Testing tubes without a tube tester???
 

Hi Folks!
Dumb Question #1: How can I test vacuum tubes without a tube tester?
Namely, 6AK6, 6BE6, 6HR6, and 12AX7.

Dumb Question #2: Is there a solid-state equivalent to these tubes?
They are from an old Knight Star Roamer that keeps dying.

Dumb Question #3: Is the above worth doing?

Thanks for your help.~~Ray

On Fri, 23 Jan 2004 15:56:51 -0600, Ray D. O'Mann wrote
(in message ) :

Hi Folks!
Dumb Question #1: How can I test vacuum tubes without a tube tester?
Namely, 6AK6, 6BE6, 6HR6, and 12AX7.

Dumb Question #2: Is there a solid-state equivalent to these tubes?
They are from an old Knight Star Roamer that keeps dying.

Dumb Question #3: Is the above worth doing?

Thanks for your help.~~Ray



Does it work for a while and then stop working?



Gray Shockley
--------------------------------------------------------
Who religiously believes it is always capacitors
(unless it's a bad power cord)

"Ray D. O'Mann" wrote in message
om...

How can I test vacuum tubes without a tube tester?

You might give your general location and maybe someone would volunteer to
check them for you. If you are in my neck of the woods (slim chance though)
I would gladly check them for you.

Lots of folks consider the Star Roamer a real collectors item. RM~

"Ray D. O'Mann" wrote in message
om...
Hi Folks!
Dumb Question #1: How can I test vacuum tubes without a tube tester?
Namely, 6AK6, 6BE6, 6HR6, and 12AX7.

You can check the heater continuity and heater to cathode for shorts
with an ohmmeter. The ohmmeter test won't catch all the shorts, but it
will catch the worst of them. If the metallic deposit on the inside of
the tube's glass has turned white, the tube is full of air and is no
good.

These tubes will probably work if they have good heaters, no bad heater
to cathode shorts and aren't full of air.

You can find out your tube pin outs he

http://hereford.ampr.org/cgi-bin/tube?tube=


Dumb Question #2: Is there a solid-state equivalent to these tubes?

There was one for the 12AX7. It wasn't very popular and probably isn't
worth looking for. If the others have equivelents, they would be even
rarer.

They are from an old Knight Star Roamer that keeps dying.

Dying in what way? Tubes can cause such problems, but I'd first suspect
capacitors, a selenium rectifier, bad connections, and bad resistors.


Dumb Question #3: Is the above worth doing?

It depends. With some effort and maybe a bit of luck, you'll end up
with a working Star Roamer and bit of expirence. Safety is worth
mentioning:

http://repairfaq.org/sam/safety.htm

Check out:

http://antiqueradio.org/howfix.htm

http://antiqueradio.org/recap.htm



Thanks for your help.~~Ray


Frank Dresser

On Fri, 23 Jan 2004 16:08:16 -0600, Gray Shockley
wrote:

On Fri, 23 Jan 2004 15:56:51 -0600, Ray D. O'Mann wrote
(in message ) :

Hi Folks!
Dumb Question #1: How can I test vacuum tubes without a tube tester?
Namely, 6AK6, 6BE6, 6HR6, and 12AX7.
only the filaments, and looking for internal shorts. Not very useful

Dumb Question #2: Is there a solid-state equivalent to these tubes?
No, they are designed to operate at something around 150 volts DC.
They are from an old Knight Star Roamer that keeps dying.

Dumb Question #3: Is the above worth doing?
There are better ways to check. However life expectancy was rarely a
problem with any of those tubes.

Thanks for your help.~~Ray



Does it work for a while and then stop working?



Gray Shockley
--------------------------------------------------------
Who religiously believes it is always capacitors
(unless it's a bad power cord)

Well, there are several things that can be done. If you have a blue glow inside
the plate, it's gassy and will cause noise. (Outside the plate is okay.) If you
tap it, holding the top with a finger of one hand and flicking it, using thumb
and index finger of the other hand, look for sparking around the cathode (and
listen for a static like noise). The tube could be intermittently leaky, even
shorting. Listen for a "bonging"sound. Although this won't affect performance
too much, it -- a microphonic -- could interfere with decent reception of
strong signals.

If the filament goes on and off, it, and a static noise without a shorting
indication, most likely would indicate a bad socket contact. Short of replacing
the socket, get a paper clip, straighten part of it, and cut barbs into the
straightened part, scattering the barbs around the wire, preferably pointing
out (up) so that they scrape any crud when the wire is removed. Then work the
clip's wire in and out of each socket pin. The clip's wire should be the same
diameter as the tube's pins. Unless there's a lot of crud in the pins, spray
cleaning doesn't help much.

Sometimes a socket's pins will spread and lose tension. Take a scribe and
squeeze the two halves of each pin closer together. Clean them first, though.

73,
Bill, K5BY

Maybe see "Troubleshooting the Stages of a Typical Superheterodyne
Receiver"
http://www.gbronline.com/radioguy/superhet.htm

--
73 From The Wilderness Keyboard
"Ray D. O'Mann" wrote in message
om...
(Ray D. O'Mann) wrote in message
. com...
Hi Folks!
Dumb Question #1: How can I test vacuum tubes without a tube tester?
Namely, 6AK6, 6BE6, 6HR6, and 12AX7.

Dumb Question #2: Is there a solid-state equivalent to these tubes?
They are from an old Knight Star Roamer that keeps dying.

Dumb Question #3: Is the above worth doing?

Thanks for your help.~~Ray

Hi All!
Thanks a bunch for the tips, tricks, and advice. It is VERY
appreciated. Everything always tests OK out of circuit and I've been a
bit reluctant to do the in-circuit testing since all I have is a DMM.
The shop where I was testing my tubes now charges a fee for using
their tester. With everything that you all have posted for me, I
believe I can get it to work right. I hope. To answer some of your
questions, it just quits. I test the tubes, then I check the caps,
diodes, connections, etc., plug it back in and it works for a day or
two and then quits. Any thoughts?~~Ray

"Ray D. O'Mann" wrote in message
om...

Hi All!
Thanks a bunch for the tips, tricks, and advice. It is VERY
appreciated. Everything always tests OK out of circuit and I've been a
bit reluctant to do the in-circuit testing since all I have is a DMM.
The shop where I was testing my tubes now charges a fee for using
their tester. With everything that you all have posted for me, I
believe I can get it to work right. I hope. To answer some of your
questions, it just quits. I test the tubes, then I check the caps,
diodes, connections, etc., plug it back in and it works for a day or
two and then quits. Any thoughts?~~Ray


I'll suggest you start looking for bad solder joints, especially if it's
on a circuit board. The hot/cold cycling can put cracks in the solder
joints, which can open up when the radio warms up. Ususally you can see
the cracks if you are looking right at them. Or maybe not. You might
try touching up all the solder pads if you end up frustrated and have
some free time.

If you can do it safely, try tapping around with the eraser end of a
pencil while the radio is working or after it's just shut down.

Here's a link to a scanned copy of the owner's manual:

http://bama.sbc.edu/knight.htm

These files are kept on a server at a small college, and it's often too
busy to access the files during the day. They are usually available
late at night.

Frank Dresser

I test the tubes, then I check the caps,
diodes, connections, etc., plug it back in and it works for a day or two and
then quits. Any thoughts?~~Ray

If it quits relatively slowly, I'd check for over value resistors, especially
in the screen and cathode circuits. Also check those in series with the plate
circuits (decoupling resistors) as well as in the AVC and oscillator control
grid (high value types).

Heck. Just go through, with the radio disconnected, and check all resistors. If
any measure more than 10% higher than they are marked, replace them.

By the way... I believe you listed all the tubes as glass miniature types, but
intermittent filaments in metal tubes can be checked by feeling for warmth.

73,
Bill, K5BY