SR45 amplifier

[Jim R.]

Hi Deb,

I'd probably go with the v-cap CuTF -- they're probably a good deal smaller, but also should you ever want to run EML tubes in the amp, the warranty on the tubes will be void if you use a PIO couupling cap, no matter how good it is.

I've heard the CuTFs and they are incredible and although I have some 1 uF CAST PIOs, I've not installed them in anything yet -- thinking I'll probably put them in the s.e.x. 2.1.  And based on the generality of film caps having somewhat lower ESR than PIOs, my guess is that the dynamics and clarity of the v-caps would be a bit better, but how that would manifest in the real world is not something I've got any experience with in this amp.

Either one would probably sound amazing, but different.  I like to think of the CuTFs as "warmly invisible" if that makes any sense -- all the nice tone of good copper caps, but just completely out of the way sonically, even if that is somewhat of a paradox. :-).

-- Jim

[debk]

Hi Jim

Thanks for the opinion.  I will probably go with the V-caps

Deb

[2wo]

Hi Xavier,
There were a couple of errors in the the Manual, I don't have what they were in front of me but you could search the old forum and find them but by looking closely at the photos and following the schematic, you should be OK.

First are the LEDs lit?, if so what do you read at pin 1 and 9 of the 6CM7? Pin 1 is the output and should be ~320, pin 9, the cathode should be ~13.5

[xcortes]

Hi John,

First let me accept that I am very stupid. Because the amp worked perfectly for 10 minutes and when I put a probe carelessly to take a pic showing the sr voltage I shorted b reg and killed something. So I replaced the board components and now the amp works but the two voltages you refer to are now 3
400 v on pin 1 and 34v on pin 9. The leds do light. I've checked and rechecked everything and can't find a problem. Thus my desperation.

Btw, I checked the forums (old and new) and indeed all the manual errors are documented.

Thanks for any ideas,

Xavier

[2wo]

Ok, the voltage at the cathode Is too high,  you may have lost the 431.  Check the voltage at the the 2 set resistors R and R2B see if they make sense...John

[xcortes]

Thanks John,

I replaced all the board components after the "accident". I'll check the voltages at the resistors and report back.

[xcortes]

But now that you mention it, I checked the bias setting resistors for the 431 and they measure ok both in resistance and the voltages were ok according to the resistances (that is, the 400 v  drop was divided proportionally to the resistances). So the most obvious suspect is the 431. I'll go ahead and replace it although it would be weird to get a faulty one. Maybe damaged it when soldered it?

[Paul Birkeland]

431's can be a little fussy.  You want to look for 2.5V at the junction of the 2.49K resistor and your Vset resistors (IIRC there are two in series for the SR-45).

Also, you want to see some voltage at Kreg, but not more than 32.  34 is above the allowable amount for the 431, so if it was't originally dead, it may be dead now.

One thing to triple check is that the grid of the regulator portion of the 6CM7 is grouded.  IIRC this is pin 8 (it's either 7 or .  If this pin floats (like from a broken carbon composition), you'll have some regulation issues. 

-PB

[xcortes]

Thanks Paul,

The grid stopper is ok and the grid is grounded ok. Yes, the voltage setting resistors are 2x 158k in series for 316k. That's what gets the 320v at the plate. I guess I'll replace the 431 and test.

[xcortes]

New 431. Old problem. Voltages are 394 at the plate of the 6cm7, 3.08  between the 316k and 2.49 k resistors and 46 v at the cathode of the 6cm7 (on top of the 431).

So the 431 is obviously not doing its job. The question is why. It's gotta be something deceivingly stupid.

[xcortes]

So checking the 431 resistances I found no connection from cathode to ground. Damaged board. A jumper wire and the regulated voltage is now 318.1 volts. Thank you guys. Good thing is I learned a lot about SR. Paul, let's think about designing an sr ps for that soul sister we've been discussing in the valve section of the board!

[xcortes]

Ladies and Gentlemen.

I'm listening to one amp, in mono, with a lesser Altec speaker (a Patio speaker with a coated 755E driver in  a small platic cabinet). And I can, without any doubt, declare that the SR45 redefine my references. The old references are destroyed, smashed, slain.

The amp in question has exo 050 Ni opts and Ni grid chokes. No fancy parts or else.

It has the ultrafamiliar (to me) BH tones and sweetness. But the detail is a notch above anhthing else. But above all the way the music "flows", wooooow.

PJ and Doc, you are geniuses.

I have to make me three pair of these for the main system. ASAP!!!

[Paul Joppa]

Xavier, I'm glad you hear what we do!  :^)  Made some progress the last day or two in the new design. I'm ready to prototype the power supply and see if my idea is actually workable...

[Grainger49]

If this becomes a special run it will be the "back to work" present to myself.  Paully's 45 amps really sing.  I'm sure the Orcas in my ~300 sq. ft. room will reach volumes louder than I could stand.

[xcortes]

Best amps ever Grainger, you deserve a pair after all your hard work