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Old 5th Jun 2021, 2:03 pm   #1
Martin_Calva
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Default KTW63 anode resistance?

Hello - my first posting here as a new member.

My question: Could anyone point me to detailed characteristics of the KTW63 valve, including its anode resistance under normal operating conditions?

Background:

My dad was an electronics engineer who worked at the GEC research centre at Wembley before WW2. He had a CR-100 comms receiver but he was contemptuous of its previous owner, as they had replaced the original Marconi-Osram KT series valves with US valves. Eg the KTW63's had been replaced with 6K7 valves.

He told me this was a daft thing to have done, as the kinkless tetrodes had higher anode resistance than their US pentode counterparts. So giving higher gain and less damping of the tuned circuits.

I have been trying to verify that statement of his. However, the MO datasheet I have for the KTW63 does not give its anode resistance, although it does give anode voltage/current curves. But the slope (=anode conductance) of the curves is so small that it essentially equates to "infinity" for the anode resistance when I attempt to estimate the value.

Many thanks for any help in resolving this query which has bugged me for many years.
Martin
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Old 5th Jun 2021, 8:22 pm   #2
G6Tanuki
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Default Re: KTW63 anode resistance?

My Babani book doesn't specify an anode-resistance for the KTW63.

I always thought that the design of such valves was such that with the right choice of anode-and screen-voltages the concept of 'anode resistance' was essentially mapped-into-irrelevance [though it may have reared its ugly head again if AGC action changed the relative anode- and screen-voltages from their static conditions - I never really liked the idea of feeding screens from HT via a relatively-high-value dropper-resistor - the guys at RCA insisted on a regulated 150V screen-supply in their AR88]
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Old 5th Jun 2021, 9:17 pm   #3
frsimen
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Default Re: KTW63 anode resistance?

From the published curves for these valves with 0V bias.

6K7 at 100V, Ia = 11mA, at 300V Ia= 11.7mA, giving Ra around 286k ohms

KTW63 at 100V Ia=12.2mA, at 300V Ia = 12.4mA, giving Ra around 1M ohm.

That suggests that your father's statement was correct.

Paula
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Old 5th Jun 2021, 9:38 pm   #4
cathoderay57
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Default Re: KTW63 anode resistance?

Radio Valve & Transistor Data (9th Edition) by A.M. Ball gives Anode AC resistance as follows:
6K7 600k
Curiously none of my databooks quotes ra for KTW63. The closest is KTW61 which states 460k which suggests lower, albeit the characteristics of the KTW61 and KTW63 are marginally different. I have found both of the latter types used in CR100.

Jerry
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Old 5th Jun 2021, 10:08 pm   #5
Heatercathodeshort
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Default Re: KTW63 anode resistance?

From the Osram valves Maintenance Types for Broadcast Receivers and Amplifiers. December 1944. J.
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Old 6th Jun 2021, 9:17 am   #6
Electrical
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Default Re: KTW63 anode resistance?

I am not sure if the attached information on the KTW63 is any different from what you already have. The data is from the Osram Valves data book from 1938-39 and does not give a value for the "ra" of the valve.
However the 1957 data book quotes a 6K7G as equivalent to the KTW63, which is listed as obsolete.
Regards Stan.
Attached Files
File Type: pdf KTW63 Osram Valves 1938-39.pdf (82.2 KB, 58 views)
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Old 6th Jun 2021, 10:58 am   #7
Robert Gribnau
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Default Re: KTW63 anode resistance?

Here the internal resistance of the KTW63 is given as 500K at Va = 175 V, Vg2 = 100 V, Ia = 8.5 mA and Ig2 = 1.7 mA:

https://frank.pocnet.net/short/054/1/181.pdf
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