This is a fairly common 7-inch electrostatic set from the late 1940s.  This is the second of these sets that I have restored.  The first I restored for a friend and this is one I purchased for myself.  I had been wanting one of these sets for a while but usually when they come up for sale on eBay they bring $150 to $200 in good condition.  This one has seen better days but is quite restorable.  I won it for $35 and with shipping I received it for just under $50.  The cabinet needs some work.  There are a number of rather large chips in the veneer and a chunk taken out of the raised portion on top.  All of the tubes had been removed from the set as well as all of the knobs and the channel escutcheon.  Tubes were not a problem and I was able to find a complete set of knobs as well as a channel escutcheon at a local swap meet.  The knobs and escutcheon were used on a number of other sets from this same period.  The 7JP4 picture tube is gassy as evidenced by the lack of silvering from the getter flash.  It is still somewhat useable for testing although I do have a couple of other 7JP4s that I can put in it.


First off here is some information on the TV-149.  This set uses 22 tubes including the picture tube.  This is a transformerless set and all of the tube filaments are wired in two paralleled series strings.  There are two rectifier tubes and a selenium rectifier used in a doubler/tripler circuit for the power supply.  The IF is of the intercarrier type with a 6AL5 video detector and an AVC style AGC system.  This same chassis was used in a few other television sets of the era such as the Firestone 13-G-3 and the Automatic TV-P490.  A schematic of the set can be viewed here in PDF format.


January 22, 2006: I started out the restoration by cleaning all of the dirt from the chassis.  I first went over the chassis with hot soapy water and a rag.  There was some corrosion on the chassis so I went back over the chassis with some #0000 steel wool and WD-40.  This got all of the corrosion and other oxidation off and left the chassis nice and smooth.

I started the electronic restoration by replacing all of the paper capacitors and checking all of the resistors for any that were out of tolerance.  Electrostatic sets use high voltage paper caps to couple the vertical and horizontal deflection voltages to the deflection plates.  In the past I have replaced these caps with high voltage ceramic units.  It has been discovered that using ceramic capacitors in this function is a bad idea.  They tend to create problems with the linearity of the waveform.  For this set I ordered some .0047uF 6000V tubular capacitors from Allied Electronics (Allied part number 225-6075).  They are considerably more expensive than ceramic caps but hopefully I will not have any linearity problems.

I needed to order electrolytic caps for this set but in the meantime I decided to try powering it up.  I inserted all of the tubes and connected the set up to my variac through an isolation transformer and a AC amp meter.  This way I could monitor the current that the set was pulling to make sure it was not excessive.  I slowly brought up the power on the set keeping an eye on the current.  After a while I could here the horizontal oscillator working and then the high voltage came up.  I was able to get a raster on the screen.  I connected the antenna terminals to my cable jack through a transformer to see if I could get a picture.  I was able to get sound but no picture.  I began troubleshooting in the video amp and found that I had high plate voltage and low screen voltage.  These two voltages are fed from two different points in the power supply.  The plate voltage comes from the output of the selenium rectifier and the screen voltage comes from the output of the 6X5 tripler.  Checking the power supply circuitry showed that I had sufficient voltage from the selenium and going into the plate of one half of the 25Z6.  The output of the 25Z6 was way too low (about 130V instead of 260V).  I thought that this could be due to the two 40uF filter caps being excessively leaky.  I disconnected them from the circuit to check leakage and reform them.  I was able to get the leakage down considerably and put them back in the circuit.  I powered the set and checked voltages.  Still I have insufficient voltage from the 25Z6.

February 4, 2006: I received the replacement electrolytic caps and installed them.  Below are a couple of screen shots from the set.  I was having problems getting enough height to fill the screen.  This turned out to be a bad 12SN7 vertical output tube.  I replaced it and now have sufficient vertical output.  I am having vertical linearity issues that I will troubleshoot next.

February 12, 2006: After looking at the waveforms in the vertical section I discovered that the output amplifier is saturating and causing the linearity issue.  If I reduce the height I can eliminate the saturation; however, I don't have sufficient output to fill the screen.  I remembered having this problem in the previous set I had restored.  My solution then was to decrease the high voltage to the anode of the picture tube.  This spreads out the raster allowing the screen to be filled with less vertical output.  I will now need to align the IF, sound, and front end.

March 18, 2006: I purchased a Jackson sweep and marker generator so that I could perform an alignment on this TV. I tried to align the IF according to the Sams Photofact.  It says to align the IF to have a fairly flat response with the rolloffs at 34.8 MHz and 36.9 MHz.  When I did that I had a very snowy picture.  I tweaked the IF coils to get the best picture with clear sound.  The result was the response shown below.  It looks more like a radio IF response than that of a TV receiver but it works.


While I was aligning the set I heard a hissing noise and a bunch of smoke began coming from under the chassis.  It looked like an eletrolytic had given way.  I immediately turned off the set and began to inspect the underside of the chassis for a failed component.  All of the electrolytics looked fine.  All of the resistors and other components looked fine.  I plugged in the set and turned it on again.  The smoke began again and revealed the source: the candohm filament resistor.  I had thought about replacing this unit but now I was forced to.  I went ahead and replaced it with a couple of wire wound resistors.

While I was under there I installed a retrace blanking modification.  This will reduce if not eliminate the white retrace lines that show up on the screen at hight brightness levels.  This is a relatively simple circuit involving the addition of a capacitor and a couple of resistors.  The circuit addition is shown here in red.  This worked suprisingly well.  I have added retrace blanking to other sets that did not have it in the past with results that were OK but not great.  This time it seemed to completely eliminate the retrace lines and not affect picture stability.  Here are a couple more screen shots after the retrace blanking mod and the alignment.

 

Now, on to the cabinet...

April 14, 2006: As you can see in the photos above, the cabinet was in pretty ragged condition.  It had numerous gouges and scratches, there were a bunch of large chips missing in the veneer, and one of the vent holes had been collapsed from damage.  After assessing the cabinet I decided it would be best to remove the raised section in the middle of the top completely as well as the veneer on the top of the cabinet.  I would use the removed veneer to patch missing sections on the sides and front.  I would also strip the finish from the sides but restore the finish on the front to retain the decals.  Namely the Tele-Tone decal that nobody reproduces.

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This site created and maintained by Sean Barton.

Last updated 4/16/2006.