[AMRadio] UPDATE: Testing Transmitting Tubes


John Coleman wa5bxo at pctechref.com
Tue Oct 19 16:50:28 EDT 2004


TRANSCONDUCTANCE can be checked by placing a audio XFMR speaker winding in
series with the plate lead and measuring output voltage from the other
winding.  The ratio of grid input voltage change from a 60 cycle source
DELTA Eg : to the measured output would be a relative value that would need
to be calibrated.  The measure output AC voltage would represent the change
in IP with Ep held constant.  Transconductance = (DELTA Eg/DELTA Ip) with Ep
held constant.  

Just some extra thoughts.

John, WA5BXO   

-----Original Message-----
From: amradio-bounces at mailman.qth.net
[mailto:amradio-bounces at mailman.qth.net] On Behalf Of Mark Foltarz
Sent: Tuesday, October 19, 2004 1:15 PM
To: Discussion of AM Radio
Subject: Re: [AMRadio] UPDATE: Testing Transmitting Tubes

Hey Don,

  Sounds good!

  How would you like to build a curve tracer also?

  I built a tube curve tracer for audio tubes about 10 years ago.  I found
the
schematic the other day. Come to think of it I also have the the actual
unit.

  The idea is to use unfiltered half wave as the plate supply - simple sweep
eh?

  Build a step generator to put successive voltges on the grid - one higher
than the previous  with each plate voltage cycle.  


  Measure the plate voltage against the current on the x & y traces of a
scope.

  And you get the family of curves for that tube.


  Let me know if you want a copy of that old schematic.


  de KA4JVY

  Mark



 
--- Merz Donald S <merz.ds at mellon.com> wrote:

> Just thought I'd throw out an update on this. I am building an emission
> tester for older, mostly 800-series transmitting triodes. It will be able
to
> measure emission current at zero bias or adjustable bias (using an
external
> bias supply) at any plate voltage up to about 2500V. The HV is full-wave,
> lightly-filtered DC. Filament voltage is adjustable 0-10VAC. I have an old
> metered, rackmount regulated supply that uses dual 6L6's for regulation.
It
> will do 100V--so he becomes the bias supply.
> 
> I gutted an old Beckman, tube-type frequency counter to use the cabinet
and
> chassis. I just happened to have this unit laying around here. It has a
> unique cabinet design with sides that come off and modular chassis
> construction--even though, underneath the covers, it's a conventional 8.75
> inch high, 19" rackmount unit. This design allowed me to remove sections
of
> the chassis to accommodate the 2 big Variacs and the big HV iron. The top
of
> the cabinet pops off with just 2 Dzus fasteners. I am going to put holes
in
> the top with the tube sockets underneath, mounted on an inverted chassis
> bolted to the top cover. This way the whole unit won't have any
protrusions
> or non-internal wiring and none of the tube socket connections will be
> exposed or accidentally accessible. 
> 
> I drilled and painted the panel Sunday. I then immediately discovered that
> the 0-300ma meter I was using did not have enough range at upwards of
2500V.
> I needed at least 6-800ma. So I replaced that meter with a 0-1000ma
Simpson.
> But of course, the hole size is different. So now I have to cut a larger
> meter hole on my already-painted aluminum front panel. I took comfort from
> the fact that the black wrinkle didn't turn out that great anyway...
> 
> Most of the parts for this thing came from a supply I bought at a hamfest
in
> 2003. For $40, it had a 7.5 amp 120V Variac, 2700V transformer (amps
rating
> unknown but probably in the 500ma range), 4 K2AN silicon HV rectifiers and
a
> bodacious capacitor bank of paralleled 800MFD, 450VDC caps. The meters I
am
> using are from the junkbox (note to self: Don't buy any more meters at
> hamfests...), as are the sockets and miscellany. But anyone seeking to
build
> one of these with new parts would have a big bill on their hands. Check
the
> prices on new 7.5 amp Variacs these days...
> 
> I expect to be able to test to following tubes in this unit: 203, 211,
805,
> 808, 810, 838, 852, 25T(G), 35T(G), 100TH, 250TH and RK-65. The test is
far
> from definitive. But it will tell me whether the spares I am saving are
worth
> saving.
> 
> The top cover is big enough that I will still have some space for tetrode
and
> pentode sockets. Screen and suppressor supplies would have to be external.
> But that is phase II--or something I may never do at all.
> 
> 73, Don Merz, N3RHT
> 
> 
> -----Original Message-----
> From: owner-glowbugs at piobaire.mines.uidaho.edu
> [mailto:owner-glowbugs at piobaire.mines.uidaho.edu]On Behalf Of Merz
> Donald S
> Sent: Tuesday, September 21, 2004 3:27 PM
> To: 'Amradio (E-mail); 'Glowbugs (E-mail)
> Subject: GB> UPDATE: Testing Transmitting Tubes
> 
> 
> Well, here's where I am with this...
> 
> -- The guy who built the tester that AES is using says that he has some
> information on that unit that he will pass along.
> 
> -- Another guy says that he has built an adapter for the Tektronix 577
curve
> tracer for transmitting tubes. He says that he will write this up for
> Electric Radio.
> 
> -- Two guys said that they built custom testers for the 4CX250 tube. One
of
> them was expanded to test other tubes and was demo'ed at Dayton. The other
> was used in the guy's job. No details seem to be available for either of
> these.
> 
> -- I checked the AWA index and found only one reference to testing
> transmitting tubes. It's a 50 word mention on page 21 of Volume 22, number
1.
> There is one diagram. The test the guy is proposing is a minimal emissions
> test using a known good tube as a reference. He does this for triodes only
> using AC both on the filament and on the plate & grid (which are connected
> together). It has the virtue of being simple. But it hasn't many other
> virtues. 
> 
> -- Finally, there is the e-mail below from the AWA's Ed Gable. This seems
to
> be closest to the lines along which I am thinking--a scaled down emission
> tester.
> 
> The GE Ham News Hartley oscillator tester is more complicated than I want
to
> get into. And the Ham News static tester is very similar to the AWA tester
> described below. 
> 
> So this is where I am headed, though still open to better ideas. Keeping
it
> simple, so triodes only at this point.
> 
> 73, Don Merz, N3RHT
> 
> 
> -----Original Message-----
> From: Edward Gable [mailto:EGABLE at rochester.rr.com]
> Sent: Monday, September 20, 2004 2:11 PM
> To: Merz Donald S
> Subject: Re: Testing Transmitting Tubes
> 
> 
> Hi Don:  We built a tube tester for Big TX tubes at the AWA Museum.
> 
> 1.  Use big filament Xfmr and variac to accomodate any FIL voltage.  Use
FIL
> voltmeter.
> 2.  Use variace on HV supply for 0 to about 1500 volts.  Need about 300
Ma,
> but not too much filtering.
> 3.  Put voltmeter and ammeter in HV supply.
> 4.  Parallel wire a bunch of convenient tube sockets and allow for clip
> leads for socket-less tubes like 833.
> 5.  To test, get tube data for tube.  Look at chart and see what the tube
> current should be for a
> tube with zero bias.  For example, a type 810 might draw 200 Ma @ 1500
volts
> with zero bias.
> 6.  Connect the grid to the filament (zero bias condition)
> 7.  Turn the FIL on and set proper voltage for the tube under test.
> 8.  Turn up the HV variac and watch the current & voltmeters.  See if the
> current vs voltage is close
> to the spec.  It varies a lot from tube to tube, but low emission,
> non-useable tubes really show up
> this way.
> 
> SAFETY FIRST !!!
> 
> 73,
> 
> Ed Gable  k2mp
> Curator, AWA Museum
> 
> ----- Original Message ----- 
> From: "Merz Donald S" <merz.ds at mellon.com>
> To: "'Amradio (E-mail)" <amradio at mailman.qth.net>; "'Baswaplist' (E-mail)"
> <baswaplist at foothill.net>; "'Glowbugs (E-mail)"
> <glowbugs at piobaire.mines.uidaho.edu>
> Sent: Monday, September 20, 2004 10:19 AM
> Subject: Testing Transmitting Tubes
> 
> 
> > Has anyone built a transmitting tube tester? Or seen any plans on the
web?
> The only thing I have seen on this subject is the issue of GE Ham News
that
> covers the subject (Vol 6, #3, May/June, 1951). I have some power supplies
I
> can use to run the static test. But I need to build something to hold the
> tube sockets, filament transformers and plate current meter. I hate to
> reinvent the wheel and would be happy to follow a pre-existing design if I
> could find one...
> >
> > Any ideas?
> >
> > 73, Don Merz, N3RHT
> >
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