I have built a tube headphone amp with following power supply.
I got transformer with only single heater supply and a pair of 6X4 so I designed a power supply using rectifier tube with shared heater supply.
The heater supply MUST be virtually grounded using 220R (in my case). But this would cause negative potential voltage between heater and cathode which is around -280V in my case. I know the negative potential voltage of 6X4 is rated 450V which my amp should be and it's being working without problem. But this make me worried cause my people said this might cause short between heater(GND) and cathode(HV) and blow all the tubes. It just a matter of time, they said. They suggest me to get another transformer for 6X4's heater which I am going to do. (6.3V 0.5A should work well🙄)
But outside this solution. Where should I put my fuse when I'm gonna prevent heater-cathode blowing? Or any other suggestion? (including 'don't do anything' one)
I got transformer with only single heater supply and a pair of 6X4 so I designed a power supply using rectifier tube with shared heater supply.
The heater supply MUST be virtually grounded using 220R (in my case). But this would cause negative potential voltage between heater and cathode which is around -280V in my case. I know the negative potential voltage of 6X4 is rated 450V which my amp should be and it's being working without problem. But this make me worried cause my people said this might cause short between heater(GND) and cathode(HV) and blow all the tubes. It just a matter of time, they said. They suggest me to get another transformer for 6X4's heater which I am going to do. (6.3V 0.5A should work well🙄)
But outside this solution. Where should I put my fuse when I'm gonna prevent heater-cathode blowing? Or any other suggestion? (including 'don't do anything' one)
Use UF4007. Job done for pennies. I feel a good PSU should not effect the stuff it powers. Unless it's a guitar amp - that's completely different. Give your hi-fi tube amp the stiffest B+ you can. Just my opinion.
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Some options for protection are:
- 1N4007 in series with each 6X4 anode (to avoid one failure mode of 6X4)
- fuse in the CT feed (to lessen chance of damage due to B+ fault - but you need to select an appropriate fuse value)
- 150V zener from gnd to heater winding (to limit amp valve heater-cathode voltage rise if the humdinger resistors open-circuit from a fault current).
- elevate the heater winding (humdinger to say +40V to reduce the rate of heater-cathode shorting)
- use a humdinger pot (to provide hum nulling and to provide a part that is more likely to open-circuit if a fault current occurs)
- 1N4007 in series with each 6X4 anode (to avoid one failure mode of 6X4)
- fuse in the CT feed (to lessen chance of damage due to B+ fault - but you need to select an appropriate fuse value)
- 150V zener from gnd to heater winding (to limit amp valve heater-cathode voltage rise if the humdinger resistors open-circuit from a fault current).
- elevate the heater winding (humdinger to say +40V to reduce the rate of heater-cathode shorting)
- use a humdinger pot (to provide hum nulling and to provide a part that is more likely to open-circuit if a fault current occurs)
My vote goes to the 'don't do anything' candidate. These kind of rectifier tubes were made to withstand these voltage differences between cathode and filament. In your case the rectifier is running far below the maximum rating of 450Vdc so I really don't get the worries.
Millions of tube radio's had their indirect heated rectifier and the rest of the tubes running from the same grounded heater winding. I never heard/read that this caused all the tubes to die on a regular basis.
Millions of tube radio's had their indirect heated rectifier and the rest of the tubes running from the same grounded heater winding. I never heard/read that this caused all the tubes to die on a regular basis.
PFL200, it is likely an insurance type call for the OP as to whether he does something or not. We don't know if the PT or the other tubes or xyz are worth only a few dollars or hundreds of dollars, or whether the OP only has old 6X4 to use (and he's not able to test the 6X4 for heater-cathode resistance), or the OP is an avid tube roller, or .....
Thanks for 'don't do anything' suggestion.
I'm wondering if it can keep turned on 24hrs/day?
It's Toshiba NOS from Showa era.
I have no knowledge to test it, neither equipment.
Attachment1: 6X4 when arrived
Attachment2: 6X4 (right of VR150) on duty
ps. Toshiba is short for Tokyo Shibaura Denki
I'm wondering if it can keep turned on 24hrs/day?
It's Toshiba NOS from Showa era.
I have no knowledge to test it, neither equipment.
Attachment1: 6X4 when arrived
Attachment2: 6X4 (right of VR150) on duty
ps. Toshiba is short for Tokyo Shibaura Denki
Attachments
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trobbins has a point. We don't know yet what the other tubes in your headphone amp are. Are they rare/expensive types?
They are not rare types.
I use Soviet 6N6P and 6N2P. It would not be a big deal if all blown.
I got 12BH7 for spare (different filament voltage) and many Soviet 6N1P.
I've heard that 6N6P is better than ECC99 in this stage so I chose a matched pair of Soviet 6N6P.
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Very nice amp!
I stick to my vote of post #4. But the third suggestion of trobbins in post #3 looks like a safety measure that's easy to install.
I stick to my vote of post #4. But the third suggestion of trobbins in post #3 looks like a safety measure that's easy to install.