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N_Cook <diverse@tcp.co.uk>: Feb 16 09:41AM > Keep in mind that "sand resistors", while not precision resistors by any description are rather delicate beasts and acted as a sort of fusible link in many radio designs from the 40s through the 60s - most especially those that were AC/DC/Battery.   > Peter Wieck > Melrose Park, PA   I'm thinking of the usually white block type, a porcelain trough holds the wire wound on a ceramic core, then sealed with something that is too hard to be Portland cement, more like the hard glass of green or grey vitreous coated ones. A dart point would not scratch either , but is would scratch the coating of those old 60s/70s buff/yellow Portland cement coated capacitors.

tabbypurr@gmail.com: Feb 15 04:12PM -0800 On Friday, 15 February 2019 23:43:11 UTC, ehsjr wrote:   > Selecting which 'scope to buy can drive you nuts. I > feel your pain. :-)   > Ed   I was offered a 1940s Cossor recently for £20-30. 339A I think it was, the world's first modernish scope. But no possibility to calibrate it, they were't accurate enough then to bother making them calibratable. I said no :)   If all you're doing is audio, any halfway sane scope will do that, even that Cossor.     NT

Phil Allison <pallison49@gmail.com>: Feb 15 04:20PM -0800 > Both of those are way above audio, which only extends to 20kHz.     ** While the audible range extends to just a little over 20kHz this has NOTHING to do with the frequencies regularly encountered in *audio electronics*.   You are making a common and BIG mistake !!!   A scope suitable for audio electronics needs a BW of at least 10MHz, preferably 50MHz and good waveform resolution - which counts out all the 8 bit "digital" toys being offered today.     .... Phil

etpm@whidbey.com: Feb 15 04:33PM -0800 >> Eric   >Both of those are way above audio, which only extends to 20kHz. To get a reasonable picture of a waveform you'd want at least 8 - 10 samples per cycle. A 1MHz scope would be more than enough for audio. You can get a 200kHz pocket scope for under £20 :) It might well suffice for what you're doing.   >NT I would like the analog scope for audio. I know that it doesn't need to be anything fancy. Just two channels and a display big enough for my old eyes to see easily. But the DSO is for the CNC machines. Even then I know I don't need a 100 MHz 'scope. I think. I have read that when it comes to digital 'scopes you want something like 5 times the bandwidth of what you are trying to measure. There are so many options with the new DSOs that I really don't understand. Which is why I am asking for advice here. I would ask in basics but more people seem to read thisw newsgroup. And the DFSO will be used for repairing electyronics. Eric

Phil Allison <pallison49@gmail.com>: Feb 15 04:28PM -0800 > I was offered a 1940s Cossor recently for £20-30.   ** So they were offering to PAY you to take the POS away ?     > If all you're doing is audio, any halfway sane scope will do that, > even that Cossor.     ** Absolute BOLLOCKS.   Audio is ELECTRONICS, not sound.   The range of frequencies found in audio electronics extends to frequencies of many MHz. Domestic AM and FM radio deceivers are considered "audio".   Radio microphones are considered "audio".   Faulty ( or badly designed / built ) audio amplifiers may exhibit oscillation upto 50MHz.   Digital audio seems to know no bounds.     ... Phil

Terry Schwartz <tschw10117@aol.com>: Feb 15 04:32PM -0800 My .02 cents....You can never have too much bandwidth. Sooner or later you will need more. Recently got a 300 MHz Tek, old CRT digital dog but I love it. So far I haven't needed 300 MHz but I know I will.

Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net>: Feb 15 07:47PM -0500 On 2/15/19 7:32 PM, Terry Schwartz wrote: > My .02 cents....You can never have too much bandwidth. Sooner or later you will need more. Recently got a 300 MHz Tek, old CRT digital dog but I love it. So far I haven't needed 300 MHz but I know I will.   There are a lot of TDS 744As out there for ~$600, which can be converted to 4-GSa/s, 1-GHz TDS 784As by moving one jumper and desoldering three 0603 caps.   I have a couple, and am very happy with them.   Cheers   Phil Hobbs   -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510   http://electrooptical.net http://hobbs-eo.com

Fox's Mercantile <jdangus@att.net>: Feb 15 07:03PM -0600 On 2/15/19 6:20 PM, Phil Allison wrote: > You are making a common and BIG mistake !!!   > A scope suitable for audio electronics needs a BW of at > least 10MHz, preferably 50MHz and good waveform resolution   For years, I had been using a Tektronics 422. Reasonable size and 2 channels. Most of the work I do is on old AM broadcast tube radios.   I had to occasion to work on a Drake R-4A receiver. It had some seriously silly problems. While tracking them down, I realized I had some band width issues with the scope not giving me accurate results.   Drag the Tektronix 2465 over. Oh my, that's different. Yeah 200 MHz vs 10 MHz makes a big difference.     -- "I am a river to my people." Jeff-1.0 WA6FWi http:foxsmercantile.com

tabbypurr@gmail.com: Feb 15 10:23PM -0800 On Saturday, 16 February 2019 00:28:59 UTC, Phil Allison wrote: > tabby wrote:   > > I was offered a 1940s Cossor recently for £20-30.   > ** So they were offering to PAY you to take the POS away ?   Vintage scopes have market value for collectors.   > > even that Cossor.   > ** Absolute BOLLOCKS.   > Audio is ELECTRONICS, not sound.   no kidding   > The range of frequencies found in audio electronics extends to frequencies of many MHz. Domestic AM and FM radio deceivers are considered "audio".   > Radio microphones are considered "audio".   I'd call those radio myself   > Faulty ( or badly designed / built ) audio amplifiers may exhibit oscillation upto 50MHz.   which can be found on a low speed scope with a capacitor & diode   > Digital audio seems to know no bounds.   though it doesn't normally tax any sane scope. The 200kHz toy scope it may do, but for some hobbyists it may be good enough. Then there are smpsus.     NT

Phil Allison <pallison49@gmail.com>: Feb 15 11:05PM -0800 > > > I was offered a 1940s Cossor recently for £20-30.   > > ** So they were offering to PAY you to take the POS away ?   > Vintage scopes have market value for collectors.   ** Still a POS and you are no collector.         > > ** Absolute BOLLOCKS.   > > Audio is ELECTRONICS, not sound.   > no kidding   ** Asinine reply, from an utter ass.       > > The range of frequencies found in audio electronics extends to frequencies of many MHz. Domestic AM and FM radio deceivers are considered "audio".   > > Radio microphones are considered "audio".   > I'd call those radio myself   ** Another asinine reply.   Folk who service "audio" are expected to do each of them.       > > Faulty ( or badly designed / built ) audio amplifiers may exhibit oscillation upto 50MHz.   > which can be found on a low speed scope with a capacitor & diode     ** Completely irrelevant.     > > Digital audio seems to know no bounds.   > though it doesn't normally tax any sane scope.     ** As if a bullshitting troll like you would know.   NT = nutcase troll.   Fuck off.     .... Phil

Jeff Liebermann <jeffl@cruzio.com>: Feb 15 07:02PM -0800 >"Whoops! It looks like the wave is over compensated. So it looks like >at the beginning of the flat waveform it has a little peak that then >drops down to form a flat line for the rest of the wave.   Under compensated or too little capacitance. The overshoot of the rising part of the square wave means you have too much high frequency response.   >This of >course repeats but in the negative direction for the negative part of >the wave.   Yep. If the negative going part of the waveform were not identical, then your input square is not symmetrical.   >I thought you meant frequency for the time dimension but now >I think what you mean is how long does it take for the waveform to >become flat.   No. The flat part of the waveform is the low frequency component, which is independent of the rise time. If the flat part sags, then you are capacitor coupling (AC coupling) somewhere, probably the AC/DC switch on the vertical input.   >It looks like it takes .1 mS. And the overshoot is about >30mV   I can't tell if that means that it sags 0.1msec or the overshoot lasts 0.1msec. Perhaps a posting photo of the screen would be helpful.   More reading: "The Secret World of Oscilloscope Probes" <http://www.dfad.com.au/links/THE%20SECRET%20WORLD%20OF%20PROBES%20OCt09.pdf>   The link in the video to EEVblog doesn't work. This does: "EEVblog #453 - Mysteries of x1 Oscilloscope Probes Revealed" <http://www.eevblog.com/forum/blog/eevblog-453-mysteries-of-x1-oscilloscope-probes-revealed/?all>   -- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558

Lucifer <LuciferMorningstar@bigpond.com>: Feb 16 10:46AM +1100 I suppose an amateur radio group would be better but they are very quiet.   The mechanical tuning dial works as it should but the radio won't tune above .783 in each band. I haven't had the cover off yet but I'm thinking the VFO variable capacitor is being prevented from full movement.

dplatt@coop.radagast.org (Dave Platt): Feb 15 04:40PM -0800 In article <cqje6edjk5aqrc9g2rrojqje26ahl1l0h7@4ax.com>, >won't tune above .783 in each band. I haven't had the cover >off yet but I'm thinking the VFO variable capacitor is being >prevented from full movement.   That's possible. It may be purely mechanical - a loose tuning cord (I can't tell if the design uses one), or a loose shaft coupling, or an obstruction (e.g. bent plate on the capacitor, or a small dead cockroach, or etc.) which binds the mechanism at some point in its rotation.   It's also possible that there's something wrong with one of the circuits to which a variable-capacitor section is connected. For example, the VFO might be stopping entirely when you try to tune it into part of its range. This might indicate (e.g.) a weak transistor, or a capacitor that has become leaky... something which causes the gain inside the oscillator loop to drop below 1.   Best way to distinguish would probably be to hook a frequency counter and/or o'scope to the output of the VFO unit. Tune it through its range, and see if you get a reasonable output signal throughput the range.   If the VFO produces a consistent signal, then the next suspect would be the PLL board, which generates the IF frequencies by multiplying the output of the VFO. The PLL might be losing lock for some reason, and shutting down. If the VFO works OK, then scope/count the IF outputs from the PLL, and see if they vanish suddenly or get "stuck" somehow.   The manual has the alignment procedures.   You should also do an "eyeball" inspection to look for obvious failures, such as bulging or leaking electrolytic capacitors. These units are old enough that it might have been built with some 'lytics that suffer from the faulty-electrolyte "capacitor plague". If so, a careful re-capping (with repair of any damaged traces on the board) would be called for.

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