Time delay start board for tube amps

gjo · 26th November 2008, 12:07 AM

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

Sheldon · 26th November 2008, 12:39 AM

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

Akita · 26th November 2008, 12:47 AM

It shouldn't be any problem if you are using tube rectifier.

gingertube · 26th November 2008, 01:48 AM

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

Sheldon · 26th November 2008, 03:23 AM

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

26th November 2008, 12:07 AM	#1
gjo diyAudio Member Join Date: May 2003 Location: Bangalore, India	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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26th November 2008, 12:39 AM	#2
Sheldon diyAudio Member Join Date: Dec 2003 Location: San Diego	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

26th November 2008, 12:47 AM	#3
Akita diyAudio Member Join Date: Dec 2006 Location: Kuala Lumpur	It shouldn't be any problem if you are using tube rectifier.

26th November 2008, 01:48 AM	#4
gingertube diyAudio Member Join Date: Oct 2004 Location: Adelaide South Oz	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

26th November 2008, 03:23 AM	#5
Sheldon diyAudio Member Join Date: Dec 2003 Location: San Diego	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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