I am working on a project using 866ax rectifiers. I have a 5V 15A transformer running the heaters for the above. I am getting fairly loud mechanical hum from the heater transformer. I haven't put it in a chassis yet so it may quiet down a bit once finalized. The amp seems to be working fine but the mechanical hum is somewhat disturbing. I can buy a smaller transformer as Hammond has a 5V 8A unit but I hate to just run out and buy more stuff just to try. I am wiring the tubes in series and pulling my B+ off the center tap. Any thoughts as how I might quiet things down? Amp is quiet through the speakers. I do have a 5V 3A unit but I am afraid to try that even for a few minutes.
TIA
TIA
Does it still hum/buzz with no load connected ?
If so just replace it if you want to get rid of the hum - this is the most reliable way of eradicating the problem, although it does depend on the quality of the part/brand in the first place
Your other choice (if the TX is rare or unobtanium) is Class AB transformer Hum - Replacement Options? - this doesn't always work
If so just replace it if you want to get rid of the hum - this is the most reliable way of eradicating the problem, although it does depend on the quality of the part/brand in the first place
Your other choice (if the TX is rare or unobtanium) is Class AB transformer Hum - Replacement Options? - this doesn't always work
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I tried without any load and the hum is not noticeable over the background hum in my shop - 55dB. With the load of just the heater of the two 866a tubes the hum increases to 64-65dB when measured 1 cm away from the coils.
I had a loud transformer - the bell ends were vibrating. I punched a dent into the middle of it and it shut up... YMMV.
Class AB transformer Hum - Replacement Options?
Another thread with good transformer advice. Not sure if this is how I should reference it. It might be helpful even though it’s from a solid state forum.
Another thread with good transformer advice. Not sure if this is how I should reference it. It might be helpful even though it’s from a solid state forum.
First try tightening the bolts, don't go mad though. If that doesn't work try taking the bolts out,power up then dribble some thinned varnish between the laminations. Power off, bolts back in and tightened,allow to dry overnight. You can put your tfmr in the oven to warm up prior to applying varnish to improve the varnish impregnation.
It could be it's under-wound, IE not enough primary turns. It's an idea to measure no load primary current, it should be about 3 - 5% of it's max loaded rating.
Andy.
It could be it's under-wound, IE not enough primary turns. It's an idea to measure no load primary current, it should be about 3 - 5% of it's max loaded rating.
Andy.
Just do not get an AM radio next to the 866 power supply.
Buzzzzz.
With really good quality choke, and no input cap until after the choke, that might not interfere with the AM radio.
Your mileage may vary.
Buzzzzz.
With really good quality choke, and no input cap until after the choke, that might not interfere with the AM radio.
Your mileage may vary.
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I had a couple of identical transformers that buzzed. Wasted a lot of time trying to make them shut up. They were even louder in the chassis which acted as a resonator.
Moral - some transformers simply buzz. Don't use them if there isn't an immediate fix. I wasted a whole day on mine. Lesson learned.
Moral - some transformers simply buzz. Don't use them if there isn't an immediate fix. I wasted a whole day on mine. Lesson learned.
If I can't quiet things down I'll try the Triads.
Is there any advantage/disadvantage to running the filaments in parallel vs series? Assuming the transformer is of appropriate value of course.
Again, these are 866a rectifiers and are 2.5V 5A.
The last time I lit up a pair us 2.5V tubes (type 82), I connected them in series and powered them from a 5V SMPS.
The advantage of series is smaller wire and 5V is easier to find than 2.5V
The advantage of series is smaller wire and 5V is easier to find than 2.5V
On the heater just like when using a transformer. The SMPS must be isolated (and rated for at least B+ voltage - most are rated at at least 2kV so no problems) as B+ will appear on the 5V output of the SMPS. You can think of it like using a 5V battery to light up the tube.
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