Filament supply modules.

[pre65]

I was thinking about buying another pair of filament modules.

The DIY hi-fi ones look good value, but there seems to be a big difference between e-bay (£48.75 + post)

http://cgi.ebay.co.uk/ws/eBayISAPI.dll? ... _828wt_704

and Hi fi Collective (£94.00 + post).

http://www.hificollective.co.uk/catalog ... -4384.html

They seem to be exactly the same thing, unless I am missing something ?

[Mike H]

Make yer own?



 

[pre65]

Make yer own?

I suppose I could ?

Were your design (yet to be built ?) CVR ? If so can you point me to your circuit pleeeeeeeeeeeeze.

[Mike H]

You've got me going now! Can't find the thread


Constant Voltage or constant current? Or probably both


 

[pre65]

Was this it ?

http://www.audio-talk.co.uk/phpBB2/file ... _3_123.gif

[Mike H]

Oh yeah, I changed it though that's too complicated


In fact I'm looking at it again now and going "mmmm...."


 

[Mike H]

I think the problem is the "constant current" bit, it does cause problems.

Maybe a more reliable approach should be a Voltage regulator with current limiting



 

[Andrew]

Anyone any idea, how in concept the tentlab stuff does it

[Mike H]

According to photo at top of this page, not a lot on the board:

http://www.tentlabs.com/Products/Tubeam ... index.html

But see also this somewhat bitter topic, started by complaints about module failures!

http://db.audioasylum.com/cgi/m.mpl?for ... ght=jweiss

That leads to this schematic, which is quite interesting:

http://www.diyaudio.com/forums/tubes-va ... post446973

Only fly in the ointment I have about that is that I have earlier tried the constant current method shown at bottom of the regulator drawing, viz "RSENSE ~ SELECT TO GIVE 0,6V AT CORRECT FILAMENT CURRENT" problem with that is junction temperature warming up causes the base - emitter Voltage (of in this case T3) to decrease, so the current drops. I.e. it's far from what might be construed as constant! It wanders about all over the place

However the top bit, "gyrator choke", with an op-amp controller could be cooking with gas


 

[Andrew]

Thanks, Mike, time to do some research.

Andrew

[simon]

Rod Coleman on DIYAudio is in the process of releasing some modules which sound very promising. Check out the Tubes/Valves section. If you're prepared to build yourself (as we are) then pricing looks favourable (Rod hasn't released prices yet on the forum, but it should work out cheaper than the ebay link )

[Mike H]

LOL I went to that, trawled through the thread, and it's exactly the same topic post of my last link





Certainly interesting though, I'm off for a play

Interesting comment about LM317 as well


 

[Mike H]

Well I never! It works

I'm using power darlingtons

I'm getting ripple of 10mV peak. The top "gyrator" bit is basically nothing more elaborate than a Voltage regulator but does a good job of smoothing.


 

[Andrew]

The trick seems to be to avoid feedback loops through the cathode, I haven't tried this yet it, tho'.

I built both current and voltage regulated using the LM317 it seems that although current is marginally better it still has a slightly strangled sound when compared to my Spud amp (6C45).

Andrew

[Nick]

I wonder if you could achieve the same with a large time constant in the feedback path. I know that runs the risk of instability, but maybe instead of the normal proportional feedback that is used, integral feedback could be used.

proportional: the error signal is proportional to the difference between the target and the actual

integral: the error signal is proportional to the integrated difference between the target and actual