Bakelite Admiral TV with Retrace Lines
Robert Seger
Admiral TV and have had some great successes with it. I had a
terrible sound problem originally where the sound was way too low and
buzzy. The volume control had to be turned up to maximum in order to
hear the program comfortably. Well I finally figured out that someone
had turned the Sound IF slug nearly all the way in which threw the
sound section completely out of alignment. About 12 clockwise turns
of the slug brought in absolutely beautiful sound.
I'm almost ready to declare success because I have a generally
beautiful picture but unfortunately it is marred by Retrace Lines.
These lines seem to be worse on some stations than others, sometimes
they are just at the top of the screen, others go almost to the
bottom. In order to get rid of these lines I have to turn the
brightness control pretty far down to where the picture is too dark to
watch comfortably and then I can still see the lines during the dark
periods in-between commercials.
I realize that these lines are caused by improper blanking, but I'm
not sure which circuit processes these signals and where I should
concentrate my troubleshooting efforts. I have replaced all the wax,
paper and electrolytic capacitors as well as all the tubes but I
suspect there still are some out of spec resistors floating around.
Can you guys tell me which circuit I would normally concentrate on in
order troubleshoot a Retrace Line problem? On my restored RCA set I
have never seen as much as a single retrace-line, but that set has a
lot more circuits so it might have a better system to prevent these.
I can easily scan and post sections of the schematic if necessary.
As always I appreciate everyone's assistance.
Andy Cuffe
about 1975 have noticable retrace lines on some channels. It's caused
by various things like closed captioning and data that have been added
to the VBI over the years. Most early sets had simple, or no blanking
circuit and relied on the VBI being totally black.
--
Andy Cuffe
balt...@psu.edu
Bonita Lee Geniac
what appears to be retrace but is actually a "new" addition (VIR) to the
TV signal which was not there when the set was engineered. Especially
strong on some stations, usually network programs, and often absent or
greatly reduced in intensity on the same channel during local programs
or commercials. Most of the time there is no way to eliminate these
strong white lines from the picture because they are not retrace lines,
just a signal that has been added to the video during a time when on a
modern set built within the past 20 years or so the picture would still
be blanked.
Having said that, some of the earlier Admirals did have problems with
blanking and there may be some factory mods to improve the blanking on
this set, what run number do you have? I can check the Admiral factory
manual when I get the time. You would normally be looking for a
resistor/capacitor combination connected from the vertical output area
back to the CRT, in a polarity that would cause the CRT to cut off
during the retrace period.
--
I don't know Jack Schitt, but once I met Diddley Squatt !!
If "nospam" appears in email address, please remove it to reply
Philip Nasadowski
wrote:
> Most early sets had simple, or no blanking
> circuit and relied on the VBI being totally black.
Is there any way to fudge the vert blanking on an old TV to stay dark
with the newer signals? It's really annoying on some sets I have :(
Bonita Lee Geniac
about spoke with a network chief engineer in NYC a few years ago and
basically the advice was you have to go in there and change
resistor/capacitor values to try to alter the time constant and the AC
level of the feedback signal from the vertical output to the CRT. Having
tried this on several vintage sets, I find that you might be able to
make a visible reduction on some sets, but in most cases you are not
going to eliminate the problem. If you want to prove that the station
signal is the source of the white lines, play back a home recorded VHS
tape (recorded from camera not off the air) and you will not get the
lines.
--
Andy Cuffe
You could always run the signal through one of those VCR copy protection
busters that blank the VBI (where the macrovision is stored).
--
Andy Cuffe
balt...@psu.edu
Robert Seger
there is an 'R' as well as a '3' stamped on it, I'm not sure which one
of those two indicators is the run number.
Bonita Lee Geniac <bg...@wdl.net> wrote in message news:<3D20FB5E...@wdl.net>...
M Nelson
that the AGC action might not be enough to push the blanking level hard
enough into black on weaker signals. As BLG said, mostly you have to play
with the time constants. You might be able to add a little width to the
blanking time to include those now-occupied lines (from about 17-21).
Active retrace blanking (like keyed AGC) circuits were improvements added to
many sets in the late '40s and early '50s that didn't originally have
them -- there were articles in early TV service magazines from time to time
on how to add the functions to older sets.
--
Mark Nelson (remove .nospam to reply directly)
A collector of TV signal boosters and UHF converters -- God help me!
http://tv-boxes.com
Bill Cohn
I looked at the schematic of an Admiral 20X1 and it has no blanking circuit.
It depends on the DC coupling of the video to blank the signal. This is not
a good idea. Admiral did not do a very good job on the design of this
particular chassis in this regard.
You could add vertical blanking to the set by coupling some of the vertical
output signal to the G1 of the CRT. This would have to be a negative pulse
from the vertical output transformer and you would have to couple this with
a capacitor in order not to upset the DC voltage on the CRT control grid.
You would have to lift the .05 mfd capacitor that is on the CRT G1 in order
to inject the blanking signal. The blanking signal from the vertical output
will have to be clean during the active picture time or it will cause
shading across the picture.
Regards,
Bill Cohn
N9MHT
"Robert Seger" <unimat...@yahoo.com> wrote in message
news:e65bfe39.02070...@posting.google.com...
Bonita Lee Geniac
chassis and the changes get extensive as you get to the later runs. In
order to add blanking to the set, add a 270K 1/2 watt resistor between
pin 2 of the CRT and the junction of the brightness control and .05
capacitor. Easiest to do this right at the brightness control. Then
connect a new .05@600 volt cap from pin 2 of the CRT to the junction of
the .05 cap and 3900 ohm resistor in the shaper network off the plate
circuit of the 12AU7 vert osc. You might need to increase the value of
the 3900 ohm resistor upwards to 8200 ohms or more, the later chassis
that had blanking incorporated did in fact sometimes have a higher
value. Changing it too much affects the shape of the vertical waveform
driving the output tube and results in nonlinear picture. If you use a
scope you can see what you are doing both to the blanking and the vert
shaping. As Bill mentioned, if you add too much of a blanking pulse, the
pix will be shaded from top to bottom on a blank raster.
Also I remember another blanking mod that we used to install on other
brands of early TV sets, involving adding a resistor of 100K or so in
series with the CRT screen grid G2, and adding a cap of about .01 to .05
from wherever in the vert output stage would give a strong neg going
pulse, usually around the yoke side of the output xfmr.
--
Robert Seger
This will be really interesting to try. Thank you for explaining the
process in very simple terms, I understand your instructions
completely. I have the day off from the office on Friday so I will
get the parts and give this circuit upgrade a try then. I'll take
pictures of before and after and post them so we can see what effect
it has.
Hey, if there are 13 runs in the 20X1 Admiral, and I have run #3 I
suspect I have a rather early version of the set, which of course the
earlier the better with antique televsions!
Thanks again for your help, more to come.
Bonita Lee Geniac <bg...@wdl.net> wrote in message news:<3D21EFDD...@wdl.net>...
Bonita Lee Geniac
factory had with the set. The run number modifications are cumulative,
that is, run 13 would have every one of the modifications done in the
first 12 runs plus the run 13 changes. No one else made as many
production changes as Admiral did. In theory at least, the set with the
highest run number should work better than one with an early run number.
It is fairly common knowledge that at that time Admiral rushed to put
sets on the market, then reengineered the problem areas as production
continued.
Try to pick up a Wallace Telaides Admiral 1947-1953 book, they are often
on eBay for just a few dollars. They are copies of the Admiral factory
service data, and some of the chassis about the same vintage as yours
had at least 26 runs. Some of the modifications they came up with
included actually rewiring a complete stage with different component
values. What is good about having all the schematics and production
changes in one book like that is you can easily compare schematics from
one set to another and often a production change from a different
chassis can be used in another one to correct a similar problem. The
blanking change I gave you was from a 20T1 chassis, but I have used it
many times on 20X1 and 20Z1's.
Robert Casey
Andy Cuffe wrote:
> This is probably normal for this TV. Most TVs I've seen from before
> about 1975 have noticable retrace lines on some channels. It's caused
> by various things like closed captioning and data that have been added
> to the VBI over the years. Most early sets had simple, or no blanking
> circuit and relied on the VBI being totally black.
I have an old Admiral from about 1950, and it also has retrace lines.
And I remember another Admiral of the same vintage we had as a kid
also having retrace lines. Must be a normal thing. You might try injecting
the vertical sweep pulse from the vertical output tube via a capacitor
into the brightness circuit (which has a cap to ground that would need to
be disconnected from ground). Though the phase my be backwards for
what you need.
Mf101723
a few stations, was explained to me as being caused by data now being placed in
the VBI and it is unfixable.
On my '49 Hoffman I DON'T get these lines, but I do get retrace over entire
screen, not just on top, if brightness turned to high, was explained to me as
just the nature of the beast of being old TV design and is what happens if
brightness is turned too high.
Robert Seger
getting rid of the Retrace Lines on the Bakelite Admiral. I followed
your instructions to the T, first I added a 270k resistor between CRT
pin# 2 and the .05mfd/brightness control junction. Then I connected a
new .047mfd cap from CRT pin#2 to the junction of the .05mfd and 3900
ohm resistor. What this did was confine the retrace lines to the top
1/4 of the screen, before this change they used to cover almost the
entire screen. Further following your instructions, I next tried
changing the 3900ohm resistor to a 8200ohm resistor and goodbye
retrace lines!!! Since making that circuit change the picture is just
beautiful, I have not seen one retrace line since! The contrasts seems
better and I can really turn up the brightness now. Since its a newly
rebuilt CRT it makes for a wonderful picture. Thanks again for all
your help and everyone's advice here at rec . antiques . radio+phono.
Here is the '48 Admiral TV installed in its new home today upstairs in
the dining room, playing a 1949 commercial for Joy dishwashing liquid
when this TV was barely a year old...
http://www.classicappliances.com/TV/Admiral-Completed.jpg
By the way does anyone know approximately how much this bakelite
Admiral $$ would have cost in 1948? I'm curious about that and were
the wood models more expensive than the bakelite models?
jim menning
pleasurable.
And I've saved Bonita's tips for some of my future projects.
jim menning
"Robert Seger" <unimat...@yahoo.com> wrote in message
news:e65bfe39.02070...@posting.google.com...
Bonita Lee Geniac
retrace lines, and since the two extra parts needed (no cost difference
on the third part, a resistor which has to be a different value) would
have cost them maybe a dime in the late 1940's, why they didnt go for it
and include blanking in production?