• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Shall I use a tube plate voltage delay?

JoeAlders

Member
2011-02-12 10:20 am
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.........
 

PRR

Member
Paid Member
2003-06-12 7:04 pm
Maine USA
www.diyaudio.com
"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.
 
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...
 
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.
 
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" ....
, 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.
 
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JoeAlders

Member
2011-02-12 10:20 am
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.
 

JoeAlders

Member
2011-02-12 10:20 am
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!
 

45144

Disabled Account
2011-06-01 12:28 am
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.

I went to electronics school in the 70s and worked as a tech after for a while. I wondered about the B+ delay everyone said was needed for tube circuits. I don't remember seeing it when I did it for a living. I got out of electronics and got into the medical field after a couple of years.

I figured I was just behind on the technology and B+ delay was needed, it seems my memory is correct, maybe?
 

JoeAlders

Member
2011-02-12 10:20 am
I went to electronics school in the 70s and worked as a tech after for a while. I wondered about the B+ delay everyone said was needed for tube circuits. I don't remember seeing it when I did it for a living. I got out of electronics and got into the medical field after a couple of years.

I figured I was just behind on the technology and B+ delay was needed, it seems my memory is correct, maybe?


I got my electronics education in the early and mid 60's of the last century. Tube theory( also semiconductor theory) was given intensively then.
I also cannot recall that plate voltage delay was mentioned at that time. Did a quick search into my books which we were using then and could not find anything about this topic.
 
I got my electronics education in the early and mid 60's of the last century. Tube theory( also semiconductor theory) was given intensively then.
I also cannot recall that plate voltage delay was mentioned at that time. Did a quick search into my books which we were using then and could not find anything about this topic.


Musical instrument amplifiers have used a switch called "standby" which kept the filament supply ON for a faster startup.
I never really understood the reasoning for it, since tubes usually "heat up" and produce "sound" in about a mere 15 seconds. - what's the rush?

Some mid-1960's television sets using tubes also had a "quick-start" feature to speed up picture and sound once the set is turned on. (and larger electric bills)

Basically a selling feature, perhaps geared towards impatient people, as was transistor radios. ("cool running, longer life, instant sound")

These "features" are simple marketing babble created to help sell products.


And of course, this "marketing babble" has naturally migrated to the internet and its hoardes of paranoid worrying souls.
 
I think a large part of the worrying started with a shift away from hollow state rectifiers and the use of solid-state diode rectifiers with their instant on performance. This topic has been debated on this forum several times in the past and the collected wisdom to my mind is that there is nothing that we tend to build on this forum that requires a turn on delay unless the particular circuit has design elements which produce unnecessary stress during start up. if I were to require a delay I would not only consider the excellent finished-product from Jan but also take a look to a DIY option, the circuit posted by member “wavebourne” which ramps the B+ up in proportion to the current being drawn - in other words it carefully pays out the rope as the tube pulls on it.
 
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JoeAlders

Member
2011-02-12 10:20 am
I think a large part of the worrying started with a shift away from hollow state rectifiers and the use of solid-state diode rectifiers with their instant on performance. This topic has been debated on this forum several times in the past and the collected wisdom to my mind is that there is nothing that we tend to build on this forum that requires a turn on delay unless the particular circuit has design elements which produce unnecessary stress during start up. if I were to require a delay I would not only consider the excellent finished-product from Jan but also take a look to a DIY option, the circuit posted by member “wavebourne” which ramps the B+ up in proportion to the current being drawn - in other words it carefully pays out the rope as the tube pulls on it.


That would be still interesting. Can you give the thread link please? Thanks in advance.
 

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A diy option for slow start with ss diode B+ rectifier is presented in section 5.5 on sequencing options in link:
https://dalmura.com.au/static/Power%20supply%20issues%20for%20tube%20amps.pdf

It uses a cheap $2 adjustable time delay relay module from eBay to provide the timing and relay contact, and two modules can be set up to provide the initial delay prior to output stage loading the power supply, and then a slowed rise B+ phase using a NTC, which is then switched out of circuit. That could be a benefit if it allowed a lower rated fuse for mains AC or secondary side protection, or the initial B+ surge voltage could stress filter and bypass capacitors (eg. if mains AC sometimes goes high).
 
All this fussing around, the added complexity of fancy relays and delays - I guess some people are not happy or satisfied with simple, reliable, time-tested designs.
Worrying about capacitor stress and failures, tube life?, then build something properly in the first place.... paranoia sets in, and isn't pretty.
Because all this crap was never implimented before, nor was it needed.
My lovely OLD (and restored) 1963 RCA Victor console stereo with 18 tubes never needed delays and relays, and still doesn't.
And it survived the decades just fine.
Some of the original tubes (date stamped 1962) are still in it and still test good!
 
Not all vintage amps survive for decades, with many examples of replaced power and output transformers. Sure some of that equipment could have won Darwin awards, but there was also a huge kit industry with many thousands of amps made for 'hi-fi', and some models have shown less than stellar long term reliability.

Nowadays forum examples of sad newbs whose newly acquired valve amp has failed in short time with stories of emitted smoke, or damaged tubes or tweeters from tube rolling, or problems from various other actions like replacing electrolytics, or realising too late that their mains AC voltage measured at more than 10% over what was originally designed for.

There is no one view on what is appropriate.
 

disco

Member
2006-04-17 6:27 pm
Holland
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.

Direct coupling is also beneficial to circumphere issues with marginal stable GNF and blocking distortion.