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Life of a 45 tube

174.102.197.19
Posted on February 6, 2016 at 15:02:55
PaulF70
Audiophile

Posts: 1427
Location: Midwest
Joined: June 30, 2006
 Is it possible to do a theoretical calculation on the lifetime (hours of use) of a 45 - I'm most specifically interested in NOS globes, but in general.

I've had many 45 amps and many 45 tubes and have had failures - meaning a *premature* end of life - but have never really (that I know of anyway) just run a pair down to wear the measure below minimum.

I'm wondering if someone can tell me what they should/do last based either on calcs (typical operating points) and/or experience.

Thanks!

 

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Depends upon total dissipation, mainly., posted on February 6, 2016 at 18:46:34
drlowmu
Manufacturer

Posts: 9730
Location: East of Kansas City
Joined: January 10, 2005
 Paul,

I learned ( from Dennis Fraker, Serious Stereo.Com ) to set up my DHT finals tubes at a " Golden Ratio " plate dissipation in my DIY amps.

The Golden Ratio is about 62%. So, think of it as a car that can do 100 MPH maximum speed, and run it on the Interstate at 62 MPH. The car will last " for a long time " at THAT speed, as will a 10 Watt rated Type 45 globe, when operated at 6.2 Watts total.

On a 2016 DIY DC two stage Type 45 SE amp, I have calculated 473.11 VDC on the plate, and 236.6 VDC on the cathode, so I am dropping 236.51 VDC P-K at 0.026 A., which is 236.51 times 0.026 A. or, 6.149 Watts plate dissipation, for a 10 Watt ( maximum ) rated plate. Can I get 10,000 hours use? Sure !! How about 20 or 40,000 hours?? I don't know, possibly so.

But run it 250 P-K at 0.035 A. , and you are pulling 8.75 Watts out of the Globe 45....stressful as running your sedan down the Interstate at 87.5 MPH.

My point is this .... YOU can decide how long it lasts, AND ALSO how it sounds, by selecting the op point. I can tell you this, the 8.75 Watt op point, besides wearing the tube out perhaps TWICE as quickly ( as a Golden ratio dissipation ), will negatively SOUND **** STRESSED **** AS ALL GET OUT!!, because the tube IS thermally-stressed.

You are likely a caring and a responsible person, pick your own poison, with the guidelines I follow and have outlined herein.

Have fun.

Jeff Medwin

 

Yep, posted on February 7, 2016 at 07:35:45
Chip647
Audiophile

Posts: 2653
Location: The South
Joined: December 24, 2012
 45 Application Data (These are average normal values)
Class Va Vg1 Ia Ra S Rk Zout Pout
A S/E 250 -50.0 36.0 1,600 2.2 1,500 3,900 1.6 Watts

Exceed Any of the following and you will shorten the tube life:
2.5 Volts on the heater,
The absolute MAX voltage across the tube is 275 (Plate to filament)
Absolute MAX is 10 Watts on the plate (Tube voltage * Current).

I will bet you $1,000 your amp is violating one or more of the above to put out more power. I have 45s that have been used on and off since the 1930's.

 

Please send me a check for $1,000 Chip, posted on February 7, 2016 at 10:35:41
drlowmu
Manufacturer

Posts: 9730
Location: East of Kansas City
Joined: January 10, 2005
 Sorry. You just lost `$1,000.

My operating points were given in my first post, above. You should have read it more carefully. I am at 6.14 Watts dissipation, while you are quoting ( 250 VDC P-K times 36 mA. equals 9.0 Watts dissipation ).

That is like going 90 MPH in a 100 MPH top-speed car. NO WAY would I ever do that, ALSO - it sounds terrible, STRESSED.

I suggested to the O.P. and am driving at 61.4 MPH, as I detailed above.

I will donate all of your payment / $1,000 check to local charities. Thank you.

Jeff Medwin

 

RE: Please send me a check for $1,000 Chip, posted on February 7, 2016 at 13:11:02
Caucasian Blackplate
Industry Professional

Posts: 8313
Location: Seattle
Joined: June 18, 2004
 You should reread his post, as he is mostly agreeing with you.

 

RE: Please send me a check for $1,000 Chip, posted on February 9, 2016 at 10:52:57
charles1dad
Audiophile

Posts: 157
Location: michigan
Joined: January 2, 2009
 Chip647 is definitely agreeing with Jeff's assertions.

 

RE: Life of a 45 tube, posted on February 9, 2016 at 19:29:34
PaulF70
Audiophile

Posts: 1427
Location: Midwest
Joined: June 30, 2006
 Anybody?

Is there anybody here that can throw out ANY figure for life (hours of operation) of a type 45 triode operated as recommended?

 

RE: Life of a 45 tube, posted on February 10, 2016 at 08:42:27
drlowmu
Manufacturer

Posts: 9730
Location: East of Kansas City
Joined: January 10, 2005
 At Golden Ratio dissipation ( 62% ) 10,000 hours minimum to 50,000 hours.

 

RE: Life of a 45 tube, posted on February 10, 2016 at 09:45:29
PaulF70
Audiophile

Posts: 1427
Location: Midwest
Joined: June 30, 2006
 Great - thanks.

 

Yep. (The bet was to the original post, not Jeff's), posted on February 11, 2016 at 13:38:05
Chip647
Audiophile

Posts: 2653
Location: The South
Joined: December 24, 2012
 Jeff is accustomed to people giving him a hard time for his interesting theories.

 

RE: Yep. (The bet was to the original post, not Jeff's), posted on February 12, 2016 at 20:16:57
drlowmu
Manufacturer

Posts: 9730
Location: East of Kansas City
Joined: January 10, 2005
 Yes, I can see that, but your post was UNDER my post, as in a reply. So you were not clear as to WHO you were betting. If you posted it under the OP's post, it would be crystal clear. Have a NICE weekend Chip !

Jeff

 

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