[AMRadio] UPDATE: Testing Transmitting Tubes


Merz Donald S merz.ds at mellon.com
Thu Oct 21 10:31:50 EDT 2004


This goes beyond what I want to accomplish. Once I've established that a tube has good emission, then the next test I'd like to see is in a live rig--amp, modulator, whatever. I know a couple guys with complete tube labs. They can do curve tracing and are set up to match one tube with another. They can even test at RF, with some appreciable power. This sounds like fun. But there's only so much time in a life. 

73, Don Merz, N3RHT


-----Original Message-----
From: amradio-bounces at mailman.qth.net
[mailto:amradio-bounces at mailman.qth.net]On Behalf Of John Coleman
Sent: Tuesday, October 19, 2004 4:50 PM
To: 'Discussion of AM Radio'
Subject: RE: [AMRadio] UPDATE: Testing Transmitting Tubes


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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