Philco 48-2500 Restoration Blog
 

Since this is probably going to be a long drawn out affair I thought I'd start a thread where I can post some notes and pictures on the progress of this set.

As many of you probably know I bought it on eBay for $37.00 and picked it up near Garden Grove CA in Orange County.

It came with a "Certificate of Authenticity" from The Hollywood Entertainment Museum", this means absolutely nothing except it was owned by them at one time for some purpose, maybe it was in a display, maybe not.

I wish it had been owned by Humphrey Bogart but then I probably wouldn't have gotten it so cheap.

The cabinet is somewhat rough, some Veneer will probably have to be replaced to get rid of some of the defects, it's all flat surfaces so if matching veneer can be found it shouldn't be too hard to do.

Looking through the lid I could see a lot of tubes were missing, I thought the seller had perhaps kept them for himself but when I pulled the back off I found a little surprise.

There is a narrow door on the right side (from rear) to access the chassis bolts, when I opened it there was a small box taped shut and labeled "Tubes out of Philco 2500" inside were all the missing tubes!

The first thing I did after removing the chassis was take apart the projection barrel and look at the concave mirror, it's not perfect, it has some scratches and a few spots of corrosion but overall it's still highly reflective and should work fine for the time being.

The trapezoidal mirror that reflects the picture on to the screen however is pretty much shot.

The chassis is in really good condition, very clean and rust free for the most part.

The CRT looks like it has a million miles on it, the Phosphor has turned dark brown in the area where the picture is scanned, it's trapezoidal in shape because it's scanned in that shape, it's reflected off center on the concave mirror to a trapezoidal mirror in the cabinet and comes out on the screen in a rectangle.
The setup procedure for the optics looks like it could take the better part of a day to complete!

Here are some pics of the CRT , the one on the right is from this set, the center tube is from a previous 2500 I owned but scrapped, the tube on the left is I hope, NOS or near to it, it has no burn at all so it either is very low hours or possibly defective.

the two tubes that I know came out of sets have similar inspection markings on them, some numbers and the letters OK with a squiggly underline, the "New" tube doesn't have these markings so I'm hoping it's a later replacement tube.


This is a long post, if anyone's still reading at this point I will post more pictures in the future. :yes:

The cabinet is at my work, the chassis is in the back of my truck here at home. Capacitors have been ordered but I have other projects in front of it.

I planned to work on it during my lunch hour at work but I'm off till at least this Thursday due to ripping a muscle or tendon in my arm this past Wednesday. :sigh:

I've got several TP400 CRTs for my set as well. Will be interesting to find out if you see a huge difference between the new one and the two with darkened phosphor. None of mine is new, and they show varying degrees of darkened phosphor, although none quite as dark as the two you show. Somewhat to my surprise, however, all of my CRTs work about the same, regardless of how much darkening of the phosphor there is.

Curious what solution you'll find to fix up the front-surface trapezoidal mirror. Mine is OK, but could probably benefit from a better reflective surface.

Good luck with the set! This one has about as many capacitors to replace as a TV can have...

Eric,

Don't worry to much about the front mirror, as long as you can see a reflection it will work. The spherical mirror in the barrel is the real key to a good picture, and of course with the Philco, the reflective screen.

If the flat mirror is really gone just use the thinnest regular mirror you can find and use a thin back board to make it the same thickness as the original.

Chuck

Has anybody here taken one of these tubes apart? I am wondering if the phosphor is brown from electron bombardment, or perhaps the glass is brown from X-rays?:scratch2:... or perhaps a little of both effects?
jr

Eric,

Those projection sets are a lot of fun to work on. The spherical mirror can be resilvered (aluminized), and front surface mirrors can be bought off the internet for not too much money. Having good surfaces on both mirrors will result in optimum brightness. While you can use an ordinary mirror for the flat one, it will produce some image degradation, dut to reflections from both the front and back surface of the mirror.

Interesting info on this site: http://www.myvintagetv.com/philco_48-2500.htm

It claims the first 25 Field Test units of the 48-2500 were Blond sets, now I can't really hope that I lucked into one of those but it would be cool. :yes:

you might have... just never know. look at the serial numbers.

Well, it looks to me like the finish was originally blonde, not stripped and refinished.

If this is a field trial set, I wonder who typically got those? Company execs? A magazine likely to write a glowing review? I presume that (at least) some of the lucky testers would be engineers, so the company could get some educated feedback.

Should be an interesting project in any event. I think you have already gotten at least $37.77 worth of fun out of it!

Phil Nelson

Phil,

All the prototype and field trial Philco sets I have found or known about, (15" color prototype, 3 prewar field trial sets, and an "Apple" prototype), have all been in the hands of retired Philco engineers. The 48-2500 field set also was from a Philco engineer.

I guess the execs had no interest in them.


Chuck

I got the answer here: http://www.antiqueradios.com/forums/...c.php?t=145288

I knew I couldn't get that lucky but it was worth checking. :D

Phil, the Blond is original on this set, the Dark Anti Reflective color inside the lid was applied over the outside finish.

Philco upgrade kit for code 125
 

Here is an interesting Philco tidbit. Philco made this kit to convert your 48-2500 projection set to a code 125 model. This is a 1X2 based tripler HV power supply sub assembly. I assume it is intended to replace the older 1B3 based tripler.

In addition to installation instructions, they have a sheet of service tips. Of interest is the suggestion that the DC restored tube be removed. This improves the focus performance in changes from light to dark scenes. They state the improvement in focus will more than offset the disadvantages of not having DC restoration

That's an interesting item.

I wonder how many made it out with the 1B3 system?

Both of my chassis use the 1X2 I think, the tube chart on the HV cage of this set had 1B3 printed on it but it was crossed out and 1X2 was written in by hand.

There's another tube chart pasted on the hardboard back of the set, I'll have to see what it has for HV Rectifier tubes.

I like the automatic discharge safety lever inside the cage, designed to keep you from getting whacked with 20 kv if the cover is off.

The DC resto mod is interesting. I had a friend who owned a 40's projection set, and he said adjusting focus was a constant problem, in fact, that is why he got rid of it. I can easily understand why one would want an in focus picture even if it meant getting rid of DC restoration. Note that the RCA Berkshire had a wired remote that was simple a focus control rheostat.

I recall doing a service call to the Board Chairman's home in 1957. He was watching a 1957 Diamond D. I doubt he would have put up with a TV 123 color with its reliability. The engineers surely did not want him to experience the failure rate of the early color TV.

I recall another executive was watching a cheap 16 inch RCA in a metal cabinet.

Don

Does anyone here have a complete 2500 Field set or know where one can be seen?

It would make sense that the Engineers would be watching them, the bean counters wouldn't be able to give good feedback about failures or bugs.

Very interesting! The aspect of my 48-2500 that I find most disappointing is that the picture doesn't stay in focus between light and dark scenes. Mine is so bad that I don't really consider it tolerable. Interesting that Philco acknowledged that this was a problem.

When I received my set, the HV supply had been removed and replaced with a homebrew RF HV supply on a separate chassis. I never understood exactly why, and since the homebrew HV supply had developed its own problems, I removed it and rebuilt the original circuit using parts from another 48-2500 chassis with 1X2s. It works, but the focus problem is severe, and the cause appears to me to be due to sag in the HV with scene brightness (perhaps made worse by using a triode CRT) affecting the focus.

Perhaps the reason it had a homebrew HV supply was because a previous owner found HV sag to be the problem, and built a better HV supply.

Sometime in the near future I'll try the removal of the DC restoration tube. On the other hand, I'm not eager to live without DC restoration, so I'll be interested in whether there is some other fix. I've wondered if it would make sense to try to build a 6BK4 shunt regulator like that used in early color sets to solve the problem?

First, I'll wait to see if Eric's set shows less of this focus problem than I am seeing. There may be problems with mine beyond what these sets typically show.

It seems that it might be possible to build a dynamic focus circuit to vary the focus coil current with varying conditions of cathode current and HV. :scratch2:
Hide the ics and transistors under the chassis somewhere...nobody needs to know!
jr

I would think it is not the focus coil current that needs to be controlled, rather the HV needs to be regulated. As the As these supplied to be rather anemic, I would think a shunt regulator would not function all that well. But it would be interesting to try it . Or, as the Philco HV supply is independent of the horizontal sweep, it should be possible to build a feedback design which compares the HV to a reference voltage and used the difference to drive an amplifier to modulate the screen grid voltage on the horizontal output drive to the flyback, or modulate the B+ voltage to the flyback. Either approach would be interesting to try.

How bout just sticking a 20Kv Neon light transformer inside the cabinet? :D

I haven't run my 2500 in a couple of years, but I don't remember having any big problems with the focus blooming. Now the RCA sets are a different matter, none of my RCA sets will hold focus with scene brightness changes. RCA "solved" that problem in the '49 sets by giving you a remote control brightness and contrast control so you could somewhat control the focus issue from your easy chair.


Chuck

I agree the origin of the problem is in the HV sag, not the focus coil. However, the HV is derived from the horizontal sweep flyback transformer, so I don't think we can apply the fix you've suggested. Or did I misunderstand your idea?

Interesting to hear that the RCA projection sets are worse. I'm surprised they marketed the sets with these design weaknesses. It can't be that hard to design around the problem.

:lmao:

Indeed, HV sag would be the most likely cause of the defocus of a bright picture on these sets, and should be addressed first. However, triode gun CRTs have a bad reputation for worse spot size growth with increasing beam current than tetrode designs.

Just saying that if that is the case, a little "dynamic focus" could improve the beam performance.

Of course, the focus coil would be difficult/impossible to drive at video frequencies, but it should be possible to provide focus correction fast enough to improve average focus.

jr

Don't know if this is the correct tube, but I came accross it whilst surfing Egay this morning: http://cgi.ebay.com/NOS-RCA-5TP4-Ult...27510791741787

Not affililated.

The Philco uses a 4" type TP-400 CRT. Philco was the only manufacturer to use this CRT. The 5TP4 is used in the RCA and many other projection sets.

The problem with these sets is most definitely high voltage sag with increasing beam current...

The sag is the result of the voltage drop across the 1X2s...

I had one of these sets once, and after experiencing the blooming issue to the point of considering the set unwatchable, I removed the 1X2s and their associated filament windings and installed a solid state high voltage tripler (extracted from an old color television chassis) in their place.

The results were stunning.

High voltage regulation was vastly improved, and the focus issue was almost completely gone (only with the brightness cranked all the way up.)

ETA: I also installed a retrace supression circuit in that set so I could crank up the brightness a bit without having retrace lines. It worked flawlessly. BTW, don't remove the DC restorer. It will just make the set more unwatchable.

If you can stand to do this to your set, this is the cure.

TV Engineer,

Any tips on where to get a solid state voltage tripler? Do a lot of modern CRT sets have them, or is it something a bit obscure to find?

Tom

The most frequent high voltage problem comes from bad "Presistors" in the multiplier circuit. They are special high voltage 2 meg resistors. There should be plenty around. I have some if all else fails.

Well I've replaced all the caps in the set except four small paper ones.

One of the paper caps I have left to do is a .005@1000 volts which I don't have in my stock, it's on the audio tube so it won't matter much as far as trying it out.

I was able to restuff all the electrolytics in the cans except for two that I had to mount underneath.

I couldn't find the box with the tubes for the set when I was leaving for work this morning, if I can find them tonight I'll probably give it a test run tomorrow and see what happens, I'm going to use the worst looking of the three CRT's in case something goes kerblooie.

Almost any American solid state color set (and a few hybrids) from the early 70s til the early 80s have them. Zenith, Magnavox, Sylvania, RCA, Admiral... they all used them at some point. You can also order one new with the ECG/NTE523 part number. They're about $25. Hook the output of your flyback to the in, ground the ground pin, and connect the output to your CRT. Ignore any remaining pins. That is all there is to it.

Somebody here mentioned the 2 Meg resistors in the original tripler circuit being bad...

They did fail, but if yours were bad, the regulation would be even worse, and you might not have any high voltage at all. I experienced this with my set too. I replaced them, but the HV regulation still sucked, which was when I came up with the solid state tripler idea.

Let us know how it works for you if you try it.

Success, after a couple false starts.

I took all the tubes with me today and tried firing the chassis up during my lunch hour, all I got was a glowing red plate on the 6BG6.

I messed around with it a little, pulling the cap off and seeing how much current it was drawing, anyway I fooled around a bit too much and cooked the 6BG6, it shorted and caused a little 50v cap on the Damper tube to explode.

fixed the cap and did a little troubleshooting around the Horiz Oscillator tube, I had zero B+, a little troubleshooting found a solder glob that had shorted a 120k resistor (R115 on the Sams) to an adjacent terminal on the strip, cleared that out and the voltages on the Osc tube fell in line.

Now that I knew it was probably working I went and borrowed a 6BG6 from a friend who lives near my work, put it in and fired it up.

The first indication that I had HV was the inch long spark that jumped from one of the doorknob caps to the second anode lead, the lead has a bad spot where I melted it with the heat gun. :nono:

Moved the lead, grounded the CRT more securely to the metal bench and tried again, this time I got a raster!:yes:

The raster fills the screen, I put in a set of tuner strips and it appears I'm getting something through the i.f strip, if I had a DVD player I think I could get a picture.

I used the CRT that came with the set, it was the most burnt so I figured I had the least to lose if something went wrong.

It works OK, decent brightness after it warms up a little but the area where the phosphors are burned are noticeably dimmer, there's also a barely noticeable vertical line burned in the screen, I think this is due to the way the set warms up, there's a brighter vertical line first then it expands and fills the screen, it could have had a horiz sweep failure at some time too I suppose.

There's also a faint image of Uncle Milty burned in the screen (just kidding but that would be cool) :D

Next I want to try my supposedly NOS TP400 and see if it actually works.

:worthless:worthless:worthless:worthless:worthless :worthless

At your command! :D

Here's a couple shots of it running, this is with the NOS tube.
It doesn't seem to get all that bright, except when you adjust the controls it'll get brighter for a moment then settle back down, I think perhaps it needs a signal to work it's best.

All I know for sure is you have to be really careful where your wires are laying when you turn this thing on, anything that gets in range of the HV area will get zapped! I don't have the cage on it yet though, wonder how much X-rays it makes if any?

BTW, when it's installed and adjusted properly the screen won't be filled like it is now, it's supposed to be a bit smaller than the tube and keystoned slightly to compensate for the angle of projection, this can be seen on the face of the old tubes in the brown Phosphor.

A pair of magnets attached to the sides of the CRT do the keystoning.

Oh yeah, earlier I said I used the old CRT in case something went wrong, it did.
I was taking everything apart to bring it home and I pulled the base cap off while trying to disconnect it!
It came off clean with the wires intact so I can put it back on, if it's even worth bothering with.

nice. comming along very nicely. wow that tube is bright..... even for a worn tube.

That's actually the new tube, the camera makes it look brighter than it is.

ooohhh ok... i was wondering why it was so bright. :banana:

Eric, you won't get a super bright raster with no signal. Once you give it video, you should get very bright highlights in the video. The CRT does emit soft X-rays, as it is operating at 20KV. A little exposure wont' hurt, but you don't want to spend hours and hours with the CRT facing you in the barrel. Point the barrel away from you on the bench, and observe it through a mirror. That will minimize your exposure.

NTE523 tripler: Found one on eBay for $16.00, shipping included, so decided to go for it and try it out on mine. Still one more left at that price for Eric if he wants to try one later.

I figure at this price, shipping included, it beats getting one for free with a 1980's TV attached. :)

Thanks Tom, I went ahead and bought the other one just in case I want to try it.