Stark 9-66 tube tester repair
 

I was wondering if anyone out there has any additional information
with respect to the dynamic mutual transconductance circuitry of the
above mentioned tube tester? For instance, there are three coils in
this circuit that must have a certain number of turns and turns
ratios. This would also allude to using a certain wire gauge.

The information I have found on places like BAMA only discusses the
theory of this design and do not specifically address this unit's
intimate repair. Any help here would be useful whereas this
information seems rather illusive. Thanks in advance.

Fabe
CBS, Newfoundland

Stark 9-66 tube tester repair
 

The Canadian Vintage Radio Society has been running a series of
articles on the Stark 9-66 in their newsletters. They covered
optimization and modifications. The author was Murray Dickerson.

http://www.canadianvintageradio.com/AboutCVRS.htm

Perhaps if you contacted them you could get back issues or an address
to contact Mr. Dickerson.

Ed.

Stark 9-66 tube tester repair
 

"WayneJ" wrote in message
news:op.vtkzcetenatzq9@dellilah...
On Thu, 07 Apr 2011 06:09:51 -0700,
wrote:

I was wondering if anyone out there has any additional information
with respect to the dynamic mutual transconductance circuitry of the
above mentioned tube tester? For instance, there are three coils in
this circuit that must have a certain number of turns and turns
ratios. This would also allude to using a certain wire gauge.

The information I have found on places like BAMA only discusses the
theory of this design and do not specifically address this unit's
intimate repair. Any help here would be useful whereas this
information seems rather illusive. Thanks in advance.

Fabe
CBS, Newfoundland



I believe the Stark 9-66 is based on the Hickok tube tester circuit,
either licensed from Hickok or possibly built for Stark by Hickok.
While the circuit may not be completely identical, repair info for
Hickok designs from the 40's and 50's is more readily available and
should be of great assistance.

WayneJ


It not only appears to be built by Hickok, it is identical to the Hickok
533(A)
- even down to an identical drawing number (677W). Even the manual is
the
same with the Stark name substituted for Hickok.

73, Dr. Barry L. Ornitz WA4VZQ

Stark 9-66 tube tester repair
 

Amazing Barry and you are astonishingly right! A detailed calibration
guide is presented here.

http://bama.edebris.com/manuals/hickok/533%28a%29/

However, while the 533A has a good parts list, only the transformer is
specified being possible COTS. I think I read somewhere that the
dynamic mutual conductance test was rather proprietary here? Well, I
have roughed in these parts by only using a hand wound guesstimate.
The original parts where in such bad shape that the number of windings
could not be counted from the shape I received this unit in. BTW I
used a micrometer to center in on the wire gauge which seemed rather
sensible to me.

One of the repairs I did was rather precise though. I sub'ed in a 5K
pot given below and shunted it with a 7.5K resistor to correct for a
solidly seized BIAS pot. 3K on the nose too... and it works just
dandy.

http://uk.farnell.com/colvern/clr400...Ntt=400111S5K0
http://uk.farnell.com/ohmite/23j7k5e...97?Ntt=23J7K5E

These parts can also be imported through Newark. The lead time on the
pot was rather insane though when they were not in stock

I appreciate all your help guys. I would have thought this coil
information would be easy to come by after all this time? While this
unit is testing out triodes well (eg. 12AX7), it is not giving me
impressive results on a tetrode (EL84/6BQ5) or a beam power tube
(6L6). Something is fishy here because I otherwise believe at least
the 6L6 is good. Sounds like a real cal problem here to me!!!!!

Take care and many thanks.

Fabe
CBS, Newfoundland, CA

Stark 9-66 tube tester repair
 

"WayneJ" wrote in message
news:op.vtlmouo7natzq9@dellilah...

Hi Fabe,

You probably know this, but the parts that look like RF coils are wire
wound "precision" resistors. No RF is used in these testers. They are
wound with resistance wire, higher Ohms/foot than copper, so rewinding
with the same number of turns of the same size copper wire will give
the wrong resistance.

Modern metal film 1% resistors can be used to replace any of them, be
sure the wattage is correct. If you want the same appearance to make
an original appearing restoration you will need to use the kind of
tricks used to make old radio restorations appear accurate when using
modern components.

You might need to parallel a couple of values to get the exact value
Hickok used but that is not likely necessary. This tester was
considered to be accurate to about 10% when new.

WayneJ


Excellent advice, Wayne.

The Hickok 533A manual at Bama lists these "spool" resistors. These
precision spool resistors were also used in analog computers. Modern
metal film 1% resistors should work well to replace them.

18670-105RESISTOR, Spool:small, 10 ohmsR9
18670-118RESISTOR, Spool:small, 135 ohmsR28
18670-412RESISTOR, Spool:medium, 41 ohmsR15, R17
18670-417RESISTOR, Spool:medium, 109 ohmsR16, R18
18670-418RESISTOR, Spool:medium, 150 ohmsR14
18679-114RESISTOR, Spool:double, 122 and 32 ohmsR19, R20


73, Dr. Barry L. Ornitz WA4VZQ

P.S. - the more recent tube testers did use ferrite beads on the long
internal leads to suppress RF oscillation.

Stark 9-66 tube tester repair
 

On Apr 7, 9:48*pm, "
wrote:
Amazing Barry and you are astonishingly right! A detailed calibration
guide is presented here.

http://bama.edebris.com/manuals/hickok/533%28a%29/

However, while the 533A has a good parts list, only the transformer is
specified being possible COTS. I think I read somewhere that the
dynamic mutual conductance test was rather proprietary here? Well, I
have roughed in these parts by only using a hand wound guesstimate.
The original parts where in such bad shape that the number of windings
could not be counted from the shape I received this unit in. BTW I
used a micrometer to center in on the wire gauge which seemed rather
sensible to me.

One of the repairs I did was rather precise though. I sub'ed in a 5K
pot given below and shunted it with a 7.5K resistor to correct for a
solidly seized BIAS pot. 3K on the nose too... and it works just
dandy.

http://uk.farnell.com/colvern/clr400...-7-5kohm-3w-5/...

These parts can also be imported through Newark. The lead time on the
pot was rather insane though when they were not in stock

I appreciate all your help guys. I would have thought this coil
information would be easy to come by after all this time? While this
unit is testing out triodes well (eg. 12AX7), it is not giving me
impressive results on a tetrode (EL84/6BQ5) or a beam power tube
(6L6). Something is fishy here because I otherwise believe at least
the 6L6 is good. Sounds like a real cal problem here to me!!!!!

Take care and many thanks.

Fabe
CBS, Newfoundland, CA


Unfortunately that won't work for this pot. It was made with a special
taper and only an original will work.

Stark 9-66 tube tester repair
 

This what happens when you are too old to be new? I confess... I never
heard of spool resistors before but the concept makes sense to me in a
circuit. You see, I am of the age of select on test when 'only one
certain part' will do. To those souls out there... you understand the
process of dating before marriage.

I have restored TO's for the most part so I am in the breed of novice
to you guys. I guess it's back to the drawing board for me. I only see
four though. Two may be considered as doubles being wound on the same
phenolic core?

Unfortunately that won't work for this pot. It was made with a special
taper and only an original will work.

I do have this pot physically apart. It does seems like a linear taper
and the install says it electrically works fine. Accuracy? This maybe
a hung jury here based on these comments. The scale is linear but
given a wet towel snap on what I thought were inductors... anything is
possible.

Thanks for your input all.

Stark 9-66 tube tester repair
 

On Apr 9, 1:08*pm, "
wrote:
This what happens when you are too old to be new? I confess... I never
heard of spool resistors before but the concept makes sense to me in a
circuit. You see, I am of the age of select on test when 'only one
certain part' will do. To those souls out there... you understand the
process of dating before marriage.

I have restored TO's for the most part so I am in the breed of novice
to you guys. I guess it's back to the drawing board for me. I only see
four though. Two may be considered as doubles being wound on the same
phenolic core?

Unfortunately that won't work for this pot. It was made with a special
taper and only an original will work.

I do have this pot physically apart. It does seems like a linear taper
and the install says it electrically works fine. Accuracy? This maybe
a hung jury here based on these comments. The scale is linear but
given a wet towel snap on what I thought were inductors... anything is
possible.

Thanks for your input all.

Well, if it's the same as a 533A then it wouldn't be a linear pot. Did
you go through the calibration procedure? Here is a typical case, the
DC voltage at 22 on the dial is only 3 volts.
http://web.archive.org/web/200602142...aub/cal600.htm

Stark 9-66 tube tester repair
 

Indeed this 3K value is totally non standard, hence the 7.5K shunt on
a 5K pot. If I can find a decent work around to repair this unit in
such precarious predicaments, I will post this information for free. I
always have in other places.

If I could post an internal postmortem pic of a dissected pot, you
would see pot appears to be an linear wire wound. All repairs do take
time and needs the advise of very many good friends.

Once again, thanks for helping out.

Stark 9-66 tube tester repair
 

Thanks to the help of this group, I shunted two 82 ohms and two 220
ohms to get the 41 and 109 values. Thanks to Ohmite for actually
selling a product where I did not need to buy 50 of something to get
some decent precision resistors. Digi Key and Ohmites 40 series was
the deal. The 150 ohms was a off the shelf gift.

Yes, I do need to do a full cal but this ancient repair just swung the
needle from going south.