Does the max voltage between cathode and heater specified by valve type refers to DC steady state values or the AC componets also should be taken in to account?
Thanks in advance
Thanks in advance
morfeas,
The Vhk max rating is a bit of a 'soft' rating, in that it is measured at a certain amount of leakage current, which may or may not be a standard between manufacturers.
I tend to try and keep Vhk as small as practicable in the circuit, so as not to stress the fragile heater-cathode insulation - which might lead to shortened life (though I've yet to meet a valve which died because of heater-cathode insulation failure - it's one way to make your own DHTs 😀)
By the way, I can't see the graph you posted, rich... Or was it an e-mail?
The Vhk max rating is a bit of a 'soft' rating, in that it is measured at a certain amount of leakage current, which may or may not be a standard between manufacturers.
I tend to try and keep Vhk as small as practicable in the circuit, so as not to stress the fragile heater-cathode insulation - which might lead to shortened life (though I've yet to meet a valve which died because of heater-cathode insulation failure - it's one way to make your own DHTs 😀)
By the way, I can't see the graph you posted, rich... Or was it an e-mail?
Hi,
No?
Let me tell you up front that sound of agony is not a pretty one...
Try keeping heater to cathode voltage within about 30V, less is even better. (Equipotential)
Once above 30V the chance of the heater emiting is a real one although it won't take too long before it will be exhausted.
And no, you don't turn a IDHT into a DHT one by shorting heater to cathode....Tsssssssskkkkk.
Cheers,😉
No?
Let me tell you up front that sound of agony is not a pretty one...
Try keeping heater to cathode voltage within about 30V, less is even better. (Equipotential)
Once above 30V the chance of the heater emiting is a real one although it won't take too long before it will be exhausted.
And no, you don't turn a IDHT into a DHT one by shorting heater to cathode....Tsssssssskkkkk.
Cheers,😉
Pffbt, heater is rated for +/-80V in most cases... I keep it within +30V most of the time. Heater should be positive with respect to cathode so it doesn't act as a parasitic diode and grab extra hum and noise.
Tim
Tim
Thanks for the replies.
But let me get a little bit more practical. Let’s take ECC81 for example that specs record 90Vhk max. Say the cathode sits on 80V steady state and the swing is 100Vpkpk. Half circle the heater to cathode will be 130V.
Will this be a problem?
But let me get a little bit more practical. Let’s take ECC81 for example that specs record 90Vhk max. Say the cathode sits on 80V steady state and the swing is 100Vpkpk. Half circle the heater to cathode will be 130V.
Will this be a problem?
The datasheets I can find don't state a DC value, so it appears to be not a question of peak and average but rather, do you want to risk this. That is, if you exceed +/-90V at any time (peak or average), you may cause faliure.
Tim
Tim
fdegrove said:And no, you don't turn a IDHT into a DHT one by shorting heater to cathode....Tsssssssskkkkk.
Sorry, that was my lame attempt at being funny. I should have been clearer.
Please, anyone out there, don't be cruel to valves!
Hi,
A datasheet stating Vhk(max) assume a DC voltage present on the cathode and either AC or DC on the heater.
Since the 12AT7A is rated at 90V Vhk Center Design rating and 100V Absolute, running this tube with the cathode at 80 VDC and the heater at either 12.6V or 6.3 V AC or DC, superimposing a 20VAC audio signal won't cause a problem in practice.
Doing this for oscillator services is a different story. I wouldn't recommend just a condition if long term reliablility is at stake.
Cheers,😉
A datasheet stating Vhk(max) assume a DC voltage present on the cathode and either AC or DC on the heater.
Since the 12AT7A is rated at 90V Vhk Center Design rating and 100V Absolute, running this tube with the cathode at 80 VDC and the heater at either 12.6V or 6.3 V AC or DC, superimposing a 20VAC audio signal won't cause a problem in practice.
Doing this for oscillator services is a different story. I wouldn't recommend just a condition if long term reliablility is at stake.
Cheers,😉
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