Tube testing question

[BackwardsBoB]

I have a friend. He found out that tube testers, especially a lot of them, get wives really upset. He talked to his ham swapfest buddy, and they decided to do a tube tester calendar to upset wives. His buddy brought him something like 30 tube testers over the years, but he never made the calendar. He did give me a Hickok for safe keeping.

[bob p]

... the tube tester was only used to convince a customer that the tech had not replaced a good tube just to make a buck - a common rumor that circulated in the press that wasn't true of any tech I knew.

Hi Rob. Its been a long time.

You bring up an interesting point about tube testers and honest techs. I've encountered a few less than honest ones. In working on gear for people, I've found capacitors that were installed that were deliberately under voltage for the required application. As you know, if a repairman uses a cap beyond its rated voltage specs, the cap will ultimately fail. Less than honest repair guys would deliberately use lower voltage caps so that the units being repaired could be counted on to fail outside of the 30-day warranty period. I know one fellow who had his gateway CRT monitor repaired 2 times by the same guy for the same problem. i got it when it failed the 3rd time. when i popped the hood, it was easy to see which part had been serviced, and it was a cap that was being used beyond its rated voltage. i repaired the monitor using the proper part, and put an end to the dishonest repairman's revenue stream. i also told the customer exactly what happened and gave them the old part.

much to my surprise, i was reading through an old thordarson catalog and i found an article that specifically addressed ethics in performing repairs on radio gear. the article specifically mentioned the practice of using "condensers" that weren't rated for a high voltage application, just so the customer could be counted upon for return business. the article specifically advised against this sort of thing, suggesting that repair techs should act ethically at all times, so that dishonest behavior would not end up destroying their business.

this sounds a lot like the kind of practice that was referred to by the news media in your TV repair days -- techs deliberately performing improper repairs for customers who don't know any better. the problem is real, and i guess its been around for a long time. thinking about this kinda makes me nervous every time i take my car in for repairs...

[schwimbo]

Can you match power tubes (with a cathode current / plate voltage bias probe) in your amp, but taking out the preamp tubes so as to not have to have them subject to the on-off cycling when you install / remove the power tubes you are testing? I wondered if this would damage the amp (to start it and check idle current but with preamp tubes removed.

[billyz]

It should raise heater and plate voltage a bit. Which will affect your readings. How much? Try it both ways and record your results, then you will know. Otherwise no damage to the amplifier will result. I doubt the the few extra on off cycles will be noticeable to your preamp tubes.

You could also do a hot swap with the standby on . Use a glove or rag to not get burned. Sometimes this is not practical though. I do it all the time when matching and balancing output tubes for an amp.

[Prairie Dawg]

It should raise heater and plate voltage a bit. Which will affect your readings. How much? Try it both ways and record your results, then you will know. Otherwise no damage to the amplifier will result. I doubt the the few extra on off cycles will be noticeable to your preamp tubes.

You could also do a hot swap with the standby on . Use a glove or rag to not get burned. Sometimes this is not practical though. I do it all the time when matching and balancing output tubes for an amp.

It might amount to a hill of beans but not much more.

[schwimbo]

billyz - Thanks for the advice!