Cheap AndEasy 6.3 Volts

>"An ordinary DC meter is all you need to monitor for 6.3V. "

Yes but that takes all the fun out of it. I was looking forward to reinventing the wheel. 

>"Small BRs typically drop around 2v, 1v per diode. 0.6v is the knee voltage, not the typical Vf under load. A lot of EEs get that wrong. "

You're right. Even if the drop is only 0.6 it would still be double with a bridge. So that is more subtraction. Or if I had used 60 Hz instead of 120 Hz it would have been accurate. 

But the fact is this stuff should be thought of in the first place.  

When the mind goes, who knows ? I guess I will have to get up and make the donuts.

>"Years ago I used this approach to create a filament lamp booster/economiser that didn't mess with the operation of CFLs. "

How the hell did that work ? I thought they had bridge rectifiers in them and an oscillator and small transformer. 

On Friday, 9 February 2018 11:43:03 UTC, jurb...@gmail.com  wrote:
nt:

> >"Years ago I used this approach to create a filament lamp booster/economiser that didn't mess with the operation of CFLs. "
> 
> How the hell did that work ? I thought they had bridge rectifiers in them and an oscillator and small transformer.

Mains is bridge rectified. Add a small cap to increase rms but not peak. Now CFLs work just the same on that, but filament lamps run hotter, improving efficacy, shortening life and reducing TCO per lumen. 

This replaced the previous incarnation which just added 18v to mains voltage with an 18v transformer. Bulkier & less cfl friendly.


NT

>"Add a small cap to increase rms but not peak."

Where do you put the cap ?

On Friday, 9 February 2018 22:32:49 UTC, jurb...@gmail.com  wrote:
> >"Add a small cap to increase rms but not peak."
> 
> Where do you put the cap ?

it's a standard linear psu type bridge & cap across the dc output, but the cap is small enough to only give a small rms increase.


NT

On 2/2/2018 2:13 AM, Phil Allison wrote:
> jurb...@gmail.com wrote:
> 
> --------------------------
> 
> 
>> I am playing around with this old scope in which the power transformer winding for the CRT filaments is arcing internally. In fact years ago I did put in a hi-pot 6.3 VAC transformer and wired it to switched AC internally and it worked for a long time.
>>
>> But now the replacement is arcing.
>>
>> The filament is elevated to about 3,500 volts negative DC. What is the possibility I could find a cheapo switched mode for this purpose.
> 
> 
> ** Much too likely to inject switching noise into you scopes' trace.
> 
>   
>> Is there something off the shelf for this ?
> 
> 
> ** I would try a 6.3V AC "wall wart" rated at say 0.5amps.
> 
> Normally, these have the primary add secondary wound on separate halves of a plastic bobbin and use plenty of insulation since they need to meet class 2 safety requirements.
> 
> Do not remove the tranny from the plastic box, just glue it inside the scope somewhere, oriented so that it causes no hum in the trace.

Get another Hi-Pot. I'm lucky to have a Hi-Pot store down the street 
from me. Every time I drive past there I think I should stop in for some 
components. 
<https://www.google.com/maps/@37.3229313,-122.0060483,3a,29.9y,172.79h,91.23t/data=!3m6!1e1!3m4!1sdYN8BEv98GIUw8AVPm7Zcg!2e0!7i16384!8i8192>

>"Get another Hi-Pot."

Apparently you didn't get the memo. I got one in the form of an AC output wall wart. Phil clued me in that they are pretty well insulated, and it works fine. We are now engaging in idle speculation about RMS and ripple voltage and all that, just for fun. The issue has been settled many posts ago, we are just having a little fun driving ourselves crazy. Welcome to the club.

jurb...@gmail.com wrote:

-------------------------
> >"Get another Hi-Pot."
> 
> Apparently you didn't get the memo. I got one in the form of an AC 
> output wall wart. Phil clued me in that they are pretty well insulated,
> and it works fine.
>

** Yesterday, I found a web forum on scope repair where the poster used an AC external adaptor the same purpose for the same reason - its twin bobbin, all plastic construction. 

Darned if I can find the same page now. 

I really don't think cardboard insulated transformers are up to handling 3700VDC for long. 


....  Phil 





 We are now engaging in idle speculation about RMS and ripple voltage and all that, just for fun. The issue has been settled many posts ago, we are just having a little fun driving ourselves crazy. Welcome to the club.

>"** Yesterday, I found a web forum on scope repair where the poster used an AC external adaptor the same purpose for the same reason - its twin bobbin, all plastic construction. "

I guess we didn't invent the wheel.

>"Darned if I can find the same page now. "

I download ALOT because of that. Sometimes you will never remember the exact search words. Some important shit gets deleted. For example they put a virus in milk now that attacks the bacteria that makes it go sour. There used to be plenty of articles on it for a short time and then poof, all gone. Also a video called College Cconspiracy defining how, in the US, people are fucked by colleges. It is funny that they picked on Trump U over their practices because other colleges are actually worse. But the people who went to Trump U were about as sharp as a bowling ball. They somehow got the notion that right out of school with no job and a ton of student debt that a bank was going to loan them money to buy a hotel or high priced property. Fat chance. Nobody teaches simple logic. So The College Conspiracy keeps getting moved around because youtube removes it after getting a DMCA complaint. Who makes the complaint ? Colleges ! No college would ever produce a video like that. You are supposed to be the copyright holder when you make a complaint, but the are pussies and don't even check, they just delete. 

>"I really don't think cardboard insulated transformers are up to handling 3700VDC for long. "

One did, but then that scope didn't see much use. I preferred my 422 over the years. 

I am thinking about that 3A1 on eBay. It would be alright as long as it doesn't have the same problem. But then this may have happened to every 561A in the world, I don't know and I bet the guy selling it doesn't either. 

If I ever get this completely done, I would like to modify the  horizontal time base variable control to make it easier to come out of the calibrated mode. Both channels of the vertical amp are stuck in calibrated because the linkage broke. It takes too much force to disengage the switch. I don't want that to happen to the time base because I frequently rock scopes to 60 Hz. But we'll burn that bridge when we come to it. (I like saying that)

What do you think of tabb's idea on reducing the gain of a bipolar transistor ? I don't have alot of confidence in it, plus I am almost out of old germanium transistors. And I am not sure this circuit would tolerate the change to silicon. 

It may never work right. After the arcing the blocking oscillator that feeds the multivibrator for the chop circuit will not run. If the transformer for that is shorted that means it will forever only run in alternate mode, and I have had occasion to need chop mode, even with aliasing if needed. It is really important to the usefulness of a dual trace scope. Most of them automatically switch to alternate at higher sweep speeds, both Teks allow you to choose. What else do you need dual trace for than to compare the timing of two signals ?