Results 1 to 16 of 16
Like Tree3Likes
  • 1 Post By Old Tele man
  • 1 Post By Old Tele man
  • 1 Post By soundmasterg

Thread: Anybody looked at tube perveance values?

  1. #1
    Senior Member Old Tele man's Avatar
    Join Date
    Oct 2007
    Location
    Tucson, AZ
    Posts
    539

    Anybody looked at tube perveance values?

    Has anybody looked into (investigated / calculated) the Perveance (G) values for the different vacuum tubes they use?

    I ask because I have (for 6L6 and 6V6 family) and others have asked about the 5687 twin triode.
    ...and the Devil said: "...yes, but it's a DRY heat!"

  2. #2
    Old Timer
    Join Date
    May 2006
    Location
    Cornelius, Oregon
    Posts
    1,233
    I'm not sure what they are honestly...or what relevance they have?

    Greg

  3. #3
    Senior Member Old Tele man's Avatar
    Join Date
    Oct 2007
    Location
    Tucson, AZ
    Posts
    539
    Quote Originally Posted by soundmasterg View Post
    I'm not sure what they are honestly...or what relevance they have?

    Greg
    Here are three illustrated examples of Perveance (G):

    • DIODE: Ip = G*(Vp)^(3/2)

    • TRIODE: Ip = G*(Vg + Vp/ + e)^(3/2)

    • TET/PENTODE: Ik = (Ip+Is) = G*(Vg + Vs/1 + Vp/2 + e)^(3/2)

    Perveance (G) is:

    1) the quotient of Ip over Vp^(3/2), ie: Ip/Vp^(3/2);
    2) the ratio of space-charge potential (Vp^(3/2) to beam kinetic energy (Ip);
    3) the coefficient of proportionality between space-charge limited current (Ip) and effective anode voltage (Vp^(3/2);
    4) a tube constant dependant solely upon physical electrode geometry (spacings, diameters, etc.);
    5) expressed in "Perv" units, ie: 1 Amp/(V^(3/2)), amps-per-volt^(3/2).
    6) tube constant almost NEVER published by tube manufacturers.
    tubeswell likes this.
    ...and the Devil said: "...yes, but it's a DRY heat!"

  4. #4
    Junior Member
    Join Date
    Mar 2011
    Posts
    10
    perveance Definition and Meaning adds remark that this parameter changes with tube aging. (Still nothing of practical importance, yet).


    Morgan Jones' "Valve Amplifiers" book says practical significance is high perveance tubes like 5687 anodes can swing anodes closer to 0V, increasing voltage swing and efficiency. I'll take a wild guess, since 5687 was a 'computer' tube (diode logic, ENIAC?), maybe the closer it can get to 0 and plate voltage, the wider the High and Low logic levels and better noise immunity. Maybe a hollow-state analogy to rail-to-rail op amps whose output can swing much closer to the power supply rails (bipolar frequently for op amps, B+ & ground for tubes).

    https://books.google.com/books?id=Qd...veance&f=false

    I am not sure, but think this makes me think lower internal resistance (rp). While that may be true with 5687 compared to smaller 9-pin tubes with (roughly similar in mu, without looking it up) like 12AU7, the reason may not be solely the perveance rating (if even related). Maybe perveance rating isn't a feature, but a figure of merit.

    I read somewhere else that makes them capable of small power applications (dwarf output tubes).

  5. #5
    Senior Member Old Tele man's Avatar
    Join Date
    Oct 2007
    Location
    Tucson, AZ
    Posts
    539
    I suspect the "changes with tube aging" can attributed more to cathode emissivity decline than anything else, because all of the 'published' Perveance parameters are physical spacings and geometries, which theoretically are static and non-changing.

    As for the "digital" use of the high-perv 5687 tube in computers, it makes sense being able to drive/slam the tube between cutoff and saturation with minimum rise/fall time, because that allowed faster computation speeds since rise/fall times are "wasted time" in digital circuits: it's only the ONE and ZERO states that count...and, time spent transiting between them is wasted time and power: 0W = 0.0A 5V and likewise 0W = (any)A 0.0V.
    ...and the Devil said: "...yes, but it's a DRY heat!"

  6. #6
    Old Timer
    Join Date
    May 2006
    Location
    Cornelius, Oregon
    Posts
    1,233
    I have a bunch of 5687's that were in a tube powered surplus nuclear radiation detector that I got for free at a surplus place like 10 years ago. I was going to try them in a build, perhaps as a phase inverter, but I didn't get around to it yet.

    Greg

  7. #7
    Senior Member Old Tele man's Avatar
    Join Date
    Oct 2007
    Location
    Tucson, AZ
    Posts
    539
    Quote Originally Posted by soundmasterg View Post
    I have a bunch of 5687's that were in a tube powered surplus nuclear radiation detector that I got for free at a surplus place like 10 years ago. I was going to try them in a build, perhaps as a phase inverter, but I didn't get around to it yet.

    Greg
    They will be VERY easy to drive into saturation--almost too much so--but you should get almost 100% voltage swing from whatever plate voltage you use. As mentioned above, they should excel at Class-B operation, having almost no cross-over distortion to contend with.
    soundmasterg likes this.
    ...and the Devil said: "...yes, but it's a DRY heat!"

  8. #8
    I'm a member? nickb's Avatar
    Join Date
    Dec 2009
    Location
    Devon, UK
    Posts
    2,121
    Quote Originally Posted by soundmasterg View Post
    I have a bunch of 5687's that were in a tube powered surplus nuclear radiation detector that I got for free at a surplus place like 10 years ago. I was going to try them in a build, perhaps as a phase inverter, but I didn't get around to it yet.

    Greg
    Have you seen what that are going for on the 'bay'?
    Experience is something you get, just after you really needed it.

  9. #9
    Old Timer
    Join Date
    May 2006
    Location
    Cornelius, Oregon
    Posts
    1,233
    Quote Originally Posted by nickb View Post
    Have you seen what that are going for on the 'bay'?
    I haven't looked lately but perhaps I should. These are all used ones...no new ones in the bunch, but they do all work.

    Greg

  10. #10
    Senior Member Old Tele man's Avatar
    Join Date
    Oct 2007
    Location
    Tucson, AZ
    Posts
    539
    Quote Originally Posted by soundmasterg View Post
    I haven't looked lately but perhaps I should. These are all used ones...no new ones in the bunch, but they do all work.

    Greg
    A quick gm-check should establish their usability.
    ...and the Devil said: "...yes, but it's a DRY heat!"

  11. #11
    I'm a member? nickb's Avatar
    Join Date
    Dec 2009
    Location
    Devon, UK
    Posts
    2,121
    Quote Originally Posted by soundmasterg View Post
    I haven't looked lately but perhaps I should. These are all used ones...no new ones in the bunch, but they do all work.

    Greg
    Seems they might make a decent push pull output tube with 7.2W total plate dissipation. You should be able to get 5 to 10 watts. I see the plate resistance is very low and that a maximum of 6.6mA grid current is specified. Does that suggest that they ere typically driven with the grid positive to get the low sat voltage? The low Rp and high currents would make them switch quickly.
    Experience is something you get, just after you really needed it.

  12. #12
    Old Timer
    Join Date
    May 2006
    Location
    Cornelius, Oregon
    Posts
    1,233
    Quote Originally Posted by Old Tele man View Post
    A quick gm-check should establish their usability.
    They all test fine on my B&K 747B tester, which is mutual conductance, but the scale is arbitrary, so I'll have to try them in a circuit to really see, which is the best way anyway. I was busy from 2010 to 2015 in EE school, and since then I've been trying to get some sort of career established to pay off my school loans, and have been trying to catch up on all the necessary things I set aside while I was in school. It will be awhile still until I have the time to build up something to use those 5687's, but they can keep company with all my other projects.

    Before I can get to those, I have to finish building up a particular solid state preamp board and test it with a tube power amp on a project I was doing with R.G., rebuild/restore an AIMS Dual Twelve, a Silvertone 1484, a late 60's Baldwin solid state amp, a Trace Elliot solid state bass amp, a 1963 B15N including cabinet refurbish, a Weber JTM45 kit I got cheap that the previous owner badly built. Then there are my own designs/projects from scratch...a Vox AC100 build with another higher gain channel, a Supro Tbolt build, an 18 watt Marshall build, a Revibe build, and more. Unfortunately they are all begun but not finished....I'm bad at that sometimes.

    Greg
    tubeswell likes this.

  13. #13
    Old Timer
    Join Date
    May 2006
    Location
    Cornelius, Oregon
    Posts
    1,233
    Quote Originally Posted by nickb View Post
    Seems they might make a decent push pull output tube with 7.2W total plate dissipation. You should be able to get 5 to 10 watts. I see the plate resistance is very low and that a maximum of 6.6mA grid current is specified. Does that suggest that they ere typically driven with the grid positive to get the low sat voltage? The low Rp and high currents would make them switch quickly.
    I've read that the hi-fi guys really like them as phase inverters. It does look like they would make a good low power output section too.

    Greg

  14. #14
    Junior Member
    Join Date
    Mar 2011
    Posts
    10
    Quote Originally Posted by Old Tele man View Post
    Here are three illustrated examples of Perveance (G):

    DIODE: Ip = G*(Vp)^(3/2)

    TRIODE: Ip = G*(Vg + Vp/ + e)^(3/2)

    TET/PENTODE: Ik = (Ip+Is) = G*(Vg + Vs/1 + Vp/2 + e)^(3/2)

    Perveance (G) is:

    1) the quotient of Ip over Vp^(3/2), ie: Ip/Vp^(3/2);
    2) the ratio of space-charge potential (Vp^(3/2) to beam kinetic energy (Ip);
    3) the coefficient of proportionality between space-charge limited current (Ip) and effective anode voltage (Vp^(3/2);
    4) a tube constant dependant solely upon physical electrode geometry (spacings, diameters, etc.);
    5) expressed in "Perv" units, ie: 1 Amp/(V^(3/2)), amps-per-volt^(3/2).
    6) tube constant almost NEVER published by tube manufacturers.
    Odd that 'G' was used for Perveance...G is conventionally conductance, inverse of Resistance; G=1/R.

    Lower case g probably tends to indicate ac, and gm indicates the 'older' term 'mutual conductance' replaced by the 'newer' term transconductance, depending how old the book is.

    My books(s?) used K for perveance. Doesn't change the limited practical usefulness of the term.

  15. #15
    Senior Member Old Tele man's Avatar
    Join Date
    Oct 2007
    Location
    Tucson, AZ
    Posts
    539
    Some old college textbooks used P, some used K, but most newer (mid-1950-60) books use G, probably (strictly MY opinion) because of it's relationship to conductance (g) which is a dynamic(*) Amps-per-Volt, and perveance (G) which is theoretically a static Amps-per-Volt^(3/2).

    However, I do see that P is used by the high-power ION-drive scientists, and they've assigned "perv" as the units instead of writing out Amps-per-Volt^(3/2).



    (*) gm varies as cube-root of plate current; per theory: gm = (3/2)*G^(2/3)*Ib^(1/3)
    Last edited by Old Tele man; 07-24-2017 at 10:17 PM.
    ...and the Devil said: "...yes, but it's a DRY heat!"

  16. #16
    Senior Member Old Tele man's Avatar
    Join Date
    Oct 2007
    Location
    Tucson, AZ
    Posts
    539
    One famous book, Radiotron Designers Handbook, 4th Ed., 1952, by F. Langford-Smith, uses G for Perveance (page 2 bottom):

    http://frank.yueksel.org/other/RCA/R...cteristics.pdf
    Last edited by Old Tele man; Today at 02:49 AM.
    ...and the Devil said: "...yes, but it's a DRY heat!"

Thread Information

Users Browsing this Thread

There are currently 1 users browsing this thread. (0 members and 1 guests)

Similar Threads

  1. Looked inside a fender vibro king and....
    By daz in forum Theory & Design
    Replies: 1
    Last Post: 02-15-2013, 11:59 PM
  2. Help with amp values
    By jvm in forum Guitar Amps
    Replies: 2
    Last Post: 02-27-2012, 05:36 PM
  3. what PI values to use?
    By daz in forum Theory & Design
    Replies: 4
    Last Post: 02-13-2010, 11:17 PM
  4. Replies: 1
    Last Post: 11-13-2009, 09:52 AM
  5. Mesa boogie recto preamp tube placement values
    By gotarock69 in forum Tubes (Valves)
    Replies: 4
    Last Post: 11-12-2009, 04:53 AM

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •