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In Reply to: WON'T Work at all Ray....... Waste of time and money posted by drlowmu on January 7, 2006 at 07:19:28:
Ray,Here is what I like to use now, iron-wise, with some minimum alternatives, done from memory so I could be off a digit or two :
Power Transformer....... " The Source "
Signal Transformer Corp's DU1/2, 500 VA, 2.3 ohms DCR, the best.Its got the STUFF man ......... provides " true old-time authority, musical freedom, and magic" to the audio's presentation!!
Signal Transformer Corp's A41-175-230, 175 VA, 7.44 ohms DCR, ( .76 A. ).No slouch, but sonically not in the same league as the DU 1/2, the MINIMUM one should use on G2. Easy to "fit in" versus a DU-1/2, but..... SO what, I 'wanna HEAR the amp at the best, so just 'gimme that DU 1/2 please.
L1
Signal Transformer Corp's CL-6-12, only .16 ohms DCR !!! at a 12 MILLI Henry rated inductance. This thing is dynamically cool to HEAR. Obviously Jeff ain't concerned ONE IOTA with "reaching critical inductance", NOR is there any concern over the much-trusted "P-Dud" computer program....this inductor just sounds good to ME and thats ALL I need to know and have.
Triad CX-40 (?) from the Allied Catalog, .32 Hy at 10 ohms DCR at .6 A. current capability, not too expensive, eleven dollars or so. But really Ray, the preferred Signal CL-6-12 .16 ohm inductor for the L1 spot just kills the Triad to my ears.
L2
Lundahl's 10 HY choke, I forgot the number, maybe LL-1338 /10 HY. But it consists of two 5 Hy / 18.1 ohm DCR windings on a common core, which I parallel to obtain 9.05 ohms DCR at 2.5 HY, for some HY. filtering with L2 !!I don't know of any alternative to this choke for G2's L2, at this time. Its about $80 from Kevin at K&K.
Now you "know" Ray, and maybe this is too much to do, but I LIKE what it does, a whole lot.
Using Pentodes?... with all else optimized, its *** ALL *** in the G2 supply implementation !!
Follow Ups:
Jeff,thsnks for the information. I'll file it away for future use. (I'm not in a position to acquire more parts at the present time).
One other thing occurs to me: the critical voltage to hold steady is the cathode-to-screen voltage and this requirement is handily met with small-signal pentode stages by use of a cap between screen and cathode. However, since that's probably not practical with a power pentode stage, it implies that the use of any resistance in the cathode, such as the unbypassed 10 ohm resistor that is often included as a handy means of checking bias, is going to degrade things. Is that correct?
Ray,Excuse me. How the hell would I know that?? All I know is what I build... and if it works ( sounds decent ) or not! I am a BIG technical dummy of sorts.
Go ask an engineer such theory questions. Many an engineer will know ALL such answers but ( often and also ) doesn't have a "clue" as to what sounds good, or, how to get it !!
I am limited friend!!
Jeff (and others) thanks for your contribution. Last question (to make it complete) what capacitors (and what values) are you using in your CLCL approach ?
Since my G2 operates at anywheres from 300 VDC to 330 VDC, You need to use 400 VDC caps as a minimum. They do not see big turn-on high voltages, due to the shunt resistors in C2 section of the supply.
HI,Good question pipo, here is the rest of my circuit implementation:
For caps, I am EXPERIMENTING STILL.
Although not applicable to you, for the ARC D-75 / D-76 series amps I actually use TWO of these supplies !!!, one for the ARC's critical Cross Coupler B+, and another for G2's B+. Its all filtered L1/C1/L2/C2.
Right now, Jeff is using 1979 Photoflashes, series/parallel, about 1,000 uF for C1 and about 1,000 uF for C2, PLUS ( on the G2 supplies - at the C2 location ) a 220 uf @ 400 VDC Panasonic TSHB cap ( DigiKey ) with a MILLS MRA-12 24.9K ohm resistor ( only a MRA-12 ) across EACH of the four TSHB caps, which becomes four paralleled Shunt Regulator resistors, which equals 6.22K @ 48 watts for G2 SHUNT - B+ to ground. All four TSHB caps are located within 1 1/4 inch lead length of Octal Socket's Pin 4, which is G2.
Total capacitance for G2's C2 is thus - 1,000 uF plus 880 uF or 1,880 uF, and those Photoflahes measure LOW in ESR, act like little atom bombs.
If you don't have Photoflashes of that era, TRY the low cost Panasonic TSHB 400 VDCers. I find caps all have different sounds and some work needs to be done with the C's to get it acceptable. For wire, I use 14 gauge stranded copper, not plated in the power supply, and on the Audio Boards, Grounds are hefty Kimber Kable TCX and B+ runs are all paralleled pairs of Kimber Kable TCSS.
Due to low DCR of supply iron, combined with high capacitance / low ESR caps, one MUST always use a 47 ohm CL-80 ( from Mouser ) " Current Inrush Limiter" / Thermistor on the primary of the power transformer, and I just ordered four 8 A. at 1200 VDC Fairchild Stealth diodes for SS rectification from Mouser, as uF4007 full wave bridges blew-up on this supply's severe turn-on surges.
Signal Transformer iron is direct-order from Signal factory in NY USA, and their full line catalog downloadable on-line. Alternatively, for a power trannie, find any equal or greater than 500 VA isolation XFR on eBay with a 120 VAC to 240 VAC capability. ( Gives about 298 to 330 VDC final B+ for G2 ). These are big and heavy, but can't be beat by anything I know of. The Signal Transformer DU1/2 is a very nice part, may be 2.15 ohms as I see in notes, not 2.3 ohms in DCR, darn low, unflappable - stable!!
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