I'm am tres confused. I went to bias up a pair of mono blocks the other week
and posted here i was noticing bias drift. Okay, couple of reasons for that I'm
told, thank you. Now, the original amp I was checking seemed like it wouldnt
bias up high enough, so i swapped the rectifier tube with another mullard 5ar4.
biased up.
Later I tested all my 5ar4's on my hicock tube tester doing all the tests and
they tested very strong. I assumed there was no problem with this tube. I stuck
it in my webourne labs mod'd st70 where I had taken the other one from and it
immediately flashes purple when i turn it on before it even warms up. Now, I
swapped a golden dragon in there because it was handy. No problem. so, if the
tube is bad, why did it test perfectly?


P h i l i p

______________________________

"I'm too ****ing busy and vice-versa"

- Dorothy Parker

Fill X wrote:

I'm am tres confused. I went to bias up a pair of mono blocks the other week
and posted here i was noticing bias drift. Okay, couple of reasons for that I'm
told, thank you. Now, the original amp I was checking seemed like it wouldnt
bias up high enough, so i swapped the rectifier tube with another mullard 5ar4.
biased up.
Later I tested all my 5ar4's on my hicock tube tester doing all the tests and
they tested very strong. I assumed there was no problem with this tube. I stuck
it in my webourne labs mod'd st70 where I had taken the other one from and it
immediately flashes purple when i turn it on before it even warms up. Now, I
swapped a golden dragon in there because it was handy. No problem. so, if the
tube is bad, why did it test perfectly?

Did you remember to test it for gas?

Also remember, when you test a tube on a tester, you're not exercising
it to its full potential; rather you're using it at only a small
fraction of its rated capability. When it's in circuit, "soft shorts"
and other manifestations will show up with a vengeance!

Which only underlines -- the only real way to test a tube is in its
actual circuit. Results on testers only give a general idea of the
tube's likelihood to work properly in circuit.

Cheers,
Fred
--
+--------------------------------------------+
| Music: http://www3.telus.net/dogstarmusic/ |
| Projects: http://dogstar.dantimax.dk |
+--------------------------------------------+

as Fred has mentioned, a tester will only place about half the actual
working voltage as the amp will.



"Fred Nachbaur" wrote in message
news:ROihc.62070$dg7.44583@edtnps84...


Fill X wrote:

I'm am tres confused. I went to bias up a pair of mono blocks the other
week
and posted here i was noticing bias drift. Okay, couple of reasons for
that I'm
told, thank you. Now, the original amp I was checking seemed like it
wouldnt
bias up high enough, so i swapped the rectifier tube with another
mullard 5ar4.
biased up.
Later I tested all my 5ar4's on my hicock tube tester doing all the
tests and
they tested very strong. I assumed there was no problem with this tube.
I stuck
it in my webourne labs mod'd st70 where I had taken the other one from
and it
immediately flashes purple when i turn it on before it even warms up.
Now, I
swapped a golden dragon in there because it was handy. No problem. so,
if the
tube is bad, why did it test perfectly?

Did you remember to test it for gas?

Also remember, when you test a tube on a tester, you're not exercising
it to its full potential; rather you're using it at only a small
fraction of its rated capability. When it's in circuit, "soft shorts"
and other manifestations will show up with a vengeance!

Which only underlines -- the only real way to test a tube is in its
actual circuit. Results on testers only give a general idea of the
tube's likelihood to work properly in circuit.

Cheers,
Fred
--
+--------------------------------------------+
| Music: http://www3.telus.net/dogstarmusic/ |
| Projects: http://dogstar.dantimax.dk |
+--------------------------------------------+

My guess is that it has a bit of gas the getter didn't get and from what I
recall ir doesn't take much to glow. I'd measure the B+ and ripple of both
tubes in the amp. My guess is that there won't enough differnce to matter.
If this is the case go ahead and use it but if you see lower B+ or lots of
ripple it might be time to put it up for use when you have no other options
Hank WD5JFR
"Fill X" wrote in message
...
I'm am tres confused. I went to bias up a pair of mono blocks the other
week
and posted here i was noticing bias drift. Okay, couple of reasons for
that I'm
told, thank you. Now, the original amp I was checking seemed like it
wouldnt
bias up high enough, so i swapped the rectifier tube with another mullard
5ar4.
biased up.
Later I tested all my 5ar4's on my hicock tube tester doing all the tests
and
they tested very strong. I assumed there was no problem with this tube. I
stuck
it in my webourne labs mod'd st70 where I had taken the other one from and
it
immediately flashes purple when i turn it on before it even warms up. Now,
I
swapped a golden dragon in there because it was handy. No problem. so, if
the
tube is bad, why did it test perfectly?


P h i l i p

______________________________

"I'm too ****ing busy and vice-versa"

- Dorothy Parker

Fred Nachbaur wrote in news:ROihc.62070$dg7.44583
@edtnps84:



Fill X wrote:

I'm am tres confused. I went to bias up a pair of mono blocks the other
week
and posted here i was noticing bias drift. Okay, couple of reasons for
that I'm
told, thank you. Now, the original amp I was checking seemed like it
wouldnt
bias up high enough, so i swapped the rectifier tube with another
mullard 5ar4.
biased up.
Later I tested all my 5ar4's on my hicock tube tester doing all the
tests and
they tested very strong. I assumed there was no problem with this tube.
I stuck
it in my webourne labs mod'd st70 where I had taken the other one from
and it
immediately flashes purple when i turn it on before it even warms up.
Now, I
swapped a golden dragon in there because it was handy. No problem. so,
if the
tube is bad, why did it test perfectly?

Did you remember to test it for gas?

Also remember, when you test a tube on a tester, you're not exercising
it to its full potential; rather you're using it at only a small
fraction of its rated capability. When it's in circuit, "soft shorts"
and other manifestations will show up with a vengeance!

Which only underlines -- the only real way to test a tube is in its
actual circuit. Results on testers only give a general idea of the
tube's likelihood to work properly in circuit.

Cheers,
Fred

You are correct. I remember one discussion where someone was whining
about tube testers not being 100% accurate. I said that sometimes a tube
that tests good will be bad in circuit, but never have I encountered the
converse.

r


--
Nothing beats the bandwidth of a station wagon filled with DLT tapes.

__ snip ___

Rich Andrews wrote:

You are correct. I remember one discussion where someone was whining
about tube testers not being 100% accurate. I said that sometimes a tube
that tests good will be bad in circuit, but never have I encountered the
converse.


The same holds true for capacitor testers . . . i.e. if a cap checker says
a cap is bad it definitely is; if it says it's good it just might be.

However, it's possible to get useful results by checking three parameters:

1. Measured leakage near rated voltage
2. ESR
3. Measured capacitance

I use three separate testers to check the parameters (wonder if there would
be any "demand" for a tester that did it all).

In my experience old caps are as likely (or perhaps more, depending upon the
set) to fail as tubes are.

- Jon


P.S. - I wonder how the O.P. likes the Welbourne Labs ST-70 mod. IMHO it's
"da bomb."

"Rich Andrews." wrote:

Fred Nachbaur wrote in news:ROihc.62070$dg7.44583
@edtnps84:



Fill X wrote:

I'm am tres confused. I went to bias up a pair of mono blocks the other
week
and posted here i was noticing bias drift. Okay, couple of reasons for
that I'm
told, thank you. Now, the original amp I was checking seemed like it
wouldnt
bias up high enough, so i swapped the rectifier tube with another
mullard 5ar4.
biased up.
Later I tested all my 5ar4's on my hicock tube tester doing all the
tests and
they tested very strong. I assumed there was no problem with this tube.
I stuck
it in my webourne labs mod'd st70 where I had taken the other one from
and it
immediately flashes purple when i turn it on before it even warms up.
Now, I
swapped a golden dragon in there because it was handy. No problem. so,
if the
tube is bad, why did it test perfectly?

Did you remember to test it for gas?

Also remember, when you test a tube on a tester, you're not exercising
it to its full potential; rather you're using it at only a small
fraction of its rated capability. When it's in circuit, "soft shorts"
and other manifestations will show up with a vengeance!

Which only underlines -- the only real way to test a tube is in its
actual circuit. Results on testers only give a general idea of the
tube's likelihood to work properly in circuit.

Cheers,
Fred

You are correct. I remember one discussion where someone was whining
about tube testers not being 100% accurate. I said that sometimes a tube
that tests good will be bad in circuit, but never have I encountered the
converse.


Sometimes tubes that read slightly weak, will work perfectly fine in a
circuit. For example, rectifiers like the 5R4, 5Y3 which "fail" on my TV-7 by
a few points work just fine in circuit.

On Thu, 22 Apr 2004 08:58:01 -0400, Jon Yaeger
wrote:

However, it's possible to get useful results by checking three parameters:

1. Measured leakage near rated voltage
2. ESR
3. Measured capacitance

I use three separate testers to check the parameters (wonder if there would
be any "demand" for a tester that did it all).


The Sencore LC-75 does all 3 tests plus it measures inductance.
Andy Cuffe

thanks for the help, it wasnt glowing in a another amp, when i took it out, but
i took it out because it seemed to not be working properly.


P h i l i p

______________________________

"I'm too ****ing busy and vice-versa"

- Dorothy Parker