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Old 8th August 2011, 11:20 AM   #1
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Talking decade bank values for a plate current tester

ive been thinking about making a home brew vacuum tube tester . for tesing small triodes and medium sized power tubes at normal operating points ,

testing all tubes whit their respective anode load voltmeter across the anode load and an ammeter in series whit it

you can calculate gain and steepness like VG1 is 5-15v current draw goes from 10 to 100ma meaning 90ma over 10 volts means 9Ma/v

now im thinking of a sort of tester that tests the tubes in variable parameters . EG curve tracer VG1/VS anode current draw

variable anode supply 100-350v 100ma maybye even more
0-30v 5A heater supply . wich will be just a lab power supply
variable 0-60v positive and negative (lab power supply

and a set of decade banks for the plate load cathode bias resistor . cathode bias resistor bypass capacitor , grid leak resistor .
optional are decade banks for the plate resistor

and 3 gas voltage regulators for grid voltages .

i was also thinking of BNC in and out so you can put a sine wave generator and your scope to watch the output . or check for microphonics

now i was guessing wich ranges the decade banks should have .
i was thinking of using 11 position switches where position 1 is 0. OHMS


for the cathode bias i thought of a decade bank whit 10 steps of 1K 10 steps of 100 ohms and 10 steps off 10 ohms all metal film resistors 3W
giving you a range of 0k01 -11k1

plate load would be 100ohms /111K 2steps of 25k 5 steps of 10k
5 steps of 1K 10 steps of 100 ohms depending on how much i want to spend on wirewound resistors . i could also just make it 0k1-11k
and a double decade bank for little high plate R double triodes .

grid leak resistor would be 10 steps of 100k

now there are some questions that come to mind .
* do i need to test the tubes whit the cathode bypassed ?
* is anode load critical . i mean if im writing my own test datasheets cant i just take a crude anode load . and benchmark against the average current draw .
* is it reasonable to make another 2 decade banks for little high plate load double triodes ? like 10x10k 10x1k 1k-110k 3w resistors



you could make the tester in a way that VG1 can be computer controlled through an interface . and the plate draw could also be computer monitored . you could make your own curves .


am i just overcomplicating ? course to me the idea of testing tubes under real test conditions is better than testing it on a machine that gives 100% readings EG good bad testers



and if somone would host a site whit custom test parameters. you could test in a more universal and precise way . better than 100%


anyway im hoping forward to hearing your idea's .





edit . my ideas are not new and possibly wrong . but feel free to use it for any purpose you want .
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Old 8th August 2011, 04:11 PM   #2
TheGimp is offline TheGimp  United States
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Gm is a small signal gain parameter withthe plate voltage held constant. So it is a little more difficult than it seems.

There are a number of threads related to this.


Tube testers which is the best?

Valve curve tracer gm tester

computer tube tester

As well as other sites:

Tube Curves Tracer

RAT Tube Tester Project, By Steve Bench

The "Sussex" Homebrew Valve Tester. - UK Vintage Radio Repair and Restoration Discussion Forum


Also RDH4 has a good section on testing tubes.
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Old 9th August 2011, 09:30 AM   #3
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the only thing i want to measure is current draw versus grid voltage .

just power the tube up under normal operating points ant put DC on G1

like testing an EL84 whit
plate voltage of 250v
plate load of 4.5k-5.2K
VG 2 = 250V tied to plate through a resistor
VG1 = -7.3v

benchmark anode current should be 48MA

and see howmuch MA's it does .

Last edited by v4lve lover; 9th August 2011 at 09:30 AM. Reason: me makes mistakes
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