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Jensens.......

Posted by Chris Garrett (B) on September 13, 2003 at 12:26:45

In Reply to: Re: Dude....if you're worried about failures, stick with SS......... posted by steve oda on September 12, 2003 at 23:17:52:

Hello Steve,

I had Cary do the Jensen oil cap upgrade ($200 for .22uF/630vdc x two per amp) when I first picked up these 2 yr. old (were built in '98) used amps and had one die. Less than a year later, running nice Tung Sol smooth plates, one died while playing some music. I waited 16 months to finally send the one in and it was a Jensen cap that had shorted, so for a total of $175, Kirk replaced the cap and shipped it back to me.

Nine days later, the amp died at turn on. I opened her up and fiddled, finding that one of the two Jensens (don't know if it was the recently replaced one) had a short in it and since I can solder slightly, Kirk send me another for free. I put it in and for the past 2-3 months, the amps have been sounding great. I check the bias every few days, noting the AC wall voltage, etc. and I rematched up the Tung Sols after the long stretch of down time. No shorts, decent gm, etc.

About two weeks ago, after puttling the left amp (not the recently dead one) into standby for a couple of minutes, I heard motorboating and turned it off. The SLAMS use 4 tubes per amp and what usually happens is that one pair goes ballistic and the other pair goes dead or stays cooler.

I figured that since Kirk stated to me that nothing can really short out the Jensens in the amps, short of bad tubes, the problem is just in the caps themselves going bad. Some have claimed that oil caps are not the most reliable, but people like Ron Welborne and Kirk have stated that they haven't had any major returns on the Jensens. I opened this amp up and found a shorted Jensen cap.

At this point, I figured that a new brand was in order. I ordered four Jupiter beeswax caps (.22uF @ 600v) for $75 from Parts Connection. I got them in and soldered one into the bad spot, just to see if it would work and no dice. I then started throwing them all in and but for one 15 min. period where I was able to actually bias up the amp before the fuse blew, I killed them all.

I checked resistors, etc., and thought I saw a Dale that was out of spec by 22% (55k vs. 68k ohms) but it tested fine when the amp had cooled the next morning, so I'm at a loss.

I can't keep shipping these amps into Cary, so I'm looking for somebody who is local and then I plan on selling these boat anchors.

When I originally sent them in, Cary said that they fixed them and updated them with parts and the newer switches for 4/8 ohms and triode/UL and I realize that they don't rebuild them, but short of the Tung Sols being the cause, I don't know what to think?

I love the sound and they work well my the Dyn Contour 3.0s, but it's frustrating. If it was just the Jensen brand, I'd be a happy camper, but a fellow inmate has the same amps w/Jensens and he had two caps short out just like mine did, after his upgrade, so either Cary runs them too hard, or the values are too light for the job.

Any thoughts would be appreciated.

Thanks, Chris

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