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Extend tube life options..

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Posted on November 24, 2015 at 07:00:09
Nickel Core
Audiophile

Posts: 870
Joined: February 11, 2005
 Hi All,

The BG WKZ capacitors I use in my amp *love* to see B+ all the time. They just keep improving when under power. So I want to keep B+ on all the time.

However, I'm using my last pair of WE300B's now and to extend the life of these tubes I have some options when I'm not using the amp.

1) Lower the filament voltage
2) Increase the bias voltage (lower the current)
3) A combination of 1 and 2
4) Pop out the tubes when the amp is not in use
5) Do nothing and keep the tubes lit.

I wonder if there is some consensus on which strategy would be best to extend the life of my tubes.

Thanks,
NC

 

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RE: Extend tube life options.., posted on November 24, 2015 at 07:23:36
Chip647
Audiophile

Posts: 2653
Location: The South
Joined: December 24, 2012
 You certainly have an issue here.

The failure modes are #1 filament breakage then #2 Emissions. If you really feel that the benefit is keeping your caps charged, you could put in a stand-by switch right before the output transformer B+ in. Then you would need separate power switches for the B+ and the filament supply.

When you are not listening you can flip the stand-by switch to cut the B+ and then switch off the filament supply. Your 300B would see no voltage but the B+ circuit would be fully energized. Then to play, turn on the filament supply for a minute or so before flipping the stand-by switch.

 

RE: Extend tube life options.., posted on November 24, 2015 at 07:27:39
Nickel Core
Audiophile

Posts: 870
Joined: February 11, 2005
 Hi,

Yes... But that would introduce a switch directly in the signal path/current loop.

I'm kind of anal about these things...

NC

 

RE: Extend tube life options.., posted on November 24, 2015 at 09:53:06
tubular.well
Dealer

Posts: 223
Joined: March 4, 2013
 6 - turn off the amp

 

RE: Extend tube life options.., posted on November 24, 2015 at 10:41:44
Nickel Core
Audiophile

Posts: 870
Joined: February 11, 2005
 Which would leave me without B+ which is the whole issue here...

NC

 

RE: Extend tube life options.., posted on November 24, 2015 at 11:08:09
drlowmu
Manufacturer

Posts: 9730
Location: East of Kansas City
Joined: January 10, 2005
 What to choose, none of them seem practical...choose Cancer...or...Polio ?

Go to WIMA DC Link Caps, and MULTIPLE BYPASS them artistically.

Ask Dennis Fraker, he tells me ( JUST LAST WEEK ) the WKZs he used drop to zilch uF when turned-off for awhile. NOT so with a modern DC LINK.

He believes he gets higher performance from a bypassed DC LINK than his WKZs. ( Used by him 1988-2013 ) You need to TALK to him, and get it from the horse's mouth. He just converted a WKZ amp last week or two !! Its fresh on his mind, and his listening experience.

Hope this helps you !! I hope DF doesn't mind me offering his help with what was a private conversation. He's real reasonable NC !! A joy to me.

Jeff Medwin

 

RE: Extend tube life options.., posted on November 24, 2015 at 11:20:23
drlowmu
Manufacturer

Posts: 9730
Location: East of Kansas City
Joined: January 10, 2005
 Anal is OK. !!

In my mid 2015 Type 45 prototype, I used doubled-up 12 AWG ( 9 AWG ) to wire my 120 VAC ALL THE WAY INTO THE PRIMARY WINDING OF THE Power Transformer- took off end bells and replaced lead outs.

Now, I have added a switch to SHORT out my turn-on Thermistor, and Safety Fuse, so its OUT of the circuit for what I call " attended listening ".

Its about a 7 % subjective DEGRADE when I have the fuse and turn-on thermistor in the AC path, on ALTEC speakers, A-7 and A-4s. On a LSES supply, being SOURCE FED, ( not a lot of excess L and C storage ), its the way I like to listen, henceforth.

The A-4 user, presently using my Type 45 amp prototype, ONLY will listen to his audio with my amp switched into the "attended" position when I am not there, 'just sounds better ...'more FUN.

Have fun.

Jeff Medwin

 

RE: Extend tube life options.., posted on November 24, 2015 at 12:52:14
Steve O
Audiophile

Posts: 12383
Location: SE MI
Joined: September 6, 2001
 I'd be inclined to modify bias and filament supplies so at shutdown time: 1. Bias the 300Bs far into cutoff, 2. Turn off filament filament supply. At turn on, reverse order. Nothing added is in signal path while "on" and B+ is on continuously. Since B+ will probably rise w/ reduced load, make sure parts can handle this condition long term.

 

RE: Extend tube life options.., posted on November 24, 2015 at 13:41:19
Paul Joppa
Industry Professional

Posts: 7296
Location: Seattle, WA
Joined: April 23, 2001
 The problem with HV on the plate is ion bombardment (cathode poisoning). This is controlled in operation by the electron cloud, which exists only when the filament is hot.

Traditional best practice is to remove the high DC voltage from the plate, and operate the filament at a lower temperature which balances heat damage against temperature cycling - for long periods of shutoff, it's probably best to shut then down completely, which shorter periods might work best at half voltage.

Note that hot-switching high DC voltage damages switches quickly; the only reliable switch is a vacuum relay. A time delay arrangement might work - switch off the HV supply long enough to discharge the caps, switch off (or down) the filament voltage, disconnect the HV from the tube, then re-activate the B+ disconnect, then re-start the HV supply. This will increase the cap voltage since there is no current drain, of course...

 

RE: Extend tube life options.., posted on November 24, 2015 at 14:01:41
Nickel Core
Audiophile

Posts: 870
Joined: February 11, 2005
 Thanks.

If we are not talking about switching anything off, would increase the bias and lower the filament voltage extend tube life? I can adjust bias to about -110v and filAment voltage to about 1.7 volt.

B+ will be left on for the BG's

Would this help, or are we still running into cathode poisoning and/or other problems?

NC

 

RE: Extend tube life options.., posted on November 24, 2015 at 18:00:17
FenderLover
 Prolly easiest thing to do is pull the tubes, when you aren't going to be using the unit for a period of time. B+ will rise a bit with the tubes out, but it seems that the PSU can handle it. May even like higher voltage? I assume this it has a solid-state rectifier.

The only issue is wearing out the socket and extra handling of those tubes. And hot tubes, too.

 

RE: Extend tube life options.., posted on November 24, 2015 at 18:02:38
Paul Joppa
Industry Professional

Posts: 7296
Location: Seattle, WA
Joined: April 23, 2001
 The filament voltage cannot be reduced very much while maintaining a decent electron cloud. The only thing quantitative I've seen was filament voltage proportional to the 13th root of the current ratio, e.g. at 10% of normal current you would need a minimum of 4.2 volts. That rule is of questionable validity since it was developed for pure (non-thoriated) tungsten filaments.

I would speculate that with a very negative bias, with or without appropriate reduction in filament voltage, the destruction of the cathode surface would proceed as if the amp were operating normally. The more negative bias provides a bit of protection, being more attractive to positive ions, but the reduced current will likely increase the power supply voltage making the ions more energetic and destructive.

Portable tube radios would sometimes switch only the filament power, leaving the high voltage connected. However, these were mostly 45v or 67.5v supplies, and nobody expected these tubes to last more than 1000 hours or so.

I have heard that the best modern 300Bs have ten times better vacuums than WE-produced NOS 300Bs. No idea how valid this information might be, but it's the residual gasses that become destructive ions so I would be extra cautious about leaving the high voltage on such difficult to replace tubes!

Van der Bijl said that oxide-coated filaments are protected from filament volatilization, so lifetime is mostly determined by ion damage to the coating. That was in 1920 though - might be out of date? If that really is the case, then mechanical heating and cooling stresses from cycling the filament on and off may be the bigger danger - suggesting that removing the high voltage with little or no filament voltage change might be a good strategy.

 

RE: Extend tube life options.., posted on November 25, 2015 at 02:14:30
Nickel Core
Audiophile

Posts: 870
Joined: February 11, 2005
 Thanks Paul for this valuable information.

For longer periods I (of course) switch the amp off. I'm looking for a solution for at the end of the day (I mostly listen to music every day).

Looking at your info, it seems best to lower the current a bit when the amp is not in use during the day. Switching B+ is not an option because of the BG's, and all other options are probably introducing more stress on the tubes then just leaving them on all the time.

Thanks,
NC

 

This is not what the O/P asked., posted on November 26, 2015 at 09:13:11
Caucasian Blackplate
Industry Professional

Posts: 8313
Location: Seattle
Joined: June 18, 2004
 More off topic pollution...

 

Why use such silly incompatible caps...nt, , posted on November 26, 2015 at 10:10:38
Balle Clorin
Audiophile

Posts: 781
Joined: July 30, 2003
 nt

 

RE: Why use such silly incompatible caps...nt, , posted on November 26, 2015 at 12:08:31
Nickel Core
Audiophile

Posts: 870
Joined: February 11, 2005
 Incompatible with what? Do you have any idea what they are?

 

RE: Extend tube life options.., posted on November 27, 2015 at 06:54:08
rage
Audiophile

Posts: 793
Joined: December 17, 2010
 how about using a new production set of tubes you like to idle the amp most of the time and drop in your WEs when you listen critically?

I run my 2a3 amp with JJ 2a3-40s on most of the time. Its definitely on a lot more than off.

Out of laziness it just stays on for days sometimes.

the only other thought I have is a set of load resistors to swap in place of the 300B and again keeping the amp on 24x7.

 

REan alterntive... , posted on November 27, 2015 at 14:04:41
Balle Clorin
Audiophile

Posts: 781
Joined: July 30, 2003
 Silly caps silly prices..
they used to cost http://www.hificollective.co.uk/sites/default/files/blackgate_wkz_data.pdf
and now...
http://www.ebay.com/itm/Black-Gate-WKZ-100uF-100uF-500V-550V-Heart-of-Muse-4-available-/181924640105?hash=item2a5b8db569:g:YDAAAOSwQoFWPPum


why not try
some "oil cans"

 

RE: Extend tube life options.., posted on November 28, 2015 at 01:06:13
shane.
Audiophile

Posts: 394
Location: S.A.
Joined: March 27, 2004
 You could from the last cap (break from the OP tube) install a series connected damper diode, heater of such diode would be switched appropriately (relay) and therefore retain the slow enough B voltage ramp up courtesy of the tube rectifier (assume). Good stuff to be thinking about (better than the proposed circuit by a million miles)\\\Shane/

 

"Note that hot-switching high DC voltage damages switches quickly", posted on December 1, 2015 at 08:12:14
Lew
Audiophile

Posts: 10912
Location: Bethesda, Maryland
Joined: December 11, 2000
 I've inserted a hefty over-rated switch between the B+ output of a power transformer and the rectifiers, in order to allow tube filaments to warm up before applying B+ to the input stage of a PP amplifier. Thus the switch sees AC (about 400V), not DC. In one of two monoblocks, I have had a catastrophic failure of the switch, whereas the switch in the other monoblock is doing fine after at least 6-7 years. I had attributed the switch failure to faulty or poor quality construction of the switch, but should I reconsider this method of switching B+ altogether? In other words, is AC voltage as bad as DC voltage for damaging or stressing a switch?

 

Move to Space..., posted on December 14, 2015 at 12:46:18
Lee of Omaha
Dealer

Posts: 1800
Location: Omaha NE
Joined: September 8, 2006
 Tube wear is caused by remnant gas being ionized by electrons crashing into them on their way to the plate and occasionally making it through the electron cloud surrounding the cathode. When an electron bangs into the cathode it can dislodge the weakly attached oxides responsible for emission. When enough collision events have occurred emission goes down and the tube wears out.

In space there are few enough gas molecules so you could remove the glass and the tube would last nearly forever. So all you have to do is move to space to prolong tube life.

 

But...., posted on December 14, 2015 at 13:42:46
Nickel Core
Audiophile

Posts: 870
Joined: February 11, 2005
 Wouldn't there be many more energetic particles present in space which could bang into the cathode compared with the current tube vacuum?

Just asking before I write a checque to Space X ;)

 

RE: But...., posted on December 14, 2015 at 15:53:47
Lee of Omaha
Dealer

Posts: 1800
Location: Omaha NE
Joined: September 8, 2006
 Fewer particles, more energetic. Some could go through the whole cathode, amp, ship, and you. But MANY fewer particles. A highly-evacuated vacuum tube still has billions of gas molecules.

 

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