calculating cathode follower impedance for random tubes

[Opcom]

Is there a simple way to calculate the circuit values needed for a specific output (load) impedance when using a given triode or tetrode?

There are some online ones for a few triodes used as audio preamps, but none for random tubes like the 6N7, 6GH8 sections, 6BQ6, 6080, or even 3-500Z or an acorn tube.. So what I'm asking is where can I find the calculations for this?

For example, I may want to make a cathode follower for driving a 150 Ohm audio load and use a single 6080 or a 6BQ6 as a cathode follower. It does not have to do specifically with radio frequency challenges, but with audio, DC, and power supply.

The calculations should help me find out what plate voltage I need, what bias/idling current should be set, G2 volts if used, cathode resistor, etc.

Thanks!

[w4bfs]

AIRC ... the Rca Radiotron designers handbook is where I would start ... Pat, let me know iffn you get stuck

[Steve - K4HX]

A pretty good start at the link.

http://www.valvewizard.co.uk/accf.html

[DMOD]

I highly Recommend:

Hollow State Design, by Grayson Evans. Available through Electric Radio.

Phil - AC0OB

[VE3AJM]

Theres always the RCA Radiotron Designers Handbook 4th edition, chapter 7 and other references there too. Its the 'bible' for tube design. Chapter 7 and other places in that book. You can download it online from many sources and/or do a search for it.

https://archive.org/details/RadioDesignersHandbook


Al VE3AJM

[Opcom]

I'll have to find a copy of hollow state, maybe used /low cost. One thing I see is that the larger 2nd edition is only $30 at ER yet amazon wants $45 for the previous edition.
Is there any reason to want the original edition for such high money? ER says the 2nd is larger and "There are many revisions and corrections throughout the text, and there is an entire new chapter on oscillator design, covering 5 important oscillator configurations.".

valvewizard explains much though. As for RDH4, it's nice to find another scan, as I had but a chapter by chapter one ripped off the web with an HTML front end and it was cumbersome. Somewhere in a 250 cubic FT stack of document boxes is my big red tube book.  I miss not having my library accessible as paper reading material.

[VE3AJM]

Nonetheless, the RTDHB 4th edition and others are available to you freely online. I bought the real book/hardcopy at a hamfest for $5 CDN a few years ago.

The entire book or chapters thereof are available in pdf format. Copyright ran out/expired in Canada in 2003 if there are concerns about that. I just did a random search on Google and found this:

http://www.ax84.com/rdh4.html

Al VE3AJM

[W7TFO]

A little more light reading on the subject:

http://www.tubecad.com/2011/08/blog0212.htm

73DG

[Opcom]

I found a model for the 6080/6AS7 and it would help me to use this with the other resources.

It is an LT Spice .SUB file. Ok.. so I need to make an .ASY file, the 'picture' of the tube (n problem), and somehow link them together.

I don't see how to do that, but the spice program probably does this. Has anyone experience with making this work?

The .SUB is inline -it includes several Triodes but I have pared it to only a few so it is short enough for discussion.

The syntax seems "*" indicates a comment line, ";" seems an inline comment, and blank lines are for humans. Some have comment "Specialized tube model" but it does not seem required.

The 6080 part also is a bit different from the 6SN7, etc.

This file is from https://gist.github.com/chanmix51/6947361


*--------------------------------------------------------------------------
* Specialized tube model
*
*    Type           : 6SN7 6N8S
*    Description    : Triode
*    Direct heated  : no
*    Screen present : no
*--------------------------------------------------------------------------
.subckt 6SN7 P G K
Bp P K  I=(0.02003791851m)*uramp(V(P,K)*ln(1.0+(-0.07740549711)+exp((4.618036737)+(4.618036737)*((20.288965)+(-110.4389272m)*V(G,K))*V(G,K)/sqrt((28.13407639)**2+(V(P,K)-(7.118597372))**2)))/(4.618036737))**(1.380047579)
Cgp G P 4.0pF
Cgk G K 2.6pF
Cpk P K 0.7pF
.ends 6SN7
 
*--------------------------------------------------------------------------
* Specialized tube model
*
*    Type           : 12AX7 ECC83 6N2P
*    Description    : Triode
*    Direct heated  : no
*    Screen present : no
*--------------------------------------------------------------------------
.subckt 12AX7 P G K
Bp P K I=((0.001149607902m)+(0.0001063352726m)*V(G,K))*uramp((91.16514401)*V(G,K)+V(P,K)+(52.29904339))**1.5 * V(P,K)/(V(P,K)+(2.177964467))
Cgp G P 1.7pF
Cgk G K 1.6pF
Cpk P K 0.46pF
.ends 12AX7
  
.SUBCKT 6AS7_6080 A G K
XV1 A G K TRIODENH
+PARAMS: LIP= 1 LIF= 0.01 RAF= 0.0058 RAS= 0.7 CDO= 0
+ RAP= 0.035 ERP= 1.5
+ MU0= 2.05 MUR= 0.0017 EMC= 0.0005
+ GCO= 0 GCF= 0
+ CGA=1.10E-11 CGK=8.00E-12 CAK=3.00E-12
.ENDS