Another tube that glows orange is VR75.

On Wednesday, October 27, 2021, 05:00:05 PM PDT, Harvey White <madyn@...> wrote:

There's pretty much three types of tubes in terms of what's inside the
envelope.? Don't mean triode, etc.

Voltage regulators, i.e 5651 or OD3, are essentially BIG neon lamps that
glow, and the ionized mixture of gasses has a relatively stable
maintaining voltage.? They act like a big zener diode, high voltage one,
though.

Mercury Vapor rectifiers are rectifiers where mercury has been added.?
In some cases, like the 2D21 thyratron, they fire, then stay fired until
the cathode/plate voltage drops below the maintaining voltage.? They
cannot be turned off, and act like SCRs.

Regular tubes act much like (IIRC) depletion mode FETs.? WIth 0 cathode
to grid voltage, they conduct fully, as the grid voltage goes negative,
the current flow drops until you hit cutoff.

Only the voltage regulators and the mercury vapor rectifiers (which need
a warmup period to vaporize the mercury) are supposed to glow inside at all.

IMHO, any *normal* vacuum tube that glows has an excess of unwanted gas
will glow, and not work properly.

Harvey


On 10/27/2021 6:16 PM, Richard Knoppow wrote:
> ?? I am curious about those glowing tubes. The one that glows pink and
> purple might be very gassy but the only tubes I've seen that glow
> orange are 5651 voltage reference tubes. I wonder if you mght have
> tubes in the wrong sockets or something of the sort.
>
> On 10/27/2021 2:27 PM, Morris Odell wrote:
>> You should replace both tubes as the gassy one at least? looks like
>> it has had a hard life. That might be all you need to get the 200CD
>> going again. BTW the voltages quoted on the schematic are all
>> measured with the unit warmed up i.e. at least 60 seconds after
>> switch-on. I'd be interested to know what the voltage across R40 is
>> once it's working. Depending on how I've recalculated it, it should
>> be between -150 and -180 volts.
>>
>> Morris
>>
>