SP 12 SE

Already have the Russian PIO's. I ordered a bunch from the Soviet eBay sellers. I have some .22 400V and some .1 10V.....I think....not sure on the voltage just sitting here, but the ones in the SP preamp were put in by Roy. I ordered mine after that. I also have them in the M-125 monoblock amps I got from VTA...REALLY NICE TUBE AMSP.......especialy for the coin. Wish they had been designed to take full advantage of the KT-120 tubes though. Roy was afraid they might not be in production years from now (the KT-120 tube) , but knew the 6550 and KT-88 probably would be, so she is capable of a lot more than the tubes are doing now...I think they pretty much idle..could be putting out 250 watts per mono or more, instead of the 125 they are rated to produce. I know they will fry some tweeters though..
 
Larry, I'll do anything you want to do on this if it will fit. As to what I'm gonna do, find the problem and fix it. Not that many parts in there. Either the regfulator is not regulatin, or some parts associated with it aren't. A steep learning curve there Larrt. I'll get er though.
 
Chased down some problems. R-24 should be--300K ohms, R24 is----3megohms. R25 should be---100K ohms, R25 is---100 ohms. R21 Should be----910 ohms, R21 is ----91 ohms.

What I don't know is if these value resistors were adjusted because of the voltage of the transformer. And these were the value resistors supplied by VTA, not the ones you upgraded.

That's the only reason I can find for the hi B+ voltage. Maybe Roy can line me out one more time.

Short review, Filament regulated is ------12.69 VDC, B+ regulated is----297 VDC at the B+ in at the phono board, and 315 VDC at the B+ pad between the 4 tubes.
 
AND I"M TRYING DESPARATELY TO HOLD MY TONGUE!!!!!!!!!!!!!
 
I know trust me. I read the email and I almost lost it. Like you said I don't understand why 2 rectifiers. LOL

Larry
 
Well Joe has got me lined out. According to Joe, he would have done it a little different. He recommended a 1uf poly cap between the anode of D14 and the junction of R23 and R25. Will make it much more stable. The value of the transient improvement cap is to large(C23). Joe's working on a sub for that also. Were gettin it Larrt.
 
PARTS ARE HERE!!!!!!!!!!!!!!!!!!!!!!!!! We're goin back in tonight!!!!!
 
A view of the cap Joe recommended to stabilize the power supply a wee bit. And he suggested that the 33uf at 450 be changed to a 10uf At 450.

the stabilizing cap is a 1uf At 400 volts. The neat thing, there were some unused holes the correct distance apart and whwere they needed to be in circuit.
 

Attachments

  • 108_0082.JPG
    108_0082.JPG
    745.1 KB · Views: 98
No , it is regulating, just not low enough. Put a 110K in series with the 330k set resistor, no go. Settles in at 302.5.
 
Let's get this tackled tonight Lee. Are you sure that the artwork matches the schematic that you sent to me? Do you have a birdseye photo of the section of the board you are working on?

Putting that resistor in series with the 330K will just make it regulate higher (right idea, wrong direction). Try reducing the 330K value to 289K = (330K * (265/302.5)) and see what you get. That value is not critical at the moment so if you just have 300K, then try that.

Did you try taking the TIP50 out of the circuit to see if the regulator alone regulates properly at 265V?
 
You must log in or register to reply here.
Back
Top