I have built a pre amp using an ECC83 and wired the heaters in series.
I have noticed on power up from cold one heater glows considerably brighter than the other for about a second and then things settle down.
Will this damage the valve or could it cause unreliability ?
I have noticed on power up from cold one heater glows considerably brighter than the other for about a second and then things settle down.
Will this damage the valve or could it cause unreliability ?
Hi,
Heater "flash" is common in the 12A_7 valves (especially nasty in many 12AT7's).
You do need a controlled heater warmup for series stringing though - denoted by an "A" suffix in the US numbering system. Don't know what it is for european types.
Cheers!
Heater "flash" is common in the 12A_7 valves (especially nasty in many 12AT7's).
You do need a controlled heater warmup for series stringing though - denoted by an "A" suffix in the US numbering system. Don't know what it is for european types.
Cheers!
Hi,
This problem is typical of series AC or DC heaters operated without a constant current source. The one and only way I know to eliminate this problem is to feed the heater series string with a DC constant current source set for the specific current of the heaters.
I have this set up in my current amplifier project and it works great. My implementation was with an LM317 wired as a constant current source and it is feeding just the front end voltage amp stage and the differential LTP phase inverter tubes.
MickeyStan
This problem is typical of series AC or DC heaters operated without a constant current source. The one and only way I know to eliminate this problem is to feed the heater series string with a DC constant current source set for the specific current of the heaters.
I have this set up in my current amplifier project and it works great. My implementation was with an LM317 wired as a constant current source and it is feeding just the front end voltage amp stage and the differential LTP phase inverter tubes.
MickeyStan
Mickeystan said:
Not that there is anything wrong with using a CCS or a current regulator of some sort, but the fact is certain tubes "flash" whether they are in a series-string or not. It's part and parcel of the heater wire material used by some makers.
BTW, a slow start voltage regulator will work well too - the circuit in the great 1982 National Semiconductor Voltage Regulator Handbook works quite well. IIRC that book has been reprinted, I think the Audio Express/Old Colony people did it but I'm not sure. They do show up on eBay from time to time.
Jim McShane said:
Due to some hum problems I changed from AC heater supply to a DC supply. Its didnt make very much difference to the hum but the flashing has now stopped ! All I use is a half wave rectifier into a 100uF cap to feed the heaters. Its possible the heater voltage is slightly lower and that has stopped the flashing.
Thanks for the advice.
Nigel
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