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OLDER DECWARE GEAR SUPPORT >> SE84A, SE84B, SE84C, SE84C+,SE84CKC >> Intermittent Amp Power-up -- Possible Causes?
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Message started by MarkBlair on 03/31/11 at 18:32:15

Title: Intermittent Amp Power-up -- Possible Causes?
Post by MarkBlair on 03/31/11 at 18:32:15

I wrote to Steve about this a few days ago, but I still haven't heard anything back -- so I thought I'd throw this open to the forum.

I've had my new SE84C+ for just over two months, and intermittently (roughly 3-5 times so far) within the past week or so when I turn the power on (using the amp's power switch), nothing happens. And there's no apparent power applied to any of the tubes. In one case I had to turn the amp off and then back on (again, using the amp's power switch) something like 4 or 5 times before it then powered on.

Then, one time when it didn't power on, removing and re-inserting the rectifier tube then made it work the next time I flipped the power switch on.

So -- any ideas what could cause this? Even though the tube is still within the 90 day warranty, I don't want to send it back for exchange if this could be something else.

Any thoughts?

By the way, even though I have a very tiny bit of hum audible from my nearfield monitoring position of about 30" away with 90dB PMC TB2S+ speakers, this is a **great** sounding amp!

Mark Blair

Title: Re: Intermittent Amp Power-up -- Possible Causes?
Post by Lon on 03/31/11 at 18:37:29

I think there's a strong possibility it's a bad connector/connection on the rectifier tube. This has happened to me recently with one of the RCA 5U4G rectifiers I was using in my Torii Mk III. I replaced both with new cryo'd ElectroHarmonix 5U4Gs and there was not a problem after that. (And I was surprised that the new tubes sounded as good as they did.)

Title: Re: Intermittent Amp Power-up -- Possible Causes?
Post by MarkBlair on 03/31/11 at 20:36:44

Thanks, Lon. I guess the rectifier tube would be the easiest fix. I have a couple more weeks before my 90 day tube warranty expires, so I'll do a bit more troubleshooting -- but I suspect you're probably correct.

Title: Re: Intermittent Amp Power-up -- Possible Causes?
Post by Brett on 04/01/11 at 19:59:12

Thing is if it were the rectifier tube then the heaters would still turn on and it would appear that the amp was on, except the B+ wouldn't be there to power the amp.

So if by nothing happens you mean the tubes don't light up when you hit the switch, then it must be a loose connection somewhere before the power supply. This could include the fuse, or even the power switch itself. First thing to look into is the IEC power cord connection. If it is slightly pulled out or in at an angle than it might not have full contact. Also the fuse itself (after diagnosing its connection within the fuse holder) can be the culprit. Could have a invisible fracture in the fuse element itself.

The tube heaters are directly wired to the power transformer so if they are not lighting up then the problem has to be somewhere from the power transformer on back to the wall plug.

Title: Re: Intermittent Amp Power-up -- Possible Causes?
Post by MarkBlair on 04/10/11 at 06:29:33

Brett -

Somehow I missed this brilliant response. Thank you! I was just about to mail the rectifier tube back to Decware for a replacement, but you're obviously much more familiar with how a tube amp works than I am, and your troubleshooting logic seems quite convincing! So I'll do more troubleshooting...

Mark