Recent Posts

1

Repair / Re: Heathkit EC-1 Analog Computer repair

« Last post by mag_therm on Today at 02:31:56 pm »

Hi Vintcomp2
I spent a little time this morning  on possible EC-1 failures which would allow higher DC voltages on the banana jacks for the Op-Amp outputs.
Failure (to high resistance) of components R10, R14 and the pentode of 6U8 could cause the triode cathode follower of 6U8 to go high.
By 6U8 data, positive grid could allow 40 mA to flow with the plate at 250V as shown on circuit.
The design  has the two series NE2H Neons partly to provide some protection. However they have no current limitation on the high side.
With uncontrolled current these can go into an arcing mode ( bright purple)  before failure by overheating.

The actual overvoltage on the jacks would have to be checked by simulating the above failure modes.

Changing the Output jacks to the present shrouded type (as in multimeters) may be possible, but that would still leave the other end of the patch leads with exposed bananas, and by the photos, changing ALL jacks may be impractical.

The EC1 has the high voltage switch and green lamp maybe as the only means of protecting the programmer.

If attempting to power this up, repair and when using it, I would use a 120:120V isolation transformer with a grounded interwinding screen, and leave the EC-1 chassis floating. That would reduce the possibility of a grounded user receiving shock, except if he was touching the chassis at same time.

I have such a transformer here, and used it when restoring  valve/tube units. I have a 1959 60W tube guitar  amplifier , a FM radio from about 1958, and a shortwave receiver Lafayette HE30 from 1963. I have bolted the guitar amp into a grounded steel rack as a practise amp and it is not to be taken out for use in gigs.

The HE30 still has a 2 pin 120V lead. I did not replace the lead with a 3 wire, as the antenna input is grounded to the ham radio ground bar on my workbench
For  the FM receiver I added a new internal isolation transformer and left the 2 pin supply because the chassis is completely contained in a wooden case.

And the analog computer that I learned on, was a EAI, fairly new in 1969. It had transistorized op-amps as plug in modules.
 
 Hope this info helps

2

General Technical Chat / Re: Need 13Amp variac device to 'modulate' a water boiler.

« Last post by paulca on Today at 02:30:31 pm »

You will find that if you set the thermostat to 99C that, most likely, some of the water will still boil because the fluid is not totally uniform and your sensor will be taking just one sample from a large container and the heating element plus convection currents will ensure some of the water has exceeded 100C.  Also, of course, environmental pressure variations and any tolerance in your sensor will need to be accounted for.

Yeah.  I was just running this buy some fellow brewers on reddit.  Enquiring to the purpose and criticality of a "rolling boil for 1 hour".

Turns out it is more an "ideal" and it's likely the thermostat set to 99.999C or as close as I can get it while still cutting out and not constantly boiling the wort away...  it should be fine.  I'm not going to ruin the beer, only drop a few percentile on my "ideals".

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Microcontrollers / Re: Signal filtering - Could this work ?

« Last post by eutectique on Today at 02:27:45 pm »

Also ...

A stored value beeing 4 bytes that make for a very big buffer !

Why not 2 bytes?

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Other Equipment & Products / Re: CFW for KSGER/Quicko STM32 Soldering Stations

« Last post by DavidAlfa on Today at 02:27:06 pm »

I can't. Set Ki to 0, adjust Kp until it doesn't oscillate, then try increasing Ki until overshooting.

5

Test Equipment / Re: Looking for a replacement general purpose oscilloscope for home use

« Last post by KungFuJosh on Today at 02:24:56 pm »

KungFuJosh

Or, in other words, I'm clueless and stupid.

Well you have every right to your own view and I respect that. Time will tell if and if so, how wrong I am.

Friendly regards nevertheless

I never said anything like that. Nothing that I said was directed at you, or with ill intent. Don't take it personally if somebody doesn't agree with you. You speculated about something, and I disagreed with your speculation and presented information. It's as simple as that.

6

Beginners / Re: Old car LED headlight issue advice please

« Last post by CaptDon on Today at 02:23:27 pm »

My old 48 international truck had that weird positive ground thing also. Many older vehicles were made that way. I flipped it to negative ground. The starter doesn't care about polarity and the generator was easy to re-polarize. I found out that generators were not specified as positive or negative ground but were polarized during installation often by leaving the fan belt off and jumping the cutout relay to run the generator as a motor for a few seconds. I did also have to switch the polarity of the ignition coil primary leads. It had a + and - terminal. The gauges worked with no modifications, they were King-Seeley hotwire gauges. Also had to reverse the ammeter leads if I recall. I wonder if the cutout relay has some sort of permanent magnetic bias? once the contacts close it seems they would be unable to open since the battery voltage would continue to energize the coil even when the generator came to a stop? Those systems were weird. We had a third brush 6 volt generator on an old Gray Marine flathead 6 cylinder. It never gave any problems. My 48 truck had a more complex regulator with current and voltage regulation as well as a cutout relay. It had 3 relays under the cover and two or three power resistors under the base.

7

Test Equipment / Re: SDS800X HD Wanted Features

« Last post by Performa01 on Today at 02:21:36 pm »

Navigation defaults to "by time". Frankly, I have not understood what that mode is needed for at all: I have a dedicated horizontal position knobfor continuous adjustment, or can call up a keypad quickly via the Timebase info box if I want to go to an absolute value.

As already explained once, the Time navigation was one of only two methods to position a zoom window at high zoom-factors or set an extreme trigger delay on the older SDS1004X-E series. It is not really needed on the touch screen instruments anymore, yet it’s the only one that is possible at any time.

I would much rather use Navigation -- and the dedicated arrow buttons on the front panel -- to navigate by history frame: Stop an acquisition, and have the buttons ready to step through the history frames right away.

I could answer like this: Frankly, I have not understood what that mode is needed for at all: I have the very same navigation possibilities directly in the history menu. And indeed, I have never ever in almost ten years used Navigate for browsing the history of a Siglent DSO.

It might have to do with the fact that the higher-class instruments (which I normally use) have increasingly less buttons on their front panels. The SDS2000X Plus still has Navigate and History buttons, whereas the SDS2000X HD has none of them and SDS3000X HD is the same. Even more importantly: none of them have the back-, pause- and forward-buttons; these are really exclusive to the SDS800X HD - which I only use if I must (e.g. to produce screenshots for a review 😉), because of its small screen and the almost unbearable (for me) high acoustic noise level. Consequently, I’m not used to these buttons at all. I’m rather used to the History button on the front panel, which I’ve consequently programmed into the Quick Action button of all the instruments that don’t have one anymore. Never using auto-hide for the menus adds to the fact that I’m not missing the button navigation at all.

In my opinion, it was a big fail to make the SDS800 so similar to the 1000X-E, despite being a touch scope. Whoever directly upgrades from 800X HD to 2000X HD will complain: “where are all my beloved buttons gone?!” I was the same when I got the SDS2000X HD after I was used to the SDS2000X Plus. Yet I realized pretty quickly that this is now the new trend – most of the front panel dedicated to the screen and less buttons – and that I just have to live with it.

Having said all that, it probably wouldn’t be a big problem to remember the last setting for Navigate, even though time navigation is the only one that is always available. So it would have to default to that one again whenever neither History nor Search results are available.

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Projects, Designs, and Technical Stuff / Re: Show us your mains waveform!

« Last post by niels747 on Today at 02:21:29 pm »

Mine has a flat top 24/7 and a nasty 17 kHz ripple on it during the day, from the solar inverter

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Projects, Designs, and Technical Stuff / Re: MAX7418EUA+ Newbie question

« Last post by Agosto on Today at 02:20:44 pm »

Thanks!! Looked at the tutorials. Will give it a try. The adapter to DIP is also a great suggestion. Found them at Digikey. Thanks again!

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Beginners / Re: Dimming signal 0-12V from microcontroller (logic level to 12V PWM)

« Last post by xvr on Today at 02:19:23 pm »

LED brightness really very NOT linear to current/PWM duty cycle. I had an experiment with dimmable RGB led. I run it with PWM in 0-255 duty cycle range.
Values of 255-128 were almost indistinguishably (but PWM work as expected - mean consumed current dropped linear).
Values 128-64 where distinguishable, but not much. And only when PWM duty cycle drops to 20-10 per 256 each change in it became clearly visible.