I think you will have to take the DC for the EF86's and keep the AC on the ECC83 as you don't want to take more DC than you have to. Then build the following on a board.
V1 is the 6v3 winding going to the existing ECC83. D1,D4 say 1n5401 R1, R2 1W which adjust the heater voltage. C1 >= 10000uF @ 10V, R5 and R6 are the heater windings of the EF86. The cap need to be large else you just move 50Hz to 100Hz.
Looking at the EF86 data sheet the hum levels are measured with the cathode with a big bypass cap to ground.
V1 is the 6v3 winding going to the existing ECC83. D1,D4 say 1n5401 R1, R2 1W which adjust the heater voltage. C1 >= 10000uF @ 10V, R5 and R6 are the heater windings of the EF86. The cap need to be large else you just move 50Hz to 100Hz.
Looking at the EF86 data sheet the hum levels are measured with the cathode with a big bypass cap to ground.
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You can feed both channels. Just the EF86 though. If you want no AC at all then this circuit would do. There are plenty of others. Make sure the transformer winding is floating. This one will need some 3A Schottky diodes as rectifiers say 1n5820. The LT1965 is low dropout - its no good using a 780x. It will need a small heatsink.
It may be better to drive all your valves EF86/ECC83 with DC as having a mixture may put noise on the ECC83. If you make the C2 15000uF @ 10v and put in a LT1764 that will provide plenty of current. Think thats what I would do.
It may be better to drive all your valves EF86/ECC83 with DC as having a mixture may put noise on the ECC83. If you make the C2 15000uF @ 10v and put in a LT1764 that will provide plenty of current. Think thats what I would do.
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Yep since is hum rather than buzz there is significant possibility of magnetic coupling between the tracks. You could cut the heater tracks and put twisted cable to each valve individually. Reading the EF86 spec the hum should not be audible. However would damage the PCB but may be simpler than DC board and cheaper.
Well I've answered my own questions. I tried feeding the valves directly with twisted pair wires instead of going via the PCB tracks - makes no difference with or without the PCB tracks removed. I still don't understand why I'm getting so much hum but my only choice is a separate DC supply for the two EF86s and ECC83s, as the power trans can only supply 6.8A of heater current, so is already 200mA over (could this be part of the problem?).
I don't suspect the PT as the culprit, as the overload is marginally. Did you try to feed the EF86 and ECC83 heaters from a battery pack, as suggested by others?
Edit: I suspect you've got a ground loop issue. With some close look at the pics in #45 and #11, I see a green wire that is connected to the input RCA jack's sleeve in the uppermost left corner. Where does this wire go to? Is there a similar wire connected to the other RCA jack?
Best regards!
Edit: I suspect you've got a ground loop issue. With some close look at the pics in #45 and #11, I see a green wire that is connected to the input RCA jack's sleeve in the uppermost left corner. Where does this wire go to? Is there a similar wire connected to the other RCA jack?
Best regards!
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Yes, I tried a battery pack and the channel was silent (with the 100ohm resistors grounding to 0v rail). The green wires are now gone.
Can anyone suggest a suitable power supply to use for the heaters of the ECC83s and EF86? Would a simple 6v wall wart SMPS be okay? I'd rather use a bridge rectifier and 15000uF cap off the current 6.3v supply, but it runs at 7A at the moment and is only rated to 6.8A, so I don't want to push it any further - unless anyone thinks this will be okay?
Can anyone suggest a suitable power supply to use for the heaters of the ECC83s and EF86? Would a simple 6v wall wart SMPS be okay? I'd rather use a bridge rectifier and 15000uF cap off the current 6.3v supply, but it runs at 7A at the moment and is only rated to 6.8A, so I don't want to push it any further - unless anyone thinks this will be okay?
I am still surprised about the AC heaters causing so much hum. SMPS would be fine although they can be a bit noisy if not loaded. You need to rate the SMPS at twice the heater current else it won't start when the heaters are cold. You could get a small 6v3 toroidal and use the linear circuit. Lots of options. Running off 12v does mean you can use normal diodes in the bridge rectifier. I used a separate transformer when I ran out of heater current.
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