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Old 26th November 2008, 01:07 AM   #1
gjo is offline gjo  India
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Default Time delay start board for tube amps

Folks

I have a couple of tube amps-a 2A3 and an EL 34 pp, both without time delays-unlike an earlier amp which had a 30 second delayed start. Sophia electric has these available for $25 for retrofitting.

Could anyone advise whether these are recommended for longer tube life?

TIA

George
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Old 26th November 2008, 01:39 AM   #2
Sheldon is offline Sheldon  United States
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A lot of talk about tube life and time delay. Delay can't hurt, but? I have seen reports that suggest shortened life with high voltage (1kV+) transmitter tubes. Yet to see any such evidence for typical lower voltage audio amps. Anyone?

Sheldon
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Old 26th November 2008, 01:47 AM   #3
Akita is offline Akita  Malaysia
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It shouldn't be any problem if you are using tube rectifier.
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Old 26th November 2008, 02:48 AM   #4
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George,
I have 1 amp with time delay high voltage switching and 8 or so amps without.

The amp with the delayed high voltage switching is an 845 SET Amp which runs a high voltage of 850 Volts.

The delay is NOT there to prevent "Cathode Stripping" or anything like that.

It is there because it has a choke input power supply. The supply is effectively "unloaded" until the tubes warm up and start conducting. The voltage of the supply would rise to probably something over 1000 Volts and Blow Up the filter caps (2 x 450V caps in series). The HV delay prevents that.

If your power supply is such that the voltage does not exceed the filter capacitor rating when tubes are not conducting then it is my view that the delay is a waste of money. IF the power supply voltage goes very close to, or exceeds the capacitor voltage rating when unloaded then it is a good invetment.

Cheers,
Ian
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Old 26th November 2008, 04:23 AM   #5
Sheldon is offline Sheldon  United States
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Good point Ian. I model all my supplies in PSUD and check both loaded and unloaded (actually very low load) voltages. I make sure my parts can tolerate the unloaded state. Protects against failure due to tube failure or open circuit. If parts rated high enough for no load are impractical, then the delay will work if everything else is OK.

Sheldon
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