[GarySP]

Good morning everyone.  Just got back from the MARC vintage electronics expo.  I could have dropped a paycheck on some of the "eye candy" there today.  I picked up some globe tube replacements for the ST tubes in my radio, and then it called out to me.  I've been looking for a reasonably priced tube tester, and stumbled upon a Triplett model 2413 complete with all the instructions and tube charts.  I know it's only an emissions tester, but I'm not hooked on this hobby deep enough to justify the price of a mutual conductance tester (just yet, anyway!). For now, good/bad/questionable for my tubes is better than nothing at all.  The unit works, but I still want to go through it and change the line cord and check internal components.  After a little negotiating, I walk out with the unit for $50.00. OK, committed and commitable phorum gurus, did  I do good, or is the vendor laughing all the way to his wallet??  Take care, Gary. 

[codefox1]

Probably all the tester you'll need for the hobby, and $50 is fair. I'd give the sockets a good cleaning with deoxit and pipe cleaners, and check to see if oft used sockets are tensiond properly.

[GarySP]

OK, gurus. Time to pick your brains a little.  I opened up my tester and found it to be in relatively good shape considering it's age.  I wanted to re-carbon it and change the only cap in it before firing it up, and install a new power cord.  It seems this is a later version of this tester, since it has a factory installed nine-pin socket.  My questions are regarding the resistors in this unit.  While most are old 1/2 watt carbons, about 6 of them are wirewounds.  Am I correct in presuming they used wire wound resistors because they had tighter tolerances than carbon of the time?  The schematic has the values for the wire resistors, but does not specify wattage of the resistors.  I haven't yet taken any readings of the resistors values.  Will do that this weekend.  My next questions are:  Are wire wound resistors subject to age drift like carbon resistors?  If I do elect to change the wire wound resistors, what wattage should I replace them with?  Only one has markings, and it is rated 10 watts.  Also, do I need to install wire wound replacements, or are 1% film resistors able to be used?  Any information provided is greatly appreciated!  Take care, Gary

[Eliot Ness]

Yes, wirewound resistors can be very accurate, especially at lower ohms, plus they have the ability to dissipate more heat.  They also do not drift like carbon resistors so they usually measure good or open.  If your wirewounds measure OK and look good cosmetically (not falling apart) I would leave them in.

As far as replacements go I would stay with wirewounds for their accuracy and heat dissipation.  Without seeing the schematic or the resistors I couldn't say what wattage they should be.  If one is marked 10W then you could probably make an intelligent guess by comparing the size of the others to the one marked 10W.

[GarySP]

Thanks for the info, John.  I'll use your advice.  If the wire wounds Ohm out to spec, they stay in.  All the old carbons are going to be replaced.  Next question is about the rectifier in the unit.  The parts list describes it as a copper oxide 1/2wave B/1 Schauer 2 lead  Triplett part # T-2248-1.  Could not find any data about this particular rectifier.  Do these rectifiers stand the test of time, or should I consider replacement with a diode?  I don't think any real current runs through it based on the fine wire leads coming from it.  They look to be about 22ga. Any thoughts?  Take care, Gary

[Eliot Ness]

Copper-oxide devices are very reliable, so if it's working, I would leave it alone. They're not like selenium rectifiers which most folks feel should be replaced.

[Chuck Schwark]

All the Simpson 2xx series meters have a Copper-oxide rect. in there for the AC scales.
Very reliable, i'd say.

Chuck

[GarySP]

Good morning everyone.  After a brief hiatus, I've gotten back inside my "new" tube tester.  After doing a little testing with my DMM, I decided to replace all the resistors in the unit.  What made it a little difficult is the schematic for the precision resistors show values, but not wattage.  They are all open air units consisting of resistor wire wrapped around pieces of phenolic board.  I ordered 5 watt, 1 percent wirewounds from Mouser.  I hope they will suffice.  The unit has one Aerovox 0.1 MFD 400 WVDC capacitor in it.  I'm replacing that with a 0.1 MFD 630V mylar film cap.  The unit also has a copper oxide half-wave rectifier, which tested open when I put my meter to it.  I'm going to replace that with a 1N4007 diode.  I've always said that I know just enough about electronics to be dangerous, so I'm calling on my Phorum Phriends for input again.  Do you think these replacement parts are correct for the unit, or am I missing something?  Any and all input is appreciated.  Take care, Gary

[Radioroslyn]

I hate to be a party pooper but why don't you put a new tube in it test and see how it reads. If it reads good or very good I'd leave it a lone
Terry

[GarySP]

Hi Terry.  In light of the fact that the rectifier read open when I tested it, I decided to go through the rest of the unit as well.  Several carbon caps were better than 20 percent off spec,  and the capacitor, just as a rule, wasn't to be trusted.  Besides, I am no pro at this hobby.  I figured rebuilding the test equipment would be good practice for more intricate circuitry down the road.  Take care, Gary

[Mondial]

Gary, one thing that may be a problem is replacing the copper oxide rectifier with a silicon diode.

As I seem to recall, copper oxide rectifiers have a very low turn on voltage, which means they begin conducting current in the forward direction at a very low voltage, By contrast, a silicon diode does not begin conducting significant current until the applied voltage reaches 600 millivolts (0.6 V). So depending on the circuit, there may be significant calibration errors at the low end of the meter scale using a 1N4007  silicon diode.

An old fashioned germanium diode like a 1N34, 1N295 etc, may be a better choice as these start conducting around 150-200 mV, which could minimize the error and give calibration closer to the original rectifier.

If you have access to the schematic and can post it, that would be helpful.

[GarySP]

Here are the schematics.

Modernization was done at the factory.

[GarySP]

And here is the parts list.

[GarySP]

Sad to say, I am really computer illiterate.  Like television, I thought this would be a passing fad!  Thanks in advance for all the help. Take care, Gary

[Mondial]

Gary, I looked at the schematic and the copper oxide rectifier was only used for the line voltage test function. The AC line voltage is reduced by the resistive divider of the 75K and 1200 ohm resistors to only a couple of volts, so the turn on voltage of the diode will be significant. You probably will be better off using the germanium diode as mentioned in my previous post. Reverse voltage rating will not be a problem as the diode will see only a few volts in the reverse direction.