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-   -   Will this work as a heater for 300b? (http://www.diyaudio.com/forums/tubes-valves/229589-will-work-heater-300b.html)

Green77 8th February 2013 08:21 AM

Will this work as a heater for 300b?
 
Hi all!

I have a TSE with 300b tubes that hum for the first 2-5 min when i power it on.
I have discust this with you people here before..but it's time to take care of it now :)

Today i use the 6,3v AC, make DC and regulate it with a AD1084 to 5V.

My plan is to do like this:


http://i48.tinypic.com/358nuo0.jpg


Will this work? Hopefully this will make it hum free..

Regards //Daniel

euro21 8th February 2013 08:46 AM

Quote:

Originally Posted by Green77 (Post 3360778)
Will this work?

Maybe.
One side of 300Bs heater (thus cathode) are common. If this point is ground (negative bias on the grid), it will work.

Quote:

Hopefully this will make it hum free..
IMHO 4700uF is too small. Try 15000uF - 1R -15000uF.


Quote:

hum for the first 2-5 min when i power it on.
If later does not disturb you, don't worry about it.

12E1 8th February 2013 11:53 AM

Quote:

Originally Posted by euro21 (Post 3360792)
One side of 300Bs heater (thus cathode) are common. If this point is ground (negative bias on the grid), it will work.

Correct. If using cathode bias, you need completely isolated transformer, bridge etc for each valve.

Quote:

Originally Posted by euro21 (Post 3360792)
IMHO 4700uF is too small. Try 15000uF - 1R -15000uF.

If the constant current circuit does its job, then 4700uF is fine. Reducing the ripple further on the input side to the LM317 will make a tiny difference to the current regulation which should be all but inaudible.

You should not place large capacitance after the regulator / resistor since this could create stability issues and will prevent the regulator from properly controlling the current. You should not think of this as a CRC filter.

@Green77 - circuit says LM317 - text says AD1084. I could not find data on the latter to check the details. LM317 would be OK provided that it was a suitable package and suitably coupled to a heatsink.

Green77 8th February 2013 12:15 PM

Thanks for the replies!
I have fixed bias to the 300b.

My bad, i have ap1084 regulator today.

Regards. /Daniel

12E1 8th February 2013 12:28 PM

Quote:

Originally Posted by Green77 (Post 3360979)
Thanks for the replies!
I have fixed bias to the 300b.

My bad, i have ap1084 regulator today.

Regards. /Daniel

Fixed bias should be OK using a single transformer so long as one end of each filament goes to ground. AD1084 may be OK - I just had trouble to find a datasheet to check the resistor value for the current control.

jrenkin 8th February 2013 01:13 PM

I thought the TSE already used regulated filaments on the output tube.
What are you trying to accomplish?

Green77 8th February 2013 01:28 PM

Yes, the TSE does. But when i build mine i wasnt abel to get the sharp regulator. So i build my one circut. With a volt regulator for 5v (ap1084).

/Daniel

12E1 8th February 2013 03:41 PM

I just found the data - the manufacturer's site was off-line earlier.

So the AD1084 is available in different versions. The circuit that you showed can work with the AD1084-ADJ part, but not with the AD1084-5.0. Which version of the AD1084 are you trying to use?

Since the AD1084 can pass high current it is important to get this right, or you could destroy the filaments in your tubes.

cotdt 8th February 2013 03:46 PM

It will work, but I used LT1084 regulator on my TSE 300B.

Green77 8th February 2013 04:32 PM

Yepp, works when the tubes are hot after some min.
How about sound? Is the 317 ccs better heater then the volt regulator?
I read somewhere on the forum that the cap after the regulator could make the sound bad...

Regards //Daniel


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