voltage regulators parallel connection ?

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how about this design... scroll down to DC heater supplies:

there is a pretty simple design for 5A
http://www.valvewizard.co.uk/heater.html


my 6.3VAC center tapped trx arrived btw...
center tap to case_ground :  wow. some serious hum going on...
i tried NYD's Mila PSU for DC elevation, it helped a lot  on 60HZ,
but, 120hz remained the same...
(heater trx was outside the case... twisted cables)
any idea ?


with regulated heaters pre_amp is dead quiet. 

 
kambo said:
how about this design... scroll down to DC heater supplies:

there is a pretty simple design for 5A
http://www.valvewizard.co.uk/heater.html
Not really simpler than other implementations.
Cons:
- ballast transistor does not include the sophisticated SOA and thermal protections that are built-in monolithic regulators
- ballast transistor needs at least same heatsink/air extraction than a regulator.
my 6.3VAC center tapped trx arrived btw...
center tap to case_ground :  wow. some serious hum going on...
i tried NYD's Mila PSU for DC elevation, it helped a lot  on 60HZ,
but, 120hz remained the same...
(heater trx was outside the case... twisted cables)
any idea ?
Assuming there is no ground loop, filament-induced hum is transmitted electrostatically, so I would check that heater wires are properly distant from sensitive grid circuits.
 
messed with AC heater wire, in every possible way, even new grounding etc.. not a chance...
my only guess is : since i have wired 5687 for 6.3V heaters, pin 4+5 - 8

pin 8 is next to grid pin 7, and heater wire need to cross from pin 4+5 junction to pin 8...
may be if i wire for 12VAC, i wont have hum !?


in case of DC heater supply :
would be a good idea to auto shut B+ down when heater supply  fails ?
 
kambo said:
messed with AC heater wire, in every possible way, even new grounding etc.. not a chance...
my only guess is : since i have wired 5687 for 6.3V heaters, pin 4+5 - 8

pin 8 is next to grid pin 7, and heater wire need to cross from pin 4+5 junction to pin 8...
may be if i wire for 12VAC, i wont have hum !?


in case of DC heater supply :
would be a good idea to auto shut B+ down when heater supply  fails ?

You shouldn't have all this problems with AC heaters if everything is right... Have you checked if power transformer really has enough current, does it have datasheet, can you find someone else online who have used it before? Or try it yourself?
Another thing could be trying artificial center tap with low value resistors, or "hum pot". Haven't tried it myself on transformer with CT, guess it should work anyway. Heater circuit has to be elevated for srpp in Slow Blow if you are not building MILA. Not sure what you are doing.
Wires comming from heater psu should go to the sides of chasis and then to tubes. So from psu to the side, from there to output tube, from there to the side and again to input tube. I don't follow this exactly when doing AC heaters, many people report it helps...
If wires are too thick you might have problems twisting/dressing them properly. Solid wire is easier to work with, although not the best solution as it could snap if very thin. Maybe use a piece of thin, well twisted solid wires near sockets if you think this is your problem, they  can connect to stranded from there...
5687 is a little more difficult tube in this regard, i would bring tightly twisted wires near pin 9 to the center of tube, connect, bend it back to pin 9 and go to another tube. Both tubes have to be in phase, heater psu first connected to output tube and then to input tube.
Not sure if HT only is damaging to this kind of tubes if problem doesn't last long time. We already wrote about it here.

I'm sure you know  what i wrote, hope it helps anyway. Regulator might work with you transformer when using LDOs, low drop diodes and heater voltages at around 5,5V. Slow Blow needs two even if they are LDO. I'm just experimenting with two on one heatsink from computer psu (fat Al L profile with fins on the top) where calculations show one is enough, but i want to see the difference in practice.
 
thanks everyone,
i will try wiring for 12VAC heaters today. c if makes any different... ordered some new resistors etc for DC elevation ...
i dont remember anyone saying AC heaters are dead quite btw...
always, "manageable hum" !!!



 
kambo said:
i dont remember anyone saying AC heaters are dead quite btw...
always, "manageable hum" !!!

Me neither, witnessed from the forum and personal experience. I have not seen a single RMAA noise plot from any piece of equipment with AC heaters besides my own tests. And those tests never performed anywhere near (the flat noise floor of) DC heaters.

The best examples have been people who say "no hum" from listening tests. We're talking something like 40-60dBu 50hz which is nowhere near acceptable in my opinion, even if grandma was okay with that.

kambo said:
would be a good idea to auto shut B+ down when heater supply  fails ?

It's a good fail safe, and relatively cheap. I've done this in the past with regulated heaters when I still bothered with them. Heater 6.3VDC to 5V relay (they are fine with a little over voltage) that is specified for high voltage AC use. You should cut the AC voltage before rectifier bridge. Relays for this kind of usage are far cheaper than for high voltage DC spec.
 
thanks for the link CJ,

hey Kinston, i used your basic heater supply, CJ 's link has some many versions...
i had 12000uf and 4700uf available... i made 1 ohm from a wire. 


mic pre, dead quiet again :)))

no more regulators, and heat sinks for me...
 

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