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legg <legg@nospam.magma.ca>: Feb 06 02:09AM -0500 On Thu, 4 Feb 2016 18:41:31 -0000 (UTC), Cursitor Doom >also hinted that it had been very hot. I couldn't see it on inspection >initially as it was hidden by HV shielding. >Now I just have to find an equivalent for it...   Your Towers would have suggested 2n3439/2N3440 or a BUY60. TO5 body sizes are no longer common, but those types are still listed by digikey.   BSW68 is 150V, 1A, 40MHz, 800mW, 30min hfe.   A ZTX857, in a silicone E-Line body, could probably do it.   RL

Cursitor Doom <curd@notformail.com>: Feb 06 12:34PM On Sat, 06 Feb 2016 02:09:03 -0500, legg wrote:     > BSW68 is 150V, 1A, 40MHz, 800mW, 30min hfe.   > A ZTX857, in a silicone E-Line body, could probably do it.   > RL   Thanks, legg. I'll have a rummage round my copious junk box. I doubt the ft figure has much bearing in this application as whatever the rate this thing switches at it won't be anywhere close to a fraction of that. Likewise the hfe is definitely on the low side, so I shouldn't have any trouble matching or bettering that in a subbed part. Just to reiterate here, this is NOT the main chopper in the smps section; it's a self-standing HT generator card with its chopper being driven by a single transistor oscillator stage. In fact it really wouldn't take much modding to swap the BJT for a MOSFET but I'd prefer to stick with the original circuit if poss.

legg <legg@nospam.magma.ca>: Feb 06 11:34AM -0500 On Sat, 6 Feb 2016 12:34:17 -0000 (UTC), Cursitor Doom >single transistor oscillator stage. In fact it really wouldn't take much >modding to swap the BJT for a MOSFET but I'd prefer to stick with the >original circuit if poss.   ft must be equal or greater, similarly beta, which puts a modest amount of doubt for the 3439/40 parts. They are slower general purpose parts, with higher voltage ratings that are accompanied by lower beta (possibly 25% lower at 1A).   The ZTX part is offered as an example of more recent physical equivalents of higher speed switches in the same voltage range. It's silicone package has the same temperature limts as hermetic and it can benefit just as much by heatsinking methods common to TO5, if present in the current application. It should gunction with whatever base drive and SOA load line tailoring that was applied to the original, with reduced switching and conduction losses.   I wouldn't advise a switch technology swap until you become more familiar with the circuit functioning as originally intended. There is seldom any noticeable benefit in low/medium power applications.   RL

"pfjw@aol.com" <pfjw@aol.com>: Feb 05 10:43AM -0800 OK, got to the p/s, it ain't nohow easy.   Total of six (6) 220 @ 63V radial caps, and four (4) 220 @ 100V radial caps. In situ, one of the 100V and one of the 63V looked bad. My first pull of the 63V units had an ESR of 1.8, and read 114uf. All will go, both voltages.   But, I still welcome any suggestions or advice!   Peter Wieck Melrose Park, PA

Trevor Wilson <trevor@SPAMBLOCKrageaudio.com.au>: Feb 06 09:25AM +1100 > engine, but I am also hoping that someone out there may have had some > experience with these beasts.   > Peter Wieck Melrose Park, PA   **I repaired one years ago. I have the full manual (paper version) somewhere, if you really need some of it, I may be able to scan and post. I do recall that it is a bastard of a thing to fix. Mine had (if I recall correctly) a failed output stage.   -- Trevor Wilson www.rageaudio.com.au   --- This email has been checked for viruses by Avast antivirus software. https://www.avast.com/antivirus

Tim Schwartz <tim@bristolnj.com>: Feb 06 07:40AM -0500 > Thoughts? Suggestions? I am searching for the manual from HiFi engine, but I am also hoping that someone out there may have had some experience with these beasts.   > Peter Wieck > Melrose Park, PA   Hi Peter,   I have NOT worked on a B251, but I have work on several B750's and other Revox products. I have often seen small 'bead' style tantalum caps short in all sorts of circuits. While I'm not a fan of wholesale replacement of capacitors, I'd ohm-meter them if accessible and change as needed. I'm not a huge fan of tantalum caps in power supplies, they have very low leakage, but are very intolerant of over voltage or reverse voltages.   Regards, Tim Schwartz

"Gareth Magennis" <sound.service@btconnect.com>: Feb 05 06:43PM "Mark Zacharias" wrote in message news:ub0ty.295537$O41.92093@fx37.iad...   > If it is a polarity problem, it could be in the outlet that the amp > is plugged into at home.   Just yesterday had a hum problem caused by the infamous "yellow glue turned brown"   The glue was apparently conductive enough to couple to a signal lead right at the edge of the goop.   Strangely, the hum was 60 hz instead of 120. Still haven't figured out that part.     Mark Z.             Just today I was clearing yet another pair of KRK Rokit8 powered speakers of black glue gone conductive. These are not particularly old, yet this problem has been around for a very long time.   How long does it take for manufacturers to stop using this shit?       Gareth.

"pfjw@aol.com" <pfjw@aol.com>: Feb 05 10:59AM -0800 On Friday, February 5, 2016 at 1:43:53 PM UTC-5, Gareth Magennis wrote:     > How long does it take for manufacturers to stop using this shit?   Keep in mind that RTV silicon materials emit (contain) acetic acid (vinegar). Which attacks copper, at least. It may not be the glue itself, but the curing products reacting with the metal(s) within the system. As long as things are dry, OK. But under high humidity conditions, the salts will attract moisture, and then let the fun begin.   Peter Wieck Melrose Park, PA

"Gareth Magennis" <sound.service@btconnect.com>: Feb 05 07:04PM wrote in message news:023350fd-2984-4adb-b6ea-9eed1ab47d7d@googlegroups.com...   On Friday, February 5, 2016 at 1:43:53 PM UTC-5, Gareth Magennis wrote:     > How long does it take for manufacturers to stop using this shit?   Keep in mind that RTV silicon materials emit (contain) acetic acid (vinegar). Which attacks copper, at least. It may not be the glue itself, but the curing products reacting with the metal(s) within the system. As long as things are dry, OK. But under high humidity conditions, the salts will attract moisture, and then let the fun begin.   Peter Wieck Melrose Park, PA             I think the problem here is the heat generated inside a small speaker cabinet by the power amps. I suspect it is this heat cycling that transforms the glue into something else.     Gareth.

"Gareth Magennis" <sound.service@btconnect.com>: Feb 05 07:08PM "Gareth Magennis" wrote in message news:mn6ty.612803$wX5.241955@fx40.am4...       wrote in message news:023350fd-2984-4adb-b6ea-9eed1ab47d7d@googlegroups.com...   On Friday, February 5, 2016 at 1:43:53 PM UTC-5, Gareth Magennis wrote:     > How long does it take for manufacturers to stop using this shit?   Keep in mind that RTV silicon materials emit (contain) acetic acid (vinegar). Which attacks copper, at least. It may not be the glue itself, but the curing products reacting with the metal(s) within the system. As long as things are dry, OK. But under high humidity conditions, the salts will attract moisture, and then let the fun begin.   Peter Wieck Melrose Park, PA             I think the problem here is the heat generated inside a small speaker cabinet by the power amps. I suspect it is this heat cycling that transforms the glue into something else.     Gareth.           Could it be that some carbon compound or something else in the glue gradually migrates to the bottom of the glue pile as it constantly softens and rehardens? This would place a nice conductive layer on the PCB.       Gareth.

Sjouke Burry <burrynulnulfour@ppllaanneett.nnll>: Feb 05 08:29PM +0100 On 05.02.16 19:43, Gareth Magennis wrote: > long time.   > How long does it take for manufacturers to stop using this shit?   > Gareth.   They do it on purpose. It ensures failure a bit after the guaranty period........ :)

"Mark Zacharias" <mark_zacharias@sbcglobal.net>: Feb 05 07:18PM -0600 <pfjw@aol.com> wrote in message news:fd310c78-4154-439c-9bc7-3404ce2ef21f@googlegroups.com...   > Just a random thought.   > Peter Wieck > Melrose Park, PA   I did wonder about that but it seemed a bit much. There was also an important but not necassarily the same circuit ground in the affected area. Possibly that coupled over somehow.   mz

"Mark Zacharias" <mark_zacharias@sbcglobal.net>: Feb 05 07:19PM -0600 > Gareth.   I don't think it's by accident.   mz

Phil Allison <pallison49@gmail.com>: Feb 05 09:48PM -0800 Gareth Magennis wrote:   > I think the problem here is the heat generated inside a small speaker > cabinet by the power amps. I suspect it is this heat cycling that > transforms the glue into something else.   ** The black glue used has the same problem as the old yellow glue - over time and with a little heat it hardens and become conductive and corrosive to metal.   Rokit8s have it poured all over the place like salad dressing and it is very tedious to fully remove and repair the damage it causes.   Users tend to leave powered speakers like KRKs or Alesis powered on 24/7 in the mistaken belief they turn off automatically when not being used - when all they do is mute. A LED indicator goes out on the front to reinforce the idea. This means the problem happens years earlier for them.   The Alesis M1s are the worst, cost the SMPS blows up and a toroidal inductor has to be stripped, cleaned & rewound.     .... Phil

Larry <f6ceedb9c75b52f7fcc0a55cf0cfbf5d_1030@example.com>: Feb 06 04:37AM 3/4 HP Frame M560   --

Chuck <chuck@mydeja.net>: Feb 05 10:55AM -0600 On Thu, 4 Feb 2016 05:09:48 -0600, "Mark Zacharias"   >I was pretty confident I could fix it, but one problem kept hiding behind >the last one, and oscillation problems kinda turn my knees to jelly.   >Mark Z.   Mark,   These were the worst! I've seen 20 or more transistors blown on these amps. I admire your tenacity. The Accuphases were so much easier to repair.   --- This email has been checked for viruses by Avast antivirus software. https://www.avast.com/antivirus

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