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 Post subject: Re: Philco 48-1000 - Brightness Failed
PostPosted: Nov Sun 12, 2017 11:44 pm 
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On the HV cable that goes to the CRT - I may want to lengthen it a bit. I could clean up the soldered end at the HV rectifier tube socket (issues there may be causing the arcing), and it's a pain to test on the bench at its current length. Can I use regular wire? Or is it a special gauge or something? Do they sell extensions?


Last edited by sdyer on Nov Mon 13, 2017 4:13 am, edited 1 time in total.

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 Post subject: Re: Philco 48-1000 - Brightness Failed
PostPosted: Nov Mon 13, 2017 3:53 am 
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Location: WI 54812
No don't use regular wire. It needs to be high voltage insulated anode lead wire. You could rob the HV cup and wire off a newer tv if you can find a junker. Otherwise there's places that sell surplus NOS parts such as Surplus Sales Of Nebraska. Scroll down the page to "High Voltage CRT Anode
Connector" http://www.surplussales.com/Wire-Cable/HVWire-2.html

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 Post subject: Re: Philco 48-1000 - Brightness Failed
PostPosted: Nov Mon 13, 2017 5:22 am 
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Location: Crystal Bay, NV
That voltmeter is used only for very high voltages (over 1000 volts). Frankly, you don't need it to fix your problem.
You need a FET Voltmeter or an old VTVM with a bunch of ranges from a couple volts to over 500 volts. You can get one used for less than $40. This is the basic tool for all electronic testing.

The CRT measurements are taken from the pin connections at the base of the CRT, not the high voltage anode on the CRT side.
We need to know the voltage on pins 11 (cathode-yellow), 2 (control grid-green) and 10 (accelerator grid-orange). Do the voltages on these pins vary with the brightness (background) control? Measurements would be by attaching the negative lead to the chassis {ground).
Typical measurements would be 0 to 100v DC on pins 11 and 2 and up to 400v DC on pin 10.

The 1 Meg resistor is likely good. The arcing must be fixed, but that does not seem to the problem with the loss of CRT brightness.
Tubes are the most likely cause of any failure, and the ones to look at are the 7C5 (video output) and the 6AT6 (DC restorer).
=======
Ron


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 Post subject: Re: Philco 48-1000 - Brightness Failed
PostPosted: Nov Tue 14, 2017 6:17 am 
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EDIT: as Kevin points out below I did these measurements incorrectly. Disregard this whole post.
EDIT: I've removed the content of this post so as not to confuse this thread. I will put up the proper, DC-based measurements shortly.


Last edited by sdyer on Nov Tue 14, 2017 6:48 pm, edited 4 times in total.

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 Post subject: Re: Philco 48-1000 - Brightness Failed
PostPosted: Nov Tue 14, 2017 6:41 am 
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Location: WI 54812
For what it's worth your meter is set to AC volts.


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 Post subject: Re: Philco 48-1000 - Brightness Failed
PostPosted: Nov Tue 14, 2017 2:11 pm 
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Well, that makes me feel like a pro. I’ll re-do the measurements on DC.


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 Post subject: Re: Philco 48-1000 - Brightness Failed
PostPosted: Nov Tue 14, 2017 6:13 pm 
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Here are the voltage measurements that Ron (TahoeTV) recommended. This time with the MM set to DC :). The measurements are different from what he said to expect. Let me know what you think the next steps should be.

Yellow wire - varied with background control, from 130V with background all the way down to 0 all the way up.
Green wire - zero volts, or very very close to it. Did not vary with the background control.
Orange wire - 275V, did not vary with the background control.
7C5 pin 2 - schematic says 270V, measured 0 (zero) volts.
7C5 pin 3 - schematic says 180V, measured 76V.
7C5 pin 7 - schematic says 12V, measured 3.8V
6AT6 pin 2 - schematic says 14V, measured about 1V.

I took a look at L312. With the MM set to resistance 1, I got a beep, so it's not open.


Attachments:
File comment: Yellow - this is with the Background control in the middle position.
Yellow CRT wire voltage.jpg
Yellow CRT wire voltage.jpg [ 155.53 KiB | Viewed 463 times ]
File comment: Green - just about zero V.
Green CRT wire voltage.jpg
Green CRT wire voltage.jpg [ 165.39 KiB | Viewed 463 times ]
File comment: 6AT6 pin 2 - about 1V.
6AT6 pin 2 voltage.jpg
6AT6 pin 2 voltage.jpg [ 241.08 KiB | Viewed 463 times ]
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 Post subject: Re: Philco 48-1000 - Brightness Failed
PostPosted: Nov Tue 14, 2017 6:16 pm 
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Here is a picture of the schematic in that area. Red dot = capacitor replaced, blue "R" = resistor replaced.


Attachments:
Background Control Schematic.jpg
Background Control Schematic.jpg [ 152.64 KiB | Viewed 462 times ]
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 Post subject: Re: Philco 48-1000 - Brightness Failed
PostPosted: Nov Tue 14, 2017 7:43 pm 
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Location: Crystal Bay, NV
The voltages on the CRT are in the range that I might expect.
The thing that jumps out at me is the 0v on pin 2 of the 7C5. This is likely the problem if you have measured it correctly -- it's easy to count the pins in the wrong direction. If it is 0 then I would suspect R337, the 1000 ohm resistor that feeds the plate of the 7C5.
======
Ron


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 Post subject: Re: Philco 48-1000 - Brightness Failed
PostPosted: Nov Tue 14, 2017 8:16 pm 
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TahoeTV wrote:
If it is 0 then I would suspect R337, the 1000 ohm resistor that feeds the plate of the 7C5.

Also R336

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 Post subject: Re: Philco 48-1000 - Brightness Failed
PostPosted: Nov Tue 14, 2017 9:28 pm 
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R337 - Ron, thanks for pointing me to R337. I replaced it last month, but I miswired it. I connected it to the ground terminal, one terminal away from where it should have been. Today I soldered it to the correct terminal and we now have a picture! See video HERE.

R336 - I had replaced this resistor in May, but took a look at it again now. It is supposed to be 2k ohms, but measured 1k ohms out of circuit. I replaced it with a fresh one, which I confirmed measured 2k ohms.

7C5 pin 2 is now around 310V.
Green is around 1.6V.

I'm not out of the woods yet, though. Remaining issues:
- picture is very dim - I turned off all the lights to take the video
- Background control has no effect on the picture
- there is a "snap" in the audio from time to time which wasn't there before - you can hear it in the video


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 Post subject: Re: Philco 48-1000 - Brightness Failed
PostPosted: Nov Wed 15, 2017 2:52 am 
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sdyer wrote:
- picture is very dim - I turned off all the lights to take the video
- Background control has no effect on the picture

Does the yellow wire to the CRT still have the same range of voltages?

If so, you may have a problem with your CRT, but don't panic yet. It sounds like the cathode of the CRT is not getting the voltage that is on the yellow wire. Sometimes that is due to a cracked solder connection at the point where the wire coming through the glass is soldered to the pin at the base of the CRT. Try heating up the end of that pin and applying some new solder to the end of the pin. If that does not fix it, get some fine wire about 24 gauge or so. Tin about an inch of it. Heat up that pin and insert the wire into the pin and then add more solder.

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 Post subject: Re: Philco 48-1000 - Brightness Failed
PostPosted: Nov Wed 15, 2017 4:39 am 
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Location: Crystal Bay, NV
I know you said that the ion trap has not been moved. However, I urge you to try moving around a little to see if that makes a difference.
Long ago, I thought I had a bad crt and spent a huge amount of time before I realized that the ion trap was incorrectly positioned.
The snapping sound is probably a high voltage arc. Observe the HV area with the room lights off.
=====
Ron


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 Post subject: Re: Philco 48-1000 - Brightness Failed
PostPosted: Nov Wed 15, 2017 6:26 am 
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TahoeTV wrote:
The snapping sound is probably a high voltage arc. Observe the HV area with the room lights off.
And if you haven't already done so, clean everything in the HV area carefully with isopropyl alcohol (rubbing alcohol).

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


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 Post subject: Re: Philco 48-1000 - Brightness Failed
PostPosted: Nov Sun 19, 2017 4:58 am 
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Also make sure that the CRT anode wire is far away from any metal parts.

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 Post subject: Re: Philco 48-1000 - Brightness Failed
PostPosted: Nov Sun 26, 2017 11:02 pm 
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I was able to grab some time to work on the set this afternoon. With the resistor properly wired now (as discussed above), here are the current readings:

Yellow wire - varied with background control, between 145V and 0V
Green wire - 0.5 volts, did not vary with the background control.
Orange wire - 250V, did not vary with the background control.
7C5 pin 2 - schematic says 270V, measured 300V.
7C5 pin 3 - schematic says 180V, measured 240V.
7C5 pin 7 - schematic says 12V, measured 20V.
6AT6 pin 2 - schematic says 14V, measured about 4V.

Operationally the set is in the same state - very dim, dark picture, brightness control has no effect on it.


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 Post subject: Re: Philco 48-1000 - Brightness Failed
PostPosted: Nov Mon 27, 2017 12:27 am 
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Look again at the previous reply from Tom Schultz.
Make sure that the yellow wire is really connected to the crt pins (could have broken loose in the socket).
=======
Ron


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 Post subject: Re: Philco 48-1000 - Brightness Failed
PostPosted: Nov Mon 27, 2017 12:36 am 
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Tahoe & Tom:
The pins on the neck of the CRT are clean and the pins are all tight. None look loose, they aren't hollow, and they don't seem to be removable. The plastic wire socket attaches to it normally and tightly as well. I tested the yellow wire to the socket with the MM, got a beep, so the yellow wire is not open. With the set on, I knocked and jiggled the rear socket, but it had no effect.


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CRT Pins.jpg
CRT Pins.jpg [ 85.88 KiB | Viewed 203 times ]
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 Post subject: Re: Philco 48-1000 - Brightness Failed
PostPosted: Nov Mon 27, 2017 3:55 am 
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Location: Crystal Bay, NV
The pins are hollow, even though they don't look it because solder fills the hole at the end.
Sounds like the cathode (orange wire) has come loose from the pin, or it has broken off further inside the tube.
The reason we say that is because a varying voltage on the cathode should cause a change in the brightness.
The suggested repair involves heating the suspect pin with a soldering iron until it is hot enough to allow you to feed a fine strand of solder into the hole at the end of the pin. How much solder, well not so much as to overfill the pin. If that doesn't work try the wire suggested by Tom.

Some crt testers have a feature for welding a broken cathode connection, but such repairs don't often last.

If the crt is a goner, don't feel too bad. It was common to replace such crts after a few years of use. This one may or may not be the original. The crt doesn't last any longer than a typical tube. The other reason to rejoice is because the 10BP4 tube is just about the easiest crt to find. It was used in every make in the yearly years of TV. If you were in Reno, NV, I could give you one.
====
Ron


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 Post subject: Re: Philco 48-1000 - Brightness Failed
PostPosted: Nov Tue 28, 2017 12:12 am 
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Ummm... please forgive my idiocy but if the owner of this absolutely gorgeous set had a 12” crt around bd such as perhaps a 12KP4 they could plug it in (with a KP4) remove the ion trap and see if they get a normal response?.

Or, if not just check if voltage actually IS varying by adjusting up and down the brightness pot while watching the multimeter response?

I also have a 48-1000 although mine is a preproduction handwired prototype but essentially the same beast. They can be tricky but they are not that difficult to scope out! Just offering a couple thoughts to help you progress forward!

George


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