I wanted to share some information with the Radio
Museum about the Conar 224 tube tester that may be of value to visitors to your
website, especially those that may have need to repair an inoperable Conar 224
tube tester. Please note this information has to do with the particular Conar
224 tube tester I have in my possession, condition may vary with other Conar 224
tube testers in circulation.
I purchased a Conar 224 tube tester on eBay about 6
months ago, it was advertised in working condition, the outside condition of the
device was pristine, like new, however after receiving the device it failed to
function properly, the seller stated that he/she had tested various tubes with
it and it was in working condition, this was far from the truth regarding the
tube tester condition.
When I received the tube tester I proceeded to
thoroughly inspect the device electronically and found several defects that
needed to be addressed. The tube tester was originally a kit version that
someone had assembled.
The first defect I found was .... when the
transformer was constructed, or when the assembly manual was written for the
Conar 224 tube tester there was an error with secondary transformer wire leads
identification, specifically the wire lead that connects to position 7 of the
rotary switch SW39.
According to the assembly manual and schematic the
transformer wire lead that’s supposed to connect to position 7 of the 18
position rotary switch SW39 is identified with the color code BLK/BRN (manual
revision 179-KM-224), this is incorrect, the actual wire lead color from the
transformer for position 7 of the rotary switch is actually GRN/BLK. Obviously
this wire color identification problem may have been overlooked/missed when the
assembly manual was written and published, perhaps Conar Instruments corrected
this in a later revision, but I felt that it was prudent to pass this
information along to anyone that owns a Conar 224. For the record, my Conar tube
tester has no single primary or secondary transformer wire lead exiting the
transformer with the color combination of BLK/BRN that came with the kit I have
in my possession.
The second defect I found had to do with the 18
position rotary switch SW39. The actual switch assembly was 180 degrees out of
alignment, I suspect that someone assembled rotary switch incorrectly either at
the manufacturer, or the kit builder tampered with it, it had been disassembled
and reassembled incorrectly, causing the switch contact solder points to be 180
degrees out of alignment, thus element voltages would be incorrect for each
position of the rotary switch, obviously, this would more than likely cause
damage to vacuum tubes under test when applying incorrect voltages to the
tubes.
Whomever owns a Conar 224 tube tester should
inspect the rotary switch thoroughly to be absolutely sure the rotary switch
SW39 was assembled correctly before wiring it and applying any power to the tube
tester. Keep in mind that depending on how one views rotary switch SW39.....from
front, back, right side up, or down, of the control panel. One could easily
become confused and assume that rotary switch SW39 was assembled incorrectly by
the manufacturer, or it was tampered with by a kit builder who decided to
disassemble and reassemble SW39 with it being with it 180 degrees out of
alignment, when in fact it was OK the way it was.
The third defect has to do with two secondary
transformer wire leads. Two of the secondary wire leads were exactly the same
color of orange. The schematic states that one lead should be orange and the
other should be brown, however, it was impossible to distinguish one from the
other. The only way to be absolutely sure of which wire is which, is to check
them with a volt meter. Given the circumstances the two transformer wire leads
could be easily reversed if voltages weren't checked. Age could have also caused
the wire lead colors to fade, regardless, it's easy to confuse these two wire
leads. Obviously, the tube tester I acquired
might not be the norm and I just wound up with one that had these issues,
however, whomever might work on one of these tube testers should keep the
aforementioned in mind just in case other tube testers got through with these
defects.
The original Conar 224 power wiring placed the fuse
on the neutral side and routed the neutral through the power on/off line adjust
switch.
Be sure to replace the 2 wire power cord with
a 3 wire ground type power cord, route the line (hot) through the power
switch (line adjust control), and place a fuse in the line side, you'll wind up
with both sides fused, that's OK. Be sure to ground the panel, if you don't
there's a good change you'll encounter ghost voltage, or could under the right
circumstances wind up with a hot control panel. (Refer to Restoration Section 2 for explanation on why to
always route the line side throught the power on/off switch, includes wiring
diagrams).
After correcting the defects the tube tester worked
perfectly.
I hope this information may be of some use to users
of this website.
Bob Krueger,
AB7CQ
Web
Administrator
RPTR 1:
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Email: ab7cqradio@ebidpal.com