I'm not sure what you are doing here. Each pair of tubes has its own filament supply, 2 supplies? That's necessary. So each tube connected in series, then 2 tubes paralleled together?
Do you have a few more 4P1L to test? Test them individually for filament specifications. I usually match the voltage and current in a pair of tubes.
Do you have a few more 4P1L to test? Test them individually for filament specifications. I usually match the voltage and current in a pair of tubes.
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I'm not sure what you are doing here. Each pair of tubes has its own filament supply, 2 supplies? That's necessary. So each tube connected in series, then 2 tubes paralleled together?
Wait, do I have to use 2 separate fillament supplies for 2 paralled tubes in the same channel?
Ok, thats what I am doing. I hope it's more clear now.
Your wiring has a apreciable high DCR or the lower filament voltage tube is a bit gassy, you can take turns and test each tube with the supply/CCS prior powering the HV to discard any issue a good 4P1L will eat ~320mA with filament in series (~4V) and the double of that in parallel at ~2V
I don't see how you can get different voltages for two tubes when they are wired in parallel - won't they be at the same potential?
That's why I'm asking, I don't understand how can it be either.
Your wiring has a apreciable high DCR
This could be a problem.
My suggestion would be to break the parallel links, and measure each tube to check they're vaguely close.
They cant be very close, given the difference you're seeing.
Are you sure you havent over-voltaged the filament?
During testing or accidental over zealous adjustment of the PSU?
I say this as I have done it with the smaller 1J29B/1J24B (I forget which), when changing between series and parallel heater connections
After that, the the operated almost as well as before...less gain, but, still usable.
I guess I aged the filament pretty well!
They cant be very close, given the difference you're seeing.
Are you sure you havent over-voltaged the filament?
During testing or accidental over zealous adjustment of the PSU?
I say this as I have done it with the smaller 1J29B/1J24B (I forget which), when changing between series and parallel heater connections
After that, the the operated almost as well as before...less gain, but, still usable.
I guess I aged the filament pretty well!
Please use multiple parallel wirewound resistors for filament bias. Parallel multiples are able to reduce the effect of bad-quality end-cap mounting in ordinary wirewound resistors.
current production recommended types:
Welwyn W24 (good, but end-caps are steel)
Ohmite AG10 (non-magnetic, probably best value)
Mills MRA10 (non-inductive)
current production recommended types:
Welwyn W24 (good, but end-caps are steel)
Ohmite AG10 (non-magnetic, probably best value)
Mills MRA10 (non-inductive)
Filament bias resistors....
- something porcelain or vitreous enamel, like Welwyn WW series
- russian resistors like this, various values
2.2 kOhm 10W Russian Precision Wire Wound Resistors 18 pcs | eBay
- something porcelain or vitreous enamel, like Welwyn WW series
- russian resistors like this, various values
2.2 kOhm 10W Russian Precision Wire Wound Resistors 18 pcs | eBay
I was talking about cost/value, I dont know why Thick film would be worse, just less economical (I'll take your word for it)
If buying Russian, please watch out you dont buy these:
PTMN-1 PERMANENT WIREWOUND RESISTOR 1 Watt 27kOhm 1% NOS Lot of 20pcs | eBay
I'm sure they have a use...just not where hifi is concerned.
If buying Russian, please watch out you dont buy these:
PTMN-1 PERMANENT WIREWOUND RESISTOR 1 Watt 27kOhm 1% NOS Lot of 20pcs | eBay
I'm sure they have a use...just not where hifi is concerned.
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