Systemic Development > Bipolar System Disorders

I think my System is virtually, finally finished

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steve:
I found out (probably should have known) that the JJ output tubes use solder without lead
in the tube pins. Unleaded solders tend to thin the sound vs quad solders with lead.

So I added some quad solder to the cathode, grid, screen, and plates pins of the KT88s. The sound
did fill out a little. I like both the JJ KT88s and the new Tung Sols (given to me years before the war).

I am also testing lower filament voltage and its effects on life on new, small signal tubes. In general
there are several causes of reduced tube life.

1. Residual gas/ ion bombardment
2. Too high of filament voltage "boiling" off of oxides
3. Too low of filament voltage causing excessive space charge depletion
4. Cathode sleeve impurities causing poisoning of the oxides

It may or may not take some time of use to hopefully arrive at a conclusion or two.

Cheers

steve

steve:
I posted this in another string but I feel it is very important as tubes are getting
quite expensive, especially NOS.

This is not a truly representative test as only 1 used JJ E88cc tube with two sections,
A, B are being tested. I will have to perform more tests with more JJ E88cc tubes for
better overall accuracy but should give us a good indication. Tube has been turned
off just a couple of times so far.

Test started on 8-11-24, measurements below are from 8-15-24.
Very early on, approximately 90 hours, the tube appears stable.

I did make a change from 2 watt to dual 12 watt plate resistors on 8-11
for increased heat related stability. Different RL resistance values A and B
are due to availability from the old parts box.

RL A are two Mills 12 watt resistors in parallel for 7.11K ohms
RL B are two Mills 12 watt resistors in parallel for 7.71K ohms

Voltages and currents are approximates.
           
Filament                  5.85 volts dc

B+ voltage              142
Plate A voltage        71.8 volts
Plate B voltage        63.8 volts

Plate A current         9.86ma
Plate B current         10.13 ma         

We'll see how the tube acts over time.

cheers

steve

steve:
Hear are some results after ~ 450 hours using a used JJ E88cc tube, at ~5.85 filament volts.

The AC line voltage varies slightly, which I can adjust, so there is only a slight DC voltage variations,
but not enough to cause a problem. I can adjust the line voltage for exactly 5.58 filament volts at
measurement times. Military Grade Mills RL's A and B values remain stable since the dissipation 
is only ~0,7 watt dissipation vs 24 watt rating.

Filament                  5.85 volts                  5.85 volts

B+ voltage              142 volts                   141.7 volts
Plate A voltage        71.8 volts                   72.2 volts               
Plate B voltage        63.8 volts                   63.7 volts

Will continue to add hours, and will check in later.

cheers

steve

 

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