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Old 11th April 2004, 11:49 AM   #1
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Default Conrad-Johnson PV6 Preamp

Hi,

I have just aquired an old CJ PV6 preamp in good working order, are there any upgrades or improvements to the CJ that you can suggest? Component changes, valve changes or cct changes?

I am using CD only at the moment.

Many Thanks.
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Old 11th April 2004, 10:09 PM   #2
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Hi,

What you could do is replace some coupling caps with more transparant ones, maybe a few resistors too.

In case you don't have the circuit diagram, it can be found here:

CONRAD JOHNSON

Cheers,
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Frank
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Old 12th April 2004, 12:38 AM   #3
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Thanks Frank,

What would you recommend for caps?

What resistors would you change?

Would you replace the rectifier diodes with schottky etc?

If the components were replaced/updated how would youu rate the PV6? What would it's more modern counterpart be?
Would it be comparible with say a PV10A or B.
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Old 17th April 2004, 07:11 PM   #4
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Hi Paul,

I also have a PV6. I would definitely recommend upgrading the HT rectifier diodes to something like RHRD6120 (this is a hyper-fast, 1200 PIV 6A type, RS 446-8523. OK, the current rating is a bit overkill, but RS have discontinued the 4A version). As you will see from the circuit diagram, the audio circuitry is an electrolytic-free zone, so no opportunity for any Black Gate therapy there. I think C-J's own polyprop. capacitors are pretty good and given that the line section has 3 per channel and the phono section 2 per channel, you may have to spend quite a lot of money for any substantial improvement.

On the PSU side, one possibility might be to replace the two main HT smoothing caps (C2A + 2B). The parts lists gives these as 40 uF 400V though the ones in mine are 33 uF 450V (whatever they had at the time, I suspect). I'm sure Black Gates would yield a good improvement here, but at a cost (65 or so for a 50+50 uF 500 V cap.) and it could be tricky getting the thing in as there's limited room in the case in that area. I don't know if mine is a later version than the schematic, but there are some components I can't reconcile with the diagram. Near the 12V regulator there is a 1K0 high-wattage resistor and another 33 uF 450V cap and by the phono stage there is a 4K7 6W resistor and a 47 uF 400V cap. These are obviously extra HT smoothing components which would also benefit from changing to Black Gates. I think there's a lot to be said for getting the HT rail as clean as possible. BGs are very good at this, but are large and are certainly not cheap.

I've had mine for a few years now and like it a great deal. It's got a smooth, open sound. Do make sure that it has the right valves in (it should have 1x12AX7, 3x5751 and 2x12AT7 - see Conrad-Johnson's web site for details as to which goes where). Mine had all ECC83s in when I got it and putting the right valves in is a big improvement.

HTH,

Tim Symons
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