Regenerating pumped tubes
Technical literature states that an
"exhausted" electronic tube can, after
regeneration, function
again for 3000 hours with characteristics close to those specified
by the manufacturer.
In the past, this practice was common for cathode ray tubes that
equipped televisions.
Indeed, the cost of these tubes justified this operation. This was
less the case for common tubes that equipped vintage radios.
Today, given the rarity of some of them, it may be worthwhile to perform this operation. Thorium and barium are the two materials used to increase the emission capability of cathodes. After a few thousand hours of operation, enriched cathodes, whether directly or indirectly heated, no longer deliver enough electrons.
Regeneration consists of bringing back to the surface the "electron reserve" still present at the core. During this operation, the cathode is overheated and a higher than normal anode voltage is applied.
The secret to good success lies in
An economical solution often used to increase the voltage heating consists of a full-wave rectification and solid filtering of the nominal alternating voltages intended for the tubes to be rejuvenated.
For example, 6.3V rectified in full-wave and filtered with a 15000µF electrolytic capacitor gives a quasi-DC voltage of 7.5V for a heating current of 1A and 8.1V for a heating current of 0.1A. The overvoltage ratio is therefore between 120% and 129%.
In the circuit described later, a transformer supplying 4 V for tubes heated under this voltage is available. The anode voltage will be obtained from 2 HT windings of 300V each, i.e., 600V rectified - or 420V RMS. In the case of pentode regeneration, grid G2 will be connected to the rectified 300V.
Today, given the rarity of some of them, it may be worthwhile to perform this operation. Thorium and barium are the two materials used to increase the emission capability of cathodes. After a few thousand hours of operation, enriched cathodes, whether directly or indirectly heated, no longer deliver enough electrons.
Regeneration consists of bringing back to the surface the "electron reserve" still present at the core. During this operation, the cathode is overheated and a higher than normal anode voltage is applied.
The secret to good success lies in
- the filament overvoltage rate (overheating)
- the anode voltage
- the duration of the operation.
An economical solution often used to increase the voltage heating consists of a full-wave rectification and solid filtering of the nominal alternating voltages intended for the tubes to be rejuvenated.
For example, 6.3V rectified in full-wave and filtered with a 15000µF electrolytic capacitor gives a quasi-DC voltage of 7.5V for a heating current of 1A and 8.1V for a heating current of 0.1A. The overvoltage ratio is therefore between 120% and 129%.
In the circuit described later, a transformer supplying 4 V for tubes heated under this voltage is available. The anode voltage will be obtained from 2 HT windings of 300V each, i.e., 600V rectified - or 420V RMS. In the case of pentode regeneration, grid G2 will be connected to the rectified 300V.
An example of implementation
The device
At the center of the device, a transformer with secondary voltages
of 4V, 6.3V, 2x300 V RMS.
The principle
- A rectified and filtered voltage higher than the nominal voltage is applied to the filament for 2 minutes.
- Then the push button is pressed; this has the effect of applying the 600 V half-wave rectified voltage to the anode. The latter changes color and goes from dark red to light red. The push button is then released. In the case of a pentode, the screen grid is connected to the rectified 300V via a 50KΩ resistor.
- It is allowed to cool for 20 minutes. The lamp is ready for use.
The case of rectifier tubes
Regenerate only one
anode at a time!
Example of implementation
The use of 2nd transformers (2x250V, 6.3V) will allow processing the
different types of tubes.
This may be necessary for television tubes of the P series or all-current tubes of the U series. I also suggest adding a second complete radio transformer providing, for example, 250 volts and 6.3 volts.
This may be necessary for television tubes of the P series or all-current tubes of the U series. I also suggest adding a second complete radio transformer providing, for example, 250 volts and 6.3 volts.
You can combine different heating voltages and especially increase the high voltage for power pentodes,
such as EL34, EL500, PLxx which require an even higher regeneration anode voltage.
With the second transformer, a second 250 Volt is thus available which, placed in series with the 600 volts,
will give approximately 850 volts aiming to regenerate the power tubes.
And if you design your system finely, you will thus have approximately: 250, 300, 550, 600, 850 V.
