Totally Black B9a glass tube

[Ian Bell[_2_]]

A friend has some 6CG7 tubes that are totally black. They have Tung Sol
JAN written on them and the tube type but other than that they are
completely black. You can't even see the filament glow - and they do
work. Are these some special type of tube?

Cheers

Ian

[Anumber1]

Ian Bell wrote:
> A friend has some 6CG7 tubes that are totally black. They have Tung Sol
> JAN written on them and the tube type but other than that they are
> completely black. You can't even see the filament glow - and they do
> work. Are these some special type of tube?
>
> Cheers
>
> Ian

You are not describing the first generation of USA produced 6cg7 with
the metal can are you?


6cg7A is a glass tube. Straight up 6cg7 has a metal case or at least a
very aggressive RF blocking coating.

This may not translate across the Atlantic well... But I have an example
of such in my collection.

Al

[Bret L]

On Aug 10, 12:44 am, flipper > wrote:
> On Sun, 09 Aug 2009 21:50:54 -0400, Anumber1 >
> wrote:
>
>
>
> >Ian Bell wrote:
> >> A friend has some 6CG7 tubes that are totally black. They have Tung Sol
> >> JAN written on them and the tube type but other than that they are
> >> completely black. You can't even see the filament glow - and they do
> >> work. Are these some special type of tube?
>
> >> Cheers
>
> >> Ian
>
> >You are not describing the first generation of USA produced 6cg7 with
> >the metal can are you?
>
> >6cg7A is a glass tube. Straight up 6cg7 has a metal case or at least a
> >very aggressive RF blocking coating.
>
> Hmm. I never heard of a 'metal case' 9-pin small button noval nor of
> an 'A' 6CG7. 6CG7s are simply 6CG7s, although, I suppose someone might
> have thought it clever to tack an A on.
>
> His is probably graphite coated to reduce 'electron accumulation' on
> the glass. or so I've heard it explained.
>
> >This may not translate across the Atlantic well... But I have an example
> > of such in my collection.
>
> >Al

A lot of such tubes were made for EEG/ECG machines in the late 50s
and early 60s. They were DC coupled and had all sorts of drift issues.

[Ian Bell[_2_]]

Anumber1 wrote:
> Ian Bell wrote:
>> A friend has some 6CG7 tubes that are totally black. They have Tung
>> Sol JAN written on them and the tube type but other than that they are
>> completely black. You can't even see the filament glow - and they do
>> work. Are these some special type of tube?
>>
>> Cheers
>>
>> Ian
>
> You are not describing the first generation of USA produced 6cg7 with
> the metal can are you?
>

NO, I am told it is definitely glass.
>
> 6cg7A is a glass tube. Straight up 6cg7 has a metal case or at least a
> very aggressive RF blocking coating.
>

The latter seems more likely.

> This may not translate across the Atlantic well... But I have an example
> of such in my collection.
>

Could you email me a pic to ianbellATukfsnDOTorg

Cheers

Ian
> Al

[Bret L]

On Aug 10, 2:01 am, flipper > wrote:
> On Sun, 9 Aug 2009 22:54:19 -0700 (PDT), Bret L
>
>
>
> > wrote:
> >On Aug 10, 12:44 am, flipper > wrote:
> >> On Sun, 09 Aug 2009 21:50:54 -0400, Anumber1 >
> >> wrote:
>
> >> >Ian Bell wrote:
> >> >> A friend has some 6CG7 tubes that are totally black. They have Tung Sol
> >> >> JAN written on them and the tube type but other than that they are
> >> >> completely black. You can't even see the filament glow - and they do
> >> >> work. Are these some special type of tube?
>
> >> >> Cheers
>
> >> >> Ian
>
> >> >You are not describing the first generation of USA produced 6cg7 with
> >> >the metal can are you?
>
> >> >6cg7A is a glass tube. Straight up 6cg7 has a metal case or at least a
> >> >very aggressive RF blocking coating.
>
> >> Hmm. I never heard of a 'metal case' 9-pin small button noval nor of
> >> an 'A' 6CG7. 6CG7s are simply 6CG7s, although, I suppose someone might
> >> have thought it clever to tack an A on.
>
> >> His is probably graphite coated to reduce 'electron accumulation' on
> >> the glass. or so I've heard it explained.
>
> >> >This may not translate across the Atlantic well... But I have an example
> >> > of such in my collection.
>
> >> >Al
>
> > A lot of such tubes were made for EEG/ECG machines in the late 50s
> >and early 60s. They were DC coupled and had all sorts of drift issues.
>
> A lot of 'what' such tubes? Metal 9-pinners or graphite coated or
> 6CG7s or...?

Glass miniatures that had unusual features, often an inside coating.

Tubes for scope use had ultra-pure cathode materials to avoid cathode
poisoning or "interface." AFAIK those variants were not used in med
equipment, but other variants were. I have seen many blacked on the
INSIDE but never the OUTSIDE. I have seen TV tubes that were blacked
outside for various purposes.

Most of the tube med equipment was converted in service to solid
state, or at least the EEG/ECG recorders were. When taping those
signals became obsolete, I want to say circa '75 or so, they were
thrown out wholesale, and the transports were sometimes pretty good.
The tape was usable for audio and in those pre-HIPAA days some
hospitals would GIVE you the tapes if you asked as they used them once
or twice and that was it. The formulation was not ideal for audio, but
it was (one of the many types) Drew Alan Kaplan would sell to audio
guys and made a fortune on, like the scam outfit in Seattle that
bought the short ends of cinema film and sold it as 35mm still film.

There were tubes in other kinds of med equipment, legit and quack,
with wildly different requirements as well. Those were a different
issue entirely.

[someone]

On 10 Aug, 00:07, Ian Bell > wrote:
> A friend has some 6CG7 tubes that are totally black. They have Tung Sol
> JAN written on them and the tube type but other than that they are
> completely black. You can't even see the filament glow - and they do
> work. Are these some special type of tube?
>
> Cheers
>
> Ian

like gray glass