Switching supplies and filaments?

[Blair]

Anyone ever run power tube filaments in series to run them off 12VDC?

I have a bunch of server supplies with 12VDC at 15A, and I was thinking this might be a nice solution for filaments on a big amp.

Thanks!

Blair

[DeathRex]

Ed has a post about using them.

[EWBrown]

I've run four 16A8s (same as 6BM8, but with a 16V, 300 mA filament) with a 16V, 2A switcher, with good success in a modified K-502 amp, it worked very well, and eliminated the otherwise unsolvable
60 Hz AC hum issue, that was a result of a combination of a poor printed circuit board design and layout.

FWIW, this amp can also run 11BM8s from the power transformer's 11 VAC winding, too - I put in a "hidden" DPDT filament voltage selector switch, inside the chassis.
They do have the "hum" issue, though it isn't really serious, just a minor annoyance...

I also have some very compact 5V, 2A SMPS which should be good for lighting up 300Bs, thoughI haven't yet tried them. They will fit very easily and neatly under a 2 inch deep chassis, one for each tube.

HTH

/edB

[Shannon Parks]

Just plan to use them in a separate chassis, as the large switching currents will radiate some decent EMI at those currents.

Shannon

[Blair]

Thanks guys!

I wired up a PS this AM, and I'm getting 12.66VDC. Does anyone know how to load it down without tubes? I want to know what my voltage will be at 6-8A. I found a nice compact little 40A at 12v supply.

Never mind. I grabbed a few 12AU7 and rand them and the voltage started to regulate down with just 450mA on it, so I'm sure it will settle at 12 VDC with a bunch of power tubes on it.

Thanks!

Blair

[TomMcNally]

6.3 x 2 = 12.6 ... why would you want 12.00 ?

Tubes are very tolerant of filament voltage. I only measure
when I'm dealing with $$$ tubes, like 300B's ...

[Blair]

Hi Tom,

I was in hopes that it would stay up around 12.6v vs. drop to 12v with a load. I'm running the PS at less than 25%, so I had hopes of the end voltage being a little higher. Not a big deal really. I'm going to have to take it out of this case and put it in a well vented cabinet though! Sucker gets HOT!

Thanks!

Blair

[logos47]

Gentlemen, I would like to know how your projects are working out. I was until today without a "rps" for my Posiedon MKIII boards. Not being an engineer, I worked with my friend and designer who used a switching supply for my linestage section, but when proposing the same be done for the monoblocks, we looked a bit further into just using a Schotkey diode-capacitor-resistor arrangement. It took little space and was mounted using a little stand-off. Just one of the two amps is using the mod is being beta tested now with the other running. My golden-eared vocalist wife pointed to the amp with the rps mod and said--"is that the one?" Now here's the deal. My SP MKIIIs have 5H choke inputs, so the power trannies are loafing--they are handling the extra voltage very well.

[logos47]

With further listening, it was evident that the 5V dc supply using the Schotky was starving the tubes for electrons--like getting a haze instead of a nice cloud; hence, no slam and that magic presence was missing. We therefore went back in and removed it and, using a low esr capacitor and resistor, set up an unregulated dc filament supply for driver and buffer which puts out 6V with a 115V line voltage set on my variac. "The pleasure is back!" Noise floor and hash have dropped out and, by turning down the voltage a bit, I can run the tubes conservatively to extend tube life.

[soundbrigade]

I have small wondering in/on this subject.

While drilling a new chassis for the Clementine I happened to start drill ing a chassis for a CC 6V6-SE as I had some spare 5K OP trannies. However I had no suitable mains transformer apart for one with reasonable HV specs but too low current for filaments, so instead I came up with a brilliant idea of using a 2x12V transformer, that was what I had, rectify, filter and then use a DC/DC converter to get a "smooth" 12,6VDC.
Having the 6V6 filaments i series and the 6SJ7 filaments also in series and then run them in parallell would result in a 0,75A @ 12V requirement. The converter (LM2596 Buck Power Supply Module.