• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Your favourite filament supply for DHT's?

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.
 
Hi Johnny,

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


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

Regards,
Bas
 
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 [email protected] and [email protected] 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
 
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.
 
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
 
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:D

it only works if you connect 22uF (tantalum) --
I've put 22uF/35 tantalums in there already.:smash:

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 ;)
 

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amperex

Member
2005-02-20 1:42 pm
MI
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.