25" Magnavox color tv - Videokarma.org TV - Video

Tomcomm · #1 08-06-2008, 03:59 PM

Greetings...I've got this 25in color TV that was probably made in 1978. Its all solidstate with a 25VCXP22 crt and what appears to be a sonic remote. The model # might be TC 95-14 and the chassis # is definitely T995-02. I think it was called the Magnavox Star System and was the top of the line. As I recall from 20 years ago, the crt was going dim, but I have two 25VEDP22s from new Heathkit TVs that I trashed (long story). I'm assuming that these crts are interchangeable? I could not find either model # or chassis # on Google. I also pulled the solidstate ultor HV module out for an experiment. I still have it but don't remember how it was wired in. Does anyone know anything about this TV or has a schematic or can suggest how to reinstall the HV module? Thanks for any information..............Tom

bgadow · #2 08-07-2008, 10:32 PM

According to the Sams index there were variations on that chassis; it lists T995-02 as being "similiar to chassis" T995-01, which is in Sams 1469-1, dated 3-75. Later versions (suffix CB, DB) are in 1700-1 while suffix DC is in 1815-1. The index doesn't list the model number you gave. I pulled my copy of 1469 but the file is missing; I might have another copy somewhere around here.

My understanding is that 25v tubes are compatible, provided they are delta gun. I don't think I have a book new enough to tell me what those tubes are. A good one to ask, if you have problems with this set, is Randy Bassham.

radiotvnut · #3 08-07-2008, 11:24 PM

Yes, most 25V delta gun tubes should work in that set. The only ones I'd be cautious about would be the first ones from the early '70's that were designed for tube sets. These usually have the bonded faceplate and are probably turning green around the edges by now. Many of the solid state sets from the '70's operated with the HV into the low 30 KV range. Many of those first 25V tubes were only rated at 25 KV or so.

Tomcomm · #4 08-08-2008, 01:19 PM

Thanks for the responces. The 25VCXP22s are delta guns with '78 dates. Who is Randy Bassham? I would like to contact him, mabe he knows how the EHV module ties into the chassis otherwise I'll have figure it out and take a chance of blowing something out. Any chance of locating that Sams folder, Bryan?.............Tom

bgadow · #5 08-09-2008, 10:48 PM

PM sent.

kx250rider · #6 08-10-2008, 11:14 AM

CAUTION: Most Magnavox 25V type delta gun tubes had permanent mounting "ears" on the corners of the tube. If you use one that doesn't have them, you'll have to make some mounts, or have it rebanded with the ears included. I used to have to get that done all the time when replacing Magnavox tubes, and I'd go to our local Dunbar rebuilder and they'd do it as a courtesy. I wonder if anyone on this board has one of those Signode pneumatic banding tools?

Charles

sampson159 · #7 08-10-2008, 12:33 PM

i know about those magnavox ears. years ago,a friend of mine cut the band off a maggie crt.installed it in a solid state admiral.powered up,set the convergance and left it on for about 30 minutes.we were talking on the phone when i heard it! implosion,explosion? i went over to look at the damage.cabinet blew apart,tube imploded,mask was in a few pieces.fortunatly,the back was still on and the electronics looked intact.could have been worse-didn t pull the nails from the walls! frank later used the chassis in another cabinet and never did he ever cut the band off again. lesson learned.

radiotvnut · #8 08-10-2008, 12:58 PM

A friend of mine attempted to install a 25V tube without mounting ears in place of a tube that had mounting ears. He did this by running a metal band behind the CRT and fastening the band to brackets that were secured in the original mounting holes on the set. I've seen some B&W tubes mounted that way; but, not a color tube. As soon as he moved the TV to it's normal position, the tube imploded. It's a thousand wonders my friend was not seriously injured. That experience taught me never to tamper with a CRT in order to make it fit in a set.

bgadow · #9 08-10-2008, 01:16 PM

I found a copy of 1469-1. If you would like it, send me a PM with your mailing address and I'll send it on the way.

andy · #10 08-10-2008, 01:57 PM

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Tomcomm · #11 08-10-2008, 08:53 PM

Thanks for warning me of the potential consequences of removing the steel compression bands from around the face plate of the 25v series rectangle crts. I have not gotten into the Magnavox far enough to determine if its 25CXP22 is held in place with four corner tabs on its compression band or even if it has a band. Fortunately, both my 1978 Heathkit 25VEDP22s are banded, one has corner tabs the other doesn't. After I get the EHV module installed and the entire CTV operating, I intend to run both 25VEDs and determine which one is best. Hopefully, it will mount the same as the original Magnavox. If not I will consider what it takes to jerry-rig it into the cabinet. Under NO circumstances will I remove or tamper with the installed band...Tom

Tomcomm · #12 10-05-2008, 03:17 PM

Got it operational a couple of week ago. Only burned out 2 horz output transistors before I got ultor voltage. I don't have a EHF voltmeter but its putting out lotsa HV. The good news is I've got a really bright full color picture with the xformer from an old roundi CRT heater booster that puts 8vrms on the heaters. Anything less than 8vrms causes the pix to go dim. Since I've got 2 spare CRTs I'll just run this original until it burns out.
After a week or so, it suddenly lost ultor voltage completely. I checked the output xistor and flyback,they were ok. When I pulled the Retrace-Screen module out a big capacitor-like component had one end blown off!
This was labeled "CRITICAL SAFETY COMPONANT" in big letters? It had 2 leads on each end and a capacity value of .0068mfd at 1600 wvdc. the parts list indicates a part #250663-11 with no substitutions.
Does anyone know what this thing is or if a simple near-value cap would work?? The chassis is a T995-02. Maybe Randy Bassham remembers what was used to replace it. How does it work to save the HOTs?? There is no 1/2A fuze.
Alert: I just Googled "250663-11" and got a cap site that lists it as a Magnavox "TV Special Capacitor" for $3.99!
800 848 6888 I'll call them Monday. Google is amazing, try them for anything no matter how special.

radiotvnut · #13 10-05-2008, 03:42 PM

That part is known as a safety capacitor and is a high failure part in Magnavox sets of that vintage. Unfortunately, they are hard to find today and one probably wouldn't last that long if you did find one. The last time I ran into this situation, I used two orange drop caps of the correct working voltage in parallel to give me the correct value. You'll notice a total of four leads on the original cap. The two leads on each end are tied together (a short) inside the cap. Just jump these end connections on the PC board when you install the new capacitor.

I did this to a 19" set and it seemed to work OK. I sold the set and it never came back; so, I guess it held up.

Tomcomm · #14 10-05-2008, 04:01 PM

Thanks radiotvnut for the quick reply. I'm wondering if the part contributes some waveshapping function to the horz drive to the output xistor? What causes them to blow, it must be heat when it breaks down. The list shows it used by GE, RCA, Zenith, Philco, Sears and Sony.

radiotvnut · #15 10-05-2008, 11:20 PM

Quote:

Originally Posted by Tomcomm

Thanks radiotvnut for the quick reply. I'm wondering if the part contributes some waveshapping function to the horz drive to the output xistor? What causes them to blow, it must be heat when it breaks down. The list shows it used by GE, RCA, Zenith, Philco, Sears and Sony.

I think that's what it does. In the mid '70's, Zenith had a problem in that their 4-legged safety capacitors would open, causing the HV to reach the stratosphere and blow the neck of the CRT off. They were a white tubular style cap. Zenith quickly released a four legged orange drop cap to upgrade sets that used the old white cap. I've never seen a bad orange drop safety cap in a Zenith. That little white joker cost Zenith a ton of $ in replacement CRT's.

I have never seen a blown CRT due to excessive HV in a Magnavox; but, someone I know that used to work on Maggies said he's seen it before. All the ones I saw would either short and kill the set entirely or would open and kill the HV. It seemed to be the 19" sets that would short and the 25" sets that would open. The Magnavox sets must have had a fail safe circuit to kill the HV in the event the safety cap opened. I think those Maggie caps were just glorified paper caps and they were not very reliable to begin with. They absorb moisture and the dielectric (insulating material) breaks down and then the cap shorts. I'm not that familiar with Maggies; so, maybe someone else will chime in here.

Modern CRT sets still use a capacitor in this application; but, it's usually either a disk cap or some form of plastic cap. I've seen these short but never have seen one open.