Your favourite filament supply for DHT's?

[Bas Horneman]

I have a Ba tube for a customer that is still getting far too much noise in via the filaments. Right now I have a LM317 as voltage reg followed by a current reg LM317...but there is still a huge amount of noise coming in through there. Diodes are Schottkey's.

Common mode filter after the regs the solution? With some 2200uF caps after the common mode filter?..

I know I'll get them silent...but was curious about how you guys solved it.

 

[bigbulb]

Hi,

May I know what tube you are using? If 2A3 even AC filaments should be no problem.
My 2A3 running AC filaments and noise level across 8 ohm load is 2.8mV RMS, should be good enough.

Regards,
BigBulb

 

[Bas Horneman]

Hi Bigbulb,

Ba tube in preamplifier type setup.

Regards,
Bas

 

[kmtang]

Hi Bas,

How is the schematic looks like for the preamp and PS?

Johnny

 

[Bas Horneman]

Hi Johnny,

Here's the schematic of the psu
http://www.triodedick.com/cleo_5/cleo_voeding_gif.GIF

And here for the preamp...
http://www.triodedick.com/cleo_5/cleo_v_versterker_gif.GIF

Regards,
Bas

 

[etalon90]

Assuming that you have a perfect HV supply (with very few mV ripple)

I`ll try a switching power supply desing for computer.
You can found 5V@1.5A and 12V@2A for less that $5...

I use it myself and feed a RC circuit to provide the exact voltage on my hum free #26 preamplifier.
And for the C, I use only a small 150Uf elna cerafine...

Of cource, common mode choke on the main to isolate the SPSU is a must because they might produce noise in your HV supply and get the sound worse... (I use an isolation transformer + some 0.1Uf)

give-it a try.



Regards

 

[Bas Horneman]

You can found 5V@1.5A and 12V@2A for less that $5...

Thanks for the tip..but aren't these units huge? And only part of a complete computer psu?

Regards,
Bas

 

[Bas Horneman]

By the way...how can I get detailed photo's from your yahoo photo's? I know in the uk version you can click on a button to download the original high quality version..I am interested in your 10 amp.

 

[agent.5]

Maybe you can tried ultrasonic heating. The transformer costs $15 on Ebay. Here are some threads:

http://db.audioasylum.com/cgi/searc...sage=&sort=score&sortOrder=DESC&forum=tubediy

 

[Miles Prower]

Right now I have a LM317 as voltage reg followed by a current reg LM317...but there is still a huge amount of noise coming in through there. Diodes are Schottkey's.

You don't have a filament hum problem, you have an instability in your regulators. These IC voltage regulators have internal frequency compensation, however, it only works if you connect 22uF (tantalum) -- 100uF (aluminum) across the outputs. The 100nF capacitors the schematic shows are too small. One or both are oscillating and feeding that signal into the tube via the cathode.

 

[exurbia]

Quite right,
Bas you need these. They are 22uf tantalum at 35 volt.
Spares from our old airforce bases, made for Dassault .
I use them in the same pre-amp although with different valves
If you send me your postal address i'll send you some to try.
TTFN,
Retep.

 

[kmtang]

From what I undersand, you need to raise the potentioal of the pentode D3a. Also, you need add a bypass capacitor to one side of the filament of it.


Just a guess.

Johnny

 

[mach1]

Sorry to say this Bas, but I reckon you may have to use a separate filament trannie to stop interaction with the other windings.

I was using a setup with schottkies and a ronan reg (vreg -vreg-ireg) on my 1LE3 pre, and the amount of crap that came through was unbelievable. Tried everything, including rf suppression measures.

Then I put a tube shunt reg in the psu which necessitated obtaining an additional filament supply. I wired up the ronan reg to a small EI trannie and hey presto ! several orders less garbage.

pm

 

[Bas Horneman]

If you send me your postal address i'll send you some to try.

I would gladly buy a bunch from you. I have those exact same tantalums in there already. I'll send you a mail.

but I reckon you may have to use a separate filament trannie to stop interaction with the other windings.

I think so to...but I thought I'd give it one more try

it only works if you connect 22uF (tantalum) --

I've put 22uF/35 tantalums in there already.

Also, you need add a bypass capacitor to one side of the filament of it.

I've run a bypass capacitor from the center tap..(tried it without..as well for a while) but with it is way better.
I think I might get a seperate supply transformer for the Ba and d3a and dc the d3a supply..

Maybe you can tried ultrasonic heating.

I'm quite interested in that idea...but will try that in the future...for now I want to try it in a more "conventional" way.

Thanks for all the suggestions guys! Here is a pic of the tantalums I am using..just in case you guys don't believe me

 

[exurbia]

Bas, my amp uses a seperate HT trafo.
All heaters and LT come from a low voltage trafo plus the aforementioned tantalums in the filters.
There is no noise problem whatever, yet i use common windings.

 

[astouffer]

Connect one side of the filament supply to ground with a .1uF cap.


Adam

 

[etalon90]

Bas

The switching psu I use are aviable at a surplus store.
they are unboxed and measure only 2x6x1.5inch.

For more detailled picture, as mentioned on my yahoo picture account, email-me

etalon9@yahoo.ca

Regards

 

[amperex]

Pain in A$$, but.....

I prefer a three section RC type unregulated power supply with chokes on the output. Using a hum balance pot on the filament to ground also is helpful. If using a cathode capacitor, connect that cap at the filament with a cap approximately 30% the size to the B+ supply. Thus, say a 100uF cap is from filament to ground, use a 35uF from filament to the B+.

No high frequency hash effects the sonics like from regulators and the chokes filter any other noise. The second cap from B+ to filament is well known to further reduce hum as much as 8-10dB. Ultra low DCR chokes are available from Hammond.