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 Post subject: Re: DuMont RA 103 5U4 tube
PostPosted: Mar Sun 19, 2017 6:52 pm 
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Posts: 904
Location: Wyoming, Michigan
I wouldn't worry about the CRT until you need it, after the recap and some sense that the TV is working. Use the tube you have with the brightener until you have a raster, then try it without the brightener. Get the set working well. Then buy a replacement CRT if you think you want one. The Q version I would call rare. The L version fits and works and is as common as round CRTs of the era get. If you post for one in the classifieds you'll probably get a few replies.

If you intend to do more than one restoration, ideally you should have a test CRT. Read this Phil tutorial:

http://antiqueradio.org/5AXP4PictureTube.htm

I use a radar tube that I got for 5 bucks at a hamfest a long time ago. A slightly modified 5FP7 that weighs nothing and is known to give a good strong picture. Rules out CRT questions until the restoration is finished.

5AXP4s show up for $30-ish. Only one on eBay right now, the seller is a little confused about its worth though.


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 Post subject: Re: DuMont RA 103 5U4 tube
PostPosted: Mar Sun 19, 2017 7:13 pm 
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Location: 07450, New Jersey
Agree. Restore the set and then worry about the CRT as there are options. 12QP4 is next to impossible to find but the 12QP4 in the set may even be usable.

12LP4's are around and will sub in but are about 1 1/4" longer, use a different anode connector type and needs a double ion trap. All these issues are not difficult to overcome. 12LP4 also has a dag coating which should be grounded and takes the place of the HV filter cap in the set.

12KP4 would be a better and brighter replacement but they are a bit harder to find. 12KP4 is the same length as the 12Q and uses no ion trap magnet as it is aluminzed. Still have to change the anode connector.

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"One of the advantages of being disorderly is that one is constantly making exciting discoveries." A. A. Milne


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 Post subject: Re: DuMont RA 103 5U4 tube
PostPosted: Mar Sun 19, 2017 7:17 pm 
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When and if it gets to that point, you can also use a 12KP4 in these sets, which is an aluminized tube and will give an even brighter, sharper picture than any of the others.

Note that some people with DuMonts have reported that while a 12LP4 and 12KP4 will physically fit the chassis just fine and work perfectly electrically, there can sometimes be interference with the mask or cabinet front requiring a bit of reshaping with a router on the inside. There is a visible difference in curvature of the faceplate as well as a less than 1/2" increase in the overall diameter of the envelope at the face. Apparently they fit up to the mask nicely on some sets, and require alteration on others.

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Experience is what you gain when the results aren't what you were expecting.


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 Post subject: Re: DuMont RA 103 5U4 tube
PostPosted: Mar Sun 19, 2017 10:05 pm 
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Joined: May Thu 14, 2015 4:15 pm
Posts: 506
Location: Dallas, TX
WeekendHacker wrote:

I use a radar tube that I got for 5 bucks at a hamfest a long time ago. A slightly modified 5FP7 that weighs nothing and is known to give a good strong picture.


I just picked up a 5FP7 yesterday.

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747, 465, 1230, 1471B, 2005A, 1075
C-3, SG-8, V-7A, TC-2P
LAG-27, LBO-517
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 Post subject: Re: DuMont RA 103 5U4 tube
PostPosted: Mar Mon 20, 2017 1:23 am 
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Joined: Nov Sun 29, 2015 1:22 am
Posts: 550
Location: Parkland, Florida
Thank you all.
It has been a very educational thread. I've learned a lot.
I'm amazed with how much knowledge you have.
Compared to you I am a baby that is not even able to stay sitting up.
I've learned a great lesson.
Now, those small CRT's that you use to check if the set is working come in different sizes and numbers.
I went on Ebay and found a wide variety...5UP1, 5AP1,3FP7, etc.
Which would you advise to get? I also just got a Packard Bell 3381 for future restoration besides the RA103.

Carlos


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 Post subject: Re: DuMont RA 103 5U4 tube
PostPosted: Mar Mon 20, 2017 2:30 am 
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Joined: Jul Wed 08, 2009 12:17 am
Posts: 904
Location: Wyoming, Michigan
Notimetolooz wrote:
WeekendHacker wrote:

I use a radar tube that I got for 5 bucks at a hamfest a long time ago. A slightly modified 5FP7 that weighs nothing and is known to give a good strong picture.


I just picked up a 5FP7 yesterday.


Pretty easy to replace the octal base (right) with a CRT base (left). Then use it in most early roundscreen chassis restorations. On occasion the anode connector ends up being too close to the yoke. I think the 5AXP4 moved it nearer the front of the tube for this reason (if I'm recalling the tube correctly). The modified 5FP7 has worked for me the times I've needed it.


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 Post subject: Re: DuMont RA 103 5U4 tube
PostPosted: Mar Mon 20, 2017 3:09 am 
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Joined: Jul Wed 08, 2009 12:17 am
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Location: Wyoming, Michigan
CLC wrote:
Thank you all.
It has been a very educational thread. I've learned a lot.
I'm amazed with how much knowledge you have.
Compared to you I am a baby that is not even able to stay sitting up.
I've learned a great lesson.
Now, those small CRT's that you use to check if the set is working come in different sizes and numbers.
I went on Ebay and found a wide variety...5UP1, 5AP1,3FP7, etc.
Which would you advise to get? I also just got a Packard Bell 3381 for future restoration besides the RA103.

Carlos


The tubes you refer to above will not work. They are not magnetically deflected (they don't use a yoke to form a raster). They are oscilloscope tubes.

There are several types that would do. As long as they are magnetically deflected. I'm not aware of an exhaustive list. I would search for an aluminized tube ending in P4. Like the 5AXP4. The 5FP7 I use just happened to show up one day and it suffices. The P7 phosphor makes an odd picture but it's good enough to prove a chassis works.


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 Post subject: Re: DuMont RA 103 5U4 tube
PostPosted: Mar Mon 20, 2017 3:41 am 
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Joined: Jul Wed 08, 2009 12:17 am
Posts: 904
Location: Wyoming, Michigan
This one maybe:
http://m.ebay.com/itm/112334141053

"Tests fair" means it might be weak or heavily used. Ought to go cheap though.

Buyer beware and no affiliation.


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 Post subject: Re: DuMont RA 103 5U4 tube
PostPosted: Mar Mon 20, 2017 5:29 am 
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Joined: Nov Sun 29, 2015 1:22 am
Posts: 550
Location: Parkland, Florida
Thanks, weekendHacker.
I looked at the CRT on the link you sent. The seller says it tested 225 on the B&K tester and it's in fair condition. Apparently a reading of 225 is on the low side of the scale, like you said it might be weak and on the way out.
What concerns me more is that the seller has only 8 feedbacks and one is negative. I don't know if he is reliable.
I'll ask him a couple of questions to see what he says.

Carlos


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 Post subject: Re: DuMont RA 103 5U4 tube
PostPosted: Mar Mon 20, 2017 5:53 am 
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Location: WI 54812
Don't overlook the more common 8XP4 rectangular test CRT. Those were advertised to work with 52-90 degree deflecting yokes, and they're really not that much more bulky than a 5AXP4. Non currently on ebay, but if you search for 8XP4 completed auctions you'll see they show up fairly often and for a resonable price.


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 Post subject: Re: DuMont RA 103 5U4 tube
PostPosted: Mar Mon 20, 2017 6:35 pm 
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Joined: May Thu 14, 2015 4:15 pm
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Location: Dallas, TX
I got that 5XP7 in a package deal with a 8YP4 at an auction. The 5XP7 is not a great choice because of the long persistence phosphor (P7) and it also requires a magnetic focus coil. Also the maximum anode voltage is 8KV. It is intended for old radar use, that means they go cheap.
The 8YP4 is intended for test CRT use and is self focused. The filament is such that it can be used at 6.3 V (450ma, 600ma) and 8.4 V (450ma). Anode voltage up to 22KV. It is also a 110 degree tube meant for more modern TV set use.
The 8XP4 is better for less than 110 degree use.
In any case these test CRTs are not must haves.

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747, 465, 1230, 1471B, 2005A, 1075
C-3, SG-8, V-7A, TC-2P
LAG-27, LBO-517
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 Post subject: Re: DuMont RA 103 5U4 tube
PostPosted: Mar Mon 20, 2017 9:42 pm 
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Joined: Jul Wed 08, 2009 12:17 am
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Location: Wyoming, Michigan
Nobody is recommending using a test CRT for permanent viewing. A self-focusing aluminized test CRT Will let you test your video response I suppose, where an unfocused and persistent 5FP7 would fail. However the main purpose of a test CRT is to get your chassis to working deflection and HV, using a tube that's nothing to lift or hold in place, and is a known quantity as far as emissions and brightness. After you've proven your chassis to that point, it's generally time to install the permanent crt and work on focus and geometry and ion trap placement and then video alignment. That given, the modified 5FP7 gets you to stage 1 adequately.

I much later picked up a 621TS 7DP4 military sub for cheap from Fair Radio Sales in Ohio. If I were to use a test CRT again I would use it from now on. It fits all of the test CRT requirements without compromise.


Last edited by WeekendHacker on Mar Tue 21, 2017 12:42 am, edited 1 time in total.

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 Post subject: Re: DuMont RA 103 5U4 tube
PostPosted: Mar Mon 20, 2017 10:50 pm 
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Joined: Jan Thu 01, 1970 1:00 am
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Location: Woodinville, WA USA
Notimetolooz wrote:
In any case these test CRTs are not must haves.
Correct. You don't need to rush out and buy a test CRT if you're only restoring one or two sets. They are handy on occasion, but by no means necessary for every restoration.

Phil Nelson
Phil's Old Radios
http://antiqueradio.org/index.html


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 Post subject: Re: DuMont RA 103 5U4 tube
PostPosted: Mar Tue 21, 2017 1:32 am 
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Quote:
Pretty easy to replace the octal base (right) with a CRT base (left).

It's even easier to make an adapter.

Quote:
The P7 phosphor makes an odd picture

But it's pretty cool to watch a car go over a cliff!

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 Post subject: Re: DuMont RA 103 5U4 tube
PostPosted: Mar Tue 21, 2017 2:35 am 
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Joined: May Thu 14, 2015 4:15 pm
Posts: 506
Location: Dallas, TX
philsoldradios wrote:
Notimetolooz wrote:
In any case these test CRTs are not must haves.
Correct. You don't need to rush out and buy a test CRT if you're only restoring one or two sets. They are handy on occasion, but by no means necessary for every restoration.

Phil Nelson
Phil's Old Radios
http://antiqueradio.org/index.html

That was the point I was trying to make. If Carlos wants to buy test equipment, a test CRT probably shouldn't be it at this time. I had happen to acquire a couple at an auction the day before they were mentioned here. They weren't on my list of things to look for but they went cheap.

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747, 465, 1230, 1471B, 2005A, 1075
C-3, SG-8, V-7A, TC-2P
LAG-27, LBO-517
5382A, 368, 260, 8024B


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 Post subject: Re: DuMont RA 103 5U4 tube
PostPosted: Mar Tue 21, 2017 2:49 am 
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Joined: Jul Wed 08, 2009 12:17 am
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Location: Wyoming, Michigan
Carlos has the unusual condition of his first restoration being a pricey hard-to-find CRT and no CRT tester and a questionably bad CRT (brightener). He could use a known good test crt right off the bat. But he doesn't need one. He should look for a Beltron 2972 first.

If his next restoration is a DuMont Royal Sovereign then yes he MUST have a test crt.


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 Post subject: Re: DuMont RA 103 5U4 tube
PostPosted: Mar Tue 21, 2017 3:54 am 
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Joined: Nov Sun 29, 2015 1:22 am
Posts: 550
Location: Parkland, Florida
I have some boxes in the garage that contain a bunch of stuff I bought almost a year ago from an ex-tv/radio repairman.
Earlier, looking through them I found a B&K model 465 CRT tester. I opened it up and looks untouched.
I plugged it and powered it and it turned on.
The needle gets stuck just before the 6.3V mark on the scale.
I connected it to the RA103 CRT and the filament lighted up with the knob set to 6.3V.
Checked for shorts and the light for G1 went on, indicating a short.
That's as far as I got.
Tomorrow I'll look at what is hold the needle at the 6.3V mark.

Carlos


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 Post subject: Re: DuMont RA 103 5U4 tube
PostPosted: Mar Tue 21, 2017 2:41 pm 
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Joined: May Thu 14, 2015 4:15 pm
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Location: Dallas, TX
Coincidence, I have the same CRT tester. You followed the directions I assume.
Did only the G1 (Grid 1) light go on? On this tester that means a cathode to G1 short. The brightener wouldn't fix that. Of course something might be wrong with the tester where this is an error reading. without the CRT connected you should be able to adjust it from 5 to 8V. Are you sure that the 'Heater' knob is set to 5-8 ?

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747, 465, 1230, 1471B, 2005A, 1075
C-3, SG-8, V-7A, TC-2P
LAG-27, LBO-517
5382A, 368, 260, 8024B


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 Post subject: Re: DuMont RA 103 5U4 tube
PostPosted: Mar Tue 21, 2017 6:34 pm 
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Joined: Nov Sun 29, 2015 1:22 am
Posts: 550
Location: Parkland, Florida
Hi Tim.
Yes, I had the tester set 5-8 at about 6.3V. Yes, when tested for shorts only the G1 light went on.
If I set the tester 0-3 the needle goes to 2.68V, when I set to 3-5 it goes to 4.7 and at 5-8 to 6.3. If I set the knob higher it stays at 6.3.
The heater adjusting knob would adjust the needle from 6.3 to 4.7, but won't go any higher, it's stock at 6.3.
How do you use the "remove short" setting?
thanks,

Carlos


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 Post subject: Re: DuMont RA 103 5U4 tube
PostPosted: Mar Tue 21, 2017 7:55 pm 
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Joined: Nov Sun 29, 2015 1:22 am
Posts: 550
Location: Parkland, Florida
I have started to replace the paper caps and E-caps.
Here is this cap in the picture that has no apparent mF value; I assume it's an E-cap. The positive lead goes to the back vertical pos. which then goes to the horizontal pos.
What's the value on this cap?
Thanks

Carlos


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