View Full Version : HV delay for GS31B??
Hello all, I have seen a couple of schematics that have a delay to allow the filament to heat for 2 minutes before applying voltage to the anode. BUT - most schematics do not show this delay - how important is the delay?
If required, what results from not having the delay in typical ham radio use where the amp is not used daily? shortened tube life? how much?
Thank all of ya'll again for all the help provided.
73 de Ken H>
I have seen a couple of schematics that have a delay to allow the filament to heat for 2 minutes before applying voltage to the anode.
BUT - most schematics do not show this delay - how important is the delay?
Ken -
The components and design for a tube-based HF linear amplifier (glass or ceramic) will vary based on the tube used.
The selected RF tube is the active component -- and hence the remainder of the amplifier is designed (schematics)
for the Care and Feeding of that Tube to the manufacturer's specifications !!
This Thinking/Selection Process is identical to that of an automotive engineer, that selects a specific engine for a new car (or retrofit) design.
That auto engine (the active component) determines the components (transmission, rear end, axle, etc.) that can be used and critieria limits for the final car design --
to optimize for desired / maximum performance !
Bob Locher, W9KNI accomplished DX operator (and CQ DX Marathon award winner) discussed this topic at the September 2010 W9DXCC.
http://www.cq-amateur-radio.com/cq_highlights/2010_cq/04_2010_cq/Apr10Highlights.html
Specifically he talked about the selection of his new HF amplifier for DX usage. He had decided upon ceramic tubes, instead of solid-state devices.
His main decision criteria was to find a tube / amplifier that would provide him with Quick Tune-up Instant-On capabilities --
in other words without a 2 to 5 minutes warm-up/time delay required by many glass or ceramic RF tubes.
RF Triode tube data sheets - G8WRB compiled listing
http://www.g8wrb.org/triodes/
BTW, Bob selected the Ameritron AL-1200 which uses a single Eimac 3CX1200 ceramic triode RF tube.
Here is the Datasheet / Specifications for your Russian GS-31b ceramic triode that you are using in your DIY amplifier build.
http://www.kb2ljj.com/manuals/85-Tubes/Russian%20tubes/GS-31B.PDF
It plainly states: Warm up time in seconds: 120, in other words 2 minutes.
SO, the Russian GS-31b ceramic triode RF tube that you selected -- has answered your quesiton.
w9gb
Thank you for the input, and as I mentioned, I had read (datasheet was one place) the tube required 2 minutes warm up before applying anode voltage, but darn if I can find very many amps using the GS31B tube with this timer circuit included. That led me to wonder just how important it was. I've got a NE555 circuit with a 2 minute delay to drive a 25 amp contact relay if required, but how do all these other folks get away with no timer?
I don't think Steve (WB3WIK) used a time delay on his 8877 6 meter amp, or maybe I missed it?
If it reduces tube life to half - then no big deal as I doubt I'll ever wear a tube out anyway. BUT if there are other valid reasons, then I want to include the timer circuit.
Thanks for the input.
73 de Ken H>
That led me to wonder just how important it was. I've got a NE555 circuit with a 2 minute delay to drive a 25 amp contact relay if required, but how do all these other folks get away with no timer?
It is a matter of proper operation ... either Automatically (having the amplifier maintain that criteria) vs the Operator (remembering to wait for warm-up) for proper operation.
Professional broadcast amplifiers and industrial/medical RF usage -- have the time delays installed. Avoiding human operator error/mistakes.
I don't think Steve (WB2WIK/6) used a time delay on his 8877 6 meter amp, or maybe I missed it ?
You may have missed it.
The G3SEK Triode board includes the warm-up function (automatically) ..
and permits indicator lights on the front panel for reminding the human operator.
http://www.ifwtech.co.uk/g3sek/boards/triode/triode-1.htm
IF this was my amplifier design .. it is a very easy decision.
Install the time delay, to prevent a human operator mistake (or dumb decision).
RF Ceramic Tubes are not cheap ...... and whether it be grid protection or time delay ...
the protection from human error is very CHEAP as far as component costs to save the tube.
You have a nice new surplus tube and already have the parts, so put it in.
For a DX operator ... the last thing he desires is for that mistake to occur at beginning of a major contest :-)
BTW, Paul - G4DCV skipped the time delay for his GS-31b amplifier build -- thinking he would manually wait the 2 minutes.
HOWEVER he realized problems with that approach -- is now going back and adding it (G3SEK Triode Board) !!
http://www.g4dcv.co.uk/GS31/index.htm
w9gb
Thanks for the info, I've read Paul's page several times, and used some of his info. From the bottom of his webpage:
"On the other hand the Triode Board costs more than the cheap Russian tube I am protecting. If I was using an expensive Eimac 3CX1500 I'd certainly use a Triode Board. It's a question of design decisions balanced against cost and risks."
As I said, I'm trying to determine just what the possible costs (blown tube of course), but what are the odds of a blown tube without timer? "IF" HV is applied at same time as filament voltage, will the tube blow "every time"? 1 our of 10? Or does it reduce tube life? Those are the type of questions I'm looking for answers to.
I had thought about a "Pushbutton" to turn on the HV, and each time the power was off, no HV would be applied until the pushbutton was pressed.
73 de Ken H>
WA7PRC
05-15-2011, 08:50 PM
As you might expect, Tom/W8JI has written some about indirectly-heated power tubes.
From http://www.w8ji.com/vacuum_tubes_and_vaccum_tube_failures.htm (http://www.w8ji.com/vacuum_tubes_and_vaccum_tube_failures.htm):
If a cathode material sensitive to positive ions is operated with excessive HV, or has excessive cathode current for the cathode operating temperature, it will suffer emission failure. This is why indirectly-heated tubes or oxide-cathode tubes must have long controlled warm-up times before any cathode current is drawn. We must NEVER operate the 3CX1500A7/ 8877, 3CX800A7, or other oxide-cathode tubes at reduced heater voltage! This would allow the cathode's protective electron cloud to be depleted, and nothing would prevent positive ions from striking and poisoning the cathode.
So, the idea is that the cathode must reach operating temperature before supplying current. It would also be a good idea to ensure the filament voltage/current is above the minimum amount.
That said, I'm of the opinion that the G3SEK boards are an excellent buy - they have control, protection and proper metering built in. I'll be adding a couple more features his board doesn't provide. Yes, his board costs more than the Russian tubes. But, IMO, the board isn't expensive... the tube(s) is/are inexpensive. And the tube being relatively inexpensive, is no reason to forego protection.
We need to get off this kick of making equipment where the cost is the most (and seemingly only) important thing. If I could build the G3SEK board cheaper, I would.
Thank you for the info and link to Tom's webpage Bryan - I had read that page a long time ago, but I didn't remember it. I do have a question - Tom writes:
Always allow full warm-up before allowing any cathode current to flow - Does that mean it's ok for the voltage to be applied to the anode but no keying of amp? For some reason I was thinking the HV could not be applied until the filament had heated for 2 minutes.
If the voltage can be applied, but the amp MUST not be keyed, that is easier to make happen. Just put the time delay in the PTT circuit so the amp can't be keyed for 2 minutes after applying power.
73 de Ken H>
For some reason I was thinking the HV could not be applied until the filament had heated for 2 minutes.
Ken -
You are beating a horse here -- for all the wrong reasons (as Bryan WA7PRC has already noted).
The cost of any of the major components for an HF amplfier are more expensive than the Russian surplus tubes (today).
For proper operation and Long Life of the RF Tube ---- it needs to come to proper and uniform temperature.
Long Ago -- I watched Glass RF tubes crack like eggs ... due to uneven heating.
The GS-31b ceramic triode is a surplus item (USA had tons of WW2 surplus in 1950s and 1960s) ..
it will NOT be available or cheap forever (aka TV sweep tubes, 8873, 8875) ..
and a direct replacement may be unobtainium in 10 years.
The RF tubes control boards are a great idea for the amateur DIY builder --
and serve as the WATCHDOG for the Tube and Amplifier. Your automobile/truck has been using them since the 1990s.
Paul Hewitt, WD7S Triode Control Board has an Adjustable Warm-up Timer that Holds OFF the HV and KEY Lines.
http://home.earthlink.net/~wd7s/triode_control.htm
ADJUSTABLE WARM-UP TIMER; HOLDS OFF HV AND KEY LINES
HV PRESENCE FAULT, HOLDS OFF KEY LINE IF HV NOT PRESENT OR LOW AFTER WARM-UP
ADJUSTABLE GRID OVER-CURRENT FAULT, AUTO-RESET
ADJUSTABLE GRID OVER-CURRENT WARNING LED
ADJUSTABLE PLATE OVER-CURRENT FAULT, SHUTS DOWN HV SUPPLY IN 8.3 MILLISECONDS OR LESS
STEP-START HV TURN ON, (SOFT-START)
TUNE/ARC FAULT, UN-KEYS AMPLIFIER WHEN SEVERELY MIS-TUNED OR DURING TANK CIRCUIT ARC, AUTO-RESET
HV PRESENCE FAULT, HOLDS OFF KEY LINE IF HV NOT PRESENT OR LOW AFTER WARM-UP
AIR FAULT, SHUTS DOWN FILAMENT SUPPLY IF AIR FLOW NOT PRESENT WITHIN 5 SECONDS AFTER POWER APPLIED (AIR SWITCH NOT INCLUDED)
This board is $45 and IF you desire a complete kit of parts, $135
w9gb
WA7PRC
05-15-2011, 09:46 PM
Does that mean it's ok for the voltage to be applied to the anode but no keying of amp? For some reason I was thinking the HV could not be applied until the filament had heated for 2 minutes.
That's what I get out of it.
If the voltage can be applied, but the amp MUST not be keyed, that is easier to make happen. Just put the time delay in the PTT circuit so the amp can't be keyed for 2 minutes after applying power.
I highly recommend reading the manual for the triode board. The answer is not written in words but rather, can be followed by looking at the schematic. It really is a well thought-out unit. I see it'll be easy to add my modification.
I'll follow this thread hoping to get a definitive answer to HV ok, but no current, OR "IF" the HV must not be applied during warmup time.
w9gb: AT $135 for the kit, and after purchasing ALL the off board components the total cost of all his protections would run much closer to $300 or more.
Bryan, I think we're both on the same track here..... except you have so much more knowledge than me:)
73 de Ken H
WA7PRC
05-15-2011, 11:02 PM
I'll follow this thread hoping to get a definitive answer to HV ok, but no current, OR "IF" the HV must not be applied during warmup time.
EP during warmup is OK. IP during warmup is not OK. Both boards prevent this. The WD7S board does this by way of turning EP off.
w9gb: AT $135 for the kit, and after purchasing ALL the off board components the total cost of all his protections would run much closer to $300 or more.
The bare PCB is $45. The PCB w/ all parts is $135. I like that the WD7S board includes the transformer. It would be even nicer if you didn't have to be stuck with either 120 or 240V.
Bryan, I think we're both on the same track here..... except you have so much more knowledge than me:)
It's not so much that I'm smarter,
it's just that I stay with problems longer."
-A. Einstein
I'll follow this thread hoping to get a definitive answer to HV ok, but no current, OR "IF" the HV must not be applied during warmup time.
w9gb: AT $135 for the kit, and after purchasing ALL the off board components the total cost of all his protections would run much closer to $300 or more.
Bryan, I think we're both on the same track here..... except you have so much more knowledge than me:)
73 de Ken H
Unless specified for operation during warm-up, you have to keep current at zero. You can apply full HV without full warm-up, but cathode current must be held below the point where emission saturates.
I can ruin the cathode in a high-power indirectly heated power grid tube in about ten -twenty starts if I warm it while drawing even 10% of rated current. Done that.
I have ruined grids in as little as 30 seconds from excessive grid current by loss of HV or by loss of load or incorrect loading. I remember prototyping a 3CX800A7 amp, and not watching grid current. With improper loading I ruined a new pair of tube in less time than it took me to notice the meter!!!
Metal oxide cathodes are very critical to not exceeding peak emission capability and to grid heating (if gold plated).
By the way, the damage is cumulative with the grid and cathode. It is NOT like the anode, where running it easy or hard makes little difference in life.
Why don't you copy or buy the Ameritron timer/overload board?? One LM358 op amp and it does timing and grid overload. The grid trip is fast!
HV AND HV STEP-START SSR's ARE OFF-BOARD AND USER SUPPLIED)
(AIR SWITCH NOT INCLUDED)
COOL - DOWN DELAY FOR BLOWER, (OFF BOARD)
FULL BREAK-IN QSK USING BUILDERS VACUUM RELAYS, LESS THAN 2.1 MS
Looks like those are the only two things that are user supplied and off board, not as much as I was thinking. I was thinking of SWR protection, but that is a different board.
I do like "ZERO CENTER TUNE METER, DETECTS INPUT AND OUTPUT POWER LEVELS AND DISPLAYS VARIATION FROM OPTIMUM GAIN" and will have to read up more on that.
First I wish to get the amp built with just basic requirements to operate safely and correctly. THEN I'll start looking at bells 'n whistles.
Tom, just saw your post and thanks - I will be looking at the Ameritron timer/overload board - I've got a NE555 circuit worked up for Ip prevention (no PTT allowed), but it doesn't do anything for grid current and might as well look at that also.
Thank you to ALL ya'll for the help - an old man like me needs all the help he can get:)
73 de Ken H>
VK6ZGO
05-17-2011, 03:30 PM
If you have a separate HT "ON" switch,you could simply have a timer which
starts when you switch on the filaments,then after 2 minutes,gives you an "OK"
light,telling you it is safe to turn the HT on.
This doesn't lock out the HT,but simply gives you a warning not to put it
on till it the timer times out.
They used this idea on some old,ex-military gear I worked on years ago, if I
remember correctly.
It is obviously not as good as a full lockout type circuit,as you can still be silly &
turn the HT on too soon,but it is better than no indication of elapsed
time,& can be modified to a full system if required.
Commercial comms staff were more regimented than most hams,& would run
the warmup time longer than the delay just to be on
the safe side, without being tempted to turn the HT on early.
Note: I used the term HT here rather than "Plate Supply" or HV,as it is what we
called it in the old days,when "HT" didn't mean "handie talkie":D
73,VK6ZGO
The amplifier should never allow drive without HV being present, so no matter what you do the antenna relay should be locked out during warmup.
Driving the tube without HV is a sure way to ruin things.
WB2WIK
05-17-2011, 09:53 PM
Like so many amplifiers of days long gone by, it's easy to add an electronic time delay just to the relay key line to assure operating bias and RF drive don't reach the tube until it's warmed up.
I still have some Amperite time delay relay tubes (they're vacuum tubes with a timer relay inside) I used for many years to do this. So did a lot of amplifier manufacturers.
There are solid state time delay relays that will plug into the same sockets as the old Amperite ones, so they're pin compatible. Not that I expect them to wear out. I have some that are over 40 years old and have been through many thousands of cycles and are still fine.