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Shall I use a tube plate voltage delay?
Shall I use a tube plate voltage delay?
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Old 21st October 2019, 03:01 PM   #1
JoeAlders is offline JoeAlders  Netherlands
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Default Shall I use a tube plate voltage delay?

Reading Jan Didden's thread about his design of a plate voltage delay circuit, I wonder if this delay is also necessary
when I have a 80V power supply voltage for my headphone amplifier design (ECL82).
Before the tubes are fully starting to conduct the plate voltages are no more than 80V.
I can imagine that if plate voltages are above a few hundred volts and it takes for the heater about a minute
to obtain its maximum emission, tube life will be extended significantly when a delay is used,
but 80V.........
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Old 21st October 2019, 03:05 PM   #2
DF96 is offline DF96  England
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You might need a delay if your supply rail is 600V or more, but normal domestic voltages are fine. Just switch it on or off.
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Old 22nd October 2019, 05:33 AM   #3
PRR is offline PRR  United States
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"Receiving" tubes (for home radio/TV) were built to be hot-started at full rated voltage (300V for this tube) many-many-many times without reduction in life.

Certainly a 300V tube worked at 80V, a readily available TV type, you do not need a delay.

Some folks work 300V tubes at 450V, some turn off/on several times a night, some use tubes so rare that any failure is a costly disaster. You don't have these problems.
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Old 22nd October 2019, 06:22 AM   #4
cerrem is offline cerrem  United States
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Usually the delay circuit is not for the sake of the tubes....as indicated by other responses here... The delay is for other components in the circuit.... If your unloaded B+ produces high enough voltages, then your caps get get over voltaged until the tubes start to conduct... The delay allows the tubes to conduct when the B+ is applied, thus avoiding the voltages stresses that could occur on caps as well as certain tube configuration such as followers and cascodes..where the Cathode to Heater potential can be an issue at cold start-up... Of course it is possible to design your circuits that avoids these pitfalls and is robust....but many of us our dealing with pre-existing circuits...
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Old 22nd October 2019, 06:38 AM   #5
wiseoldtech is offline wiseoldtech  United States
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For decades, manufacturers made quality equipment.
These well-designed pieces lasted through the decades, so did their tubes.
And none of this equipment used any B+ delay stuff, the "delay" stuff started,.. ahem, once the internet came around,... and people with tube paranoia and obsessions warned others "of the dangers" ......oh my!..... "news travels!... believe it!"

Chalk this up to tubes becoming more scarce, prices going up (inflation/greed) and of course our lovely internet blabbering.


Tubes usually have a long lifespan, despite what some people believe.
When you've serviced as many 1930's-1950's radios and console stereos as I have, with originally installed tubes which tested fine, perhaps you'll understand things more clearly.
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Old 22nd October 2019, 07:40 AM   #6
trobbins is offline trobbins  Australia
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It's similar to how something is interpreted as a 'fact' that is then perpetuated by others, such as the start to this thread used "will" ....
Quote:
Originally Posted by JoeAlders View Post
, tube life will be extended significantly when a delay is used,
That said, if your amp over-voltage stresses the filter and coupling caps in your amp during turn-on, or you would like to reduce your fuse size to provide better protection because your amp has expensive or unobtanium parts, then some form of judicious delay may provide a benefit.

Last edited by trobbins; 22nd October 2019 at 07:45 AM.
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Old 22nd October 2019, 08:36 AM   #7
disco is offline disco  Netherlands
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The issue with direct coupled stages (that pull up the grid of the elevated tube at turn on) is that the elevated tube is fully conducting. That puts stress on its filament...
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Old 22nd October 2019, 02:58 PM   #8
JoeAlders is offline JoeAlders  Netherlands
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Quote:
Originally Posted by trobbins View Post
It's similar to how something is interpreted as a 'fact' that is then perpetuated by others, such as the start to this thread used "will" ....


That said, if your amp over-voltage stresses the filter and coupling caps in your amp during turn-on, or you would like to reduce your fuse size to provide better protection because your amp has expensive or unobtanium parts, then some form of judicious delay may provide a benefit.

I always look at components which have to face full power supply voltage at startup. Especially Elco's have my full attention not to exceed their maximum voltage rating.
Was more concerned about the tubes.
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Old 22nd October 2019, 03:00 PM   #9
JoeAlders is offline JoeAlders  Netherlands
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Quote:
Originally Posted by disco View Post
The issue with direct coupled stages (that pull up the grid of the elevated tube at turn on) is that the elevated tube is fully conducting. That puts stress on its filament...

Do not have the intention to build DC coupled audio amplifier stages. If you want to design fast switching
circuits with tubes then you have a point here.
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Old 22nd October 2019, 03:02 PM   #10
JoeAlders is offline JoeAlders  Netherlands
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Quote:
Originally Posted by wiseoldtech View Post
For decades, manufacturers made quality equipment.
These well-designed pieces lasted through the decades, so did their tubes.
And none of this equipment used any B+ delay stuff, the "delay" stuff started,.. ahem, once the internet came around,... and people with tube paranoia and obsessions warned others "of the dangers" ......oh my!..... "news travels!... believe it!"

Chalk this up to tubes becoming more scarce, prices going up (inflation/greed) and of course our lovely internet blabbering.


Tubes usually have a long lifespan, despite what some people believe.
When you've serviced as many 1930's-1950's radios and console stereos as I have, with originally installed tubes which tested fine, perhaps you'll understand things more clearly.

Ah, you have convinced me here!
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