Looking for some picture tube help

[leadlike]

Hello folks, I'm very new to the forum but figured that since I've been reading it for so long I'd better join up. I have an RCA 21'' from 1955, it is the only really vintage tv that I use and we just love it. Sadly, that old 21amp4a is wearing out, and I need to find a suitable replacement. I don't mind doing modifictations and the like to get a new tube in, but I would really like to know what my options are with this set. I don't have the chasis number with me at the moment, but would be happy to supply it if it would be helpful in finding a substitute. Thanks in advance for all your help.

[leadlike]

chasis is kcs96

[eberts]

Your options, call video display in stone mountain georgia, see if they have a 21FLP4 in stock, how much ? Install that and remove the magnetic focus coil.
Tie the focus pin on new tube to the G2 pin.

Your other option is to get it regunned by Hawkeye and spend $250 plus shipping.

You can buy a new color LCD if you want to, it is year 2008 now.

[kx250rider]

Fortunately, that's not a rare tube. You can even have it rebuilt by Hawkeye if you want to keep your original, and especially if it's your main vintage set which you plan to keep for a long time.

Basically, any 21" glass tube of that deflection angle (70 degree, I think, on a 21AMP4) will work fine in that set. I'm sure someone on AK in your area may be able to point you to a good used one.

Where do you live?

Charles

[kx250rider]

Originally Posted by eberts

$250 plus shipping

WOW! They went up.... I remember not too long ago, getting any B&W tube rebuilt for $16.95 . I knew they were up in the $100 range now, but $250 would price me out in most cases.

Charles

[eberts]

21AMP4 is 90 degree def with a magnetic focus gun.
It was considered obsolete in 1965.
I just read a post about some old guy who had a basement full of TV's and didn't know the basement was flooded. Did his nose stop working ?
Some of these TV hobby guys remind me of vultures.

[leadlike]

kx250rider- I live in central pa, about two hours outside of philadelphia. This seems to be a dead zone for old tv stuff, as I have never seen any for sale here. Lots of nice old radios, though; which is something I am much more knowledgeable about.

I did find this ebay seller who has a number of 21'' tubes. If anyone thinks there is a match here, your help would be greatly appreciated. Hopefully the link won't get too muddled, but the seller has a store called The Old Radio.

http://stores.ebay.com/The-Old-Radio...dZ2QQpZ2QQtZkm

I see for instance he has several crts that have the proper deflection stats and the like, but the pinout is different, and I don't think that any of them require an ion trap, which mine does. So with his 21cxp4 for example, would I disconnect pin six (g4) and use the ion trap (after making the anode pins line up properly of course) instead?

[electroking]

As far as I know, replacing a tube with an ion trap by a tube without an ion trap just involves removing the trap.

Regarding your other question (pinout), I will let those that are more experienced comment about that.

Regards.

[electroking]

There is a little tube substitution book by H. G. Cisin that sometimes
can be found on e..y. I used to have the 1965 edition, which
I misplaced, but I now have an earlier edition (missing its cover, but
I believe it is from 1959).

This book provides an extensive table of CRT substitutes. Tubes are
sorted by group, having the same deflection angle and pinout (and
screen size of course). The author gives advice regarding certain
changes, in particular he says that if a magnetic focus coil is to be
discarded, it should be left in the circuit and mounted as far as
possible from the new CRT.

Hope this may be helpful. Good luck.

P.S.: I will get my copy by Sunday and post the relevant table if
you are interested.

[radotvguy]

i will take a look tonight , i have a bunch of NOS crts in my attic

[kx250rider]

Originally Posted by electroking

As far as I know, replacing a tube with an ion trap by a tube without an ion trap just involves removing the trap.

Regarding your other question (pinout), I will let those that are more experienced comment about that.

Regards.

Correct on the ion trap. On the pinout, the only differences are whether the replacement tube is electrostatic focus or magnetic. Again, you can swap by making a couple changes. But most all TVs made after appx 1953 had static focus.

Charles

[mattdavala]

Originally Posted by kx250rider

Correct on the ion trap. On the pinout, the only differences are whether the replacement tube is electrostatic focus or magnetic. Again, you can swap by making a couple changes. But most all TVs made after appx 1953 had static focus.

Charles

I'm sure most TV's did have static focus although my 21 inch Majestic console has electrostatic focus and it is from 1955. Its CRT is a non standard replacement, 21EP4B. Its on its way out. ..... Brightness almost full, slight blooming, retrace lines on dark scenes.

If I never plan to sell my TV, spending 250 dollars for a CRT rebuild might be worth it. The TV is a joy to watch.

Best regards,
Matt Davala

[eberts]

The 21CXp4 is physically the same as a 21FLp4, but the G2 voltage uses about 50 volts instead of 300-450 volts. I tried it once using a resistor network to lower voltage, but the set had other problems, so into the trash it went.
21CBP4 would work.

I remember once some guy was going out of business, he had the whole second floor filled up with 100 brand new picture tubes from the early 50's still in their cartons. The cartons were so old if you touched them they fell apart. I know they were tearing the building down, he wanted big money for his so called inventory. Oh well.

It's sad to watch these old TV repairmen go senile.

[electroking]

Originally Posted by mattdavala

I'm sure most TV's did have static focus although my 21 inch Majestic console has electrostatic focus and it is from 1955. Its CRT is a non standard replacement, 21EP4B. Its on its way out. ..... Brightness almost full, slight blooming, retrace lines on dark scenes.

If I never plan to sell my TV, spending 250 dollars for a CRT rebuild might be worth it. The TV is a joy to watch.

Best regards,
Matt Davala

What do you call 'static focus'? According to my RCA RC-29 Tube Manual
(1973), all B&W CRTs listed have either Electrostatic focus (a grid that
you connect to the correct potential, sometimes with taps, sometimes
with a potentiometer) or Magnetic focus (a focus coil). The only two
tubes that list a different focusing method (Automatic) are two test
tubes (8XP4 and 8YP4).

My two TVs, from 1956 and 1960, use electrostatic focus tubes
(21ALP4A, 90 deg. and 21DEP4, 110 deg.).

Regards.

[mattdavala]

Originally Posted by electroking

What do you call 'static focus'? According to my RCA RC-29 Tube Manual
(1973), all B&W CRTs listed have either Electrostatic focus (a grid that
you connect to the correct potential, sometimes with taps, sometimes
with a potentiometer) or Magnetic focus (a focus coil). The only two
tubes that list a different focusing method (Automatic) are two test
tubes (8XP4 and 8YP4).

My two TVs, from 1956 and 1960, use electrostatic focus tubes
(21ALP4A, 90 deg. and 21DEP4, 110 deg.).

Regards.

Here is where my lack of electrical knowledge is going to kick me in the butt. I thought electrostatic focus was from a focus coil, and a static focus was using an adjustable PM maginet around the neck of the tube.

Now that I have thought of it my 66 color roundie uses a grid in the tube for focus. Electrostatic. My 21 inch B/W uses a focus coil, and my other B/w TV uses a PM maginet for focus.

Someone help me get my ideas straight here!
Thanks!!
Matt Davala