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6,3V PSU

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Posted on November 5, 2009 at 22:43:19
François
Audiophile

Posts: 13
Location: "Annecy"
Joined: April 19, 2007
 Gentlemen,

I have made some tests in order to be able to use the Soviet 6N2P-EV valves in my ARC SP-8 preamplifier.
AS you might know, the heating of these valves is 6,3V.
Now: the SP-8 uses quite a discussable way to heat the 4 12AX7 (2 for phono and 2 for line), that is the power supply is 24V for 2 12AX7 and their filaments are placed in series for, in the best of the worlds and on the paper, a result of 12V.
To have an idea of how the 6N2P-EV would sound, I have modified the wiring and placed all 4 filaments in series so I would get 6V.
In spite of the fact that the feeding of the filaments is less than perfect (in theory 6V instead of 6,3V but likely to be different as the resistance of filaments might differ from one valve to the other), I enjoy very much the result (better than with Sovtek 12AX7 LPS).

So, let's go to the point!
I would like to make this circuit a bit more correct and thus feed all 6N2P-EV with 6,3V and in // instead of series as it is now.
I live in France and mains is 240V. My SP-8 comes from Canada and runs under 120V with a 240/120 transfo placed ahead.
I can find in France a regulated PSU 240VAC/6,3VDC but this would imply running an extra mains wire to the SP-8.
Below, a link to the regulated PSU 240VAC/6,3VDC I can find here.
I hope not to have been too confusing.......
Kind regards,

François.
Do any of you could point me to a regulated PSU 120VDC/6,3VAC similar to the one in the link?

RE: 6,3V PSU, posted on November 7, 2009 at 23:10:59
FenderLover
Audiophile

Posts: 3308
Joined: July 31, 2007
Contributor
  Since: May 17, 2009

You know after re-wiring, I'm pretty sure you can use your 6.3VAC tap off the tranny, no problem. Most amps wire the 12AX7 heaters using the 6.3VAC tap, by wiring 4,5 together as one connection and pin 9 as the other for the heater. Effectively doubling the voltage to 12.6VAC (see schematic). Pretty sure that ARC uses heavy duty enough power tranny to cover the extra wattage needed. I've used the 6N2pi-EV in several amps with very good results. Caution, as they need a TON of break-in time. Does your tubes have triple mica spacers? Mine all have three-mica spacers with the electrostatic shield. So the 9-pin should be wired to ground, to take adavantage of this shield. Similar to wiring of a 6CG7. See link. (right next to Zelda). :^)
You'd disconnect 9-pin wire on socket and break the 4,5 couplet. Wire one heater line to the 5-pin. Resolder the other to the 4 pin. 9 pin should now be grounded. Do this for all 6N2pi-EV tubes.


One word of CAUTION here: I always mark the sockets which I've rewired for 6.3 volts on the heaters. Just to prevent you (or a future owner) from putting 12AX7 tube back into the re-wired socket. The socket would need to be wired back to OEM positions, if you want to go back to using 12.6VAC rated heater tubes.

RE: 6,3V PSU, posted on November 6, 2009 at 08:08:02
Triode_Kingdom
Audiophile

Posts: 623
Location: Travelin' Man
Joined: September 24, 2006
 I wouldn't use a switching supply for this. In fact, I wouldn't bother raising the voltage to 6.3V. You're already within 5% of the design, and that's close enough for small amplifier tubes. I've seen commercial designs in which tubes like the EF86, also a 6.3V filament, are actually run from a 5.7V transformer tap. If there's any difference in performance, it isn't apparent to me.
RE: 6,3V PSU, posted on November 6, 2009 at 22:19:20
François
Audiophile

Posts: 13
Location: "Annecy"
Joined: April 19, 2007
 Hi Triode Kingdom,
What would be your main concern regarding the use of a switching supply? The risk of RF pollution?

switching power supplies, posted on November 7, 2009 at 09:43:56
FenderLover
Audiophile

Posts: 3308
Joined: July 31, 2007
Contributor
  Since: May 17, 2009
 The way swtiching PS work they tend to be noisy (inject noise into power lines, for instance). It's why most ppl put isolators inline with computers. As computers have switching PS powering their systems. Anyhhow, that's what I've been told. I have isolators on all my computers. DVD burners. And one LCD TV screen. Not sure if I need all of them, but have accumulated many through the years from ppl after fixing guitars and amps (as partial payment).

Check Link:

RE: switching power supplies, posted on November 7, 2009 at 12:05:54
Triode_Kingdom
Audiophile

Posts: 623
Location: Travelin' Man
Joined: September 24, 2006
 Yes, there's the risk of HF noise through radiation, as well as line noise from the switcher entering other equipment through the mains. OTOH, the latter can be pretty well eliminated through use of a mains filter ahead of the switcher, and certain types of switchers can actually improve isolation between the mains and load (filament) due to their small internal transformers. All things considered though, I just don't think it's worth the trouble and expense to install a switcher for small, IDHT filaments. Linear DC supplies at this power level are easy to build and cheap to buy.
RE: 6,3V PSU, posted on November 6, 2009 at 06:20:16
FenderLover
Audiophile

Posts: 3308
Joined: July 31, 2007
Contributor
  Since: May 17, 2009
 double post (see above)

RE: 6,3V PSU, posted on November 9, 2009 at 23:04:28
François
Audiophile

Posts: 13
Location: "Annecy"
Joined: April 19, 2007
 Hi Fender Lover and Triode KIngdom,

Thanks for the tips regarding pin 9 (i was indeed wondering what to do with it) and for info re switching PSU.

I ended in purchasing the one mentioned above and will get it measured and tested to check the quality of the 6,3.

Rgds,

F.

off topic question..., posted on November 6, 2009 at 06:17:46
LowRedMoon
Audiophile

Posts: 646
Location: Lake Cayuga
Joined: February 28, 2006
 François,
If I may...
In a French-drawn schematic, what would the abbreviation "Bob." stand for if refering to the composition of a resistor?

Merci,

Adam

If you find yourself frequently repeating the phrase, "garbage in, garbage out," you may need to rethink your system.
RE: off topic question..., posted on November 6, 2009 at 22:22:43
François
Audiophile

Posts: 13
Location: "Annecy"
Joined: April 19, 2007
 Adam,

"Bob." stands fore "bobiné" that is wirewound resistor.
à ton service ;-)

F.

Merci, Francois -- c'est agreable a lire francais!, posted on November 9, 2009 at 16:09:57
LowRedMoon
Audiophile

Posts: 646
Location: Lake Cayuga
Joined: February 28, 2006
 ...

If you find yourself frequently repeating the phrase, "garbage in, garbage out," you may need to rethink your system.

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