CJ PV-3 voltage values for schematic

[arlekin]

Hi, does anybody knows A/B voltage values for this schematic and transformer ratings?

I'm thinking about trying to build it without the phono stage.

Thanks

 

[llwhtt]

With just the schematic you can guesstimate the B+ by looking at the zener string (D6-13). Those are 33V zeners and there are eight in series for a total of 264 Volts. The B+ should be close to 264VDC.

Craig

 

[arlekin]

Ok, thanks.

So, a transformer should give be something like 200V before Gretz?

Would 220V be too much?

 

[llwhtt]

The raw supply needs to be higher than the regulator output. The regulator needs some extra voltage to work with but I am not sure how to figure how much extra. A 220VAC secondary will give you approx. 286 VDC, is that enough? I don't know without some research.

Craig

 

[arlekin]

Ok, but wasn't that supposed to be 220VAC X 1.414 = 311VDC?

 

[llwhtt]

If you use 1.3 as the x factor the voltages come out closer, always seems to work for me.

Craig

 

[ronaldw441]

arlekin,

Here are voltage taken from my PV-3 referenced to your schematic;

Transformer secondary high voltage - 277vac
Transformer secondary low voltage - 11.86
Rectified DC (at top of C11) - 344vdc
B+1 (at top of R3) - 249.5vdc
B+2 (at top of R14) 248.2

Transformer does not have ratings marked on it but it does have the manufacturer and part number - Northlake Engineering, Antioch, IL, Part No. C126-112

I believe they are still in business but are now in Wisconsin.

You might try them if you need more info;
Northlake Engineering, Inc. > Exceeding Your Current Needs

 

[arlekin]

Thank you both! You've helped me a great deal!

I guess that would be loaded?

I think I will go with back to back transformers. The first one 220VAC>15VAC, and the second one would be 12VAC>220VAC. That should give me about 275VAC.

Or maybe rather with a 220VAC>9VAC /12VAC>220VAC what should give about 293VAC. Just for safety because of the load.

I guess that the second secondary is just for the LED? Can be left out? Any other uses? Where is the heating?

I'm just not shure what power ratings for transformers should I use? Is 6VA too little?

 

[arlekin]

Maybe a more reasonable question would be:

If I use back to back trafos would 15VA be enough or should I use 25VA?

I would like to save some space.

 

[ronaldw441]

arlekin,

The measured voltages are in circuit (loaded).

The second secondary is for the filaments as well as the power LED. The crooked lines to the right of C17 represent the filaments.

I measured the actual resistance of R25 and the voltage drop across it & found the current at this point to be a little under 12ma.

 

[arlekin]

Thank you very much Roland! Your info is very useful!!

Ok, so I=12mA with 320VDC will have about 3.84W. Maybe the 6VA trafos can really be enough!

One more question. How's the sound of the preamp?
What tubes are you using? I see that people are using 12AX7 for both V3 and V4 but the fabric amp supposed to have 12AT7 for V4.

 

[ronaldw441]

arlekin,

Don't forget that you'll need to power the filaments.

I haven't listened to my PV-3 in years. From what I remember it sounded quite good. Better than expected. All the tubes are Telefunkens. V4 is a 12AT7.

You might consider the Norm Koren Spiced PAS. See;

Spice and the art of preamplifier design, Part 2

That's what I most often listen to when I need a preamp.