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Lets settle the b+ on cold tubes issue!
Lets settle the b+ on cold tubes issue!
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Old 24th June 2010, 08:22 PM   #101
rmyauck is offline rmyauck  Canada
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I was concerned about the inrush on the filament as that's which seems to really shorten the life of lightbulbs. After reading about inrush current limiters being used on aircraft landing lights (which are very expensive) 10 yrs ago I tried it on a frequently used reg 100W bulb always turning it up and down with the slide pot switch. Lasted 7 yrs! Seemed I was always changing light bulbs before. I also noticed outside lights on photocells last for years as the ones I have slowly power the light up. I don't know about the off part or if down voltage speed matters. Reading the forms made me purchase a 10A variac last year and have used it power old tube amps and radios slowly that haven't been used for years.
This leads me to continue to use it to power up this equipment over a few minutes stopping at around 60v for the longest, then slowly up to 110-115 v as they were designed for 117V max. I try to stay at 111-112V for longer life? Is this good for filament? Maybe a good compromise?
Is this better than inrush limiters which I intend to install. Will this short period of below normal cathode voltage hurt? What about the life of the variac?
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Old 24th June 2010, 08:23 PM   #102
Pano is online now Pano  United States
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Lets settle the b+ on cold tubes issue!
Quote:
Originally Posted by Wavebourn View Post
Did rectifiers in that radios survive? Providing "HT delay" they run with anode voltage applied BEFORE they are hot.
Good question! I don't know... But it's quite possible they went thru a few rectifier tubes before I got them. I'll have to check to only 30s radio I have left.
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Old 24th June 2010, 08:26 PM   #103
Joshua_G is offline Joshua_G  Israel
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Quote:
Originally Posted by jlsem View Post
Who says otherwise?

John
For instance:

Quote:
Originally Posted by ethermion View Post
If you read MJ carefully (or at all), he offers that what does kill a tube is just turning it off and on.
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Old 24th June 2010, 08:37 PM   #104
SY is offline SY  United States
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Quote:
Originally Posted by jlsem View Post
My own opinion is that the best medicine for long term reliability in tube equipment is a thermistor on the primary of the power transformer. Bendix recommended current limiting resistors on the plates of their high-reliability rectifiers and, get this, a 45-second warm-up time for their amplifying tubes but with plate and filament voltages applied simultaneously.
I would agree with your first point- but not because of fears of cathode stripping. It's useful for surge limiting in heaters, power supply caps, and rectifiers.

As for the Bendix data, very interesting!
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Old 24th June 2010, 08:42 PM   #105
BZed is offline BZed  United States
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I've been using and building tube amps for 40 years, not all of them for audio. The only time you need a delayed turn on for B+ is with high power transmitter tubes. Well over 1000 volts, up to 25000VDC and/or amps, not milliamps, of plate current.

It's just doesn't have any affect on tube life in audio amps. Now, the thing that will made a difference is a soft turn on. Thermisters can help or series resistors in the AC primary that are bypassed by relay contacts after some delay both can limit the current surge in the heater circuit and allow the B+ to charge the filter caps slowly saving your rectifier. That is the thing that will help extend the life of your tubes, a slow easy turn on that keeps them from being shocked by sudden full voltage.

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Old 24th June 2010, 08:42 PM   #106
Michael Koster is offline Michael Koster  United States
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Quote:
Originally Posted by Wavebourn View Post
I heard a theory as if 3 Great Pyramids on Giza Plateau are precise aligned to North Pole, and resemble projection of 3 stars in Orion belt in December 2012, in order to stop Earth's crust shift, caused by precession angle and planet's paradise.

Can somebody prove/disprove this "theory"?

The Earth's crust is more valuable than selected quad of EL156 tubes, so it is better to be cautious and believe in the theory, right?
Unproven potential after all. Better safe than sorry

Seriously, if the B+ is applied with the cathode already hot, then it might be a good idea to make sure the g1 voltage is stable and that the g2 and plate voltages come up smoothly with g2 below plate. Also good to think about the case where power is briefly interrupted and restored before the cathode has a chance to cool off. Smooth B+ ramp-up will cover both cases and is IMO all that is needed.

Sure there are other reasons to sequence the B+ but IMO cathode stripping is not one of them.

Last edited by Michael Koster; 24th June 2010 at 08:56 PM.
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Old 24th June 2010, 09:06 PM   #107
el156 is offline el156  Portugal
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Quote:
Originally Posted by Michael Koster View Post
Unproven potential after all. Better safe than sorry
I have several types of tubes in my box, and ONLY the 12AT7 from BRIMAR makes a big Flash in the filament when turned on, almost like a lightbulb,and after a 2 or 3 seconds goes normal, maybe they used different material in the filament?
I think this is not good for the tube .
Does someone has this experience with this Brimar tube?
Silvino
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Old 24th June 2010, 09:17 PM   #108
Wavebourn is offline Wavebourn  United States
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Quote:
Originally Posted by Joshua_G View Post
Different people say opposing things.
Different people may say whatever, but tube manufacturers guarantee lifespan when operated in specs.
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Old 24th June 2010, 09:48 PM   #109
el156 is offline el156  Portugal
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Quote:
Originally Posted by rmyauck View Post
I was concerned about the inrush on the filament as that's which seems to really shorten the life of lightbulbs. After reading about inrush current limiters being used on aircraft landing lights (which are very expensive) 10 yrs ago I tried it on a frequently used reg 100W bulb always turning it up and down with the slide pot switch. Lasted 7 yrs! Seemed I was always changing light bulbs before. I also noticed outside lights on photocells last for years as the ones I have slowly power the light up. I don't know about the off part or if down voltage speed matters. Reading the forms made me purchase a 10A variac last year and have used it power old tube amps and radios slowly that haven't been used for years.
This leads me to continue to use it to power up this equipment over a few minutes stopping at around 60v for the longest, then slowly up to 110-115 v as they were designed for 117V max. I try to stay at 111-112V for longer life? Is this good for filament? Maybe a good compromise?
Is this better than inrush limiters which I intend to install. Will this short period of below normal cathode voltage hurt? What about the life of the variac?
A lightbulb ONLY brakes when it is turned on , i never saw a lightbulb blowing up when is on! why ? do you guys know why?
I would like to know!
Thanks
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Old 24th June 2010, 11:00 PM   #110
BudP is offline BudP  United States
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Lets settle the b+ on cold tubes issue!
Jeez, what a lot of fluff.

If you have a tube amp and you expect your wife to turn it on, or off, you must have solid state rectification and no time buffer for the HT, along with one on off control and one volume control. If your wife is not involved, what difference does it make to a bunch of old farts, fooling around in their man cave, how many different switches must be thrown in the proper sequence?

Back in the day, no one expected their tubes to last forever. Electronics repair shops were legion and all of them had stocks of tubes, due to their limited life time. The tube manufacturers didn't have to be concerned about extended lifetimes, especially for tubes in televisions. Tubes were a commodity and it was a profitable business model to replace them often. We don't live in those times, so why would anyone advocate treating tubes as they were treated, once upon a time, in a far gone land?

AudioPrism got around the issue by adding a 50% extended primary winding as their first switch position step, with both heater and B+ coming on together, and this from the mind of a noted RF amplifier designer. I haven't noticed the tubes lasting any longer or shorter, than what I found with a Dynaco 70. They wear out, no matter what. So, just decide upon the matter by who has to use the amplifier and how complex an arrangement they are going to tolerate.

Or is this the new popcorn corner?

Bud
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