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 What the heck is a "Dim Bulb Tester?"

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Rod Clay
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Technician
Rod Clay


Join date : 2018-08-01

What the heck is a "Dim Bulb Tester?"  Empty
PostSubject: Re: What the heck is a "Dim Bulb Tester?"    What the heck is a "Dim Bulb Tester?"  I_icon_minitimeOctober 21st 2019, 5:48 pm

Frank,
I guess I was lucky with the sets that came my way for repairs. When I found a set with a shorted Horizontal Output Transistor replacing the flyback transformer along with it took care of the sets I was working on at the time. My background in Television receivers was not that strong and I was drawing on general electronics knowledge to do the repairs.

Chas,
Yes. I replaced quite a few triplers myself. I bought them from surplus parts dealers when I could. I had a curve tracer to try and figure out which transistors I had picked up at hamfests could be used for TV repairs. The flybacks I got were usually generic replacements. Back in those days it wasn't too hard to please the customer. Most of them liked the way their set performed after they got it back especially the color. I would spend time on that getting it right.

73, Rod  WB6FBF
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chas
Technician
Technician
chas


Join date : 2017-04-09

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PostSubject: Re: What the heck is a "Dim Bulb Tester?"    What the heck is a "Dim Bulb Tester?"  I_icon_minitimeOctober 20th 2019, 5:20 pm

Rod Clay wrote:
I started using a 100W lightbulb in series with the 120VAC input on solid state TV repairs if the set had trouble in the horizontal output stage. Back then I had a bag of TO-3 style horizontal output transistors to burn hi, hi.
Oh boy do I remember those sets. Wiping out the HOT in a fraction of a second. not only would the flyback fault but the tripler too...

I haven't had my ham rigs up and running in years. They will likely need caps. I know the HA-460 does. Hums like heck receiving...

Funny, when I put the 460 away worked absolutely fine... Rolling Eyes 

Disadvantaged load topic: I have a Dentron Big Dummy, picked up at an estate. Can was quite rusty, paper label falling off. I set it aside in my wooden floor shed for a while then decided I would clean it up. Poured off the oil and sent it to waste. I noticed a rust dot one the inside bottom. After cleaning carefully and wiping I pressed on the rust dot, out popped the tiny rust button and a hole in the can Shocked WOW, if that rust had popped in the shed I would have had oil all over heck!

I de-greased everything and bought a new paint can at Home Depot. I still have not put new mineral oil in nor have I been able to find a new load curve to re-label the new can.

Chas
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FrankB
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FrankB


Join date : 2010-11-22

What the heck is a "Dim Bulb Tester?"  Empty
PostSubject: Re: What the heck is a "Dim Bulb Tester?"    What the heck is a "Dim Bulb Tester?"  I_icon_minitimeOctober 20th 2019, 4:37 pm

BTW Rod,
"light bulb dummy loads" is not politically correct any more.
 They are "Disadvantaged loads".
jocolor
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FrankB
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FrankB


Join date : 2010-11-22

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PostSubject: Re: What the heck is a "Dim Bulb Tester?"    What the heck is a "Dim Bulb Tester?"  I_icon_minitimeOctober 20th 2019, 4:28 pm

Rod,
 Many times the FBT is not the problem, and is perfectly good.

 There are 2 things (Actually more but these are the most common) that will quickly take out the HOT.

1. Bad solder on the driver transformer. Even if it looked good, I resoldered it.

2. The spike suppression 'lytic capacitor on the driver transformer.
Typically a .1 to 2.2 mfd Polarized ELECROLYTIC. Replace with same value in 105c temp range.
  The cap goes bad and causes a voltage spike to hit the HOT and it lets out the factory smoke. I always replaced it if the driver tx had bad solder and/or I replaced the HOT (Especially in Sony sets). it was dirt cheap insurance I wouldn't get a callback.

(As for testing the FBT, I have published a couple of posts here and on another board for a sure fire test for the FBT's. I never had it indicate a FBT was good or bad when it wasn't. Saved me hundreds of hours of testing.)
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Rod Clay
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Technician
Rod Clay


Join date : 2018-08-01

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PostSubject: Re: What the heck is a "Dim Bulb Tester?"    What the heck is a "Dim Bulb Tester?"  I_icon_minitimeOctober 20th 2019, 1:17 pm

Chas,

I can't think of seeing an article on using one of them from the 1930s or 1940s either. Where the term "Dim Bulb Tester" came from I can't say. I don't think it is a very descriptive term for what it is. The idea of it has been around for a long time though. Simple enough to get together and use.

I started using a 100W lightbulb in series with the 120VAC input on solid state TV repairs if the set had trouble in the horizontal output stage. Back then I had a bag of TO-3 style horizontal output transistors to burn hi, hi. I eventually learned that if the horizontal output transistor shorted then the flyback transformer was the problem and needed replacing first.

Might be a good item for some newcomers to have on hand and use.

Not to be confused with the light bulb dummy loads that ham operators have used for years. I have one set up for the Johnson Viking II.

I bought a supply of 100W bulbs a while back before they all disappeared from the shelves. The 130V "Rough Service" bulbs were the last of them.

73, Rod  WB6FBF
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chas
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Technician
chas


Join date : 2017-04-09

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PostSubject: Re: What the heck is a "Dim Bulb Tester?"    What the heck is a "Dim Bulb Tester?"  I_icon_minitimeOctober 20th 2019, 11:26 am

In 60 years of Radio/tv repair I never used or built a "Dim Bulb tester".  In actuality such a tester, says what is already known about a radio that there is a short. That the tech should replace electrolytic caps and make a B+ resistance check before powering on.

IMHO it is a lame excuse for poor technician practice and still can't save the bacon when the repairs create a new short. It does, often happen to a noob who uses YouTube to shotgun rebuild the radio...

Only on one occasion I used a variable transformer to "first power-on" a Radiola 28/104. Such a radio is equipped with '99 tubes and a 210 power amp at 575 volts. The power supply does soar to almost 700 volts as the ballast tube gets under control.

Any wiring error, despite careful checking could spell disaster for those tubes as will as explode other caps in the power supply.

Ummm, Yes, the radio was fine and worked a treat...

I seldom, use an isolation transformer too. Only when I have to connect generators or other line powered equipment to the radio I will isolate it.

Anyone ever see a "dim bulb" setup in a 30's-40's era radio technical publication?

Chas
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Rod Clay
Technician
Technician
Rod Clay


Join date : 2018-08-01

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PostSubject: Re: What the heck is a "Dim Bulb Tester?"    What the heck is a "Dim Bulb Tester?"  I_icon_minitimeOctober 19th 2019, 4:26 pm

Sal's Capacitors has these for sale in case anyone would like to get one ready made.
73, Rod  WB6FBF
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FrankB
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FrankB


Join date : 2010-11-22

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PostSubject: What the heck is a "Dim Bulb Tester?"    What the heck is a "Dim Bulb Tester?"  I_icon_minitimeAugust 26th 2017, 6:11 pm

I was recently asked this question, so here is the answer:

The Dim Bulb tester is simply a light bulb (NOT AN LED or flourescent bulb!) that is placed in series with the hot side of the power cord feeding your radio, amp, etc.

I used a couple of old outlet boxes and was lucky to find a screw in fuse holder, with switch on the same face plate, and the fuse holder has just the same basing as a light bulb has. (Habitat for Humanity here has some nifty things at times.)

I placed the single outlet/ SPST switch in one duplex box, and the fuse holder/bulb socket in the other duplex box. I added a bit of leftover spray paint and VIOLA! it was done. 

It's not fancy. I do plug it into my PR57 or a Variac (r) (with an isolation transformer. ALWAYS use an isolation transformer, especially on "hot Chassis AC/DC sets.

 Screw in a bulb that is of higher wattage than I expect the radio, amp, etc. to draw.

  Embarassed  (Don't ask! "What do you mean, the main breakers for the building tripped again?" "All I did was to hook up the ground lead from the Telequipment scope to the chassis......")   (Gotta love tech school teachers that know theory, but nothing practical. :twisted:)

If the bulb lights up really bright, likely you have a short (Mainly filter caps') in the radio.
 If it stays dim, the radio will likely have no major fault.
 Basically, it's a current limiter. I keep several different wattage bulbs around to screw in as needed.

One day, I will build another "Test Panel" version, in which I can select the bulb wattage with a turn of a selector switch.

With experience, and a bit of plugging in good sets, you can make a good guess as to just how bright the bulb should be, and what wattage you should use.
 (And yes, the brightness can vary, depending on how loud you have the radio also. The louder it is, the more current that is drawn.)

 Note: This tester will NOT work on many of the more modern TV sets, as the SMPS are fussy, and some need that initial current surge to "Get up and going" . But on any of the old transformer operated sets, I never had any problems with it, excepting some TV's that did need a faster current draw than the bulb would let through. Mainly a few models of RCA color sets.
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PostSubject: Re: What the heck is a "Dim Bulb Tester?"    What the heck is a "Dim Bulb Tester?"  I_icon_minitime

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