[amandarae]

Hello everyone,

Seem like an odd question but please here me out.   The way I understand it, the two 12AX7 tubes on the Cornet 2 are voltage amplifiers, the 12AU7 is a Cathode Follower(CF).  In theory, the CF gain is zero but this tube takes care of the output current drive, minimizing the output impedance in order to sink the current to the load and it helps the voltage amplifiers tubes independent to the variations of the load connected to the output of the preamp.  I hope I am correct so far.

Now the question, what parameters in the tube data characteristics ensures better performance as a cathode follower if there's any?  I am trying to figure out and differentiate if the 12Au7, 5814, 6187, etc. or any other 12AU variants have an advantage when use as as a CF, not voltage amp, in a circuit.

regards,

Abe

[hagtech]

Cathode follower gain is almost one.  Best choice would be one with highest Vkh rating.

jh

[amandarae]

Cathode follower gain is almost one.  Best choice would be one with highest Vkh rating.

jh

Hello Jim,

Ahh yes, gain almost unity not zero.  Okay, what is Vkh?  If I can guess, is that the maximum voltage from heater to cathode before breakdown for IDHT tubes?  I am just guessing of course since I do not know what Vkh really is    Is there a simple way to find this out in a tube?  I searched my tube manuals and I cannot find any literature related to Vkh.

regards,

Abe

[hagtech]

Yeah, it's the breakdown voltage.  Good insulation and quality and purity of materials during tube manufacture make a difference.  NOS during cold war production is probably best.

jh

[amandarae]

Yeah, it's the breakdown voltage.  Good insulation and quality and purity of materials during tube manufacture make a difference.  NOS during cold war production is probably best.

jh

Thanks a lot Jim!

regards,

Abe

[tubesforever]

One other thing to consider, other than the strict electrical values is sound quality.

I have used Mullard 50's issued, Sylvania JAN, Raytheon, JJ Tesla, GE 60's, and RCA Cleartops and each dramatically effects the overall sound of the phono section.  The most clear difference is in the depth and slam to the bass and midbass region.

I would recommend voicing the tubes you have available to see what sounds best on your system.  Then look to buy the best measuring tube of that type if it is used old stock. 

BTW the Sylvania JAN were new (unused) old stock.  They sounded great in several systems I  plugged into on my trip to Portland this year.  I generally use either the JJ or the Mullard in my system because I am forced to sit just 7 to 8 ft from my speakers.   I need a super smooth response so it doesn't clobber me like fingernails on a chalk board.

[amandarae]

One other thing to consider, other than the strict electrical values is sound quality.

I have used Mullard 50's issued, Sylvania JAN, Raytheon, JJ Tesla, GE 60's, and RCA Cleartops and each dramatically effects the overall sound of the phono section.  The most clear difference is in the depth and slam to the bass and midbass region.

I would recommend voicing the tubes you have available to see what sounds best on your system.  Then look to buy the best measuring tube of that type if it is used old stock. 

BTW the Sylvania JAN were new (unused) old stock.  They sounded great in several systems I  plugged into on my trip to Portland this year.  I generally use either the JJ or the Mullard in my system because I am forced to sit just 7 to 8 ft from my speakers.   I need a super smooth response so it doesn't clobber me like fingernails on a chalk board.

Hey Tubes,

I agree!  But surely, you would not think that the tube that sound good in your system in this application is because they have black plates, gold pins, blessed every 21st of the month at exactly 9:00 AM at the local parish etc.etc.

I am trying to figure out why certain tubes work well in CF config and other work well as voltage amplifiers and vice versa.  For example, a little OT, but the Tungsol Round Plate VT 231 smoke glass cost $$$ in the current market because it sound great as a voltage amplifier but wimpy as a CF compared to an RCA or GE 6SN7GTB's.  I am curious as to why do some have that "drive" better than the other if most if all the parameters involve in the circuit are the same (bias voltages etc.)

 Don't want to bore you but here's where my curiosity started.   I have tried many 12AU7 and its variants on my Cornet 2.  Name it, I probably tried it.   But I have this tube that is labeled "JHS6189" made by Sylvania dated 11/66, round getter 2 mica contruction-gray plate.  Nothing special on its appearance but it drives the bass and midbass in the Cornet 2 much "harder" than any tubes I tried!   Just of personal curiosity, I am trying to figure out why.

regards,

Abe

[tubesforever]

Why a tube sounds better or worse....

That is a question I keep asking every tube guru I know.

Why do 50's issued Mullards sound so different than their military CV tubes that came out later?

Why?  The only explanation I get is that the older metal used in the plate construction is not as pure as the metal used in new production.  There is a group of folks that seem to think the impurities of the former led to a different and more desirable tube sound.

I am not sure I buy into this....I think every brand tube that went through production sounds differently even when built to the same spec sheet.  Buggle boys for instance sound different that Orange Globes and they are both Amperex 12AX7 tubes.

RCA clear tops sound different than later production RCA black plates. 

I agree that the GE JAN tubes are outstanding.  I am not sure what JAS stands for.  JAN stands for joint army navy.  JAS would be joint army submarine?????

I think my brain is submarined right now.  But I agree that it would be really great to know exactly how an outstanding tube would measure in every possible way.  That would make it easier to specify the build of a perfect tube!  I bet Groove Tube would build it if you could specify it!

[amandarae]

Hey tubes,

JHS is a military designation to identify the manufacturer of the tube.  JHS is for Sylvania as well as CHS.  Here, I researched this for you:

Tungsol = JTL /CTL
Raytheon = JRP / CRP
NU = CNU
CAHG = Chatham
CHS = Sylvania or JHS
CKR= KenRad
JHY = CBS Hytron
CBRZ = Lansdale
CRC = RCA

regards,

Abe

[tubesforever]

Abe thanks for the chart listing mil spec tube designations.  I have copied this to a private file.  Great stuff.

I am listening to a set of JHS 6189 this week and they are very dynamic and very detailed in my system.  They were the best tubes for one of my friends systems in Portland Oregon. 

It is fascinating to me to see just how much the Clarinet and Cornet 2 are impacted by the 12AU7 or variants.

I wonder if JimH will design an Octal Clarinet fully balanced?  I want one.  That and a kit Trumpet!  I need more balance in my life!

[Rocket]

Hi Tubes,

Where do you purchase your NOS tubes from?

I need 12bh7 x 2 and 12au7 x 2 in my preamp.

Thanks

Rod

[amandarae]

Abe thanks for the chart listing mil spec tube designations.  I have copied this to a private file.  Great stuff.

I am listening to a set of JHS 6189 this week and they are very dynamic and very detailed in my system.  They were the best tubes for one of my friends systems in Portland Oregon.  

It is fascinating to me to see just how much the Clarinet and Cornet 2 are impacted by the 12AU7 or variants.

I wonder if JimH will design an Octal Clarinet fully balanced?  I want one.  That and a kit Trumpet!  I need more balance in my life!

Jim,  easy on the comments regarding the JHS 6189.  I have not collected enough yet

But seriously, the longer I use this tube, the better it gets in my Cornet 2.  Wonder why the synergy?  

There is a difference between the tubes base on this specs though.  For 12AU7, Vp is 300V, PdMax is 2.75W, Ip is 20 mA while for the 6189, its 330, 3, and 22 respectively.  Following the logic comparing the difference spec wise of how a 6SN7 GTB with greater Plate voltage rating (and Plate Dissipation and current I assume than the 6SN7/VT-231) works better in CF than a plain 6SN7 or VT-231, it  is possible that the Vkh rating that Jim H. mentioned as a criterion for a tube having "good drive" in CF mode was increased also due to the increase of the voltage and current capacity the tube can handle.  I like to say "eureka" but I do not know if my line of thinking is correct really.

Anyways, hope some Cornet owners finds the same "character" in their system using the 6189.  By the way, I am using Radiotron 5Y3-ST or Tungsol 5Y3-ST as rectifier.  Nothing special but this tubes gives me an almost "dead on" voltage reading on the PCB test points value.  Was using Mullard 5AR4 and Bendix 6106 before, they are good too.

regards,

Abe