How long should I let my tubes warm up?

[KR4WI]

Hello Crew:: I hear a lot of ops saying I need to let my tubes warm up. I was just wondering what is a good time limit for the tubes say 5r4, 6146, 807 to warm up before applying plate voltage to it? My understanding for warm up time is to keep from damaging the tube. Matthew KR4WI

[WBear2GCR]

I seem to dimly recall that directly heated tubes should be warmed up before B+ is applied to prevent stripping of the cathode? (3-500, 4-400, 811, etc...)

Indirectly heated tubes (6146,807, etc.) have less of an issue in this regard, iirc, but it's still probably good practice to let the fils come up to a nice orange glow before sucking power...

generally speaking 60+secs...

Correct me if I have this wrong, please.

        _-_-WBear2GCR

[w3jn]

Yeah, 60 seconds is fine for the toobs; some big power tubes need a few minutes, others are almost instant heating (811As and 572Bs are two examples). 

Most guys though let stuff warm up for 15 minutes or so to let the internal temp of the rig stabilize so the VFO doesn't go drifting all over the place (assuming the rig in question has a VFO).

If your rig has 866 mercury vapor rectifiers, you should let 'em warm up a few minutes before throwing the plate switch.  Even then those miserable SOBs will arc over and wreck a power transformer.  Better they be replaced with 3B28s or solid stated.  OTOH some like the blue glow and have never had trouble with 866s, me, I don't like to take the chance.

73 John

[K1JJ]

Just to complete the info...

Some indirectly heated power tubes like the 8877 (3CX-1500)  need 90-180 seconds warm-up time before use.

Even the directly heated  YC-156 (3CX-5000) needs at least 6 minutes warm-up before use according to Eimac.

But as said, some directly heated power tubes like the 811A, etc, are instant, though I would give them a minute anyway to decrease the thermal shock to the glass seals, etc before drawing power out of the plates.

Bottom line, for any tube, I like to warm them up a few minutes no matter what they are, and longer if the specs say so.


Of course, with most small tube type gear, you have no choice. The fils and HV are applied at the same time unless you modify it with separate switches.

The question now becomes, "How long should Big G warm up his FETS in his soon-to-be-finished class E rig before use"?


T

[John K5PRO]

Yep. Indirectly heated cathodes, should be turned on 1.5 - 3 minutes before HV is applied, according to Eimac. Look in their datasheets or online catalog for the info applicable to your tube. You don't want to shortcut here, as cathode damage might occur. Most smaller glass tubes are easier, and could be energized in about 30 seconds after heating. Remember, in receivers the HV is applied to them as soon as the filament power is applied. Direct heated (thoriated tungsten filament) power tubes can make RF or audio in about 30 - 60 seconds after power on. 3-500Z is especially good at this, in a matter of seconds. Big TT tubes need 15 minutes at least, for the getter to do its work. Eimac has a separate publication on high power tubes for that, as does Burle Industries (RCA).

[k4kyv]

According to RCA, with directly-heated thoriated tungsten tubes, tube life can be extended by  running the filaments at 80% voltage during standby and switching the voltage instantly to 100% during transmit.

[Jim, W5JO]

If your rig has 866 mercury vapor rectifiers, you should let 'em warm up a few minutes before throwing the plate switch.  Even then those miserable SOBs will arc over and wreck a power transformer.  Better they be replaced with 3B28s or solid stated.  OTOH some like the blue glow and have never had trouble with 866s, me, I don't like to take the chance.

73 John

You got me thinking so I pulled out my trusty RCA TT-5 to check the time required for the 866.  Given proper filament voltage, when the filament is turned on until application of plate voltage is 15 seconds.  For the 3B28 is is 10 seconds. 

These are much shorter times than I had always thought.  Remember I orginated in the time frame when they were the only HV rectifier.  Don't dare laugh!

[w3jn]

Jim, if they're at room temp, and you use the xmitter regularly, you're prolly OK.  But I had a Glob Queen 400 that apparently hadn't been used in a while, and that damn thing blew a fuse first time I threw the plate switch.  I replaced the 866s with 3B28s, no further problems. 

Then there was my Valiant, it's a wonder I didn't blow the power tranny in that one for the 866 arc overs.  I solid-stated that one.

I **hate** 866s.

73 John

[Jim, W5JO]

I don't use them either John, for the same reasons you mention.  When I was training to become a JN, my elmer told me to let them warm for about 10 minutes.  The RCA book has a coupla pages of general information about them, particularly the hash they can create.

My practice has always been that if 866s or any merc type tube hasn't been used in a long time, to leave it on for about 30 mins so the mercury will evaporate and get any deposits out of the tube elements, particularly if they have been stored on their side.  Just good practice.  I was surprised to see the book didn't call for a longer warm up time.

I replaced or replace them in all my equipment.  I have the plug in SS rectifiers in my Glob King 500A.

73  Jim
w

[WBear2GCR]

Hey now!

Wonder if you can use a Mercury Vapor light bulb as a rectifier?? 
Good glow action... 

              _-_-bear

[k4kyv]

Hey now!

Wonder if you can use a Mercury Vapor light bulb as a rectifier?? 
Good glow action... 

              _-_-bear

Back in the late 20's and early 30's they used to do that. There was a particular type of mercury lamp that looked like a giant light bulb, with two electrodes sticking out each side.  Those served as plates for a fullwave rectifier.  Instead of a filament, the bulb used an arc.  You started the arc by tilting the rectifier bulb.  To keep the bulb from self-destructing from the heat, the base was submerged in a bath of transformer oil.  There are pictures and descriptions of the contraption in the early editions of ARRL Handbook.

[KB2WIG]

All,
     I'm cooking an art-13 thats been sleeping for 30+ yrs.... No HV yet as I don't have the plywood for the lv and HV supply(s) yet. The 13' has (2) 811A, (2) 1625, (1) 813 and a few others. My QueSTion fer ues is how long to cook the filiments??  I've put 8 hrs on her so far today......      klc

[Gary - WA4IAM]

Hey now!

Wonder if you can use a Mercury Vapor light bulb as a rectifier?? 
Good glow action... 

              _-_-bear

Back in the late 20's and early 30's they used to do that. There was a particular type of mercury lamp that looked like a giant light bulb, with two electrodes sticking out each side.  Those served as plates for a fullwave rectifier.  Instead of a filament, the bulb used an arc.  You started the arc by tilting the rectifier bulb.  To keep the bulb from self-destructing from the heat, the base was submerged in a bath of transformer oil.  There are pictures and descriptions of the contraption in the early editions of ARRL Handbook.

An old timer friend of mine has one of those "kick start"rectifiers still mouted in its original swivel base. Very cool!