Tung Sol 7591A Tests
- Thread starter dcgillespie
- Start date
Guitar amps tend to be somewhat more variable and subject to differences in parts though. They often have little feedback, and are specifically NOT designed to be flat and immune to minor variables like that. A guitar amp is part of the instrument, and changing its bits is a form of tuning.
Hifi amps on the other hand are not supposed to impart any particular voice or character to the music. An amplifier that does that to a significant degree is by definition a poor amplifier for accurate music reproduction.
As to why people bother about 7591 amps, a lot of high quality amplifiers ran that tube. Its not the tube itself, it just happened to have been used in a number of good designs. Scott and Fisher amps are nice performing pieces of gear, and they used a 7591 tube. I would imagine that if they ran 6L6GC tubes and had the same kind of performance, they would still be popular amps. Maybe even more so since 6L6GC tubes are extremely common and easy to source.
Hifi amps on the other hand are not supposed to impart any particular voice or character to the music. An amplifier that does that to a significant degree is by definition a poor amplifier for accurate music reproduction.
As to why people bother about 7591 amps, a lot of high quality amplifiers ran that tube. Its not the tube itself, it just happened to have been used in a number of good designs. Scott and Fisher amps are nice performing pieces of gear, and they used a 7591 tube. I would imagine that if they ran 6L6GC tubes and had the same kind of performance, they would still be popular amps. Maybe even more so since 6L6GC tubes are extremely common and easy to source.
Hey -- Great points, and all are appreciated! To my mind however, I couldn't have said a response any better than Gadget did. When it comes to sound PROduction (not reproduction) amplifiers, there is no doubt at all that different output tubes will impart different tonal qualities when running clean and into overload, for a number of reasons (peak current capabilities, load impedance required of the OPT, clipping characteristics, etc). In THAT venue, where very little if any corrective measures are taken, the type of tube used will in fact have a notable impact on the sound produced.
For REproduction equipment however, major efforts are made to remove such colorations, so that reproduction is true.
As for why (manufacturers) bothered with the tube? It's a fairly small tube that provides an easy path to making a fairly large amount of power output, while using the barest of bare bones driver circuits. No other tube outside of the 7591 family can make the amount of power it does, with as high of quality as it does, with as little parts count needed to get the job done. That translates into fewer tubes, smaller chassis, smaller power transformers, less weight, less shipping costs, and on and on, which all translates into more profit for the manufacturer. When viewed in that light, the 7591 family of tubes was an absolutely huge development in power tubes for audio use, leaving an undeniable and well earned place in the history of vacuum tube development.
A great discussion!
Dave
For REproduction equipment however, major efforts are made to remove such colorations, so that reproduction is true.
As for why (manufacturers) bothered with the tube? It's a fairly small tube that provides an easy path to making a fairly large amount of power output, while using the barest of bare bones driver circuits. No other tube outside of the 7591 family can make the amount of power it does, with as high of quality as it does, with as little parts count needed to get the job done. That translates into fewer tubes, smaller chassis, smaller power transformers, less weight, less shipping costs, and on and on, which all translates into more profit for the manufacturer. When viewed in that light, the 7591 family of tubes was an absolutely huge development in power tubes for audio use, leaving an undeniable and well earned place in the history of vacuum tube development.
A great discussion!
Dave
I already understood that very often the goal of a musician and/or recording engineer is to produce distortion in a controllable and repeatable manner. In fact, I believe Groove Tubes has a rating system to help the musician get repeatable results.
This is of course fundamentally different from the perspective of playback equipment, where accurate reproduction is the goal.
I guess Fisher had to watch the bottom line too and did the best they could to keep their product affordable as the power wars began to rage. I thought perhaps they offered different amp lines and consoles to keep up with and cater to the evolving musical styles of the times. One amp designed and tuned for Classical music reproduction, another for Country Folk, British Invasion, etc..
I was looking for an opinion such as "this amp with such and such tubes sounds great if you like The British Invasion, but mediocre when playing back classical music.
As I composed the Original Post, I took into consideration that other "standards" have changed over time (playback equalization, Cutting Angle, VTA). It therefore seemed plausible to me that Fisher might have been "tuning" some of their products to target specific listening groups in order to gain a larger overall market share even at the expense of accurate reproduction.
One console aimed at the Rock and Roll Crowd, another tuned for Classical music listeners. I was wondering it this tube (7591) and the amps Fisher designed around it were designed with a specific audience in mind.
If it was all about power and money...well, that just blows a hole though my theory.
This is of course fundamentally different from the perspective of playback equipment, where accurate reproduction is the goal.
I guess Fisher had to watch the bottom line too and did the best they could to keep their product affordable as the power wars began to rage. I thought perhaps they offered different amp lines and consoles to keep up with and cater to the evolving musical styles of the times. One amp designed and tuned for Classical music reproduction, another for Country Folk, British Invasion, etc..
I was looking for an opinion such as "this amp with such and such tubes sounds great if you like The British Invasion, but mediocre when playing back classical music.
As I composed the Original Post, I took into consideration that other "standards" have changed over time (playback equalization, Cutting Angle, VTA). It therefore seemed plausible to me that Fisher might have been "tuning" some of their products to target specific listening groups in order to gain a larger overall market share even at the expense of accurate reproduction.
One console aimed at the Rock and Roll Crowd, another tuned for Classical music listeners. I was wondering it this tube (7591) and the amps Fisher designed around it were designed with a specific audience in mind.
If it was all about power and money...well, that just blows a hole though my theory.
Hey -- Your thoughts about different units for different types of music is interesting. From the perspective of back in the day, it would have been considered visionary, since today, many folks do in fact employ different design formats for different types of music (SET for Jazz, SS for hard rock, etc.). I'm afraid that back in the day however, the closest that any of the manufacturers got to that line of thinking was in recognizing that "music" (all types that is) as a signal, is very different than nice smooth sine waves, which is the signal of choice for measuring power output and distortion.
This understanding gave rise to the use of square waves, whose transients are actually much more severe than that of any recorded music. But that's about it. The idea of further subdividing the category of music into types of music, and then building unique equipment for those categories was just not there.
That concept was totally born from the guitar amp industry, starting with the most basic understanding that Fender = Clean sound, and Marshall = Overload sound. But even these guys largely remained true to a sound. To this day, Fender is still recognized when clean power is needed, while Marshall is recognized when overload is needed. They have both dabbled across each others concepts, but the main understanding still stands. The gap between them has filled in with a bazillion different boutique offerings, so that today, just about any type of sound you can imagine can be achieved -- but again, this is all on the PROduction side of the issue.
Avery was a classical music man, personally playing the violin as The Red1 has so ably described. His whole goal was high quality, accurate, low distortion reproduction of any type of music, so it would have taken someone else in the industry to conceptualize the different music classification line of thought for reproduction equipment. I just don't think that type of thinking was in his DNA.
Ultimately however, for any business, the bottom line is always about money, as that's how you stay in business. But the attitude in how you achieve that bottom line is everything. Avery was a man of class, who did the world a lot of good with the money he made. But he was up against some stiff competition who were also equally determined to succeed as well. So profits ruled the day then as now, as without them, there can be no success.
To that point then, and for the period of time represented, Avery was in fact very forward thinking, as he made a major (actually brilliant) shift at Fisher when transitioning from Mono to Stereo. And his early efforts with FM Stereo are well documented as well -- being so forward thinking that he actually jumped the gun in producing equipment designed for the Crosby based broadcasting system instead of that which was ultimately approved. Oops. So his forward thinking was there, but just not to the degree you were maybe thinking.
Finally, there was a power war going on to be sure, but the other war going on was one of features -- a war that Fisher was VERY caught up in as well. Just look at his opening list of all the "firsts" he considered Fisher as having achieved. Today, some of the features are simply silly. But back in the day -- silly or not -- features helped drive the business, as evidenced with the endless array of controls, most of which we don't even use today.
To me, it is fascinating to study how Avery guided and drove his company to make the decisions it did, and produce the products it did. But it's equally important to understand what it was for what it was, and not make something of it that it wasn't. However, it is also equally as fascinating to see how his enduring concepts are integrated today into what must be considered as an "enlightened" audiophile environment.
For me, I have absolutely no issue with all of the myriad of approaches and opinions out there today, and respect all of them. I do champion however keeping the basic design and engineering concepts of what drove The Fisher Radio Corporation to become what it was -- and indeed the overall engineering practices of the day -- accurate. The audiophile world of Fisher in the 60s was worlds apart from those of the 21st century today. In keeping that history accurate, it is important then to not distort what actually was with what today's enlightened thinking might have liked for it to have been.
Dave
This understanding gave rise to the use of square waves, whose transients are actually much more severe than that of any recorded music. But that's about it. The idea of further subdividing the category of music into types of music, and then building unique equipment for those categories was just not there.
That concept was totally born from the guitar amp industry, starting with the most basic understanding that Fender = Clean sound, and Marshall = Overload sound. But even these guys largely remained true to a sound. To this day, Fender is still recognized when clean power is needed, while Marshall is recognized when overload is needed. They have both dabbled across each others concepts, but the main understanding still stands. The gap between them has filled in with a bazillion different boutique offerings, so that today, just about any type of sound you can imagine can be achieved -- but again, this is all on the PROduction side of the issue.
Avery was a classical music man, personally playing the violin as The Red1 has so ably described. His whole goal was high quality, accurate, low distortion reproduction of any type of music, so it would have taken someone else in the industry to conceptualize the different music classification line of thought for reproduction equipment. I just don't think that type of thinking was in his DNA.
Ultimately however, for any business, the bottom line is always about money, as that's how you stay in business. But the attitude in how you achieve that bottom line is everything. Avery was a man of class, who did the world a lot of good with the money he made. But he was up against some stiff competition who were also equally determined to succeed as well. So profits ruled the day then as now, as without them, there can be no success.
To that point then, and for the period of time represented, Avery was in fact very forward thinking, as he made a major (actually brilliant) shift at Fisher when transitioning from Mono to Stereo. And his early efforts with FM Stereo are well documented as well -- being so forward thinking that he actually jumped the gun in producing equipment designed for the Crosby based broadcasting system instead of that which was ultimately approved. Oops. So his forward thinking was there, but just not to the degree you were maybe thinking.
Finally, there was a power war going on to be sure, but the other war going on was one of features -- a war that Fisher was VERY caught up in as well. Just look at his opening list of all the "firsts" he considered Fisher as having achieved. Today, some of the features are simply silly. But back in the day -- silly or not -- features helped drive the business, as evidenced with the endless array of controls, most of which we don't even use today.
To me, it is fascinating to study how Avery guided and drove his company to make the decisions it did, and produce the products it did. But it's equally important to understand what it was for what it was, and not make something of it that it wasn't. However, it is also equally as fascinating to see how his enduring concepts are integrated today into what must be considered as an "enlightened" audiophile environment.
For me, I have absolutely no issue with all of the myriad of approaches and opinions out there today, and respect all of them. I do champion however keeping the basic design and engineering concepts of what drove The Fisher Radio Corporation to become what it was -- and indeed the overall engineering practices of the day -- accurate. The audiophile world of Fisher in the 60s was worlds apart from those of the 21st century today. In keeping that history accurate, it is important then to not distort what actually was with what today's enlightened thinking might have liked for it to have been.
Dave
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audiodon
Addicted Member
Dave,
So, if one is going to use Tung Sol 7591s, some will want to just plug them in as replacements.
Do you have any thoughts about the 330k to 200k grid resistors change and changing the value of the coupling cap from .047 to 0.1 to maintain the corner frequency?
Would there be any changes to IBAM or your bias/balance workaround in light of this new replacement tube selection?
Screen stability resistors would be helpful protection on the output tube screens in all but the most well designed circuits.
I believe that I know your answers, but it should be recorded in this thread for those who may be newbies.
So, if one is going to use Tung Sol 7591s, some will want to just plug them in as replacements.
Do you have any thoughts about the 330k to 200k grid resistors change and changing the value of the coupling cap from .047 to 0.1 to maintain the corner frequency?
Would there be any changes to IBAM or your bias/balance workaround in light of this new replacement tube selection?
Screen stability resistors would be helpful protection on the output tube screens in all but the most well designed circuits.
I believe that I know your answers, but it should be recorded in this thread for those who may be newbies.
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Dave,
One last thing about "signature sound".
Cathode vs Fixed bias in reproduction units. Any difference in the sound? I've read people describe Fisher amps as having a "wall of sound" quality.
Do you have any thoughts?
My long term plan has been to collect different amps using different tubes and different bias methods. Just personal curiosity and something interesting to pass the time.
Deep on the back burner are some Heathkit W-5M's and a Pilot 232. After my experience with rolling tubes, I thought it might be interesting to roll amps.
I've also considered bi-amping my speakers, using the SA100 for the tweeters and the SA300B for the woofers. That's just a notion of mine that will probably never happen.
One last thing about "signature sound".
Cathode vs Fixed bias in reproduction units. Any difference in the sound? I've read people describe Fisher amps as having a "wall of sound" quality.
Do you have any thoughts?
My long term plan has been to collect different amps using different tubes and different bias methods. Just personal curiosity and something interesting to pass the time.
Deep on the back burner are some Heathkit W-5M's and a Pilot 232. After my experience with rolling tubes, I thought it might be interesting to roll amps.
I've also considered bi-amping my speakers, using the SA100 for the tweeters and the SA300B for the woofers. That's just a notion of mine that will probably never happen.
Hey -- Within the usable power range of a REproduction amplifier with either bias approach, there is little difference sonically, although fixed bias designs are capable of producing lower distortion Class AB amplifiers than cathode bias designs can produce. However, and here we go again with the PROduction end of things, when a traditional fixed bias amplifier reaches clipping, it develops a particularly nasty form of distortion known as "blocking" distortion, caused by the coupling caps trying to drive the grids of the output tubes positive. Since they can't do that, the event then disturbs the normal charge that appears on these caps. Whats worse, it takes a few cycles for the charge to iron itself out after the clipping signal is removed. During that time however, the blocking distortion that is produced is unmistakable in its sonic nature, and is caused by the temporarily increased charge developed across these caps which drive the output tubes further into cutoff than they should. This shifts the whole operating point, causing the increased distortion.
On the other hand, cathode biased output stages are more immune to such events, because the cathode resistor tends to counter the blocking action. As a result, the overload can be a smoother event sonically, rather than the harsher event blocking produces in fixed bias designs. Therefore, in production amplifiers, cathode bias designs can have a more bluesy or jazzy overload sound, while fixed bias designs more favor a harder rock overload sound.
I hope this helps!
Dave
On the other hand, cathode biased output stages are more immune to such events, because the cathode resistor tends to counter the blocking action. As a result, the overload can be a smoother event sonically, rather than the harsher event blocking produces in fixed bias designs. Therefore, in production amplifiers, cathode bias designs can have a more bluesy or jazzy overload sound, while fixed bias designs more favor a harder rock overload sound.
I hope this helps!
Dave
Don;
As these are supposedly plug and play (some say plug and pray
) I don't see any changes from current practices.
I would advocate keeping the 330K to 200K-220K change in force. If it's true that the T.S. 7591 is a reincarnation of the 7868 in a 7591 pinning as some people say it looks like, then it makes sense. I just wish New Sensor would supply Data Sheets for their tubes. (The KGB and GRU must still be active, and everything from the size of baby buggy wheels to tank treads are still "STATE SECRETS"!) Watch out KOMRADE! 330K is too high from a standpoint of the old stock tube manufacturer's for these tubes (Even JJ says 300K max for fixed bias). No data sheet available from New Sensor that I can find. So going off the old Data Sheets I CAN find 300K is max for the grid.
As for the IBAM or IBBA (Improved Bal-Bias Adjustment), I don't see a change needed as the pin-out is the same. Adjust for Max dissipation if it's higher or lower (if a data sheet can ever be found!). Presume 19W max diss and go from there.
Screen resistors? Same thing. I'd put them in for piece of mind. I don't really want to use my gear as the test mule to see if these tubes have a tendency to arc from or to the screens, so I'll minimize or alleviate the chances as much as I can.
Larry
As these are supposedly plug and play (some say plug and pray
) I don't see any changes from current practices. I would advocate keeping the 330K to 200K-220K change in force. If it's true that the T.S. 7591 is a reincarnation of the 7868 in a 7591 pinning as some people say it looks like, then it makes sense. I just wish New Sensor would supply Data Sheets for their tubes. (The KGB and GRU must still be active, and everything from the size of baby buggy wheels to tank treads are still "STATE SECRETS"!) Watch out KOMRADE! 330K is too high from a standpoint of the old stock tube manufacturer's for these tubes (Even JJ says 300K max for fixed bias). No data sheet available from New Sensor that I can find. So going off the old Data Sheets I CAN find 300K is max for the grid.
As for the IBAM or IBBA (Improved Bal-Bias Adjustment), I don't see a change needed as the pin-out is the same. Adjust for Max dissipation if it's higher or lower (if a data sheet can ever be found!). Presume 19W max diss and go from there.
Screen resistors? Same thing. I'd put them in for piece of mind. I don't really want to use my gear as the test mule to see if these tubes have a tendency to arc from or to the screens, so I'll minimize or alleviate the chances as much as I can.
Larry
Don -- None of the design modifications would change with the Tung Sol tubes. Contrary to popular belief, those modifications are not the product of or specifically relevant to any one version of the tube, but are based on the specifications of a bogey 7591.
Now granted, tubes of poorer manufacture will get into trouble sooner than those of better manufacturing. But the fact remains that the modifications are principally a requirement of the equipment's design for the tube -- not the tube's design for the equipment.
Dave
Now granted, tubes of poorer manufacture will get into trouble sooner than those of better manufacturing. But the fact remains that the modifications are principally a requirement of the equipment's design for the tube -- not the tube's design for the equipment.
Dave
Don,
Fools errand (And I am not calling you or anyone a fool)
This subjective argument has been around this whole century.
My answer has and always will be the same.
If you like it and the way it sounds that's all the matters .. no one is harmed except feelings perhaps if you take this too seriously.
Now where is my dang flying car ??
I was promised one in back the 70's to be here 20 years ago dang it ??
Marketing .. sheesh!!!
Frannie
Fools errand (And I am not calling you or anyone a fool)
This subjective argument has been around this whole century.
My answer has and always will be the same.
If you like it and the way it sounds that's all the matters .. no one is harmed except feelings perhaps if you take this too seriously.
Now where is my dang flying car ??
I was promised one in back the 70's to be here 20 years ago dang it ??
Marketing .. sheesh!!!
Frannie
eduarsan1
Luis Eduardo Sanchez
Don;
As these are supposedly plug and play (some say plug and pray
Larry good pont of view!!! :yes:
@Dave thanks for you great support :thmbsp:
Try this....... And it has the T-S 7591 Re-Issues in it for comparison. http://www.tronola.com/html/7591a_tubes.html
After reading the article in the link, based on an admittedly small sampling, it if fair to infer the EH is the best ( electronically?) of the new breed with no truly clear conclusions being drawn?
NJ Phoenix; My conclusion is that they are so close, it's not worth worrying about. Case in point. I have Tung-Sols in the 63' Executive(800c based), mainly for heat reduction on the top, and EH's in the 800c stand-alone. They are pretty much identical underneath, with the stand-alone having Dave's Alternate Balance/Bias adjustment board, and the Exec's 800c having the original IBAM. NO EFB, but they both have Phono PEC Replacement boards. Exec has IC MKP .068uf output coupling caps and the standalone has Cornell Dublier DME series .082uf output coupling caps. Both sets are biased to plate voltage of 432 volts for the standalone (15.55W per tube not including the screen dissipation) and the Exec. @ 390V on the plate and 40ma for 15.6Watts per tube not including the screen dissipation) If you include the screen dissipation of 3ma you get 12.55w and 12.6w. This is as high as I will set them up. These are close enough to be indistinguishable by ear.
My Sansui 1000A is using Tung-Sols now. The EH's were too close to the transformers and each other that the ambient temps in those two valleys were above 160*F. Even tho they ran very well at ear bleed volume levels, I was concerned about their longevity. I don't advocate the use of fans normally but the 1000A is one that damn near requires it. After placing HVAC Aluminum tape on the transformer bells, opening up the metal heat shield between the tube area and the front of the unit, and replacing the power resistors with surface mounted ones (spread around the chassis now) I got the temps to about 140*F. Putting in the Tung-Sols further reduced the heat to under 140*F in the tube valleys. No difference in SQ that I can tell. They are run @ 32ma with 478 on the plates and 425 on the screens (nominal is 470v and 420v ) for 15.3W on each tube.Subtracting screen dissipation would give 12.3W per. I would highly recommend the Tung-Sols in the 1000A over the EH's due to heat load in the normal 1000A. Same thing with most Scotts and Sherwoods with the small chassis and angled tube sockets.
BACK TO THE FISHERS;
Using Sansui SP-200's (2 sets) and doing an A/B test using 2 turntables with identical V15-III cartridges and Elliptical styli, I hear no difference between them. I didn't push them above 12:00 on the volume. All controls were centered or in the off position for testing.
If you have the room above and around the socket and don't really care about the large bottle, get the EH's. If you have OCD bad enough to make a blind man see, or have money burning a hole thru your leg again, get the Tungsols. In any event, they are better than the JJ's. (At least you don't need an EOD tech on call for the EH's and Tung-Sols
). And I WOULD highly recommend getting a MATCHED CATHODE DRAW QUAD (Jim McShane) and putting either an IBAM or IBBA(DAVE's board)in to balance and bias them equally. Then cursory checks 6 months to a year, adjust as necessary.
One NOTE! The Tung-SOLS require more Bias voltage than the EH's at any bias level.
FOR EXAMPLE:
Bias an EH to 32ma, and the bias voltage is roughly -19V
Bias a T-S to 32ma in the same amp, and the bias voltage is approx -22v to -23V
Adjustments might be needed to your board to allow the T-S to Bias that high/low. It a resistor change and it's documented on the forum.
All of the above is based on FIXED BIAS. Now we'll go to Cathode Bias.
My X-101-B has all new tubes in it with the exception of the Phase inverter tubes which are NOS Sylvania long plate 12ax7's, and a IEC branded MULLARD GZ34. OUTPUT TUBES ARE TUNG-SOL 7591's. Bias is set to FISHER spec's per the manual. I fixed or replaced a minimum of wiring when I recapped it. Due to lack of Room I used .047uf 400v IC MKP caps for the output couplers. Cathode resistors and screen stab. res. installed. NO EFB. I did add an additional shield plate in the phono input area which killed some hum. Otherwise it's bone stock. "It sounds mahvelous" (insert Billy Crystal doing Fernado Lamas here). It has less power output than the fixed bias setup but it's got more stage presense. I tried the EH's in it but they sounded somewhat 1 dimensional. Don't know if it's the tube or the amp design. But the Tung-SOL's do very well and look outstanding in this amp.
With the stock of "NOS" 7591's all over the map (pricewise, non matching, diminishing stocks,etc) both the EH and the tung-sol's are good replacements. So they average 90% of the original 7591's in power, you aren't going to tear down the barn doors with them. I would imagine, if you run them btwn 70% and 80% of max dissipation, they'll last damned near forever
My Sansui 1000A is using Tung-Sols now. The EH's were too close to the transformers and each other that the ambient temps in those two valleys were above 160*F. Even tho they ran very well at ear bleed volume levels, I was concerned about their longevity. I don't advocate the use of fans normally but the 1000A is one that damn near requires it. After placing HVAC Aluminum tape on the transformer bells, opening up the metal heat shield between the tube area and the front of the unit, and replacing the power resistors with surface mounted ones (spread around the chassis now) I got the temps to about 140*F. Putting in the Tung-Sols further reduced the heat to under 140*F in the tube valleys. No difference in SQ that I can tell. They are run @ 32ma with 478 on the plates and 425 on the screens (nominal is 470v and 420v ) for 15.3W on each tube.Subtracting screen dissipation would give 12.3W per. I would highly recommend the Tung-Sols in the 1000A over the EH's due to heat load in the normal 1000A. Same thing with most Scotts and Sherwoods with the small chassis and angled tube sockets.
BACK TO THE FISHERS;
Using Sansui SP-200's (2 sets) and doing an A/B test using 2 turntables with identical V15-III cartridges and Elliptical styli, I hear no difference between them. I didn't push them above 12:00 on the volume. All controls were centered or in the off position for testing.
If you have the room above and around the socket and don't really care about the large bottle, get the EH's. If you have OCD bad enough to make a blind man see, or have money burning a hole thru your leg again, get the Tungsols. In any event, they are better than the JJ's. (At least you don't need an EOD tech on call for the EH's and Tung-Sols
). And I WOULD highly recommend getting a MATCHED CATHODE DRAW QUAD (Jim McShane) and putting either an IBAM or IBBA(DAVE's board)in to balance and bias them equally. Then cursory checks 6 months to a year, adjust as necessary. One NOTE! The Tung-SOLS require more Bias voltage than the EH's at any bias level.
FOR EXAMPLE:
Bias an EH to 32ma, and the bias voltage is roughly -19V
Bias a T-S to 32ma in the same amp, and the bias voltage is approx -22v to -23V
Adjustments might be needed to your board to allow the T-S to Bias that high/low. It a resistor change and it's documented on the forum.
All of the above is based on FIXED BIAS. Now we'll go to Cathode Bias.
My X-101-B has all new tubes in it with the exception of the Phase inverter tubes which are NOS Sylvania long plate 12ax7's, and a IEC branded MULLARD GZ34. OUTPUT TUBES ARE TUNG-SOL 7591's. Bias is set to FISHER spec's per the manual. I fixed or replaced a minimum of wiring when I recapped it. Due to lack of Room I used .047uf 400v IC MKP caps for the output couplers. Cathode resistors and screen stab. res. installed. NO EFB. I did add an additional shield plate in the phono input area which killed some hum. Otherwise it's bone stock. "It sounds mahvelous" (insert Billy Crystal doing Fernado Lamas here). It has less power output than the fixed bias setup but it's got more stage presense. I tried the EH's in it but they sounded somewhat 1 dimensional. Don't know if it's the tube or the amp design. But the Tung-SOL's do very well and look outstanding in this amp.
With the stock of "NOS" 7591's all over the map (pricewise, non matching, diminishing stocks,etc) both the EH and the tung-sol's are good replacements. So they average 90% of the original 7591's in power, you aren't going to tear down the barn doors with them. I would imagine, if you run them btwn 70% and 80% of max dissipation, they'll last damned near forever
