• 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.

Quick tube wear question

Miniwatt

Member
2004-11-01 5:46 pm
L.S.

I've been using an amp with a 6.8V heater voltage.. Rather high, isn't it?
It used one half of a 5751 as a driver, all the connections of the other half were grounded.
I'd like to use those 5751 again, but I'm afraid the used half will have worn out too much. Is this realistic? They performed their duties for years..
 

bob91343

Member
2010-03-11 10:43 pm
The specifications for most tubes claim 10% tolerance for heater voltage. For special tubes (maybe including 5751, not sure) they say 5%. You ran those at about 7.5% high so I'd not be too concerned. (The tighter limits on heater voltage for special tubes are only there for consistency of characteristics, not life concerns.)

Having said that, failures in tubes are only rarely in the heater. Go ahead and use them and they will probably work fine.
 
Heater voltage, has NOT been critical in my past 3 months of tube work, It was pointed out a few threads ago, that during the factory burn in of a tube, the heater voltage was ran higher then "normal" for quite some time, and heck, I ran a 2.5v heater in my 866a's on 6+ volts for days, there still working as expected, back on 2.5v



I was told that higher voltage on the filament *could* "clean" your cathode up a little, making the tube work/test better as a whole.


as soon as my new digital tube tester gets here, Ill be testing that exact process to see If i can pump some life into a few super rare tubes I have sitting idle..


copper plate smooth top 7868's anyone? lol
 

taj

diyAudio Member
2005-02-23 8:49 pm
L.S.

I've been using an amp ...
It used one half of a 5751 as a driver, all the connections of the other half were grounded.
I'd like to use those 5751 again, but I'm afraid the used half will have worn out too much. Is this realistic? They performed their duties for years..

I wonder if it would be worthwhile (or useful) rewiring the socket to use the other half. It would quick and simple enough if it's p2p wired.

..Todd
 
some 6922s kept going bad in one of my projects. loud snap n crackle type noises as well as general poor sound. After going thru a nice stash of NOS tubes, I finally vhecked heater voltage, and it was 7.5volts. I've tried the tubes in later projects with correct voltage, and they are still bad. So at least for these tubes, 7.5volts was destructural.
 
Heater voltage, has NOT been critical in my past 3 months of tube work
Not really long enough to tell.

Short periods of over-running a heater will not do much harm, as this is part of the manufacturing process anyway. Longer periods are likely to shorten the cathode life, which is one of the main ageing mechanism in valves. Under-running the heater is also bad for the cathode, but for a different reason.