T.V. power supply for tube amp / chip amp combo ?

[Brymus]

I recently pulled the circuit boards out of a Sony projection TV that was being sent to dump.(along with all the metal and aluminum mounting brackets)
Someone had bashed in the screen and taken the spkrs.
BUT the power supply board is intact and works,it had a built surround sound with amps as well,it was a really cool TV at one time.
So I salvaged 2 x( 2 x 25W) stereo chip amps (front and rear) and a 50 watt chip amp for sub woofer along with their power supply which works too.

My question is can I use the power supply for the CRT's to drive a tube amp?
It has +135V and -135V along with +/- 15V and +5,+7,+11V too.
I was wondering if I could wire the -135V as ground and use the +135V (Just leave the regular 0V unhooked ?)
To get 270V to drive a tube pre amp?

Then use the +/- 15 to drive a chip amp ? ,I believe that the lesser models used this supply as its labeled AU (audio) for the sound.

I also tested the dedicated audio PS board (another separate board with its own AC in and rectifiers,filters ect) and its rated +/- 18V but is putting out +/- 21V with no load,so that I am definitely keeping for a chip amp or lab supply.

I have yet another working PS board pulled from another TV it was a regular CRT that had a sudden stop and broke the PCB where the CRT gun was mounted. It has +/- 15V and +135V ,135V should sound OK with a couple pre amp tubes.

Sorry if this is a dumb question,it just seems a waste to scrap two good PS's for parts.Especially since they are on their own PCB's already working.

[PRR]

The 135V is surely not driving the CRT. That is a 30,000 Volt supply, potentially lethal, and nothing I would want laying naked around the house. (You may have noticed a pretty beefy cabinet and cage.)

135V sounds like the video amplifiers. 1V video signal is boosted to 100V swing on the CRT cathodes.

> Sorry if this is a dumb question

No, but I think telling you to mess with the insides of a TV is dumb. You are known and respected around here, we don't want to read a write-up in the Mohave News. We don't really know how calm and careful you are.

If the AUDIO power supply is a neatly separate unit, and you won't kill yourself patching the 120V AC wiring, go for it. Carfully!

[PRR]

Also nearly all TV sets use NON-ISOLATED power supply: one side of the DC IS one side of the AC outlet (and in US wiring, you can never be sure which side).

[Brymus]

The 135V is surely not driving the CRT. That is a 30,000 Volt supply, potentially lethal, and nothing I would want laying naked around the house. (You may have noticed a pretty beefy cabinet and cage.)

135V sounds like the video amplifiers. 1V video signal is boosted to 100V swing on the CRT cathodes.

> Sorry if this is a dumb question

No, but I think telling you to mess with the insides of a TV is dumb. You are known and respected around here, we don't want to read a write-up in the Mohave News. We don't really know how calm and careful you are.

If the AUDIO power supply is a neatly separate unit, and you won't kill yourself patching the 120V AC wiring, go for it. Carfully!

Thank You for the replies PRR,yes I am fairly careful.
I always check for voltages with my DMM,before messing with a PCB,and then I try to trace the circuit from the AC in through the inductors,transformers and such to have a general idea of where to probe for voltages.Then when actually applying power I clamp one probe to ground (or the other side) and probe with one hand.
Plus these Sony PCB's are clearly labeled with part types and voltages at the connectors,which is one reason I thought to check the main PS before de soldering it for parts.
It just seems a waste of a good PS to use it for parts,but not worth frying parts I paid for or myself.

Yes the audio PS is a separate PCB AC in +/- 18V out (21v no load is what I read)
So I would just need to use ohms law to find what fuse to add and add a fuse for safety as it was linked from the AC in on the main PS after going through its fuse (6.5amp) and it's AC input inductors.

[psychedelicfish]

For a preamp, I wouldn't bother risking my life poking round an old TV (this is coming from someone who built a Tesla Coil). I'd just make myself a 555 SMPS like this:

leaving out the caps/diodes for the negative voltage.

[GibsonGM]

+1    we've all gone that route, tried to "save' something like that, or avoid having to 'make it new' since it was already designed for us.  I think it's in the genes...letting something good like that go to waste really bothers us!  We feel driven to salvage this stuff, myself included.   

However, if you DIY, you will know exactly what is going on, you'll control the assembly, and it will be reliable after you test it. You can get troubleshooting help right here.  Chances are the thing you want (Nixie supply above) will be small and simple, and cheap - will fit in an enclosure better, and will be line isolated.

We don't KNOW that the PSU's we find in the junk pile work ok, even tho we get voltage....could be some intermittent problem there, or it could be on the way out.  Could need caps badly. So we do all this work, and the thing could die after an hour of operation!   Not a good return on the investment of RISK, I think.    Even the caps on those HV suckers can do a big number on you that you never saw coming, no power applied, from an area you didn't see.   

I limit that kind of 'salvage' to Jacob's Ladders made from oil burner trafos, lol...no TV stuff for this guy.   

[PRR]

> ohms law to find what fuse to add

Not sure how Ohms helps. What would you Ohm?

However, you can guess. How big is the audio amp? 1,000 Watts? 50 Watts? I suspect it is two 10W-30W channels. (It IS a projector so it has more than the 2W of a home TV; if used in a huge venue you would hook-up a PA system so Sony would not build-in hundreds of Watts.) Say 60 Watts total output, 50% overall efficiency. 120 Watts input. You have 120V power, so a 1A should do. Slow-blow because it may start-up hard. If something goes horribly wrong (a short), it is likely to pull dozens of Amps, so a 1A slo-blo will shut-down quick.

Back to the TV circuits. There is a long tradition (both RCA and Muntz) of building TV sets to do EXACTLY what they need to do. No more. No less. The load of a TV is fairly constant: the 30,000V is always there, the H-sweep is always slapping both sides of the CRT. Many minor loads change somewhat with level, but the big loads don't. And TV sets were pioneers in strangely efficient schemes like switchers, even SCR(!) switchers. So it is possible that if you don't hold that "right" load, it will shut-down (or worse: run wild).

It's your life. And I assume you won't burn-down the woods like I could.

[Brymus]

PRR,
I really appreciate your feedback.
I am going to take your advice and not use the main PS for the TV,I can always get more after my skills progress to allow me to implement them safely.
(There was a central (coil/gun?) supplying the three CRT's I believe that is where the +/-135V was stepped up to the 30,000V you mentioned the CRT's need.)
Plus that's extra relays,transformers,inductors, power supply resistors,and some nice film caps for me as well.

To clarify this model had built in speakers but also included surround sound outputs via RCA jacks (front,rear,center,sub)
ALSO it included speaker hookups via the red and black spring clips ,for using the extra amps provided to run surround sound directly from the internal extra chip amps.I have never seen a TV with this many options.the caveat was that the TV speakers (I believe) were used for center channel.
The data sheets show that the one type of chip amp (TDA 72**) is a 50w stereo amp(2 x 25w),there are two of those(front L/R and rear L/R),the third chip amp is a 50w (TDA 2***) for the sub output.
So all total that's 150 watts,then I have a +/- 18V power supply, using these two I was going to use ohms law to find amps (I) for the fuse.

Since the audio PS was designed to power all three chips it seems a wise choice for making a stereo amp,leaving off the 50watt chip would/should mean the power supply shouldn't be stressed even at max output from the other two chip amps.

I found a newer CRT TV (made in end of 2006) yesterday in an alley someone had dropped it to open it (it used all torx) cut the HV wire to the back off the CRT then kicked the end of it off, stripped the copper windings from around the end of the tube and the thick copper that wraps the outside of the picture tube and left the rest.To my suprise the rest of the PCB's were still in good shape,it yeilded lots of goodies,along with two 10W 8ohm shielded speakers.

[R.G.]

I found a newer CRT TV (made in end of 2006) yesterday in an alley someone had dropped it to open it (it used all torx) cut the HV wire to the back off the CRT then kicked the end of it off, stripped the copper windings from around the end of the tube and the thick copper that wraps the outside of the picture tube and left the rest.

It had probably been stolen, then junked for the copper. Copper has become a target for theft because of the money available by selling to metal recyclers. There have been instances of air conditioning units being stolen for the copper tube and heat exchangers; of brass kick plates on doors being stolen for the brass (and therefore copper) content. In at least one instance, a pickup drove out into an area of large irrigated fields, hooked the wiring to the pumps and irrigation valves onto the bumper, and drove off, tearing the copper wire out of the ground.

As one instance of how far copper theft goes, one fellow was found dead at the bottom of a power pole on a country road. He had been rippling loose the copper ground wires that run down the poles, and pulling the wires loose from the staples in the pole from the ground by pulling hard on the wire from the bottom of the pole. There is a little leakage at each pole, and the ground wires keep this distributed into the earth. When you cut the grounding wires loose, the leakage current finds other paths. Pull loose a LOT of grounding wires, and at some point you find one with a lot of local leakage or the accumulation of leakage from the other ungrounded poles, and - well, there's a lot of leakage. Power in the wires is commonly 1300V to 13kV, so there's plenty of voltage available to drive it. Apparently the thief had a firm grip on the copper wire, pulled hard, it parted from the ground end of the pole, and he became the leakage path, arms, through the chest and into the feet.

There is no appeal from the ruling of a natural law.     Sentences are carried out immediately.

[PRR]

There's zero value in a CRT today except that small wad of copper.

Around here we have a few pole-ground fools who have not caught the death penalty yet.

And we had one who knew what he was doing, pretty much. He got $26K of copper, though one job at a power substation caused a major black-out.

Please don't steal ground wires in my area. My service grounding is poor enough as it is. I'd probably come "help" you and hand you the live wire.

The scrap dealers take IDs, pay by check, report odd hauls to the Police.

There are wire-makers who can laser-engrave the power company logo and a running number every foot on ground wire. If that stuff comes to scrap it better come in a company truck. If not, the company can track the number to a certain pole, which may aid prosecution.

Lot of summer homes here. Very likely you come up in spring, someone has popped the door, taken all the pipes and wires out, and let porcupines nest in your bed.

That was a small reason I took all of my copper plumbing out, scrap-sold it, and put in plastic. (The big reason is that the previous owner's pipe routing and soldering was worse than some of the bad-examples of pedals we see around here; second we moved sinks and toilets; third I've probably drank enough Lead already and won't learn no-Lead pipe solder.)

[PRR]

> There is a little leakage at each pole, and the ground wires keep this distributed into the earth.

The dirty little secret is: there can be a LOT of "leakage".

The distribution voltage is generally 13,000V. Fully built-out it will be 3-phase, and the "neutral" current nearly cancelled. But it never quite cancels. Especially since neighborhoods are often run with just 2 of 3 transformers until fully occupied.

Since "neutral current is low", it is often run in a lesser wire than the phase conductors. Often in steel (the phases are wired in aluminum or copper-Weld).

So there could be a huge ground potential at "neutral".

To "protect linemen", and really to divert lightning strikes, they drop all these ground rods along the way.

It is not unusual for HALF the neutral current to flow back to the substation *through the dirt, through YOUR dirt*, instead of over the wires.

I have ~~~3V of ground potential here, and while some of that is "my" current, some of it must be running from the line south of me to the substation north of me in my dirt.

In other places, the "neutral conductor" has rotted right off, undetected, the neighborhood "has power" through dirt conduction, but every bit of metal in the ground is "hot". There's one case of a power main laid right through a lake (only in Florida? here we stick trees in the lake and wire overhead), the neutral does what wet steel does, and kids swimming were dying "for no reason".

[Tony Forestiere]

GEEZE LOUISE! Kids dying in a lake for "no reason"    Thanks to Paul and R.G. for the summary (fishing lesson) on pre-tranformer voltages and "Earth" potential current leakage to the dirt. R.G.'s oft-used reference to Mother Nature's Rules is spot on.

It is not unusual for HALF the neutral current to flow back to the substation *through the dirt, through YOUR dirt*, instead of over the wires.

In other places, the "neutral conductor" has rotted right off, undetected, the neighborhood "has power" through dirt conduction, but every bit of metal in the ground is "hot".

There is no appeal from the ruling of a natural law.   icon_eek  Sentences are carried out immediately.

High Voltage, Current, and Frequency AC has always been scary to me. Now that I know a bit more, I think I am terrified. 
I am very comfortable with the 240/120 VAC in my house after the transformer.

[PRR]

> I am very comfortable with the 240/120 VAC in my house after the transformer.

I'm not.

I don't care to get between domestic "ground" and any dirt or damp (including concrete).

Nearly all my outlets in such locations have GFI breakers, mostly plastic boxes, mostly with cut-off switches so a bystander can kill power without going near a victim.

And I still can think of dangers.

That's not even thinking about Strange Stages.

Be careful.

[Brymus]

That's just crazy.
We have what we call snowbirds, a lot of people come here during winter as ours hardly qualifies as such.
Freezing temps are VERY rare,usually low 40's or high 30's at night is the coldest it gets.
But the same thing will happen,people will break in and steal all the wiring and anything else of value during the summer months when a good percentage of the homes are empty,especially when the new construction was booming they would go in and strip copper before the drywall went in.A lot of meth addicts in this area,sadly...

I saw online where most E waste gets dumped in Africa from all over the world,thats one reason for so many scams and idenity thefts from there.Used hard drives are actually a commodity for this reason.They showed some that were marked Top Secret DOD 
They had some from law enforcement agencies all throughout Europe,AU,ect
A lot of so called "Green" recyclers use this shady method to turn a bigger profit.

But my point was the children will go to the huge dumping grounds and strip wiring then burn it to remove the insulation from the copper,they make an average of a dollar a day doing this.It causes the local communities to be engulfed in a constant cloud of toxic smoke full of heavy metals and other carcinogens.

[Jdansti]

In Houston, there have been thefts of aluminum light poles from the road medians along as much as 1/2 mile in one night!

I was told about a 300 yard long warehouse on the Houston ship channel that had all of the wiring in it stolen overnight. People came to work one morning and found huge piles of insulation on the floor and no wire. The thieves brought machines to strip the wire.

[duck_arse]

here in australia a little while back, some rail line-workers had a scam where they just took drums of overhead cable from their depots and sold it to scrap merchants. in their state rail trucks, to save using their own petrol.