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 Post subject: 5U4 instead of 5V4 in damper socket
PostPosted: Jun Thu 21, 2007 4:54 am 
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I am working on a Motorola TS-9D chassis (circa 1948, 10"). I have recapped it (including electrolytics) and powered it up and found that the raster is out of focus, kind of dim, and and has a circular shadow over more than half the screen, which appears as though the ion trap was misadjusted. I tried readjusting the ion trap and it wants to be well toward the bell of the picture tube (more than normal) in order to get the best raster, yet still has shadowing problems. I'm wondering if this is the effect if the ion trap were to be on backwards (front end facing rear)?
It also appears that the beam is well out of focus, and this may be part of the shadowing problem. I checked the resistors around the focus control (and the control itself, and the focus coil continuity) and these appear to be good. I find that the damper tube is a 5U4, not a 5V4 as called for. I know that the 5U4 has a directly heated cathode and the 5V4 is indirectly heated. However, the cathode of the 5V4 in this circuit is connected to the filament anyway, and the pinouts otherwide correspond. I imagine that the characteristics of these two tubes must be different (voltage drop, etc) so I'm wondering if anyone knows how this might affect the raster, focusing, or linearity. I'm going to try to dig up a 5V4 or order one, but for now I'm wondering how "close" the 5U4 is supposed to work. I'm sure this topic was brought up somewhere before in this forum, sorry if I'm being redundant.
I did also find that the large tapped bleeder resistor has 7K ohms for its largest section, and mine reads 11K. The other sections (1.5K and 1.0K) read OK. There is a 270 ohm resistor that connects the bottom end of this network to the cathode of one of the sync tubes (12AU7). This tube has a heater to cathode short, effectively shunting the 270 ohm resistor. It appears that the only problems these would cause would be a slightly higher B+ voltage on one of the lower voltage B+ lines, and causing no or little sync with the sync tube having a grounded cathode instead of a cathode resistor.
Let me know what you guys think.


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PostPosted: Jun Thu 21, 2007 5:29 am 
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I'd put the correct tube in. Charactoristics, including voltage, and current capabilities are different. 5U4 NOT good replacement.
Bill Cahill Make sure first that no one made modifications. If so, wire it the way the schematic shows for the 5V4.
Bill Cahill

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 Post subject:
PostPosted: Jun Thu 21, 2007 11:35 am 
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Yes, you need the correct 5V4 tube.
The only 12AU7 I can see that has a 270 ohm resistor is the video amp, not one of the sync tubes. If any tube has a short, replace it.
Your focus coil may be out of position, or the 1B3 may be bad.
That 7K resistor needs to be replaced. And check the 390 ohm resistor to ground that is right after it.
I am going by the TS-9D1 schematic in Riders; if you have the TS-9D it might be a little different.


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 Post subject:
PostPosted: Jun Fri 22, 2007 12:33 am 
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First, as to the 5U4 in the damper socket, I see no reason it wouldn't work just fine. It has the exact same pinout as a 5V4 and most of those other dual diodes. The only question would be the filament current; the 5U4 is 3 amps and the 5V4 is 2 amps. The original 5V4 is good for less current than the 5U4. Nonetheless it should work. I would get to the correct tube just to reduce the load on the sacred power transformer.

I would check the position of the focus coil (I believe this set has a focus coil), is the focus coil turned around possibly?

You could also turn the ion trap around and see if that fixes the problem. Has the CRT been replaced with a later aluminized tube that doesn't need an ion trap? (Look for the diagonal slice in the electron gun and usually there are two little tabs to either side of the gun inside the neck of the CRT that match up with the ion trap.

Jim


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 Post subject:
PostPosted: Jun Fri 22, 2007 12:49 am 
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Jim

I agree with you in theory but in actual practice a 5U4 doesn't work well as a damper. It may be the higher voltage drop? I've seen some TV's with vertical lines or poor linearity when a 5U4 is tried as damper.

I don't know of any dampers using filament type tubes.

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 Post subject:
PostPosted: Jun Fri 22, 2007 5:00 am 
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Thanks for the responses, guys, they do seem to make great sense. This weekend, when I have more time, I'll try to find a 5V4 in my tube collection and put that correct tube in the set and see what happens. I'll play around with the focus coil and the ion trap magnet (including removing it), and see if I can get the raster and focus more proper. I think the CRT might have been replaced, it is a 10BP4A, which I started to think might have been the type that does not requre an ion trap, but my GE tube manual says that that type number requires it, unless all later types even with original tube numbers started to not require the ion traps.
I'll replace the 7K resistor in the bleeder if I can come up with a decent wattage of resistors, I don't know how many watts it should be, since it is a Candohm type. I would guess at least 10, maybe more, though.
I think there may be a resistor mod in the horizontal lin/damper circuit that might have been added because of using the 5U4, I'll try to set everything back to the original schematic.
The shielded tuner tube, most toward the front, is awfully loose in its socket, and it seems impossible to get it out without removing either the picture tube or tuner, I'm suspicious of it, since I can't get any signal through the set, even for sound, yet.
I'll post progress reports as I go along... Dave


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 Post subject:
PostPosted: Jun Fri 22, 2007 3:58 pm 
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This set requires agc signal from the flyback. If that's not working properly, you may not be getting enough agc voltage.
Bill Cahill

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 Post subject:
PostPosted: Jul Mon 02, 2007 5:05 am 
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Here is an update on this set. I replaced the damper tube with the correct 5V4 type. There are two power rectifiers in this set, a 5Y3 that puts out a somewhat lower B+ for all the IF stages, and a 5U4 for everything else. I found that there was a low resistance short at the final output (after filter resistors) of the 5Y3 supply for the IF stages. Voltages across the filter caps were there, but some low, but the short was at the B+ line with respect to ground. This was putting the B- line more negative than normal with respect to ground, due to the increased current in the B- line from the short. This must have been what was throwing the focus way off, due to the fact that the focus control is betwen B- and ground (along with other resistors).
I found that the short was in one of the video IF coils! It was about 10 ohms between the primary and secondary of the coil that couples the 2nd with the 3rd video IF tubes. I wa able to unwind a few turns of the coil from one end to find that I could remove the short, so I was able to repair the coil, but of course I'm sure the alignment is now off a bit.
The vertical sweep had quit (after working for a bit), it turned out that one filament section of the 6SN7 vertical tube had gone out. I replaced the tube, and restored the vertical sweep.
The raster was a lot better, and even in focus, so I was happy at this point to find that the picture tube was likely good.
I still could not get a signal through it though, and after further investigation, I found that the tuner RF amp tube had gone out as well! Replacing that helped, but now guess what, still no sound. I get sounds through the audio circuit. but none from stations. I'll have to keep you guys posted as to what is next! Dave


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