In experience I have had with tubes checking good but not working in a radio had a lot to do with the design of the circuit they are in. If the circuit doesn't take into account things like plate to grid capacitance and such properly, they can be a problem for high gain tubes. There is a lot of discussion about this if you want to read it. I had an FM tuner that used a 6BE6 mixer that would not work with tubes that were in the normal range on my tester. If I put one with low transconductance in the circuit, it worked fine. Some tubes would even cause an oscillation if they had high enough gain. I did a little circuit redesign and solved the problem of high gain tubes. I don't think you will experience anything like that with a 75A2 so if you find a bad tube with a tester, chances are it will be bad in the radio.
One of the things about using a tube tester is you can find shorted tubes before you put them in your radio. If they are shorted screen to G1 you can cause damage to some radios. A tester will find this type of problem before you put the tube in the socket. I use a Western Electric KS-15650 L2 tester. It is a Hickok and is a transconductance tester. Don't get one that measures emission, look for one that tests transconductance. There are several that will, made by Hickok, B&K and the venerable I-177 made for the military by Hickok and others. One of the things about tube testers is if you get a late model it may not have the test setting for the old tubes. If you get an early model it may not have the sockets and test setting for some of the newer tubes. So I suggest you find an emission tester of later manufacture that has the obsolete tube data available. Are tube testers the end all of repairs? No but used correctly and knowing their limitations, they are a useful tool. Jim/W5JO ----- Original Message ----- >I can see a tube tester in my future... Any recommendations? > Thanks Bob, John WB5CW > > -----Original Message----- > > > > John, Todd is quite right. The only thing for sure with a new > tube is that > it is new. I've had several radios that worked quite well with > tubes that > tested poor to bad. Some receivers will perform well with a fair > tube and > others won't with the same tube, If it works, leave it alone. > Good luck, ______________________________________________________________ Our Main Website: http://www.amfone.net AMRadio mailing list Searchable Archives: http://www.mail-archive.com/amradio@mailman.qth.net/ List Rules (must read!): http://w5ami.net/amradiofaq.html List Home: http://mailman.qth.net/mailman/listinfo/amradio Post: AMRadio@mailman.qth.net To unsubscribe, send an email to amradio-requ...@mailman.qth.net with the word unsubscribe in the message body. This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
