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[W4MSL]

I'm new to amplifiers, so try to be nice as I attempt to reduce my ignorance.

I own an Acom 1000, first purchased DEC 2021, then by me JUN 2022. Warranty for parts, sans labor, transferred to me, per Acom. Tube warranty is limited to one year, which is the component of most concern regarding future replacement availability. Right now, all is working splendidly, but w GU-74B prices being what they are and future availability uncertain, I'd like to know what is recommended regarding spares.

1) should spares be tested and known-good before assigning to (hopefully) long-term storage?
2) when is gettering before testing indicated? (I assume warranted and tested tubes from DXE might be exempted from further testing?) I'd be more concerned w a $200 tube from eBay than a warranted $600 one from DXE.
3) what is considered necessary when moving a GU-74B tube from storage to active use?
4) should a known-good spare GU-74B be left alone until needed, or should it be placed into a scheduled rotation so that both two (or more) tubes get used in, for example, six or 12 month cycles?
5) is "in-place" gettering reliable/safe? Cannot find the link of someone who did this w their Acom 1000...if anyone has it, please post.
6) what has been the general experience w "NOS" GU-74B tubes purchased on eBay and at hamfests?

Lots of questions, but lots of ignorance...

Many thanks.

[W7CXC]

Suggest you check out W8JI website.  Some will differ in opinion but I find his info informative.

[W4MSL]

Thanks. And the reason I could not find the info about "in-place" gettering of the GU-74B in an ACOM is because the article was for an ALPHA amp:

https://dh1tw.de/how-to-exchange-the-gu74b-4cx800-tubes-on-your-alpha91b-alpha99-amplifier/

Don't know how or if this could be applicable to the Acom 1000.

EDIT: Memory did not fail. The article I had first seen WAS for the Acom 1000. Here's the link:

https://www.ve1dx.net/acomtube/

[VR2AX]

Hi,
1) 'sans labor' means the component only is under warranty, the time cost or hourly charge of repair and replacement 'time' is at buyer's expense (even under so called warranty - but applicable law to the sale may give additional rights (check)
2) All those tubes are old they are basically Cold War surplus
(3) if the amps in regular use and works it should not need gettering.
(4) gettering for this type of tube (not 3-500z types) is running the tube under filament only (HV voltage removed) for 24 hours If the tube is unused, longer gettering is sensible. Usually done in the amp

Maybe try refocus. Be carful of too much detail. Yes take HV care.

[AE0Q]

(4) gettering for this type of tube (not 3-500z types) is running the tube under filament only (HV voltage removed) for 24 hours If the tube is unused, longer gettering is sensible. Usually done in the amp

Screen voltage should always be removed from a tetrode if the HV is removed.  If not, and the tube is bad, shorted internally, the screen supply could be shorted instead of the HV.  In some amps the screen supply can not take the short like the HV (which is designed to take a short) and the screen supply would fail.

[AJ9C]

I have an Acom 2000A and replaced the tubes a couple of years ago. There is a big deal about gettering and as some other have said opinions may differ. That said, all I did was replace the tubes and turned the amp on without engaging the HV for a period of time (8-12 hrs maybe can't exactly remember), then adjusted the bias for the tubes and was ready to go. Anyone need a 2000A? I purchased a PGXL to go with my Flex and have one for sale. Good luck with your tubes but I have not had any problems in the past.

[AE0Q]

That said, all I did was replace the tubes and turned the amp on without engaging the HV for a period of time (8-12 hrs maybe can't exactly remember), then adjusted the bias for the tubes and was ready to go.

Is there a special maintenance command for enabling the filaments with no screen V or HV applied in the 2000A amp?

[W4MSL]

Is there a special maintenance command for enabling the filaments with no screen V or HV applied in the 2000A amp?

Now that would be elegant sophistication! The only thing I've seen entails  substantial dissembly of the amp to disable HV. The article made no reference to screen voltage, per se, as far as I could tell.

[K6AER]

As a general rule ceramic tetroids do not need getttering for the pin to ceramic bonding does not allow oxygen migration into the tube cavity like glass tubes, 572B, 3-500 etc.

The gettering process requires the anode to be glowing red to enable the gettering process. Running the tube on filaments only will do nothing for the gettering process.

[G4AON]

Not wishing to put anyone off having a spare tube for their Acom 1000, we all tend to have a “squirrel” mentality and feel the need to carry a spare tube… even though it may never be needed.

Vine Antennas in the UK were official Acom dealers before ceasing trading in 2016. They offered tested and guaranteed GU74B tubes, check out their page on the GU74B via the Wayback internet archive:
https://web.archive.org/web/20160114133518/http://www.vinecom.co.uk/

The above makes very interesting reading.

73 Dave G4AON

[M0HDX]

Here is a link on gettering the GU-74B
https://www.qsl.net/gm3woj/conditioninggu74b.htm

jim.

[VR2AX]

(4) gettering for this type of tube (not 3-500z types) is running the tube under filament only (HV voltage removed) for 24 hours If the tube is unused, longer gettering is sensible. Usually done in the amp

Screen voltage should always be removed from a tetrode if the HV is removed.  If not, and the tube is bad, shorted internally, the screen supply could be shorted instead of the HV.  In some amps the screen supply can not take the short like the HV (which is designed to take a short) and the screen supply would fail.

Absolutely correct, I got that wrong. Was thinking triodes such as the GI7B/GI7BT... good catch!

[LZ1VB]

Is there a special maintenance command for enabling the filaments with no screen V or HV applied in the 2000A amp?

Now that would be elegant sophistication! The only thing I've seen entails  substantial dissembly of the amp to disable HV. The article made no reference to screen voltage, per se, as far as I could tell.

There is no special command. Nevertheless it is pretty simple. When installing the new tube (tubes) just do not complete it initially - do not put the plate  to the plate choke connection. Then power up and leave the amplifier in standby mode as long as you want. The screen voltage is off in standby mode.

[KD6VXI]

As a general rule ceramic tetroids do not need getttering for the pin to ceramic bonding does not allow oxygen migration into the tube cavity like glass tubes, 572B, 3-500 etc.

The gettering process requires the anode to be glowing red to enable the gettering process. Running the tube on filaments only will do nothing for the gettering process.

This isn't true.

You do t want to have an external anode tube glowing red.  Yes, for glass ebvelope tubes you do.  For a ceramic, the tube would destroy itself LONG before you ever got color on the anode.

It also isn't true that it has to be glowing red to getter, on tubes such as the one being talked about in this thread.

Install the tube.  Don't connect the anode.  Let filaments run for 24 hours.  Install the anode connector.  Enjoy your amplifier.

I've had problems with Russian tubes buly not following this methodology.  After using this methodology, never had a turn on failure.

Also, your tube isn't an 800 watt tube.  It's a 600 Watt tube. Run it like a 600 Watt tube and lifetime goes up.  A lot.


But, as mentioned, the ceramic style tubes do a lot better sealing the pins than glass tubes ever did.  They still have gassing problems, especially after shelf life measured in decades.

--Shane
WP2ASS / ex KD6VXI

[KX2T]

I find the last comment about the GU74B tube run as a 600 wat tube very interesting it also reminds me of how many AL80 series amps (al80,al80a,al80b) heathkit SB1000, QRO1000 plus I may have left out a few more amps that use a 3-500Z tube which may be rated for 500 watts plate dissipation if properly cooled with a pressurized chamber with chimney. The Acom 1000 has been in production since 1998 or there about, I had first seen the amp at Dayton were Krassi was showing the amp opened up and he said to me "hey look its got a a KW on Six" and my thoughts were wow how to get to know all my neighbors.
These same tubes were designed in before Acom's birth the Alpha 91B  and many contesters bought these amps, many ran them at 2Kw or better all weekend long then Acom brought there A2000 out and many ran the pants off at 3Kw out but at that level they might have had a short life on those tubes but at around 2Kw they did fine and lasted a long time. You may not like Russian tubes at this time but those tubes are allot more rugged than some will make them out to be plus last allot better than 3CX800A7 at and around the 2Kw output level. I have seen a lot more Eimac 800 go south before the GU74B's.
If you run the Acom 1000 around 900W to maybe 1000W pep I see no real issue and on CW right around 800 cause the extra 200W will do nothing on the other end. I have seen some push the amp on You Tube vids for much higher output but at 1200 to 1400 wats you might be taxing the power supply a bit plus generating excessive heat for which the cooling system may not be properly designed. Driven between 60 to 70 watts should give you proper output plus your exciter is not really being pushed at that point but if you kick it in the pants at 100W that is not really needed unless the tube is going south.