开云体育

I recently bought a 3B3 via ebay, that I got cheap because it had been damaged. The only obvious damage was that one of the long, round, chrome plated chassis rods was badly bent. I thought I had some good, salvaged, 3-series rods so I figured this might be an easy fix.

First surprise: I don't find any chassis rods in my stash of Tek spares. I managed to straighten this one. It's not bad, but if someone has a good one they'd like to part with, I'll pay a reasonable price for one. Note that the 3-series chassis spacing rods are ~12-3/16" long, longer than the 1 or Letter series rods. This is a late rod, with the crimped hex at one end.

Second surprise: One of the 6DJ8s has the getter turned completely white. It had been knocked sideways by whatever had bent the rod, so I figured there must be a crack around one of the base pins, which had been bent. No such cracks appeared, but I finally noticed that the pinch tip at the top of the tube had been completely broken off. Sad, but at least I have a few spare 6DJ8s.

However, this dead 6DJ8 is unusual. There is no etched ID anywhere. In typical red ink, it says NATIONAL, with the National logo, then the Tek part number, 157-0125-00, then MADE IN JAPAN. Oddly, 6DJ8 does not appear anywhere.

The 157-0125-00 is an aged and selected version of the 6DJ8. So, with the Tek part number inked onto the glass envelop, the ageing and selecting must have been done in Japan, by the original manufacturer. Or perhaps they were able to control their production carefully enough to make the ageing and selecting unnecessary. I'd love to know how this was done.

Or maybe this was done so late in Tek history that no one cared. There are some additional numbers in red ink on the tube: 51A, 83781, and 8729. The last one might be a date code.

So, at some point in time (1987?) Tek contracted with Richardson Electronics, in the Chicago area, to make 157-0125-00s (6DJ8s) for them, with the National label on them. Then Richardson turned around and subcontracted them to Japan (Toshiba, Matsushita, Hitachi?) to make the actual tube. I have to assume that this was all done with Tek's approval, but it still seems odd, especially with no 6DJ8 marking. This was probably a very nice tube, and probably still is, except for being full of air and the consequently blown getter.

Have you ever seen a National, or any other brand, tube with the 9 digit Tek part number printed right on it?

--
Jim Adney
Madison, WI USA

Jim,

I had gotten some of those very tubes in the 1990s. I didn't use them until I (tried) to calibrate my 547 a few years ago and found them a little less than wonderful than actual 6DJ8s to the point that I wondered if they were even related to 6DJ8s. They didn't always work well in place of 6DJ8s. I hope you have better luck with yours.

(As I have only 1A1 plug-ins, I can't help you with the chassis rods.)

The aging process for 157-0125-00 is documented on page 36 of the tube aging pdf on tekwiki.



It’s also mentioned on page 110 in the tube specification list which shows the tek part numbers of the raw tubes they would have used and later reassign the part number to the selected one



Nothing about specific brand names but still interesting info if you haven’t seen those documents

On Sat, Apr 12, 2025 at 01:49 PM, Jim Adney wrote:

perhaps they were able to control their production carefully enough to make
the ageing and selecting unnecessary.

AFAIK, the 'aging' was significantly about... but not only about, stabilizing the emissivity of the cathode.
Again... AFAIK... despite decades of research ... the exact mechanics of thermionic emission from oxide-coated cathodes... from substances like barium oxide... remain somewhat mysterious.
At least from the published literature.
I'd speculate that give cathode X, constructed with process Y... the engineers knew that Z amount of hours under process alpha... for instance... achieved a stable emissivity...within the desired specification.
I don't know... but I don't think... the scientists... knew... or even now know... what was happening in microscopic regions, and layers, of the thermionic emissve materials that were used in the manufacture of cathodes.
Even if they did... IMO... its akin to heat treating steel... you may know the final microscopic properties of the material; but, you have no way to effect them directly.
--
Roy Thistle

If CRTs were recently invented and people were trying to improve them, we’d probably see faceplates with cermet bonding to the body using induction heating.

We’d probably see indirectly heated lanthanum hexaboride cathodes or maybe even some sort of diamond or carbon nanotube material possibly as a moderately or even unheated field emitter depending on the beam current density required.

Who knows…with modern high voltage components, electrostatic deflection might be cheaper than large amounts of copper, or even see a hybrid with a horizontal scan via electrostatic and vertical via a yoke for raster displays.

________________________________
From: TekScopes@groups.io <TekScopes@groups.io> on behalf of Roy Thistle via groups.io <roy.thistle@...>
Sent: Wednesday, April 16, 2025 3:31:38 PM
To: TekScopes@groups.io <TekScopes@groups.io>
Subject: Re: [TekScopes] Damaged 3A3 with Unusual 6DJ8

On Sat, Apr 12, 2025 at 01:49 PM, Jim Adney wrote:

perhaps they were able to control their production carefully enough to make
the ageing and selecting unnecessary.

AFAIK, the 'aging' was significantly about... but not only about, stabilizing the emissivity of the cathode.
Again... AFAIK... despite decades of research ... the exact mechanics of thermionic emission from oxide-coated cathodes... from substances like barium oxide... remain somewhat mysterious.
At least from the published literature.
I'd speculate that give cathode X, constructed with process Y... the engineers knew that Z amount of hours under process alpha... for instance... achieved a stable emissivity...within the desired specification.
I don't know... but I don't think... the scientists... knew... or even now know... what was happening in microscopic regions, and layers, of the thermionic emissve materials that were used in the manufacture of cathodes.
Even if they did... IMO... its akin to heat treating steel... you may know the final microscopic properties of the material; but, you have no way to effect them directly.
--
Roy Thistle

On Sat, Apr 12, 2025 at 05:58 PM, PMF wrote:

I had gotten some of those very tubes in the 1990s. I didn't use them until I
(tried) to calibrate my 547 a few years ago and found them a little less than
wonderful than actual 6DJ8s to the point that I wondered if they were even
related to 6DJ8s. They didn't always work well in place of 6DJ8s. I hope you
have better luck with yours.

Okay, then it appears that by this time Tek had given up on trying to provide the same careful spares that they used to provide. In this case, I'm glad that this is the tube that was destroyed.

--
Jim Adney
Madison, WI USA

On 12 Apr 2025 5:58 pm, PMF wrote:

They didn't always work well in place of 6DJ8s.

Unfortunately 6DJ8s have gotten horribly expensive because people who think they are audiophiles (but who lack the requisite theory) have been buying them up to use as audio amps, and then sometimes criticizing the results. That is not surprising - they are not audio tubes. They were designed to be cascode amps in VHF TV tuners. Given that design they were a good choice by Tek.
--
Dale H. Cook, GR/HP/Tek Collector, Roanoke/Lynchburg, VA

Hi Jim,

Quite a bit of vacuum tube tooling was sold of and moved to Japan in the 1970's and 80's, including I believe many small signal pentodes and dual triodes like the 6DJ8. That U.S. built tooling was moved and put back in service in Japan. This was an industry wide cooperative effort. That started in the 60's with the inter-manufacturer's agreement to each produce and specific tube lines and allow rebranding across brands after the fact. The purpose of this was to ensure warranty and service support for tube based consumer devices of many types, without each brand having to absorb the cost of manufacturing of identical types. This effort was a part of the planned end-of-life close down of vacuum tube technology. That was something manufacturers began planning for as far back as the late 1960's. Quite a bit of upper management maneuvering went into the mechanics and logistics of this effort.

The tooling that was sold to Japanese interests was phase 2 of this same inter-corporate strategy, and operated for a number of years - building stockpiles of a large number of unbranded tubes of various types - which were only brand-inked when delivered. This is one reason why one cand find many identical tubes with Japanese origins but familiar "competing" U.S. brand names on them.

This same tooling was eventually sold again, mostly as a tax break, with the plan to move the tooling to South Korea and continue manufacturing with even cheaper labor rates. Unfortunately for the tooling, at the last minute the large U.S. manufacturer making the move discovered that their anticipated business tax break for the move to S. Korea would not pass muster with the IRS. The tooling was never brought online in S. Korea. The result was that quite a bit of tube building equipment was taken out to international waters on a barge and dumped into the ocean for disposal.

re: "bad 6DJ8". A lot of "not 6DJ8" tubes of Russian origin floated around not so long ago. They were deceptively rebranded other types, but with 6DJ8 labeling. They are obvious frauds, but can sort of work in some 6DJ8 applications if you don't mind ignoring the poor performance. :-) But that's a separate issue from these supposedly "bad" Japanese 6DJ8 you guys are discussing.

re: Tube aging. Yeah, so maybe Tek had some magic aging process, but FWIW, manufacturers aged tubes too. In fact, in the golden era of U.S. tube mfg., you could get manufacturers to do with your tubes whatever you were willing to pay for. It was - as always - a unit cost issue. Some tubes were SORTED to higher standards, some were built to higher standards, and some tubes were built to higher standards and then more aggressively sorted out after the fact, to ensure that they were as uniform as possible for key factors like gain, noise, vibration resistance, heater current demands, or whatever the user said was important. Extreme examples include Red Bank dual triodes like the 7591/7592/7593. To my knowledge, Tek never used these very fine tubes, and yet they are by far better than any average 6SN/6SL/6SJ7 ever built by anyone else. So the idea that Tek always had "the best" tubes doesn't hold muster IMO. They had what worked for them at their price point. They picked trusted manufacturers and then maybe they secondarily sorted those tubes using the magical Tek method of deciding what was so wonderful about a subset of those already tested and quality assured tubes.

They didn't throw away the ones that didn't have the magic Tek stamp of approval, either. They just stuck them into applications that didn't require the magic version. It is my opinion that this is why there are multiple Tek p/n for 6AU6 and 12AU6 (for example) Some are "magic" (i.e. aged/sorted/fiddled with whatever) and then the rest of that entire lot became regular generic 6AU6, because no U.S. tube manufacturer was deliberately shipping out measurable quantities of quantifiably bad 6AU6 to Tektronix. That's nonsense.

re: Audiophiles - I know it is easy to hate on them, and there are some extremely silly things afoot in that community at times, but on the whole you should thank your stars that audiophiles continue to create a market for a variety of discrete components, including vacuum tubes. If it weren't for audiophiles and guitar players, the American vacuum tube market would have disappeared a long long time ago. For every guy and gal who loves old Tek scopes like we do, there are a thousands of guys or gals who love tube based guitar amps. Fender Musical Instruments uses more 12AX7/7025, 6L6 and 6V6 than every other U.S. user combined, and it is that kind of volume that maintains interest and support for all things vacuum tube out in the larger electronics community.

Cheers,

Keith