I figured I would "go back to the drawing board" and try to find out where all my video gain has gone. I tested all the video section tubes and found that the 12AL5 video detector /AGC tube has one section (out of two) that is almost non-existent , emission-wise. That would directly impact my video ( and hence my sync ) output, or put the AGC way out in the wrong place.
So-o, does anyone have a 12AL5 tube to send me? I have dozens of the 6AL5 type ( common ) , but not a 12ALS. It would have to test "good" on both diode sections, and I would gladly consider a "tube trade".
Thanks
Lou
T.
Another thing not to rule out is an element to element short within one of the other tubes. When you test tubes on an emissions tester, often all of the grids and plate are tied together. Test for shorts between each one while hot. I had quite a bit of trouble with some 6SN7s in my BT-100, one of which controls the horizontal oscillator. Blasting the short with high voltage solved the problem, though it kept coming back on later occasions, so I finally just replaced the tube.
T.
Here is a copy of my schematic. Don't know if it's at all like your's. For one thing, I haven't found it too common for there to be a separate video and audio IF string. The main focus is on the sync. separator circuit, which might give you a few clues about your own....or maybe not. I do know that the horizontal oscillator circuit in the RCA 630TS is a bit different than many other televisions.
http://www.clarisonus.com/Archives/Television/630TS.pdf
...And, like another friendly guy said, if you have a scope, check to see that the proper sync. singal is making it through to the horizontal oscillator. I don't have a good scope, so I just rely on following the schematic, and what results I get.
Dave Froelich works a lot with vintage televisions. Perhaps he has some ideas?
T.
I know that detector tubes dont need much emission to work, but this one was almost totally dead on one diode! Seems like it probably has been in there since the TV was made.
Yes, I have been lazy about using the 'scope. Maybe when I get more time, I will sit down and give the video string a going over. I just seemed to notice that my video was slowly deteriorating with more use of the set. It started out fine , and then slowly started to disappear. Well, I will replace the 12AL5 and go from there.
Thanks
Lou
:I don't know what your schematic looks like, but you say that there are some things in the sync/horiz. section that don't follow the schematic. Have you tried wiring the circuit according to the schematic? If replacing tubes doesn't help, perhaps try that.
:
:Here is a copy of my schematic. Don't know if it's at all like your's. For one thing, I haven't found it too common for there to be a separate video and audio IF string. The main focus is on the sync. separator circuit, which might give you a few clues about your own....or maybe not. I do know that the horizontal oscillator circuit in the RCA 630TS is a bit different than many other televisions.
:
:http://www.clarisonus.com/Archives/Television/630TS.pdf
:
:...And, like another friendly guy said, if you have a scope, check to see that the proper sync. singal is making it through to the horizontal oscillator. I don't have a good scope, so I just rely on following the schematic, and what results I get.
:
:Dave Froelich works a lot with vintage televisions. Perhaps he has some ideas?
:
:T.
T.
The tubes are in a series string. I would rather not modify the receiver.
Thanks
Lou
:You got my note about using a 6AL5, right? Put a 20 ohm resistor in series with the filament lead...unless the tube is in series with others...then a 6AL5 might not work.
:
:T.
I just now caught this separate string on the Raytheon…as per the ‘AL5. It is using one of its sections for the delayed AGC and the other for
the detector of the unit, with the AGC clamp diode being the less critical of the two functions. All in accordance as to which section was wired up
in the particular section in the set.
I just checked my FULL schematic to see the possibility of them having utilized another’AL5 over in the FM audio, detection area, but they
had used a 19T8 tube there…. thus, keeping in their theme of using up all of the old radio parts stock.
To make an analysis of the functionality of your detector circuit WITHOUT buying a new ‘AL5 just make a technology jump forward and use what was to be used just a little later. Solder tack in a 1N34/or/1N60/or/1N270 germanium detector diode across the detector diodes pins....polarized
accordingly [tube plate – diode anode….tube cathode – diode cathode].
The existing circuitry is geared towards a high Z load but the sub should suffice for evaluation, considering that the drive level is not impinging
upon the PIV threshold of that germanium device. If that is the case, a fast silicon switching diode like the very common and venerable 1N914/ 1N916/ 1N4148 could be utilized for a like testing in that spot.
The end result may be a higher recovered video level and a much contrastier picture, as compared to the original maximum shade of grey available from the thermionic tube detector circuitry.
Plus, the end result being no correction of the Hoz phasing differential problem, since a vert sync pulses extraction and shaping is much more problematic than the short / simple hoz sync pulses, and your set is already handling the vertical aspect adequately.
Thassit…
Larger schema…….. LINK
Standing by for findings….
73's de Edd
:Thanks Tom
:
:The tubes are in a series string. I would rather not modify the receiver.
:
:Thanks
:Lou
:
::You got my note about using a 6AL5, right? Put a 20 ohm resistor in series with the filament lead...unless the tube is in series with others...then a 6AL5 might not work.
::
::T.
:
:I figured I would "go back to the drawing board" and try to find out where all my video gain has gone. I tested all the video section tubes and found that the 12AL5 video detector /AGC tube has one section (out of two) that is almost non-existent , emission-wise. That would directly impact my video ( and hence my sync ) output, or put the AGC way out in the wrong place.
:
:So-o, does anyone have a 12AL5 tube to send me? I have dozens of the 6AL5 type ( common ) , but not a 12ALS. It would have to test "good" on both diode sections, and I would gladly consider a "tube trade".
:
:Thanks
:Lou
Lou,
I show that I should have just a few 12AL5 available - I am currently fond of tubes like 6F5G, 6H6G, also a #58 - what sort of thing could we work out? (I'll be out of town for a week.)
Eddie
I am sorry, I did go ahead and order the 12AL5. I didn't get any responses for awhile on this tube.
Thanks Again for the thought
Lou
:Well, I have found one problem.
::
::I figured I would "go back to the drawing board" and try to find out where all my video gain has gone. I tested all the video section tubes and found that the 12AL5 video detector /AGC tube has one section (out of two) that is almost non-existent , emission-wise. That would directly impact my video ( and hence my sync ) output, or put the AGC way out in the wrong place.
::
::So-o, does anyone have a 12AL5 tube to send me? I have dozens of the 6AL5 type ( common ) , but not a 12ALS. It would have to test "good" on both diode sections, and I would gladly consider a "tube trade".
::
::Thanks
::Lou
:
:Lou,
:I show that I should have just a few 12AL5 available - I am currently fond of tubes like 6F5G, 6H6G, also a #58 - what sort of thing could we work out? (I'll be out of town for a week.)
:Eddie