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Old 16th September 2012, 08:27 AM   #1
slaikan is offline slaikan  South Africa
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Default Refurbising Conrad Johnson Premier One

Hi

I'd like to embark on a project to have this classic 30 year old amp brought up to spec with newer components. The amp still works, but has a hum, so I'm guessing things have been in better shape under the bonnet. Its cost prohibitive to send the amp to an authorized dealer as the nearest one is half way around the world.

I think the first things that need replacing are the electrolytic caps. The ones in there are probably in desperate need of replacement, they are Sprague Atom 150uF 150VDC axial caps.

Been looking around the net and have found Sprague Atom 100uF 350VDC caps for $10.60 each. I'm guessing they will work, will there be issues due to the higher rated voltage? Also, any suggestions to better caps, maybe slightly more expensive?

Then there are the coupling caps... a few of these around. These are currently Seacor 2.0uF 630V. What would you suggest here, don't want to break the bank with Teflon caps, I think anything over $50 per cap is over my current budget at the moment. I need 6 of these caps. Any experience with Auricap, Sonicap, Solen?

Do I need to replace resistors? There are quite a few 5W 20ohm resistors under the valves.

Thanks for the advice
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Old 16th September 2012, 04:28 PM   #2
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You might want to have a professional technician do the refurbishment. Based upon your questions it seems that you don't have the experience and probably not the tools and test equipment necessary to do a thorough job on this complex amplifier.

I found a schematic on the web here. According to this schematic the B+ power supply capacitors are 1300uF @ 350V and 3300uF @ 350V. The bias supply has 100uF @ 100V caps although 150uF @150V will work fine. The coupling caps are .47uF not 2uF.

Find a qualified technician in your area to rebuild this amp for you and you will enjoy it for another thirty years.
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Old 17th September 2012, 09:49 AM   #3
slaikan is offline slaikan  South Africa
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Thanks for the schematic. I agree that I don't have the experience many of the forum members have here and I'm aware of the lethal voltages involved with valve amplification. But i'm interested in doing this, that's why I'm here asking questions, and its my hobby, hence I'm learning about it. It not my first diy project, I've built Tangent's PPAv2 and as well as Peter Daniels DAC without any problems. The PPAv2 seemed a lot more complex IMO. I'm great with a soldering iron, have a decent multimeter and a lot of patience, so I'm thinking why not?

Provided we're replacing like for like (or as close to the original as possible) and I'm paying attention to details like not putting in electrolytic caps in the wrong way, I don't see why I cant DIY this with the help of this forum or am I still missing something here?

I'll enquire locally to see if anyone is interested, although I still think I'll purchase the parts required.
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Old 17th September 2012, 02:17 PM   #4
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Have work on a Premier one . The bias supply need attention the single diode and atom sprague cap hurt the sound alot . Go full wave and use a cap choke cap supply with film as the last cap you will be very pleased with this. .47 is large enough for the coupling caps 600 volt. the large elec.caps in the power supply are near there usefull life those cost money . The diode bridge used for high voltage is worth looking into .
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