Tube Testers: Threat or Menace?

[Jeffhs]

Tube testers probably will make a comeback, if they haven't already. There are brand-new tube-type high-power home-theater amplifiers being offered for sale these days, and for good reason. Any real audio purist will tell you the only way to get real high fidelity sound from an audio system is by using tubes in the output stages. Solid-state amplifiers, even those with high-power output transistors, cannot hope to match the warm sound of audio processed using vacuum tubes. (Those of you who have old radios such as high-end Zeniths, et al. with push-pull or other types of hi-fi audio stages will know what I mean.) When those tubes short or become weak, there will have to be some way to test them (short of physically replacing the defective tube with a new one).

This is where tube testers come in. Until or unless high-power home-theater audio systems are again designed with transistors some years from now (however, I don't see that happening any time soon, if at all, for reasons I mentioned above), we will be seeing quite a few HT audio amps with vacuum-tube output stages. The tube tester used to ascertain the condition (cathode emission, etc.) of these tubes need not be anything fancy such as a mutual-conductance (Gm) tester or an in-circuit one like the old Hickoks, etc. I would think any type of emission tester would do just fine to test the bottles in these new home-theater amps, as long as the tubes are not so new as not to be listed on a recent ('60s-'80s) tube chart.

[Tubejunke]

Originally Posted by Jeffhs

I would think any type of emission tester would do just fine to test the bottles in these new home-theater amps, as long as the tubes are not so new as not to be listed on a recent ('60s-'80s) tube chart.

I run into that problem even with old tubes. It's why, besides physical characteristics like not having a certain type socket, I have several testers. I would like to have one, but it just doesn't work that way.

And as far as new tubes and equipment go, I have nothing that tests something like the EL34 which has been common for years now. There should be a similar old school tube that one could use as a reference to set up an old tester.Thank God for the popularity of the 12AX7 and I believe the 6LG and maybe 6SN7. I can handle those.

[miniman82]

Originally Posted by Tubejunke

And as far as new tubes and equipment go, I have nothing that tests something like the EL34 which has been common for years now. There should be a similar old school tube that one could use as a reference to set up an old tester.

My Eico 625 does 6CA7's, and a lot of other funky tubes too. Pretty sure it came out in the late 50's, so your tester much be a lot older I'm guessing? It does list a procedure for trying 'new' tubes, so it should be possible to figure out settings for one not listed. (pdf page 7, manual page 6)

http://diyaudioprojects.com/Testeq/E...ons-Manual.pdf


Perhaps the manual of your unit says something similar?

[Tubejunke]

Originally Posted by miniman82

My Eico 625 does 6CA7's, and a lot of other funky tubes too. Pretty sure it came out in the late 50's, so your tester much be a lot older I'm guessing? Perhaps the manual of your unit says something similar?

I didn't even think about subs. If the 6CA7 is an older sub for an EL-34, then I could just use those settings for a test. I know that amp tubes like the EL-34 aren't new news by any stretch. However, the part # doesn't go back as far as a lot of, probably most of, the vintage scrolls provide data for. Out of the 4 or 5 testers that I have, I am sure that more than one will do the 6CA7.

Heck, although I do play guitar and have one tube amp, I don't expect to be worried about any EL-34s soon if ever. My Epiphone is circa late 50s. No octals; just miniatures.

[maxhifi]

Originally Posted by Tubejunke

I didn't even think about subs. If the 6CA7 is an older sub for an EL-34, then I could just use those settings for a test. I know that amp tubes like the EL-34 aren't new news by any stretch. However, the part # doesn't go back as far as a lot of, probably most of, the vintage scrolls provide data for. Out of the 4 or 5 testers that I have, I am sure that more than one will do the 6CA7.

Heck, although I do play guitar and have one tube amp, I don't expect to be worried about any EL-34s soon if ever. My Epiphone is circa late 50s. No octals; just miniatures.

European tube designations start with letters, American ones start with numbers. E is a 6 volt filament L is a power pentode, and 34 is the sequential number. 6 is a 6 volt filament CA is the sequential desinator, and 7 means 7 elements inside the tube, i.e. a pentode. The reason it is 7 for a 6CA7 is the supressor grid is brought out as a separate element, unlike the 6L6 where the beam forming plates are internally connected to the cathode.

All that said, when the EL34 was introduced in North America, in the 1950s, it was called the 6CA7, under the American naming convention. It's exactly the same tube, just under an American title. Other examples exist, for example

EL84 = 6BQ5
ECC83 = 12AX7
GZ34 = 5AR4

And on and on and on All are european tubes with American designations, probably to make them easier to sell and categorize in existing US inventory systems at the time.