[Amps] Conditioning Spare Tubes After Storage

[Traian]

Hi all amp fellows,

This topic was discussed before and at that time I draw attention about,
but seems that few observed this.

On the very first page of the Harris RF-110A amplifier manual is stated:

"INITIAL START-UP NOTICE
The tubes used in the final amplifier stage of the RF-110A Power Amplifier
may occasionally liberate minute amounts of gas during prolonged storage,
according to the manufacturer. To prevent degradation of performance,
it is advisable to run the tubes without high voltages applied following
storage periods, to remove any gas from the tubes.
Therefore, it is strongly recommended that upon installation of this system,
or following any period of three or more months duration without operating
the system, that the system be run for at least 30 minutes in the STANDBY
mode before going to any operate mode"

Note the "according to the manufacturer" specification.
Note also that, at least for the millitary, storage for long time is not
something unusual (see also the date code for some "surplus" western
and russian tubes)...
The RF-110 include two 8122 drivers and two 4CX1500B finals,
all indirect heated cathode type tubes.

As I know, the getter is intended to remove the very small amount of gas
(i.e. molecules of gas) that may be liberated during the time by the tube's
internal structure. So, important amount of gas, like in the case of broken
seals or important leakage, may not be eliminated by "formating" the
tube and these tubes should be considered out of question (i.e. dead).

Some may notice that for the filament cathode (i.e. thoriated tungsten)
glass envelope tubes the getter (if any) may be located at the anode, so
"formating" the tube with filament voltage only may not help.
For the indirect heated (i.e. oxide) cathodes, the getter is usually
located closer to the cathode  system so the getter may work with
the filament voltage only.

These are confirmed by Joe's experiment.

You may also look to Svetlana Technical Bulletin 54 for some info about.

My conclusion:
I followed the specified procedure (actually let the tubes for few
hours with filament on) and did nothing harmfull to the tubes, hi!


All the best,
Traian



SM0EJR 'Joe' wrote:

> Hello Jeff, Rich, Skipp Et. al
>
> I have had some experience in this....
>
> After buying a few different russian tubes....(GU-43B, GS-35B, GU-84B,
> GI-6B/7B).
> I've made some tests:
>
> I have about 10 of each type, except for the GI-7B, for which I have about
> 20 or so.
>
> Here's the story:
>
> A GS-35B which could handle max 1100 volts before it started to
> 'leak'/spark...
> After 24 hours of heaters on, the tube can withstand 7800 volts on
> Anode-Cathode potential.
> It now works in HF-PA without problem...I don't think it would if I didn't
> do this heating-up!
>
> Another GS-35B had 3kv as upper limit, but after cooking it, a 8 kv limit was
> reached before a leakage 50 microamps occured!
>
> One of the GU-43's had a 2200 volt limit, but after letting it cook for a
> while,
> it can 'take' 6 kv before leaking.
>
> A copule of GI7Bs had about 1500 v, but after ritual, I think at end, I had
> approx 3900 volts on both...
>
> The gadget for these measurements was a K8CU High voltage breakdown tester.
>
> http://www.realhamradio.com/High_Voltage_Breakdown_Tester.htm
>
> I even tried it on 5CX1500A's ( I have four of them on hand )...all were
> about slightly below 6 kv before...
> Not much happened after heating them up...They were already quite healthy!!
>
> So to finalize the whole story:
>
> 1) Western tubes with external anode MIGHT be more stable..
> But I only tried one type of tube..
> I have a 4CX5000A, but no transformer for it's filiament, so I don't know
> that much about that one!
>
> 2) Russian tubes with external anode gains, at least if storage/shelf time
> is long.
> Some tubes were quite good, but wouldn't bet too much on that!!
> The methods for gettering might be different from western tubes?.
> Or just that the sealing for russian tubes is just more leaky, so that you
> have to use
> the mechanism of gettering to solve it  ;o)
>
> So, I WOULD NOT PASS this 'cooking ritual' before kick-starting a new PA
> with russian tubes!!
>
> I don't know anything about the glass-tubes of the GU-81M-type...
>
> Regards
> /Joe
>