Carlson Violated A Cardinal Rule

[Zenith]

I had a Tek 1502 with a buggered transformer and battery.

I removed the transformer, inserted an AC->12V converter, and connected that to the battery terminals.

Perfect, except you couldn't use it in a field in these conditions...

That's the problem. It's one of those pieces of kit, like a TV signal strength meter, where most of the utility is that it's easily portable.

I imagine you could replace the NiCd pack with NiMh or Li-ion, but they have much more stringent charging requirements and it might be something of a mission.

[bd139]

The ohms failing happened to mine as well. Check the electrolytic capacitors. They go short. That and some crusty trimpots and the dead NiCd was all that was wrong with mine.

They are a very nice design actually. The FET input leakage is compensated using a temperature compensated diode to reinject the leakage current back in. That gives it a "stupid high" input impedance.

I paid £10 for mine so a good deal

Worth remembering as that sort of tip can avoid a lot of messing about.

Offhand I remember the manual saying that the input impedance was 10MegOhms, but it's not a point I'd defend vigorously.

I paid £10 for mine, in a moment of weakness. I'd always been curious about them and that's the main reason I bought it. I'm not suffering from major purchaser remorse, but I've had better value for a tenner or less on several occasions. It's small and light which is an advantage. There'll be several hours of innocent amusement in sorting out its problems. I'm not noted for my enthusiasm for cleaning things, but it's very satisfying when you take some of this TE which is in a grotty state, with mould, grime and stickers, dose it with kitchen cleaner and maybe IPA, rinse it off and dry it, and it's transformed.

They are actually fairly well specified bits of kit. All the goodness of a VTVM without the associated issues of warm up time and being horrible to use in summer . Got to say I rather like cleaning things, just not houses.

The input impedance is a nominal 10M which is set by the divider networks but as always the issue with the actual FET buffer is it needs an input impedance considerably more orders of magnitude higher than the divider impedance or it'll act as part of the divider itself.

[tggzzz]

I had a Tek 1502 with a buggered transformer and battery.

I removed the transformer, inserted an AC->12V converter, and connected that to the battery terminals.

Perfect, except you couldn't use it in a field in these conditions...

That's the problem. It's one of those pieces of kit, like a TV signal strength meter, where most of the utility is that it's easily portable.

I imagine you could replace the NiCd pack with NiMh or Li-ion, but they have much more stringent charging requirements and it might be something of a mission.

1502s [1] are also useful in a lab, to investigate the quality[2] of cables, connectors, and PCBs. They have a resolution of ~15mm, i.e. they can distinguish two fingers side by side on a track. Yes, they can see "inside" a typical in-line 50ohm attenuator

It is actually not easy to replace the batteries due to the peverse^h^h^h^h^h^h^h novel design of the battery charger. It is so novel that, to Tek's displeasure, Tek had to issue a service note contradicting the manual "don't charge for more that 16 hours" (as well as do charge once per month!). NiMH cells are more fragile than NiCd, and don't even think about Li cells!

[1] 1502b, 1502c, 1503 don't have that resolution

[2] cable impedance is often 52ohms rather than 50ohms, the effect of kinks and snags, the VSWR of connectors, etc.

[vk6zgo]

Interesting about the domestic radio transformers. During the early to late 80s I was forever hawking for old valve radios being discarded because the transformers were easy to rewind, or at least unwind. I couldn't afford batteries so the mains was the place to get your juice from for early transistor experiments. Unfortunately 6v was a little too low and 150-200v or so was more than a little too high. 15-25v was about right. Didn't need a lot of current so the winding would take it fine. So the trick was to carefully unpick the HT secondary and unthread it until you got the volts you needed. Due to the not too high price of copper at the time, the wire was thick enough to be able to do this without breaking it so it'd get unwound a few turns carefully, then measured via a rectifier and smoothing cap until it was about the right voltage.

Typically those transformers are pretty expensive now and the transistor ones are the ones in the trash! I dread to think how many I mutilated!

They would have ended up in the trash, anyway, so if you could offer them a "glorious Resurrection", I believe you were "on the side of the Angels".
I used to find a lot of such things at ordinary General swap meets, but these days, they are mostly dealers in overpriced junk.

I found a prize in my shed a few weeks back-----a transformer out of a Saltwater pool chlorinator.
Nice ratings, safety rated, but huge!
Dunno what I will ever use it for!

[Zenith]

They would have ended up in the trash, anyway, so if you could offer them a "glorious Resurrection", I believe you were "on the side of the Angels".
I used to find a lot of such things at ordinary General swap meets, but these days, they are mostly dealers in overpriced junk.

Domestic radios and TVs have a following here and there's an organisation called the British Vintage Wireless Society which organises its own swapmeets and auctions. I see a few domestic radios and bare chassis and parts at the ham rallies. I've never asked about prices. They also turn up a lot on ebay. I'm sure if you wanted one just for the transformers and weren't worried about the state of the cabinet or missing knobs, you could get one for £5, something like the price of a pint in a pub.

[vk6zgo]

They would have ended up in the trash, anyway, so if you could offer them a "glorious Resurrection", I believe you were "on the side of the Angels".
I used to find a lot of such things at ordinary General swap meets, but these days, they are mostly dealers in overpriced junk.

Domestic radios and TVs have a following here and there's an organisation called the British Vintage Wireless Society which organises its own swapmeets and auctions. I see a few domestic radios and bare chassis and parts at the ham rallies. I've never asked about prices. They also turn up a lot on ebay. I'm sure if you wanted one just for the transformers and weren't worried about the state of the cabinet or missing knobs, you could get one for £5, something like the price of a pint in a pub.

Indeed, but I would feel bad about it, with the possibility that someone might have ended up rebuilding it to a showpiece.
I saw a nice "collectible" domestic radio at the Perth Hamfest last Sunday, but I already have enough old radios---mainly ham ones, but I also have a 1950s plastic cabinet Kriesler & a late 1940s veneer cabinet Hotpoint, which are the least likely to ever get fixed.

It looks like the Hotpoint may have been "laid up" originally because of a broken dial cord, but it sat in a back shed for decades after that, so who knows what is wrong with it now.

[Zenith]

The vintage radio scene is mainly about case restoration. The electronic problems thrown up by domestic radios are not exactly challenging. I'm sure a lot of this stuff still finds its way into landfill. If you see a bare chassis or a radio with a tatty case for next to nothing, have no qualms about snapping it up for the transformers or tuning capacitor, or whatever bits and pieces you have a need for.

[mnementh]

Old bookshelf stereos... the ones with all the LED/VFD bling... are a great source of power transformers. The Aiwas especially have a secondary with 40-60V CT rated 3-4A continuous, so good for 6A all afternoon... plus a standby 14V winding good for 1-2A. Sometimes another at approx 8V for 5VSTBY.

And of course HT receivers have delicious ones, often double 50-80V CT windings good for 6-10A each set, plus several rando standby voltages.

mnem
I've shamelessly murdered hundreds for the cadavers. I'm like the Burke & Hare of consumer audio.

[mnementh]

Carlson is a gifted amateur; the kind who would probably have been a crackerjack TV repairman back in the hollow-state days. But his advice where modern stuff is concerned can be just plain wrong.

His advice to follow where preinstalled cable-paks "tend to fall of their own accord" is a good one, which tactic I've used for decades when sleuthing out how a "borked unit in a box" is supposed to go together.

But his "fix" on the memory batteries made me cringe; not just because he soldered directly to a Li-xx primary cell (which I've done too using the same "work hot & fast" technique), but his reasoning vs spot-welding a tab to the battery is just plain ignorant. The amount of heat delivered to the guts of the cell is still easily 3 orders of magnitude greater when soldering.

Now that I actually own a tab-welder I'd never do it again, and since nowadays they come as a cheap commodity PCB that can be had for as little as $12 delivered, I could not in good conscience ever recommend the soldering technique, just as a matter of personal safety for the person being advised.

That was cringe enough, but he didn't put any heat-shrink over the cell, just in case it did decide to puke its guts out, and to make a "finished" repair that doesn't have live battery terminals exposed with absolutely no strain-relief. A lot of his "repairs" are similarly "half-finished".

And finally, he never even mentioned the very obvious tactic (at least for those of us in here), and what should've been his first step in determining the polarity of those memory battery plugs; identify which pin is connected to the GND plane of the board.

While not absolutely true every time, at least with memory batteries it will be true most of the time... and if that coincides with your "small positive measured voltage" when probing the board, almost certainly correct. Of course, you can also usually easily follow said battery traces back to the IC they're backing up, and look up the datasheet for said IC. That is the way to be absolutely certain.

His identification of the pads by shape is not what I'd consider good general advice, even if it is applicable to this model... the square pad usually identifies pin 0 or pin 1 (depending on the numbering schema) which often is the first "GND" plane pin, but not always.

mnem
I do wish I could playback faster than 2X speed when watching one of his vids...

[BU508A]

I do wish I could playback faster than 2X speed when watching one of his vids...

You can. Download the video to your harddisk and then play it at whatever speed you like.

Example:
https://ssyoutube.com/en137zD/youtube-video-downloader

[AVGresponding]

Carlson is a gifted amateur; the kind who would probably have been a crackerjack TV repairman back in the hollow-state days. But his advice where modern stuff is concerned can be just plain wrong.

His advice to follow where preinstalled cable-paks "tend to fall of their own accord" is a good one, which tactic I've used for decades when sleuthing out how a "borked unit in a box" is supposed to go together.

But his "fix" on the memory batteries made me cringe; not just because he soldered directly to a Li-xx primary cell (which I've done too using the same "work hot & fast" technique), but his reasoning vs spot-welding a tab to the battery is just plain ignorant. The amount of heat delivered to the guts of the cell is still easily 3 orders of magnitude greater when soldering.

Now that I actually own a tab-welder I'd never do it again, and since nowadays they come as a cheap commodity PCB that can be had for as little as $12 delivered, I could not in good conscience ever recommend the soldering technique, just as a matter of personal safety for the person being advised.

That was cringe enough, but he didn't put any heat-shrink over the cell, just in case it did decide to puke its guts out, and to make a "finished" repair that doesn't have live battery terminals exposed with absolutely no strain-relief. A lot of his "repairs" are similarly "half-finished".

And finally, he never even mentioned the very obvious tactic (at least for those of us in here), and what should've been his first step in determining the polarity of those memory battery plugs; identify which pin is connected to the GND plane of the board.

While not absolutely true every time, at least with memory batteries it will be true most of the time... and if that coincides with your "small positive measured voltage" when probing the board, almost certainly correct. Of course, you can also usually easily follow said battery traces back to the IC they're backing up, and look up the datasheet for said IC. That is the way to be absolutely certain.

His identification of the pads by shape is not what I'd consider good general advice, even if it is applicable to this model... the square pad usually identifies pin 0 or pin 1 (depending on the numbering schema) which often is the first "GND" plane pin, but not always.

mnem
I do wish I could playback faster than 2X speed when watching one of his vids...

That's an old vid, one of the first of his I watched, I think. I had only recently got my TDS420A (cheap-ish, because the vendor thought it didn't boot, because it takes so long...) and found it mildly interesting iirc. I did like his turn of phrase "galloping relays" which is very much what it sounds like.

[Zenith]

Carlson is a gifted amateur; the kind who would probably have been a crackerjack TV repairman back in the hollow-state days. But his advice where modern stuff is concerned can be just plain wrong.........


mnem
I do wish I could playback faster than 2X speed when watching one of his vids...

Well of course, electronics can be approached as a branch of applied mathematics........

Cut the kid some slack. He puts on a show and if you don't like it you don't have to watch it - even at double speed.

I think one of the best of the electronics Youtubers is w2aew. Dave Jones has his moments and his off days.

[mnementh]

I do wish I could playback faster than 2X speed when watching one of his vids...

You can. Download the video to your harddisk and then play it at whatever speed you like.

Example:
https://ssyoutube.com/en137zD/youtube-video-downloader

And have to curate "Carlson bits" in my filesystem?

I think not; it's bad enough having him infest my browser cache until it gets randomly purged...

mnem
*pisses off to do that right now, while I'm thinking of it...*

[mnementh]

Well of course, electronics can be approached as a branch of applied mathematics........

Cut the kid some slack. He puts on a show and if you don't like it you don't have to watch it - even at double speed.

I think one of the best of the electronics Youtubers is w2aew. Dave Jones has his moments and his off days.

Ehhh... where's the fun in that? We all need something to pick on when we're bored...

mnem
fortunately, the SKIP FWD/BACK buttons still work at 2x speed.

[Specmaster]

Hey guys, it really is simple to play back any YT video at many speeds, including twice normal. Simply click on the gear wheel icon even when opening the videos direct from here, you will be presented with 3 options as the attached photo shows.

options.jpg

[mnementh]

Yeah, that's what I was ragging on. It only goes up to 2X speed.

mnem
which is almost enough to make Carlson sound like Alvin, and therefore amusing instead of mind-numbing. almost.

[bd139]

Youtube videos should all be like this:

https://www.youtube.com/watch?v=tLhPhscC4F4

[Specmaster]

Yeah, that's what I was ragging on. It only goes up to 2X speed.

mnem
which is almost enough to make Carlson sound like Alvin, and therefore amusing instead of mind-numbing. almost.

Oops I missed that last bit

[mnementh]

Youtube videos should all be like this:

"Ducks are morons, don't overthink it; they sure don't..."

mnem