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Hmm in this case they are most likely not using that LM386 op-amp as a 'voltage-follower' or as 'buffer' which would be the analogous transistor circuit. The LM386 has a preset gain of 20DB, so it will always amplify the input by at least that. I can only guess at what they are doing but the LM386 is often used as a 'Bass Boost' in amps, perhaps this is what you are seeing. If there is a cap then resistor that can be traced from pin '5' (V-out) to pin '1' (GAIN) odds are that is what you are looking at. Thanks for you comment.

Opps I think I got that dead wrong. I misread you comment. I would say yes there is a very good likelihood that there is a buffer into a tone stack before it goes to an LM386 though the gain of the LM386 can be as high as 200DBs so any lost 'oomph' could be easily added back in. ;)

Yeah you could write a few book chapters on them unfortunately most of them are long out of print ;). I just stuck to the very simple example as it is a 'Short' video. I just started playing with an old Tek scope (545) and it looks like (to me) 1/2 of the tubes in that are using the cathode is some way. So much to relearn.

@@byterock They will need to get an exact gain so cathodes will likely get doing something

Funny how that works out ;)

THEIR SHOULD BE A GRID RESISITOR FROM GRID TO GROUND TO PROVIDE THE NEGATIVE VOLTAGE ON THE GRID.

@@davidluther3955 Yes that is true . For simplicity I left all the 'Normal' bits off, like the coupling caps, out of the first example. A real circuit can be seen at the 4:00 mark, After all it is suppose to be a 'Short' video. Oh by the way you do not 'Need' a '-' voltage on the grid, you just need a '-' potential difference between the grid and the cathode. Thanks you gave me an idea for another short circuit 😉

I guess it all depends on what you are working on. I had a 30A PS on it the other day I had to use 2 100s and 2 60s to even get it to start up. but that is extraordinary ;)

Well I guess but it is incomplete, missing speakers and the spindle is not the correct one, would be very expensive to ship.

Where are you located?

If you look at about the 8min point I explain the formula P(w)=VI, so for 40w it would be 40=120/X so .333 of an amp for a 40w bulb. (varies by the bulb and the state of the mains voltage) Normally most items have either a working wattage or amperage listed so I just select bulbs for about that working amperage /wattage If I do not know the working amperage /wattage then follow the 'old' rule of analog meters but in reverse. I start with the lowest bulb and then add in as I go. If you have a look at this video th-cam.com/video/MIWz8RlloLU/w-d-xo.html at about the 10min point I use bigger and bigger bulbs to load an old HP Nixi Counter 🙂

Yes that is an option. But what am I going to do with 9 left over boards. ;) In this case I made a few goofs on the layout not sure if I could correct them on a PCB-way board.

Ok this answer is only valid for North America. You have just proven that your 'Isolation' transformer is not galvanically Isolated. More than likely you have a 'Medical Isolation Transformer' If both your transformer and the socket it is plugged into are correctly wired what you are seeing is 'Hot' (black or small slot) looping back to 'Ground' (Green ground) which is correct for this type of transformer. Obviously I cannot tell you 100%. I do suggest you do not use this transformer for working on old transformerless (ie AA5) radios until you have someone say from your local radio/HAM club, someone else with High Voltage lab experience or a professional electrician to have a look at your set up. It might be a simple mod to the remove the ground or you might be unlucky and the transformer winding itself is grounded. I cannot say one way or another. I did a more detailed video here th-cam.com/video/XUxFGyNiyhI/w-d-xo.html As well as a link in the description of the link above on isolation transformers from Uncle Doug

@@byterock 'Gravimetric' isn't the correct term ...it refers to a chemistry technique .... galvanically isolated is the proper term

@@barrysilver2075 Yes you are quite correct. I will correct the above. Must of been the auto correct combined with the fact I am a horrid speller. ;) thanks

Ouch. Like I said in the video the power cables of these old HP instruments are as rare as hens teeth. Almost unubtainium. As a mater of fact at out last radio club auction one of these sold for 75$. All I know it is a Bendix type and there are some old vacuum cleaner cables that will fit but they are rare as well. They do come up on ebay but the price is usually in the 50~75 range. As a matter of fact I have two HP boxes that are missing power cords and one where the cord is beginning die so I think I will have to do a project on converting them over to a modern plug. Sorry I could not be more help.

Sorry for the late reply, been away. Yeah I had a longer version but I wanted to keep it short a sweet. If I remember correctly my old teacher spend well over 4 classes on just the theory of series vs parallel light bulbs, but that was a long time ago ;)

@@byterock yeah, no problem. I didn't mean to sound too critical. Any effort that helps people is to be applauded. When I give feedback, it is with the best of intentions. I have a Rock solid understanding of ohm's law and have watched many vid's about Dim tester's. But I am still having trouble visualizing how the voltage drops are distributed across the bulb and the Device Under Test, in quiescent conditions, after the initial inrush surge (assuming there is nothing wrong with the device). I really need to sit down with a calculator and pencil and work it out. The variable resistance of the bulb from cold to hit is slightly tricky to figure in, especially when the voltage across it is less than rated voltage, so we can't rely on the wattage rating to mean much, except in limiting initial inrush current. I am hoping to build my own tester soon, ultimate deluxe version, with analog panel meters for voltage and current, and about 5 different load bulbs that can be switched in or out for different conditions. Thank You. -from Minneapolis

@@douglas2lee929 No problem Douglas I love feedback. It is a very tricky subject and there are whole physics and engineering books written about ''Non-Ohmic" conductors or resistors. The whole point of a 'Dim Bulb' is that is does not follow 'Ohms Law', maybe I should of pointed that out better in the video. I will change the description an add in a good link on 'Non-Ohmic' thingy. Yeah good old 'ohms' law goes only really good when dealing with DC wait until you get into 'Impedance' I am still trying to work that one out ;)

@@byterock Thanks. Yeah, my schooling included impedance and reactance. Sometimes I have to look up the formula's. Never did get totally comfortable with the phase shifts from the inductors and caps. 😥

Unfortunately mine didn't I only figured it out reading an old 'RCAF' 1950s training manual that had a good section on it. Used very practical examples vs the theory of waves 2d graphs one use to see. There are some good 3d animations out there as well that demo it TTFN

It we are talking about a Mixer for Audio like an MG-12 it more than likely does does not have a power transformer but a SMPS. My guess what you are seeing the SMPS starting and stopping (shuttering) and what you are seeing is SMPS turning on giving the correct power so LEDs come on and then shorting out causing the DIM Bulb will flash and then turning itself off. I usually a never use a Dim Bulb on an SMPS device as there is no transformer to burn out. I think 700w might be the Audio output and not the input power requirement that should be between 35~100w. My guess it is limited the current but the SMPS is resetting by itself so the dim bulb is not doing much.

@@byterock hello Sir, thank you for replying to my comment. The power mixer is 400W per channel. 700W power consumption. Labelled back panel. I took the chance and plug it in directly to the wall plug. Works fine. Yes the dim was limiting the current. It has a 6.3A fuse as well.

And yes it a big SMPS power supple.

@@anoushan Wow 700w power consumption. and a 6+ amp fuse. You would need like a 1500+ watt bulb. But that makes sense the Dim bulb would limit the current and the SMPS would detect that and then turn off suspecting that there is some fault with the power coming in. If it was designed to that sometimes low current can cause as much damage as high current 😆

Yep it is an old style apparatus, we had one in our high school to show the difference between parallel and series resistance, Good old days before they where safety standards, lawn darts, BB-Guns,Vac-U-form I do not how any of us survived to now. Any way I did build one with a load of bulbs here th-cam.com/video/7ME1iPrkhOU/w-d-xo.html

Thanks Mike

Yeah to owner has been playing with it a little more and it seems the electrolytic capacitors on the panel meter board are key to getting the voltage regulation to work, So far just trying to find the right caps as they are a very obsolete value. Glad you liked it Cheers John

Thanks JM

Thanks Comments are great

If memory servers me correctly I was searching for Perpetumm Ebner and it came up. I believe it is an old Signal Corps/USAF picture so copyright free. I can check to see if I kept the original download someplace but it may take a few days

Thanks that meas a lot to me.

100% Yes. An variable transformer or more properly an Auto Transformer never offers isolation. Unless it is a special and says so on the front. Try this test and you will see th-cam.com/video/u3jXDfSWUnU/w-d-xo.html

Here is the basic schematic www.qsl.net/w/w2aew//youtube/W2AEW_ESRmeter.pdf Not my design. The only major change is I used a LM555 for the square wave generator with a 56pf timing cap and and 47K for Resistors the to get a 100Khz square. Send me an email and I can send you my version

Thanks, yep that is an idea. This is more a 'How Does' video vs 'How To'. This is the DBCL I created th-cam.com/video/7ME1iPrkhOU/w-d-xo.html How it is employed is based on what I am testing. Lots of bulbs for a 5 amp CRO one 40w bulb for an old 100ma AA5 portable. With the Dim Bulb it always best to start low and add more. Unlike say an old analog volt/amp meter measurement where you start with a high voltage/amperage and then scale down.

: The in-series DIM BULB must be able to supply the required load current - when running the DUT loaded. The bulb is intended to limit the current - so one can determine if the DUT is presenting a Short Circuit. In the example shown - the objective is to protect the DUT. The light bulb used as the example load - hence the light bulb should glow dimly. Using a higher Wattage bulb reduces the protection - since it allows larger and a potentially damaging current to flow in the DUT. : Higher wattage bulb lets through more current than a lower wattage bulb so a 60W bulb is generally enough Also DUT means “Device Under Test” not DUT means “device under test” Pay attention that the first letter is in ALL CAPS Learn also that all CORPORATE {Legal NAMES} are always in ALL CAPS ** There are writing rules that you do not yet understand and have not mastered. Undertake an extensive reading program to better educate yourself. Also study the Chicago Style Manual. Writing is an art form that you should master - and you can ONLY do that by reading and studying manuals. I have authored /co-authored eight for the USAF and a number of manuals for the purpose of obtaining ISO 900/9001 Certification. These manuals were in excess 1200 pages Understand that such Manuals have to be a very high standard of detail - clarity and grammar.

No real difference that I can think of off the top of my head. The point here was to show that is does not really matter if the Variac or IOS goes first. The choice to use and ISO or not could be the subject of another video. It is a 100% required IMHO when working on say a hot chassis AA5 but only required on a amp with a transformer if you want to float the chassis so you can use a common point to hook your scope ground into.

Odd sound ok to me though there is some tonal changes. I wonder it it a problem of where it is streaming from. Will have to do a remote download and check the outgoing quality.

Yeah I tested that as well. Wanted a short simple video so did not add that part in.

Hey saftey first

Yeah that is true but you do not want to mix them up, as neutral in NA is connected directly to ground while live is not. Don't want a grounding error.

@@byterock yes, but it doesn't matter. If you insert the plug the other way around, your neutral will become live, no matter how you wired them inside. There are some appliances that won't work if you insert the plug the other way around, but we are talking about 0,5% from all electronics. Also, a ground lift button is needed, if you want to take measurements safely, without blowing up your DSO. Those dim bulb testers without a ground wire, are actually better.

@@Atelierul29 Well it does use a three prong plug, and of course it is only as good (ground wise) as the socket it is plugged into. ;) I am not sure you would ever want to float a DSO. but that is a good subject for a video

Thanks glad you like it. don't forget to asks you friends to subscribe as well. ;)

Long answer: 'Yes' with a 'But' Short answer: 'No' with a 'Maybe' The big plus for me is space and variety of parts/ All of my SM part can fit neatly in 1 drawer, while I have a full wall for about the same number of through hole. One other problem, very few if any ICs are coming out in DIP packages, and many older IC can no longer be found in DIP TI for example no longer makes 555 in DIP. If you want to use a very high quality audio op-amp you would be very hard pressed to find something in a DIP package. You can of course mount a SMD on a breakout board but that really just adding an extra step. Thanks for the comment, Don't forget to subscribe.

Yep it is a Forstner (a very cheap chinesium one ) and it was 100% trashed from hitting a nail some time ago. I have found that there are very useful for cutting though metal (thin) no good for wood anymore. I have a hole press now so I now use that instead. Cheers.

Thanks don't forget to subscribe ;)

Isn't that the whole point of the dim-bulb current limiter ;). Take a big wack of current to start vs the DUT. But I see your point on the little graphs I created. A even bigger spike on the graph might of been better.

Ask yourself the question. 'What do I want to use if for?' For high frequency work you will only get the sine to work at the max and only just. If you want to do radio alignment well I had to make my own AM modulator for that is is ok for low voltage but for very low voltage it is a little distorted <5 micro volts For high speed logic work the square wave was only good to 2MHz but for learning logic circuits it is quite handy as you can program a signal into the AWG. Originally I intended to use the FY8300 for bench testing/burn in of tube amps. Well it failed at that as using it for that caused it to die after 72 hours of use. (overheating no doubt) Still going to keep it about as the one can add all sorts of digital/ sounds/waves to the AWG so useful for testing when you need a base vs regular guitar. I just used it to test a power supply the 12v 60Hz was the signal I used as I did not have a mains transformer handy. Didn't overheat this time. So for about 80$ it was worth it. Hope this helps

Yep we learn from our mistakes, as long as we do not release the magic smoke, though that gets lots of clicks and views.

@@byterock I wanted to add that I once tried to resurrect an AA5 radio that was AC DC combo. Used a 45V and I think 6 volt batteries, plus you could throw a switch and use 120 Volts. This was pre TH-cam days, I was hopelessly lost and gave up. Now I wish I still had it!

Yep. You must be like me 'A Hands on Learner' or as my Dad use to say 'A Hands on Destroyer'

Glad it was helpful!

Oh ok what part and what was wrong?? I have been trying to improve it over the past while. Any suggestions will help ;)

Yep I would guess they would do though there is no easy way to tell if you have a short until they start to glow red. I have seen them used in RF dummy loads for HAM work but they one I saw was also in a sealed oil bath to disperse the heat more quickly.

No it is a design used way back in the day from high school physics to explain series and parallel circuits. You would not see it today as it is a little dangerous for today's standards. It is just a demonstration apparatus. Here is a good design of a Dim bulb CL th-cam.com/video/7ME1iPrkhOU/w-d-xo.html

please share

Yep 100% on all fronts. In the back you can hear a fan running in that room. Though FeCl or the liquid tin is not that volatile. What is nasty is the acetone. I only do this a few times a year so the risk is low.

I do that as well but that tends to cause the FeCl to lose its reactivity much faster, I would rather just let it take an extra 45min then spend the time and effort heating the FeCl. And yes I did wear gloves except for the liquid tin as one does not need to agitate that. I did wear gloves when I put the remains back in the bottle. Cheers

I am sure there is a Mock German pun in there some place but jsut for fun here is the original ACHTUNG! ALLES TURISTEN UND NONTEKNISCHEN LOOKENSPEEPERS! DAS KOMPUTERMASCHINE IST NICHT FÜR DER GEFINGERPOKEN UND MITTENGRABEN! ODERWISE IST EASY TO SCHNAPPEN DER SPRINGENWERK, BLOWENFUSEN UND POPPENCORKEN MIT SPITZENSPARKEN. IST NICHT FÜR GEWERKEN BEI DUMMKOPFEN. DER RUBBERNECKEN SIGHTSEEREN KEEPEN DAS COTTONPICKEN HÄNDER IN DAS POCKETS MUSS. ZO RELAXEN UND WATSCHEN DER BLINKENLICHTEN.

Thanks. I never though of it in that way. I just did it the way I though it should of been done. Very encouraging, Thanks again

Thank you. Nice to see people enjoying the effort. Don't forget to subscribe to see more ;)

Thanks, The key for me is we are always told to use one but no-one really explains how it works at least from the serial vs parallel point of view. Thanks again and don't forget to subscribe ;)

Thanks good to hear more builds very soon. Don't forget to subscribe ;)