Amazing replacement for Mullard Ecc83
/ 12ax7
Everyone That I had listen to the 5755 tubes in place of the Mullard old stock 12ax7 was blown away. What an awesome tube.
Best sounding tubes. All you have to do is switch a few wires on the tube socket and for 15.00 ea. you will get the very best sounding 12ax7.
I Rather pay 15.00 bucks then over 100.00 ea. for the best sounding 12ax7
This is one of the best discoveries ever.
I bought some Raytheon 5755 tubes and replaced all my 12ax7 vintage mullard tubes not only saved over 500.00 I Even think they sound better.
This is cool
Andrew
I bought some yellow branded Raytheon 5755 tubes think they are best
/ 12ax7
Everyone That I had listen to the 5755 tubes in place of the Mullard old stock 12ax7 was blown away. What an awesome tube.
Best sounding tubes. All you have to do is switch a few wires on the tube socket and for 15.00 ea. you will get the very best sounding 12ax7.
I Rather pay 15.00 bucks then over 100.00 ea. for the best sounding 12ax7
This is one of the best discoveries ever.
I bought some Raytheon 5755 tubes and replaced all my 12ax7 vintage mullard tubes not only saved over 500.00 I Even think they sound better.
This is cool
Andrew
I bought some yellow branded Raytheon 5755 tubes think they are best
Have you tried rigging a 6SL7 tube in the amplifier to compare? $10
Anyone have a datasheet with a Mu curve for the 5755?
The Raytheon datasheet isn't very complete:
http://frank.pocnet.net/sheets/138/5/5755.pdf
http://frank.pocnet.net/sheets/093/6/6SL7GT.pdf
http://frank.pocnet.net/sheets/093/1/12AX7A.pdf
5755 is a little lower rated than 12AX7A for some things, so some checking needed for an ampl.:
250 Vp versus 330 Vp
1 Watt versus 1.2 Watt
75 V Htr to K versus 100 V
Anyone have a datasheet with a Mu curve for the 5755?
The Raytheon datasheet isn't very complete:
http://frank.pocnet.net/sheets/138/5/5755.pdf
http://frank.pocnet.net/sheets/093/6/6SL7GT.pdf
http://frank.pocnet.net/sheets/093/1/12AX7A.pdf
5755 is a little lower rated than 12AX7A for some things, so some checking needed for an ampl.:
250 Vp versus 330 Vp
1 Watt versus 1.2 Watt
75 V Htr to K versus 100 V
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Found a WE420A datasheet with a Mu curve:
http://www.westernelectric.com/spec_sheets/420A.pdf
Hmmm...., the WE420A/5755 Mu is varying from 60 to 78 over the operating range, worse variation than a 6LS7 or 12AX7. The steady increase in Mu across the grid voltage range like this has, would mean mainly 2nd harmonic generation.
You are listening to euphonic distortion.... or some cancelation with a later stage. (12AT7 will probably sound even better, and no circuit changes required.)
http://www.westernelectric.com/spec_sheets/420A.pdf
Hmmm...., the WE420A/5755 Mu is varying from 60 to 78 over the operating range, worse variation than a 6LS7 or 12AX7. The steady increase in Mu across the grid voltage range like this has, would mean mainly 2nd harmonic generation.
You are listening to euphonic distortion.... or some cancelation with a later stage. (12AT7 will probably sound even better, and no circuit changes required.)
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Got any good stories to share? Love to hear some insider scoop about WE!
The 5755 was designed for dc amps, servo systems, and other applications where low noise, low drift and excellent matching between the sections are required. Low distortion was not a design criteria. It doesn't look like a drop in for many 12AX7 designs. The 5755 wants to be run at a low current and millivolt signal levels. A phono stage might be the only legitimate audio application. They don't work in a guitar amp.
I had a box full of WE and Ratheon tubes an could not find a design where they were measurably superior to other tubes even when the design was optimized for the 5755. I sold the box at a hamfest.
Most of the tubes that I had did not have a getter. It was stated that the activation of a getter could cause more problems than it solved on these specialized tubes.
Looking for something to stuff into a 12AX7 socket, try the 5751 especially the triple mica GE. It has less gain than the 12AX7 but more than the 5755. It drifts less over time that the 12AX7. This is good for LTP stages that are DC coupled to the next stage.
I had a box full of WE and Ratheon tubes an could not find a design where they were measurably superior to other tubes even when the design was optimized for the 5755. I sold the box at a hamfest.
Most of the tubes that I had did not have a getter. It was stated that the activation of a getter could cause more problems than it solved on these specialized tubes.
Looking for something to stuff into a 12AX7 socket, try the 5751 especially the triple mica GE. It has less gain than the 12AX7 but more than the 5755. It drifts less over time that the 12AX7. This is good for LTP stages that are DC coupled to the next stage.
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5755 / 420a Data sheets
Remember there are many designs of the 5755 / 420a
the RELIABILITY CONTROLLED Raytheon 5755 / 420a with large getter is different from western electric clear top and Raytheon or Tungsol clear top.
Must have large Getter for the very best result to replace the 12ax7 ecc83
Thank you all for the interest in this topic. My passion is tubes. Any questions about tubes. Please let me know. I worked for Western Electric and been involved in vacuum tubes for many decades.
Semiconductors are cool ,but tubes are HOT!
Remember there are many designs of the 5755 / 420a
the RELIABILITY CONTROLLED Raytheon 5755 / 420a with large getter is different from western electric clear top and Raytheon or Tungsol clear top.
Must have large Getter for the very best result to replace the 12ax7 ecc83
Thank you all for the interest in this topic. My passion is tubes. Any questions about tubes. Please let me know. I worked for Western Electric and been involved in vacuum tubes for many decades.
Semiconductors are cool ,but tubes are HOT!
Looking at the last page of the WE datasheet for the WE 420A/5755, in the lower left corner. If one keeps 200 V minimum across the tube, then the Mu can be held nearly constant in the 0 to -1 V input range.
The limited 2nd harmonic generated otherwise (ie, with less than 200 Vp min.) is probably useful for cancellation in most amplifiers anyway.
Odd that there are 20 or so versions of the octal 6SL7 around, but only one or two (dual) versions (ie, the 5755/420A , 5751) available in 9 pin.
If a single section 6SL7 9 pin sub is useable, and higher gm is needed, take a look at the triode in the 10LW8.
Its got the same Mu curves as the 5755, and the gm is up at 4000 and Rp down at 18.7 K. Its got some grunt to it. The pentode can be used for the driver stage of the amplifier too. So use two of them for a double LTP: triode input, pentode driver. (if one is designing from scratch)
http://frank.pocnet.net/sheets/135/1/10LW8.pdf (page 7)
The limited 2nd harmonic generated otherwise (ie, with less than 200 Vp min.) is probably useful for cancellation in most amplifiers anyway.
Odd that there are 20 or so versions of the octal 6SL7 around, but only one or two (dual) versions (ie, the 5755/420A , 5751) available in 9 pin.
If a single section 6SL7 9 pin sub is useable, and higher gm is needed, take a look at the triode in the 10LW8.
Its got the same Mu curves as the 5755, and the gm is up at 4000 and Rp down at 18.7 K. Its got some grunt to it. The pentode can be used for the driver stage of the amplifier too. So use two of them for a double LTP: triode input, pentode driver. (if one is designing from scratch)
http://frank.pocnet.net/sheets/135/1/10LW8.pdf (page 7)
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Looking at the data sheets, the 5755 seems closest to a 6SL7. The bias is about 1.15v different - that is, the 250v/2.3mA operation occurs at -2v for the SL7, and -0.85v for the 5755. I presume this indicates "special" grids (platinum plated?) with a different contact potential. It would be interesting to check what the grid current is at zero bias ... a rough calculation of transconductance at the 250v/2.3mA point gives 1500uMho, similar to the SL7.
Because of this difference, you can't compare mu vs. grid voltage. Mu is from 75 to 78 over a range of 0.3 to 0.8mA at 110 plate volts, compared to 62 to 69 for the SL7 (Ge data sheet at 100 plate volts) - less than half the variation.
FWIW, I got a mixed bag of 10 - all Raytheons - some years ago. Never did anything with them. I opened the boxes just now to check and three have significant top getter flash, the others have no getter flash.
Because of this difference, you can't compare mu vs. grid voltage. Mu is from 75 to 78 over a range of 0.3 to 0.8mA at 110 plate volts, compared to 62 to 69 for the SL7 (Ge data sheet at 100 plate volts) - less than half the variation.
FWIW, I got a mixed bag of 10 - all Raytheons - some years ago. Never did anything with them. I opened the boxes just now to check and three have significant top getter flash, the others have no getter flash.
????
If you look at the Tung-Sol datasheet (link below) for 6SL7 it has the Mu curve versus grid volts for an apple to apples comparison with the 5755/WE 420A datasheet. True, the zero grid point is shifted between the tubes by a contact potential offset. But the gm is quite similar between the tubes for the same current. So just compare the Tung-Sol Mu curve (6SL7) between -1.15 and -2.15 V versus 0 and -1 V for the 5755 for the same current/gm range. 5755 Mu varies between 60 and 78. 6SL7 Mu varies between 70 and 72.
http://frank.pocnet.net/sheets/127/6/6SL7GT.pdf
OOPS edit:
I just noticed that the Tung-Sol 6SL7 Mu curve was at 250 Vp, while the WE 420A quoted above was at 110 Vp. There is a set of Mu curves on the last page of the WE 420A datasheet for 250 V which is comparable and quite similar to the 6SL7 after all. So quite similar tubes (except for 1 V grid offset).
On the downside however, both tubes probably need to maintain 250 V minimum across them to remain linear.
Going back to the 10LW8 Mu curves, they are nearly the same regardless of plate V. A much better triode than either of these.
So the Big question now:
What makes some tubes have different Mu curves versus plate voltage, while others have little difference?
If you look at the Tung-Sol datasheet (link below) for 6SL7 it has the Mu curve versus grid volts for an apple to apples comparison with the 5755/WE 420A datasheet. True, the zero grid point is shifted between the tubes by a contact potential offset. But the gm is quite similar between the tubes for the same current. So just compare the Tung-Sol Mu curve (6SL7) between -1.15 and -2.15 V versus 0 and -1 V for the 5755 for the same current/gm range. 5755 Mu varies between 60 and 78. 6SL7 Mu varies between 70 and 72.
http://frank.pocnet.net/sheets/127/6/6SL7GT.pdf
OOPS edit:
I just noticed that the Tung-Sol 6SL7 Mu curve was at 250 Vp, while the WE 420A quoted above was at 110 Vp. There is a set of Mu curves on the last page of the WE 420A datasheet for 250 V which is comparable and quite similar to the 6SL7 after all. So quite similar tubes (except for 1 V grid offset).
On the downside however, both tubes probably need to maintain 250 V minimum across them to remain linear.
Going back to the 10LW8 Mu curves, they are nearly the same regardless of plate V. A much better triode than either of these.
So the Big question now:
What makes some tubes have different Mu curves versus plate voltage, while others have little difference?
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Another observation:
The GE datasheet for the 6SL7 gives Mu curves for 100 Vp and 250 Vp, and both are nearly identical (unlike the WE420A/5755).
So only the 5755 needs to maintain a high voltage across it for linearity.
-----------------
Answer to the Big Question above:
The grid cross-section must conform to the equipotential surface (Laplace eqn.) between the cathode and plate. Conformal mapping between cathode and plate shapes, or modern computer finite element analysis can figure that out.
5755/420A does not have the correct cross-sectional grid shape, while 6SL7 and 10LW8 do.
The GE datasheet for the 6SL7 gives Mu curves for 100 Vp and 250 Vp, and both are nearly identical (unlike the WE420A/5755).
So only the 5755 needs to maintain a high voltage across it for linearity.
-----------------
Answer to the Big Question above:
The grid cross-section must conform to the equipotential surface (Laplace eqn.) between the cathode and plate. Conformal mapping between cathode and plate shapes, or modern computer finite element analysis can figure that out.
5755/420A does not have the correct cross-sectional grid shape, while 6SL7 and 10LW8 do.
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OOPS, another Backtrack:
The 5755/420A Mu curves versus plate V are plotted versus grid 1 voltage, not plate current. So the failure to self overlap is normal. They must be plotted versus current to compare them. However, from the similarity of shape (except stretched out versus Vg1), they could be overlapping on a current plot. No direct comparison plot is provided on the datasheet. Cannot tell without considerable work from the data as given. So the 5755 might be optimised for constant Mu versus plate V like the other tubes, cannot tell for sure.
In any case, linearity will be maximised if a couple hundred volts minimum is maintained across the tube.
The 5755/420A Mu curves versus plate V are plotted versus grid 1 voltage, not plate current. So the failure to self overlap is normal. They must be plotted versus current to compare them. However, from the similarity of shape (except stretched out versus Vg1), they could be overlapping on a current plot. No direct comparison plot is provided on the datasheet. Cannot tell without considerable work from the data as given. So the 5755 might be optimised for constant Mu versus plate V like the other tubes, cannot tell for sure.
In any case, linearity will be maximised if a couple hundred volts minimum is maintained across the tube.
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Forum rules one thread per member per subject, while I am sure that the 5755 is a great tube, one thread is surely enough to discuss it.Also need to mention all the data sheets you find on the 5755 / 420a tubes on the internet are incomplete. They do not show all data for ac current and a partial for dc
The raytheon 1960's ck5755 / 5755 valve is the best replacement for the mullatd 12ax7 ecc83 with adapter or modification of the socket wires.
The raytheon 1960's ck5755 / 5755 valve is the best replacement for the mullatd 12ax7 ecc83 with adapter or modification of the socket wires.
Electrometer? Femtoamps: tube type CK5886
http://www.philbrickarchive.org/vacuum tube electrometers using operational amplifiers(k2-x).pdf
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I just got a couple of CK5755 tubes in today. Been comparing it on the curve tracer with a 10LW8 triode, a triode configured 6BN11 and a triode configured 6JC6. The 6JC6 is a frame grid design. They look similar curve-wise, except for about 3X higher gm at 2.2 mA plate current, and a slightly higher Mu too, around 75 to 80, except for the 6JC6 which has lower Mu at around 60.
The 6JC6 shows zero grid1 offset, while the others act like they have +.5V on g1 when 0 V is applied. The CK5755 looks like its got -1V on g1 when 0 V is applied. I see about the same amount of tilt-over in all the triode curves.
I tried a 12AX7 too. Definitely higher Mu, 100 versus 70 to 75 for the CK5755. About the same amount of triode curve tilt over for both.
The differences in all these tube curves are small enough that an FFT will be required to differentiate linearity.
http://www.philbrickarchive.org/vacuum tube electrometers using operational amplifiers(k2-x).pdf
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I just got a couple of CK5755 tubes in today. Been comparing it on the curve tracer with a 10LW8 triode, a triode configured 6BN11 and a triode configured 6JC6. The 6JC6 is a frame grid design. They look similar curve-wise, except for about 3X higher gm at 2.2 mA plate current, and a slightly higher Mu too, around 75 to 80, except for the 6JC6 which has lower Mu at around 60.
The 6JC6 shows zero grid1 offset, while the others act like they have +.5V on g1 when 0 V is applied. The CK5755 looks like its got -1V on g1 when 0 V is applied. I see about the same amount of tilt-over in all the triode curves.
I tried a 12AX7 too. Definitely higher Mu, 100 versus 70 to 75 for the CK5755. About the same amount of triode curve tilt over for both.
The differences in all these tube curves are small enough that an FFT will be required to differentiate linearity.
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