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Old 22nd November 2004, 11:28 AM   #1
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Default Solid State delay on turn on relay.

Over the course of the time I have been on this board there has been a lot of talk about using a SS rectifier and the worry of cathode stripping and all the associated horrors involved in the use of the nasty animal.

So, I will pose this thought. Would the use of a delay on turn on relay be of a benefit? I was going thru my shelves of junk I ran across a Narional Controls Corporation Model T 1K-120-461 adjustable timer with a range of 1.2-120 seconds delay. This timer when fed a source of 120V will delay the activation of its relay that would control the secondary main from the transformer to the SS rectifier. Thus controled B+ operation after the heaters are on and the tube warmed up. The relay is rated at 10A @ 240V. I'm sure it would withstand higher B+ without a problem.
Also its a octal mount unit that will fit in most rectifier sockets if there is room enough for its body. Just rewire and lable the socket for this device only and I would think it would work.

Any thoughts?
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Old 22nd November 2004, 05:57 PM   #2
mcs is offline mcs  Denmark
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That should work fine. But what is your application? Most tubes have no problems with SS rectifiers. Only large directly heated tubes and mercury vapour tubes actually need a turn-on delay, as far as I know...

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Old 22nd November 2004, 10:19 PM   #3
Wodgy is offline Wodgy  United States
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Believe it or not, Amperite still manufactures the same vacuum tube time delay relays they made in the 30s. Another option to consider.
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Old 22nd November 2004, 10:24 PM   #4
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Quote:

Believe it or not, Amperite still manufactures the same vacuum tube time delay relays they made in the 30s. Another option to consider.

Wodgy do you happen to have a link to the information?

Quote:

That should work fine. But what is your application? Most tubes have no problems with SS rectifiers. Only large directly heated tubes and mercury vapour tubes actually need a turn-on delay, as far as I know...


I was under the impression or misimpression that Solid state rectifiers caused problems in any setup and caused cathode stripping. I figured tube rectifiers were better because of the voltage delay upon startup. So, I was wrong?
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Old 22nd November 2004, 11:45 PM   #5
Wodgy is offline Wodgy  United States
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Amperite's web site is here:
http://www.amperite.com/

They manufacture a variety of TDRs, from extremely vintage to modern solid state. Click on "product info" and scroll down to "time delay relays" or click on "glass tube products" to jump to the tube stuff still in production.
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Old 23rd November 2004, 01:24 AM   #6
mcs is offline mcs  Denmark
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Quote:
Originally posted by burnedfingers
I was under the impression or misimpression that Solid state rectifiers caused problems in any setup and caused cathode stripping. I figured tube rectifiers were better because of the voltage delay upon startup. So, I was wrong?
No, not quite. SS rectifiers can cause cathode stripping. But the problem, as I understand it, is completely theoretical in "normal" tubes. Big transmitter tubes are a different matter, but I guess your not building a transmitter

A power-on delay doesn't cause any problems, but I don't think it's really needed either.

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Old 23rd November 2004, 01:36 AM   #7
Wodgy is offline Wodgy  United States
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There's no real consensus out there on cathode stripping. Everyone seems to agree that it's a real phenomenon for high power transmitter tubes, but there is disagreement about its effect on signal and audio output tubes. Some people (e.g. http://hometown.aol.com/kasman01/weyer.txt ) claim that the effect is more important on low-level preamp tubes than audio power tubes.

Without any convincing evidence either way, IMO it makes sense to be careful if you're going to be using expensive NOS tubes. If you're just using cheap modern tubes, it's probably less of a concern.
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Old 23rd November 2004, 02:40 AM   #8
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Hi,

What IS cathode stripping?

Before you even consider implementing a time delay in order to avoid this you should first look at what can cause it.

The answer is pretty simple: the only way it can be caused under normal conditions is by the user.

It doesn't really matter whether or not your amp/preamp/whatever uses SS rectumfriers or airless bottles: anyone can damage a tube by asking it to do something it either can't or isn't ready to do yet.
IOW let your gear warm up prior to use so it's ready to deliver the current that's being asked of it.
If the tubes' cathodes aren't sufficiently heated up then those cathodes can be stripped to the point that little emissive material remains rendering them utterly useless.

So, if you're careful with your gear you don't need this extra gizmo, after all it too can fail. Remember Murphy?
If you're a guitar player it can be useful in order to keep the amp warmed up...
I wonder how many players actually use that switch once on stage but what do I know.

Simply mute the preamp output while the amp is warming up and nothing can go wrong. Simple as that.

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Old 23rd November 2004, 10:50 AM   #9
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Frank

Thanks for your explanation of cathode stripping.

Not really trying to invent the wheel here but it makes sense to me to use this device to avoid the possibility of cathode stripping.

Quote:

It doesn't really matter whether or not your amp/preamp/whatever uses SS rectumfriers or airless bottles: anyone can damage a tube by asking it to do something it either can't or isn't ready to do yet.
IOW let your gear warm up prior to use so it's ready to deliver the current that's being asked of it.
If the tubes' cathodes aren't sufficiently heated up then those cathodes can be stripped to the point that little emissive material remains rendering them utterly useless.

By using the delay on turn on relay the voltage is delivered after the tube has warmed up.

As to the life span of this device. Being an industrial device it is rated in hundred of thousands of cycles and is virtually fool proof.
I have design control circuits for machines in the past that use repeat cycles and use this same family of controls with no problem. With a use rate of 4 times a day this device would still be running after 300 plus years. I think Murphy would be proud.
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Old 23rd November 2004, 12:09 PM   #10
EC8010 is offline EC8010  United Kingdom
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Quote:
Originally posted by Wodgy
Amperite's web site is here:

http://www.amperite.com/
Good grief! Thanks for that. It never occurred to me that they might still be in production. I think the note at the top of those data sheets ought to be amended from "long life" to "extremely long life."

Thanks again!
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