12AX7 failure

Yikes!!

a) If the tube was Chinese, 6 weeks of "on-time" would be a lot in some cases. b) Current-production tubes are readily available. Not for free, and one may vastly over-pay, but it is not as if it were a 19T8 or some- such. c) After determining that the equipment itself was not at fault, then yes s&*t-can the tube and move on.

Peter Wieck Melrose Park, PA

So? Most tubes were only 90 day or one year warranty when they were in full production. It wasn't uncommon to replace a failed tube, under warranty. There are a lot of things that are involved in MTBF.

An interesting link, for further analysis of what could bring the demise of

of

Could you check the URL

googling 1 c or cc or subdirectories, or similar domain got nowhere, unusually. Nothing found via kloth.net domain whois

-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on

Yes, indeed. But I guess that we are interested in those which we can influence. Like e.g. (?)

- heating before applying anode voltage,

- avoiding long periods without anode current,

- ??

Regards, H.

I hear that presently there are only russian and chinese productions going on. Hard to get at - if you'd agree that an eBay-buy from Ukraina or China is somewhat "hard" :-).

I think that most of the post-war radio tubes are available only as NOS (ECH81, EF4x, EF8x,ELxx ...). Somebody should make some fivehundred EM34/35 and earn himself a good meal.

Generally I found that to buy tubes is a lottery except if you have a known and trustworthy dealer. Many deaf nuts being handed around.

Regards, H.

Useless on low power vacuum tubes that are not used in some bizarre circuit. Its a different matter on high power transmitter tubes.

How about this link?

Oh, Omer (Polly). What are we to think of you? Sigh.

-ex

nope, and networksolutions.com says that doesn't exist as a domain either.

Jeff

Same problem here.

I googled vaccuumtubefans and all I got was pointers back to this thread.

The fellow who parroted and corrected another guy's link has a reputation for not having verified his sources of info. Nuff said.

Back up and check the attributes Bill, The only one Omer is parroting is himself.

Jeff

Your kind posting shares a property with many usenet postings: It provokes the most valuable question: "Why?".

Regards, H.

Try this one!

Omer

Why, what? Have you ever seen any provable problems with low power receiving tubes, or ar you just another tube freak repeating fairy tales and folklore? Do you have decades of real experience with all types of vacuum tubes behind you, or are you YAKIAH?

In article , Heinz Schmitz wrote:

So the real question is, is there anyone out there that can give a comprehensive answer as to why?

Even the belief stated above that "Its a different matter on high power transmitter tubes" with respect to "heating before applying anode voltage" appears questionable.

Some 45 years ago I worked at several different stations as a broadcast engineer and the old-timers there trained us young kids to be sure we thoroughly warmed up the filaments before applying the plate power. The precise reasons for doing this were never made completely clear. With the notable exception of one newly installed RCA BTF-10D,the vast majority of the transmitters I worked with used mercury vapor rectifiers, one even used two stacked banks of mercury vapor rectifiers to provide the 17 kV B+ voltage. Obviously in transmitters using mercury vapor rectifiers it is necessary to warm the rectifier filaments up before applying power to the plate transformer(s), since dire things would transpire if the mercury wasn't properly vaporized before the rectifiers where hit with power from the plate transformer(s). But ignoring the mercury vapor rectifiers was it really necessary to warm up the power tubes before applying plate power? I was surprised a few years back to read in the instruction manual for a tube transmitter the statement that it was not necessary to warm up the power tube filaments before applying plate voltage! And they weren't just saying that the automatic sequencer would take care of the correct sequencing of the filament and plate power, the statement made clear that they were talking about actually applying filament and plate power to the tube simultaneously. I found this surprising since I had been trained to warm up the power tubes before applying the plate voltage, and there are other reasons for warm up, so I asked about this on a forum or newsgroup, the exact one has escaped me. A current broadcast engineer replied and said yes that was true, it was generally not necessary to warm up most power tube filaments before applying the plate voltage. He did go on to explain that this was not universally the case however and said there were certain types of tubes that did need to be warmed up first, but I have forgotten what the reason was that he gave, probably something about filament construction or material.

So does anyone have a comprehensive explanation of this cathode warm up issue, for both low power and high power tubes?

Very funny ;o) At least I know how the taskman works! - JP

Not funny! I didn't think of taskman, and had to shut down the computer to get out of it. Nelson