes though.
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I have a 7241 here, off of Ebay, $50. (next one up was $950, guess I won't find another one for P-P soon ) My 36V, 12 Amp bench supply, for difficult heaters, can't get this monster heated up, The clip leads get smoking hot and it needs more than 12 Amps to get it up over the initial surge current. Can just make out the filaments starting to glow. I do have a 0-7.5V 130 Amp 1000 W bench supply in the basement, have to dig it out now, with some heavy wires and battery clips.
smoking-amp,
Thanks for the reminder!
Cold Filaments typically draw 4X current, versus when the 1X filament current when it is warmed up.
Hint: Always accurately measure the Cold filament resistance.
Smoking Hot Wires . . . Yes!
I worked in an industrial environment with 208V 3 phase, plus Neutral and Ground.
The 110V was pulled between one phase, and Neutral.
Then, one day . . .
A 3 wire, grounded oscilloscope user decided to measure from one phase to Neutral.
He connected the scope Ground Clip to Neutral.
There was 8 Volts rms from Neutral to ground, both Neutral and Ground wires were very large gauge.
The poor 22 gauge scope ground clip wire smoked-off all its insulation, trying to make 8 Volts to be Zero volts. Ouch!
Thanks for the reminder!
Cold Filaments typically draw 4X current, versus when the 1X filament current when it is warmed up.
Hint: Always accurately measure the Cold filament resistance.
Smoking Hot Wires . . . Yes!
I worked in an industrial environment with 208V 3 phase, plus Neutral and Ground.
The 110V was pulled between one phase, and Neutral.
Then, one day . . .
A 3 wire, grounded oscilloscope user decided to measure from one phase to Neutral.
He connected the scope Ground Clip to Neutral.
There was 8 Volts rms from Neutral to ground, both Neutral and Ground wires were very large gauge.
The poor 22 gauge scope ground clip wire smoked-off all its insulation, trying to make 8 Volts to be Zero volts. Ouch!