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Phil Allison <pallison49@gmail.com>: Dec 29 04:32PM -0800 **Hi,   what specs does an audio generator need to make it ideal for servicing guitar amps? I suspect most would say practically any budget priced bench generator will be fine - but is it ?   Most guitar amps have very high gain, wide range tone controls and built in treble boost. They also can output plenty of hum, noise and harmonic distortion all of which is unlike regular audio gear.   So, there are some special needs the generator ought to meet.   1. Ability to adjust the output level to well below 1mV and smoothly up to several volts.   2. Circuitry not linked to the AC safety ground to avoid hum loops.   3. Have a fixed level output to connect to the external trigger input on a scope - so the trace remains in synch despite noise, hum and harmonics.   3. Square wave output for checking tone circuits and amplifier stability.   4. Frequency from 10Hz to 100kHz, preferably in four overlapping ranges.   5. Amplitude remains steady when frequency setting or range is changed. 6. THD not more than 0.1% with low order harmonics.   If #6 is not met, then those amps that have large amounts of fixed treble boost (like Mesa Boogie) will amplify the harmonics coming from the generator far more than the fundamental - resulting in a dirty looking wave on the scope. Function generators are best avoided.   BTW: use an analogue scope - using DSOs with guitar amp repairs just makes life hard for yourself.     .... Phil

Wond <gboot.phil@gmx.com>: Dec 30 03:53PM On Mon, 29 Dec 2014 16:32:16 -0800, Phil Allison wrote:     > BTW: use an analogue scope - using DSOs with guitar amp repairs just > makes life hard for yourself.   > .... Phil   Do you have a favourite?

Sam Seagate <saseag44419@yahoo.com>: Dec 30 09:45AM -0500 On 12/27/2014 11:08 AM, N_Cook wrote: > make a bit more failsafe add some heat insulation around each polyswitch > and reduce the thickness of insulation if they falsely cutout. If you > don't want to go overboard with current limiting circuitry   Thanks for the tip! A "polyswitch" wasn't something I was familiar with until I looked it up. It looks like a fuse that resets itself once a fault is corrected, is that right?   The configuration I've gone with is four LED's for each C7 bulb. The LED's are driven in series by a 12 V power supply with current set at 10 mA.   I have a current resistor set for each four LED candle since each one drew a different current amount with the same resistor. All set for 10 mA.   The question is, where do I place the polyswitch and how do I determine what amperage/ voltage I need? For two rooms, I have a 12 V supply powering two candles, with each candle set as above (3V @ 10mA) and in another room, I have four candles powered by a 12 V supply. Ideally, I'd like to place the polyswitch at the power supply output before it branches off to either the two or four candle arrangement.   Any tips here would be helpful.   Thanks, Sam

Tim Schwartz <tim@bristolnj.com>: Dec 29 12:30PM -0500 Hello all,   Just a warning that I was about to use a "2N5401" that is marked as follows:   2N 5401 CH13   and on the back, molded in a circle on the rear is K1 or K7 - the ones with the K7 have the lettering slightly rotated.   On these devices, the middle pin is the COLLECTOR not the Base, as a genuine 2N5401 would be. These devices are on a paper tape strip of 20 I bought, and unfortunately I did not keep them in the original package, so I don't recall where they came from.   Just thought I'd mention it here, as it could cause a lot of grief when repairing something. I did not bother to curve trace these to see if they otherwise meet spec, as I plan to trash them. I've since ordered some proper 2N5401's from Digikey.   Regards, and Happy New Year Tim Schwartz Bristol Electronics

N_Cook <diverse@tcp.co.uk>: Dec 29 06:36PM On 29/12/2014 17:30, Tim Schwartz wrote:   > Regards, and Happy New Year > Tim Schwartz > Bristol Electronics   Why would anyone bother faking such tiddlers? I've never heard of anyone gorging 1 cent or 1 penny coins, equally it just makes no sense

dplatt@coop.radagast.org (Dave Platt): Dec 29 11:24AM -0800 >Why would anyone bother faking such tiddlers? I've never heard of anyone >gorging 1 cent or 1 penny coins, equally it just makes no sense   Since they're a part which is listed as "obsolete" or "end of life" by most manufacturers, there still may be a bit of "boutique" demand from some customers who either have to use the same part number (e.g. for servicing) or re-quality their design.   I sorta suspect that once a counterfeiter has a parts-marking line set up, it's no big deal for them to just re-mark a few thousand of whatever unlabeled overrun transistors they've got their hands on, with every conceivable part number, and then just list them as "available" in their catalogs. The incremental cost of ginning up fakes for any given part number would be next to zero.

Phil Allison <pallison49@gmail.com>: Dec 29 03:10PM -0800 Nutcase Kook     > Why would anyone bother faking such tiddlers? I've never heard of anyone > gorging 1 cent or 1 penny coins, equally it just makes no sense   ** Fake semiconductors are almost always created by removing the old markings and adding new ones that dramatically increase the value of the part.   It relies on the fact that semiconductor packages are all standardised with only the markings revealing who made it and what chip is inside.   So there is no similarity with fake bank notes, shoes or handbags.   I have seen only one example of a fake transistors that were specially manufactured: steel TO3 paks labelled as being Motorola MJ15003/4 from "MEX1C0" (no kidding) while inside were two chips attached directly to the steel base and wired in parallel.   I once purchased some fake BC639/640 transistors in TO92 pak - performance tested much the same as BC548/549 parts.   Neither of the above were usable in place of the real thing.   OTOH I have bought fake electros that were "made": 22uF,450V NipponChemicon caps were faked by fitting used 22uF, 400V radial electros inside an axial lead can with a shrink plastic label that was faked. Ingenious.       .... Phil

Tim Schwartz <tim@bristolnj.com>: Dec 29 08:23PM -0500 On 12/29/2014 2:24 PM, Dave Platt wrote: > with every conceivable part number, and then just list them as > "available" in their catalogs. The incremental cost of ginning up > fakes for any given part number would be next to zero.   Dave,   I suspect you are correct. There is someone somewhere who will take scrap/surplus/defective parts and put whatever number on it that they think they can sell.   Take the Japanese marking system of transistors (2SA,B,C,D) each number is unique to a manufacturer. So, if Sony wants to make a transistor that is identical to an NEC device, it will still get its own number. This is different from JEDEC devices where many manufacturers made the 2N3055 for example. They also don't generally revise parts. So while On-Semi relabeled the MJ15003 to a MJ15003G when the part went RoHs, Toshiba replaced the 2SC3281 with the 2SC5200. So, any 2SC3281's still on the market are fakes or surplus, because Toshiba doesn't make them any more.   Regards, Tim Schwartz Bristol Electronics

Phil Allison <pallison49@gmail.com>: Dec 29 07:15PM -0800 Tim Schwartz wrote:   > There is someone somewhere who will take > scrap/surplus/defective parts and put whatever number on it that they > think they can sell.   ** Absolutely - a bunch of fakers on Florida called "TIC" for Transistor Instrument Company bought up heaps of obsolete TO3 pak devices and labelled them with whatever number the customer ordered.   Under the number "MJ15003" I saw 400V, 5A switching transistors and even power Darlingtons.     > Toshiba replaced the 2SC3281 with the 2SC5200. So, any 2SC3281's still > on the market are fakes or surplus, because Toshiba doesn't make them > any more.   ** You can bet any being offered by HK dealers on the net are fakes.   FYI: Motorola and ON played dirty sometimes too. There was still a demand for old numbers like MJ802/4502 and 2N3773 devices for repair work etc - so Motorola listed them in their catalogues. They were NOT the original types but current production MJ15003/4s relabelled by them. They typically sold for double the price of MJ15003/4s.   They can legally do this, as MJxxxx numbers are proprietary to Motorola and ON.   Also, along with MJ15003/4s, types like MJ15024/25 have gone through many die changes and current production examples are very different to ones made 10 or 20 years ago. IOW they do not match when mixed in parallel groups.       .... Phil

Cydrome Leader <presence@MUNGEpanix.com>: Dec 30 04:06AM > that is identical to an NEC device, it will still get its own number. > This is different from JEDEC devices where many manufacturers made the > 2N3055 for example. They also don't generally revise parts. So while   didn't know this. interesting.

N_Cook <diverse@tcp.co.uk>: Dec 30 11:26AM On 30/12/2014 01:23, Tim Schwartz wrote:   > Regards, > Tim Schwartz > Bristol Electronics   I'm aware from a medical devices manufacturer of fraudulent RoHS but otherwise genuine componenents being supplied with false documentation into RoHS exempt supply trains for RoHS derogated industries like medical , nuclear , military and aerospace. Good money in that mark-up just for printing off false documentation. Its not that simple testing for the absence/presence of elemental/alloyed lead.

"Mark Zacharias" <mark_zacharias@labolgcbs.net>: Dec 30 05:28AM -0600 "Tim Schwartz" <tim@bristolnj.com> wrote in message news:54A18FCA.8070503@bristolnj.com...   > Regards, and Happy New Year > Tim Schwartz > Bristol Electronics   Tim,   The 2N5401's used by Yamaha on most models the past six or more years, are not fake and are based E-C-B like the Japanese signal transistors. Don't know why, and I don't know why they used American designation. I mentioned it to our tech rep and he kinda snickered.   But they aren't fake. For example, Q1071 shown on page 125 of the RX-V773 service manual, is a "2N5401C" . I picked this manual almost at random, but many Yamaha models use these.   Q1069 and Q1070 are '2N5551C" same ECB basing.     Mark Z.

N_Cook <diverse@tcp.co.uk>: Dec 30 11:34AM On 30/12/2014 11:28, Mark Zacharias wrote: > random, but many Yamaha models use these.   > Q1069 and Q1070 are '2N5551C" same ECB basing.   > Mark Z.   So for more general application, not just 2N5401. From the OP device marked 2N 5401 CH13 so could the suffix be C and then perhaps H fortnight of year 2013 as a datecode? and a genuine 2N5401C , C designating the pinning varient?

mroberds@att.net: Dec 30 07:27AM Hello all!   I recently replaced the power supply in a Dell Optiplex 760 mini-tower PC. I found out that not any random ATX power supply will fit; the hole in the Dell case is a little smaller than is standard. You need a power supply where anything that sticks out on the back panel, like the AC line connector, isn't too close to the edge of the power supply. I couldn't make an Antec Basiq 350 fit - its line connector was too close to the edge. An Antec VP450 fit and worked OK.   I made a small writeup about it: http://birdbird.org/electronics/optiplex-760-power/optiplex-760-power.html   Also note this is *not* one of the "small case" versions of the Optiplex 760; those take a non-ATX supply that I don't know much about.   Standard disclaimers apply: I don't get money or other consideration from any companies mentioned.   I hope this helps!   Matt Roberds

sam@repairfaq.org (Samuel M. Goldwasser): Dec 29 04:45PM -0500 Google comes up empty.   This is a hockey puck SCR. Based on its performance, it is also unusually fast for a garden variety SCR. The closest I can find is for the C387 series found in a 1977 GE datasheet, which is similar and fast and may be its predecessor, but doesn't go up to anywhere close to the voltage I've been using it at (!!) without problems.   Thanks!   -- sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/ Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/ +Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm | Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html   Important: Anything sent to the email address in the message header above is ignored unless my full name AND either lasers or electronics is included in the subject line. Or, you can contact me via the Feedback Form in the FAQs.

mroberds@att.net: Dec 29 10:39PM > datasheet, which is similar and fast and may be its predecessor, but > doesn't go up to anywhere close to the voltage I've been using it at > (!!) without problems.   Is this the data sheet you found? http://www.datasheetarchive.com/dl/Scans-005/Scans-00102816.pdf The charts at the top say 120 to 550 A, depending on the frequency, 2 uS typical turn-on, 30 to 40 uS typical turn-off. The "N" in the part number implies that it's an 800 V part. The flange on the top is 2.2" diameter. It also talks about a "new high-frequency rating" for rectangular pulses, but that seems to have more to do with current and pulse shape, than voltage.   Some other sources say that the GE designation for the above data sheet was "specification sheet 170.44".   Google Books has a few different versions of the GE SCR manual, but they won't show the scans. I found a scan at (slightly munged) www dot introni dot it /pdf/GE%20-%20SCR%20manual%201972 dot pdf , but all it has on the C387 is a similar overview sheet to the two documents above.   Matt Roberds

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