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Old 17th October 2010, 12:13 AM   #101
piano3 is offline piano3  United Kingdom
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JohanB,

Yes,of course high mu valves but what I was talking about was a higher than published values of Cg-a experienced with high gm RF valves in actual use. Many valves claim 1 point something pF but when you factor this value in when designing the 75 microsecond pole and then listen to the result it is clearly wrong-and I really mean clearly! D3a pentode triode wired specs own up to 3 point something pF as far as I remember. I think MJ found a very large discrepancy with the EC8010 valve.
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Old 17th October 2010, 12:33 AM   #102
JohanB is offline JohanB  Sweden
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Quote:
Originally Posted by piano3 View Post
JohanB,

Yes,of course high mu valves but what I was talking about was a higher than published values of Cg-a experienced with high gm RF valves in actual use. Many valves claim 1 point something pF but when you factor this value in when designing the 75 microsecond pole and then listen to the result it is clearly wrong-and I really mean clearly! D3a pentode triode wired specs own up to 3 point something pF as far as I remember. I think MJ found a very large discrepancy with the EC8010 valve.
OK, I hav'nt checked these high-gm tubes. My stock of NOS 5751's are within specs what i've found out so far. With the D3's you have to encounter the screen grid as well in triode mode. But it is only the Cg(a+g2) that multiplies. All other caps are as is.
Strange that these proffesional "telecom" tubes dont keep the datas as you say. I have to measure this. Should be easy as you just can measure them cold with a socket on your desk.

JohanB
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Old 17th October 2010, 12:45 AM   #103
piano3 is offline piano3  United Kingdom
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I wish I had measuring equiptment that could measure a pF or so reliably! Are you aware of any effects that could cause the Cg-a to be frequency dependant?

Last edited by piano3; 17th October 2010 at 12:48 AM.
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Old 17th October 2010, 12:50 AM   #104
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Quote:
Originally Posted by piano3 View Post
DualTriode,

Have you looked carefully at the Valley and Wallman page you are talking about? If you have the same reprint as I do there are mistakes/printing errors. There are superscripts missing on the rp,gm and mu terms-I was very confused until I figured out what was going on.

Regards,N.A.
I try to avoid first editions.
The copy I am looking at is Boston Technical Publishers, 1964.
There may be an understanding on the way here, I hope.
I do not have a scanner at my home. On Monday I will scan and make pdf’s of the items referenced in my previous posts.
I would rather sort this out. In my mind it will add more value to the thread than letting it hang.
DT
All just for fun!
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Old 17th October 2010, 05:47 AM   #105
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Hello,
If you have intrest in the gm' of the common cathode and Cascode circuits they are the same on this page. Google found it. Improving the Cascode's PSRR (page 2)

DT
All just for fun!
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Old 17th October 2010, 11:27 AM   #106
piano3 is offline piano3  United Kingdom
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DT, that was interesting to read, thank you.

JohanB; if you are able to measure accurately Cg-a on triode connected E180F, E280F and E810F that would be very useful information!
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Old 17th October 2010, 01:23 PM   #107
JohanB is offline JohanB  Sweden
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Originally Posted by piano3 View Post
DT, that was interesting to read, thank you.

JohanB; if you are able to measure accurately Cg-a on triode connected E180F, E280F and E810F that would be very useful information!
Hi, I'll try to do E180, 280 & 282 next, but during the last hour I've been busy measuring:

Socket A = Noval PC-type brown micanol made by NSF (germany) 1958
Socket B = Noval PC-type White ceramic made by Nuval 1990 in Italy

ECC83 Telefunken NOS orig. plain anodes 60's
ECC82 Telefunken NOS orig. plain anodes 60's
ECC88 Ultron NOS (Germany) 60's
5751 Sylvania NOS 1957

Measure between pin 1 & 2 . Other pins not earted
On the sockets were soldered 2 pcs of L=25mm dia. 0,6mm solid copper wires,
to jack into the meter. This to be able to repeat the exactly position of the tube/socket.

Residual capacitance on meter Escort ELC-131D is a stable 1,1pF that is substracted from the readings below. Resolution on the meter is 0,1pF

Calibration check: a 4,7 pF 2% gives exactly 4,7 on the meter with a Dissipation Factor of 0,005

Socket A alone = 0,7pF D= 0,011
Socket B alone = 0,6pF D= 0,010
ECC83 in socket A = 2,8pF D= 0,012
ECC83 in socket B = 2,7pF D= 0,011
ECC88 in socket A = 3,0pF D= 0,011
ECC88 in socket B = 2,8pF D= 0,007
5751 in socket A = 3,0 pF D= 0,009
5751 in socket B = 2,7pF D= 0,008
ECC82 in socket A = 3,0pF D= = 0,011
ECC82 in socket B = 2,8pF D= 0,010

Calibration check the 4,7pF again........4,7pF D = 0,005

In my 1958 book "Valves for A.F. Amplifiers" by Philips Technical Library, says 1,8pF for the ECC83, but datasheet Philips shows 1,6 and for ECC82 1,5.
My Vade-mecum 1961-1963 says 1,4 for the 5751, 1,6 for ECC83 & 1,5 for ECC82.

Conclusion: You have to calculate 3pF as Cag IRL for most designs and all small trodes, both on circuit boards and hardwire. Do not let the g & a leads cross each other on opposite sides of the board.

These measurments is also a little inaccurate, as they dont include the parasitic capacitances through the other electrodes, that was left floating (not connected to ground). So readings could be 0,1-0,2pF higher than the actual capacitance.

The only way to measure exactly, is to put a 47KOhm series resistance input resistor, and find at what frequency the -3dB point is. If the normal MM load resistor is 47K, then the generator impedance is 23,5 KOhm (47/2) and you have to calculate from that.

But 2,5 -3pF seems to be a rule of thumb for almost all small Noval triodes for now.......


JohanB
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Old 17th October 2010, 04:19 PM   #108
JohanB is offline JohanB  Sweden
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Quote:
Originally Posted by piano3 View Post
DT, that was interesting to read, thank you.

JohanB; if you are able to measure accurately Cg-a on triode connected E180F, E280F and E810F that would be very useful information!
Sorry, I don't find my E810F, so I showed the E282F instead.

Hi, these tubes as triode connected and including a ceramic tube socket. All other pins floating:

Telefunken E180F S= 16,5mA/V @ 13mA, u=50 Cg1 to (g2+a) = 4,0pF, to (g2+g3+a)= 4,4pF

Siemens E280F S= 26mA/V @ 20mA , u= 60 Cg1 to (g2+a) = 4,4pF, to (g2+g3+a) = 4,5pF

Siemens E282F S= 26mA/V @ 35mA, u= 27 Cg1 to (g2+a) = 5,3pF, to (g2+g3+a) = 5,6pF

Rp (or Ri) = u/S More data here Frank's electron Tube Data sheets

JohanB
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Old 17th October 2010, 05:08 PM   #109
JohanB is offline JohanB  Sweden
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I was a little stupid there. It is of course only the capacitance between g1 and g2 that is of interest. The anode is shielded from g1 by the internal shielding!! New figures!!

Measured in a ceramic PCB socket with 0,3 pf capacitance without tube inserted.

E180F C from g1-g2 = 3,3pF
E280F C from g1-g2 = 3,7pF
E282F C from g1-g2 = 4,5pF

JohanB
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Old 17th October 2010, 05:16 PM   #110
piano3 is offline piano3  United Kingdom
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That is tremendous work JohanB! Many thanks for that and I hope many members read it. I had estimated by ear on 75 microsecond RIAA stage that the values for these triode connected pentodes had to be in this region though I had not suspected quite as high as 5.6 pF!


your last post was while I was writing this-yes that seems more believable!

Last edited by piano3; 17th October 2010 at 05:18 PM.
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