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What Op amp was used?
Regards
M. Gregg
It is a CA3240 .
But here is another interesting circuit also from elektor wich makes a small delay to the tube heaters with Re1,wich you can add a thermistor between the contacts C an D for heaters soft start, and after 2 minuts more or less it activates Re2 for the HT supply. Also if needed can be connected an audio signal to the input K1, and when there is no audio signal in this input, the circuit turns off to protect the life of the tubes.
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Yes another interesting circuit..
Have you tried this circuit?
Thank's for posting!
Regards
M. Gregg
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Yes another interesting circuit..
Have you tried this circuit?
Thank's for posting!
Regards
M. Gregg
No, i did not tryed this circuit because at the time i bought this elektor magazines, i was not interested in valve amplifiers,and only recently i am having a better looking to this old elektors and finding old interesting circuits that i can use later in tube amps.
Best regards
I suggest investigating a polyswitch between supply and load. The recovery time from an overload appears to be of the order you require. It should not activate if the supply retains a charge such as turning off and on say to change signal connections, speakers etc. It may be possible to tune the turn on time with a suitable value resistor load in parallel to take the heat off the polyswitch during the turn on process.
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Hi.
Why not make it simpler ?
Increase the supply and add a simple series resistor.
That damps the initial start up current, but still well above the running current. There is mass to heat. All you want is a sligtly lower starting current.
As a starting point i suggest:
Initial resistanse is abt 24 Ohms running, use 12 Ohm series and increase psu by 1.5
have fun.
Edit: worried abt heat loss: after abt 5 sek a relay can change to lower transformet tapping without series resistor.
Why not make it simpler ?
Increase the supply and add a simple series resistor.
That damps the initial start up current, but still well above the running current. There is mass to heat. All you want is a sligtly lower starting current.
As a starting point i suggest:
Initial resistanse is abt 24 Ohms running, use 12 Ohm series and increase psu by 1.5
have fun.
Edit: worried abt heat loss: after abt 5 sek a relay can change to lower transformet tapping without series resistor.
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Thanks, I see there are caveats however polyswitches are slow to trip. Looking now at some datasheets, this is nearly twice the time for the filaments to heat up (judging by the 10 second delay circuit). My original thinking was the polyswitch might to enough to prevent tripping the protection.
Considering reliability now, if the filaments heat up and increase in resistance before the polyswitch trips (the internal melt) the critical point, the load on the supply will reduce accordingly. If meltdown points can be avoided and if it is possible to contrive an arrangement to avoid that with a suitable polyswitch it ought to a little more reliable. You could temper heat effects with a clip on heatsink.
Sometimes Heath Robinson ideas can be made to work sometimes not. Trying things is half the fun.
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