Testing B7971's

[Mefistofelix]

I am more of a collector than an engineer I'm afraid but I have just got my fabuloso MOD-6_7971 for which I purchased 6 tubes last year, unfortunately I had nothing to test them with when they arrived, and now having installed them, one segment on one tube is out (top right vertical) .

 

I swapped tubes around to prove it was the tube at fault - but wondered if there would have been any way to test these sort of tubes just with a meter ?

 

Meanwhile I am trying to work out whether there is any tube position/font that doesn't involve that segment lighting up until i can find a replacement - there are 4 B7971's on eBay but they are currently at £280 so look as if they will be out of reach !

[David Forbes]

On 2/16/12 3:55 AM, Mefistofelix wrote:
> I swapped tubes around to prove it was the tube at fault - but wondered
> if there would have been any way to test these sort of tubes just with a
> meter ?

Unfortunately, the only way to test a tube like this is to apply high
voltage and see what happens.

--
David Forbes, Tucson AZ

[Mich...@aol.com]

I don't believe there is a direct way to test with simply a volt meter.

 

As for font. - Use stolen.  It may not have had that particular segment stolen; however, it will match the idea between the other tubes having lost segments.  :)

 

Back when I was in a position to not test tubes, I have bought several.  Ended up with more bad tubes (b7971's) than I thought I would.  ouch.   But, I do have a tube that actually lights 2 segments together  (bottom and low-right-diagonal).  Umm, no font that adds segments.

 

The auction for 4 is beyond normal pricing.  There are other others as well.  One issue I believe pricing have gone up is that we are all competing against each other for them.  We should all get together and not bid against each other.  I am SURE it will help.

 

Michail

[Terry Kennedy]

On Feb 16, 10:08 am, Micha...@aol.com wrote:
> I don't believe there is a direct way to test with simply a volt  meter.

Nope. But the MOD-6 has a nice SEGTST function.

I use the MOD-6's power supply, a couple of clip leads, and some 22K
resistors. For partially-poisoned segments, I just parallel more 22K's
(decreasing the resistance) until the segment fully lights, then let
it bake for a bit. That's cleared up the tubes I had with partially-
lit underscores. I have a couple weak tubes where parts of some
segments will go dark at the lower brightness settings.

> Ended up with more bad tubes (b7971's) than I thought I  would.  ouch.   But,
> I do have a tube that actually lights 2  segments together  (bottom and
> low-right-diagonal).  Umm, no font that  adds segments.

I've only ever received 2 duds, both from the same seller. I'll wait
for him to make good before deciding whether or not to name him. One
had the anode wire completely vaporized inside the tube (tested
without current-limiting) and the glass sleeve rattling, while the
other had a bad segment (left-side upper vertical).

I've received tubes that were partially cathode-poisoned and some with
weak segments. Most were recoverable.

> The auction for 4 is beyond normal pricing.  There are other others as
> well.  One issue I believe pricing have gone up is that we are all  competing
> against each other for them.  We should all get together and not  bid against
> each other.  I am SURE it will help.

There's a US eBay seller who frequently lists pairs at $190, buy-it-
now. The duds weren't from him. The best I've done recently is $75-ish
per tube.

[MichaelB]

I like it! That's getting the most out of the MOD-SIX, Mr. Kennedy!

[Mefistofelix]

The tube in question (B7971 with just the one dodgy segment) now on eBay at £0.99p (about $1.50)

 

http://www.ebay.co.uk/itm/260963179117?ssPageName=STRK:MESELX:IT&_trksid=p3984.m1555.l2649

 

Oh - if only perfect ones were still that price !!!

 

[jb-electronics]

> Oh - if only perfect ones were still that price !!!

You might be needing a time machine for that ;-)

Jens