>Hi all, Iím new here so please forgive me if these questions have been
>asked before!
>
>I have recently purchased a Drake L7 amp, which I was told was in good
>working order but after some examination I believe requires attention.
>Apparently it has not been used for 18 months and the seller was unable
>to demonstrate. I have not attempted to power it up at all, opting
>instead for a close examination to hopefully correct any weaknesses
>before they cause any further problems.
>
>My findings so far:
>
>Nine of the PSU diodes have been replaced with new 1N5407ís. I can
>clearly see where at least one of the previous diodes had blown leaving
>black marks on the adjacent filter caps. The remaining 5 diodes look to
>be originals. Also, three of the 150K ohm resistors are replacements
>
** replacing all of the diodes with the same type number is good
engineering practice.
>Some quick checks with a multimeter revealed one suspect shorted
>(original) diode ñ it measures 4K ohm across it rather than about 160K
>ohm I found across the others (all still in circuit).
>
>Iím also concerned about the filter caps ñ 4 of them have what looks
>like small ruptures on the paper covered positive ends. Is this a
>problem? If they measure OK on a capacitance meter can I retain them or
>are they ready for the bin? If so I wonder if replacing them with 330
>mfd, 450 v Nichiconís as per instructions on the following webpage is
>safe and/or recommended? ñ
>
** 200 - 500 uF. 450v units should be ok.
>www.wb4hfn.com/DrakeArticles/TechTips/ElectrolyticRelacements.htm
>
>
>What diodes and resistors should I use?
** Equalizing resistors are not good engineering practice.
>I assume it is best to replace
>them all as a matter of course? Should the diodes be rated higher than
>standard due to the bigger capacitors?
>
** No, but a step-start would be a circuit improvement.
>I have read about replacing the 0.82 ohm fuse resistor with a 10 ñ 15
>ohm glitch resistor, what is the best one to use?
** A resistor that will limit fault-I to <200A and not come apart in the
process..
>
good luck, Tyron
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