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Old 11th March 2010, 01:25 PM   #1
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Default Phase Linear 700 Series Two recapping

Hello everyone, I recently purchased a vintage PL700 II which needs new power transistors and filter capacitors. No doubt about the choice of the new transistors among the recent production: I'm going to purchase the complementary couple ON MJ21195/21196, as suggested in the latest PL tech bulletin.
As for the main caps, having to spend a certain sum for brand new large devices, I was thinking to double the capacitance. The possible substitute, apart the usual 100V 10,000uF, is a CDE 100V 18,000uF which costs something like 60/70 USD each. Anyway I've recently found on eBay a seller which has a large stock of capacitors of any type and brand who is selling a brand new couple of ADCOM 100V 18,000uF for the same price. The questions are:

- is it true ADCOM caps were CDE made?
- what are the pros and cons of doubling the capacintance of the filter caps?
- do I need to change also the rectifier with a new device with better diodes in order to avoid any possible damage from short circuit overheating when turning on the amp?

Suggestions about any substitutes of the old caps will be appreciated.

Thanks for your kind attention.
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Old 11th March 2010, 03:19 PM   #2
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You might find the switch on surge current starts to blow fuses with larger capacitors.
Murton-Pike Systems PCBCAD51 pcb design software.
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Old 11th March 2010, 06:51 PM   #3
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Yeah , was about to say inrush current could be an issue. Anti-surge fuse could be the answer.
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Old 12th March 2010, 06:11 PM   #4
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Originally Posted by thermal runaway View Post
Yeah , was about to say inrush current could be an issue. Anti-surge fuse could be the answer.
I've thrown off some line to Don Imlay, former Phase Linear technician, asking his opinion. He replied doubling the capacitance is possible but he suggested to use the dim-bulb test to limit the current when first turning on the amp and to replace every other electrolytic and the main resistors which regulate the voltage for the ICs LF351, even if it seems they work well.
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Old 12th March 2010, 07:32 PM   #5
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As for myself I can say I've seen on eBay many 400 and 700 restored by Phase Tech (two other former PL technicians) with 18,000/20,000uF caps.
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