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'[EE]: Tube testing'
2006\11\11@180906 by Dave King

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Can anyone fire up a way back machine and throw me a bone on how to
test tubes with a multi meter?
I know it can be done (to a point) but can't find any specifics on
what to look for. I have a pile of mil-spec
tubes I need to go through and find out if any are good. The primary
ones are some triodes and a few power
beam pentodes. Other than being able to tell if filaments are not
shorted will a meter be able to tell me any more?

Dave

2006\11\11@190357 by David VanHorn

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> Other than being able to tell if filaments are not
> shorted will a meter be able to tell me any more?


About all you can tell with a meter is filament connection, and wether the
filament is shorted to the cathode, (it may be designed to be) and wether
the other elements are shorted.

If you want to do a basic operational test, you'll need at least plate and
grid voltages, and some resistors to set other grids up properly.

2006\11\12@040901 by Richard Prosser

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Once the cathode heats up, won't the grids etc develop a negative voltage
due to electron emission (space charge?).

Also, if the multimeter is set to the high megohms range, there may be some
resistance measurement cathode - anode which should be polarity dependent -
and should vary depending on voltages placed on the control grids. I
wouldn't have a clue as to likely values, but it _may_ be useful for
comparitive purposes (with a known good valve as a reference).

RP


On 12/11/06, David VanHorn <spam_OUTdvanhornTakeThisOuTspammicrobrix.com> wrote:
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> -

2006\11\12@114725 by Peter P.

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Richard Prosser <rhprosser <at> gmail.com> writes:

>
> Once the cathode heats up, won't the grids etc develop a negative voltage
> due to electron emission (space charge?).
>
> Also, if the multimeter is set to the high megohms range, there may be some
> resistance measurement cathode - anode which should be polarity dependent -
> and should vary depending on voltages placed on the control grids. I
> wouldn't have a clue as to likely values, but it _may_ be useful for
> comparitive purposes (with a known good valve as a reference).

Once the filament heats up a negative voltage appears between K and G1 (or the
'first' anode if there is no grid). This, when measured with a 10MOhm DVM will
be somewhere between -0.2 and -1.5Vdc. No voltage will appear on the other
anodes or grids usually. Keep your hands off the probes when doing this to avoid
false readings. The voltage depends a lot on the type of cathode used and little
on its emission although conclusions can be drawn by referencing the voltage
generated by the emission current with that produced by a known new tube of the
same type.

Conduction tests can be made using the same DVM on volts scale (!) and as little
as 24Vdc of anode supply for all known tubes. This implies putting the DVM in
series with the anode and the 24V supply, applying heater, and then polarising
the grids as appropriate to 'open' the tube. The tube is expected to pass as
little as 10uA in this mode when good (which reads as about 10V on the DVM used
as a current meter).

Peter P.


2006\11\13@105114 by Howard Winter

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Dave,

On Sat, 11 Nov 2006 15:08:40 -0800, Dave King wrote:

> Can anyone fire up a way back machine and throw me a bone on how to
> test tubes with a multi meter?
> I know it can be done (to a point) but can't find any specifics on
> what to look for. I have a pile of mil-spec
> tubes I need to go through and find out if any are good. The primary
> ones are some triodes and a few power
> beam pentodes. Other than being able to tell if filaments are not
> shorted will a meter be able to tell me any more?

Well it will be able to tell if the filament is open-circuit too!  That will give you an instant go/no-go, anything else needs the thing to be powered-up
and some sort of high voltage supply set up.  Remember to keep one hand in your pocket when messing about with this stuff live!

Cheers,


Howard Winter
St.Albans, England


2006\11\13@120925 by Paul James E.

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Dave,

Were are you located?  If you're in the US, and not too far from Texas,
I'd be happy to test them for you.  Just send them to me, or if you're
close enough, stop by, and I'll fire up the tube tester, and we can have
them finished in a short time.

                                            Regards,

                                              Jim


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> --

2006\11\13@150333 by Dave King

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Thanks Jim but I'm a wee bit far from there. ~2000 miles NW. I'd have to
get more than a bit lost to get there from here. Used to work for
Bell in Sagniaw
so I know the way, just need a better excuse than a dozen tubes. (not
much more tho)

Dave



{Quote hidden}

2006\11\13@150818 by Dave King

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Yup. From what I can see, I would have to build a testing chassis with
the right setup for each tube type. Then crank it up and put a signal through
the tubes. Seems I'm not going to learn much with the meter but it
was worth a try.

450 volts pah, it just bites a wee bit harder than 110 ;-]  I cheat
(in a paranoid way) and
wear doeskin gloves when I play with this stuff. Also use chopsticks
and a few other tricks
I was told about.

Dave



{Quote hidden}

2006\11\13@152019 by Shawn Wilton

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110 doesn't hurt.  It tickles.  Trick is to not touch it in such a way that
you will be stuck holding on when you get shocked.  Sure makes changing
outlets and switches faster (and you can do it at night!).  :-)

BTW, this is not an endorsement of any sort.  :-P


On 11/13/06, Dave King <.....KingDWSKILLspamspam@spam@shaw.ca> wrote:
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2006\11\14@072644 by Peter P.

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> Yup. From what I can see, I would have to build a testing chassis with
> the right setup for each tube type. Then crank it up and put a signal through
> the tubes. Seems I'm not going to learn much with the meter but it
> was worth a try.

Did you read my previous posting on this thread ? You can test most tubes with
only 24V anode voltage and the correct filament voltage. You can perform
comparative tests between known good and suspected tubes with this setup.

Peter



2006\11\15@020326 by Dave King

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Not sure if l saw your post. Problem is I have no known good tubes to compare to.

Dave

-----Original Message-----

Did you read my previous posting on this thread ? You can test most tubes with
only 24V anode voltage and the correct filament voltage. You can perform
comparative tests between known good and suspected tubes with this setup.

Peter



2006\11\15@045051 by Tamas Rudnai

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I am not sure in Canada, but here in the EU you can still buy some tubes --
which may or may not the same as you have :-) but might be a good start.
Some people still prefers tubes in high-end audio amplifiers.

Tamas



On 11/14/06, Dave King <KingDWSspamKILLspamshaw.ca> wrote:
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2006\11\15@210113 by Dave King

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I thought about doing just that but unfortunetly it seems the audiohhhphiles have created quite a demand for a few of these. As an example the rectifier was selling for anywhere between $50 and $150!. The triodes and the power amp tubes were the ones that were really nuts as they were types in demand for the high end stuff.  I was thinking that they might have been worth maybe $5-$10 etc as I can buy sovtek 12ax7's locally for $12. Be waaaaay cheaper to find a tester or just build a chassis for the ones I do have.

Dave

{Original Message removed}

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