[R-390] RE: tube testers

[Bob Camp]

Hi

Pretty much what I am proposing is a simple transductance tester that 
runs at 60 Hz just like the TV-7 and TV-10 testers did. That makes the 
circuit fairly easy to build and just about any reasonable AC voltmeter 
can be used as the "detector" in the plate circuit.

A quick scan of the tube tester schematics suggests that a fixed bias 
goes on the plate and screen. A variable dc bias goes on the control 
grid along with about a volt or so of AC. I suspect we would use 
something like a dozen or so resistors to set the whole thing up for 
the tubes in the R-390.

The advantage of doing it this way is that the data from the TV-7 or 
TV-10 can be directly compared to our tester. This will give us a way 
to be sure that we got the design right.

I have never seen a frequency drop off in a tube. Certainly they do get 
noisy but they don't seem to get roll off problems. You can see 
capacitance variations but those are normally tuned out in the circuit. 
We could measure electrode capacitances and that would give us a pretty 
good idea of what is going on. I suspect that we wouldn't find out to 
much though ...

In order to measure high frequency gain on a tube we would need a tuned 
load to run into. The same thing would apply to the grid circuit. If 
you are going to do that we might as well just check them with a signal 
generator in the radio.

Noise figure would be a *very* interesting thing to measure on a tube 
by tube basis. The same issues about tuning the input and output 
circuits would apply but we might get some useful data. That project is 
a bit more involved than what I had in mind.

So I guess there's been enough interest. I'll go off and see what I can 
figure out for a circuit. When I do I'll let the group know.

	Thanks!

		Bob



On Oct 27, 2004, at 8:53 PM, Michael Murphy wrote:

> Steve,
>
> We are not that interested in DC gain or even DC Transconductance I 
> think.
> Lets talk AC and High frequency. There probably are only four tube 
> types in
> the 390 worth testing if you are talking about sensitivity and signal
> handling (which seem to be the hot buttons). I think these could be 
> handled
> with a  high frequency bench generator at say 500 kHz and 10 MHz, a 
> chassis
> with wired tube sockets and a high gain low noise amplifier and 
> finally a
> Scope or high frequency AC meter to test high frequency gain and 
> noise. This
> would not be the simplest way to find "Good" or "Bad" tubes but it 
> would be
> a possible way to find "Better" tubes with good high frequency gain 
> and low
> noise characteristics.
>
>
> Mike WB2UID
>
> ----- Original Message -----
> From: "Steve Hobensack" <stevehobensack at hotmail.com>
> To: <r-390 at mailman.qth.net>
> Sent: Wednesday, October 27, 2004 6:49 PM
> Subject: [R-390] RE: tube testers
>
>
>>
>> -----BEGIN PGP SIGNED MESSAGE-----
>> Hash: SHA1
>>
>> The RCA Receiving Tube Manual has lots of good info on tube testers
>> and tube tester circuits. There
>> are simple schematic diagrams on tube tester circuits that can be set
>> up on the bench using variable power supplies , variable rheostats,
>> and ac/dc milliameters.  These test jigs are good for testing a lot
>> of  the same kind of tube. I have several manuals dated from the
>> forties to mid sixties and can be found on Ebay , hamfests , etc.
>>
>> 73....Steve...N8YE
>>
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>> zJRozFyfNW0eHjUj+iyB7lhk
>> =jI15
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