Hot on the heels of a Sobell T21, my next adventure is with a seemingly very small Bush TV53. It is not especially small, but going from a 21 inch screen down to a 14 inch, it certainly seems so.
The set is in extremely good condition with no damage to the cabinet and no sign of any rusty bits or corrosion to the chassis. Furthermore, there are no signs of any past repairs except a replacement Telefunken PCC84 valve in the tuner and the EY86 EHT rectifier, which has gone to air with a crack in it's base so this will have to be replaced of course. (Early versions of the chassis used an EY51).
I have already removed the two chassis sections and it is quite clear that a considerable amout of rubber insulation of some cable looms are rock hard and crumbly. This will all need to be replaced.
The good news is that the CRT test with my B&K shows excellent emission after a short period of running the heater. Before I connected the B&K, I used a PSU to check that the heater had no partial shorts. This was done by applying a current limit of approx. 300mA and as the heater warmed up, the voltage settled at 6.2 volts. If there was a partial short in the heater, the voltage would of course be quite a bit lower at the 300mA current limit. In the series heater string, the current will naturally be around the 300mA region as I am sure you well know.
Anyway, here is the set and the chassis with the LOPT screening can removed.
To understand the black art of electronics is to understand witchcraft. Andrew.
Looks like it's a later production model because the CRT is the electrostatic focus AW36-21 so it's likely the set was made in 1956.
Later that year the TV63 was introduced with changes to the cabinet presentation. Same shape as the TV53 but with a darker finish and gold trim lines at the outer edges of the cabinet.
Till Eulenspiegel.
Indeed, the finish designed to harmonise with the VHF64 table radio and many a German radio set of the time.
I'm led to believe that these sets are capable of outstanding pictures and IIRC, have a plug-in LOPT?
Looks like it's a later production model because the CRT is the electrostatic focus AW36-21 so it's likely the set was made in 1956.
Till Eulenspiegel.
You are spot on there Till, it has a date stamp of 11th June 1956 and most certainly is electrostatic focus. I can't confirm the CRT type as the lable has long gone, but it is a Mullard and looks to be original and undisturbed.
To understand the black art of electronics is to understand witchcraft. Andrew.
Now, the LOPT is easily removed as it is secured by just two screws and can be unplugged very simply. Last night I gave it a ring test by using the cal. square wave output from my 'scope. Deliberately placing a shorted turn of wire around the core reduced the oscillations considerably. This, as you may well know, is to simulate the effect that an internal shorted turn might have. Incidentally, removing the EY86 produced a slight increase in oscillation as of course it's heater completes a circuit of turns around the LOPT too.
Anyway, the LOPT would appear to be fine, so I went on to clean it up and to replace the badly decayed rubber insulated wiring. The wax surround that is usually applied to the outer overwind had pretty much fallen off so I simply removed the remainder. I will at some point use a psu voltage to warm the overwind to drive off any trapped moisture.
So far it would seem then that two critical ingredients are in good condition, the CRT and LOPT. Here below is the ring test shown on the 'scope followed by a slightly refreshed LOPT, complete with a new EY86.
To understand the black art of electronics is to understand witchcraft. Andrew.
We had one of these in the mid-sixties. I was just getting interested in radio and TV then with the help of my brother who was a TV engineer. One of my first jobs was to change the audio coupling capacitor....I think it uses a PCL83 for the audio amp/output. Excellent pictures. I shall watch the thread with interest.
I can't remember if the front implosion glass can be removed for cleaning or if you have to remove the chassis/CRT.
I'm led to believe that these sets are capable of outstanding pictures and IIRC, have a plug-in LOPT?
Indeed, the 50 series Bush TV sets are truly excellent performers and because of the extra stage of IF amplification and a good flywheel line sync system made these sets ideal in fringe reception areas.
The scanning coils are of the high impedance type and are connected between the "top" of the transformer primary and the boost capacitor.Till Euenspiegel.
Phew ! I have just rushed into the workshop to measure the resistance of the scan coils. Thanks for mentioning them Till, as I have had fun with open circuit scan coils before.
However in this case, I have no need to worry as both line and frame measure almost exactly according to the data in the Trader Sheet, which is downloadable from the Library and I will use this for any future circuit references.
I shall sleep easier now ! ?
To understand the black art of electronics is to understand witchcraft. Andrew.
The circuit diagram of the line timebase in the Peto-Scott TV1720. The line output stage is very similar to the same in the Bush TV53. Interesting to note the Peto-Scott has a stabilised line timebase. The diode V20 (OA71) rectifies a portion of the flyback pulse to control the current in the output valve.
Till Eulenspiegel.
As I have already removed and checked the LOPT, it would be sensible to perhaps concentrate upon the timebase section of the chassis. One capacitor in particular that will certainly need to be re-stuffed is C94, seen in the below photo on the left. Clearly with all the molten wax, it may not be in the best condition.
It is an 0.5uF in series with R108, a 2.2k ww resistor between the HT line and the beginning of the heater chain, just before the NTC thermistor. The purpose for these components is to neutralize residual HT mains hum, according to the Trader sheet. Anyway, with this removed for the moment, it will aid cleaning of this area.
To understand the black art of electronics is to understand witchcraft. Andrew.
In the folowing photo of the chassis I took at the weekend after a light dusting down, I want to draw your attention to the lower right hand side. Here there are four preset controls, width, line hold, height and frame hold.
Upon examining this group, I noticed that the line hold control (R60) has been replaced with a 500k RS potentiometer. It should be a 1 meg, and resistors have been added to make up roughly the right value. I may well replace this with the correct value as I do have a small selection of this type of control.
The control at the extreme lower right of the photo is for the width, R71. This is a wire wound potentiometer and upon testing of this, I found that the rotation of the spindle had no mechanical end stop and there was no variation of resistance either. In other words, it was stuck at 2 k, the value of the pot. I was able to remove the pot and it's rear metal cover. Inside, I could see it had been forcibly rotated and the small metal portion that hits a plastic end stop was riding over it. The wiper was also not making contact with the wire track.
I was able to repair it though. The small front plastic knob of the control fits tightly on the brass spindle and upon removal of this, the wiper and end-stop section could be withdrawn and straightened out. In short, putting it all back together, everything now works ok and I have a good pot.
To understand the black art of electronics is to understand witchcraft. Andrew.
Whilst we are all familiar with fixed resistors going high in value, I've found on almost all the sets I've repaired that the pots & presets seem to go low in value! 2 meg pots that have gone down to just over 1 meg or 500k ones down to 300 odd K.
Replacing such items is often a bit difficult, so I end up cheating and padding the value with resistors to get the range of the control where it needs to be!
I guess it must be the type of resistive element used in such pots that causes the lowering of the value, but it's caught me out several times!
It's handy that your width pot lent itself to being dismantled and repaired- rather satisfying!
At least you're not wrestling with a huge tube on this set and it looks quite convenient having two separate chassis.
Cheers
Nick
I like these Bush sets, and have a couple of 53s, a 63 (from Jon Evans) and the TUG version of the 63 from Luke (Mendip Views). They do indeed give fantastic results (vision wise) and the frequency gratings will bear witness to that when you get that far. The audio stage will almost certainly need attention, and if allowed to run as is, you will most likely hear a rather distorted audio, and lacking volume. I won't spoil your fun, just don't let the set run in that state - unless you have a good supply of PCL83s! (The anode of the pentode section takes a hit and glows like a South American sunset!).
The next thing I did was to reform the main smoothing electrolytics (C95,6 and7) and I am pleased to say they are fine. I am in the process of replacing all of the perished rubber insulated cables on the timebase chassis. It is still possible to tell what colour they are, so like for like but with PVC insulation of course. This is quite a time consuming task and at the same time, I am cleaning the under chassis.
To understand the black art of electronics is to understand witchcraft. Andrew.
I am nearly sure this is basically the same chassis that was in the Bush 21inch TV my parents bought in 1958, it had two chassis side by side like this one. Perhaps some changes to accommodate the larger screen.
Frank
Yes we saw a somewhat similar TV briefly in Australia, when a major whitegoods maker Simpson joined up with Bush to make Bush Simpson TVs in 1956. They launched with a 17 inch model. And yes, it had a proper mains transformer!
The first 21 inch model used the same chassis as the 17 and a 70 degree CRT in a gigantic cabinet. It was one of very few 21 inch 70 degree TVs. It also had all its normally internal controls brought out, in this case under a hinged flap in the top of the cabinet - a customer could really mess things up if they played with these.
The following much improved 110 degree chassis had a 4 button push-button tuner and carried forward the idea of a separate "signal" sub-chassis, which in this case was hinged off the main chassis, unusually made from aluminium. By then, deflection and other parts were sourced locally. I have one of these sets in the garage waiting its turn to be restored.
Bush Simpson were one of many local TV manufacturers to not survive the 1961 credit squeeze.
The next thing I did was to reform the main smoothing electrolytics (C95,6 and7) and I am pleased to say they are fine. I am in the process of replacing all of the perished rubber insulated cables on the timebase chassis. It is still possible to tell what colour they are, so like for like but with PVC insulation of course. This is quite a time consuming task and at the same time, I am cleaning the under chassis.
I too found the rewire to be quite a time consuming job, but thankfully, some of the original wiring was still sound. I found the best way was to detach each wire, one at a time, at one end, then solder the new wire to the end of the old one, using the old wire as a 'pull through'. It was necessary at times to carefully guide the soldered joint through the grommets and securing loops and clips, but at least the new wiring was very amenable to being pulled along its path. Once pulled through, I attached the new wire to its solder lug at one end, checked the fit of the wire along its entire run,then snip off the surplus wire, remove the still attached old wire, and finally connect the new wire to its tag. I did this, one wire at a time, and only ever disconnected one end at a time.
One advantage of doing it this way was that the wires always followed the exact same run as the original, which in some instances was critical to avoiding mutual interference - like the vision output lead from signal chassis to CRT base, which must be spiralled around the entire CRT wiring harness.
For the replacement wiring, I used the coloured cores from "7 core" trailer lighting cable - it was just the job! nowadays we have "13 core" trailer cable, so even more colours to choose from!
I agree, and this was the best way. To disconnect them all at once would be to invite an error !
The old insulation was flaking off like a hailstorm and getting everywhere. A right pain in the wotsit.
To understand the black art of electronics is to understand witchcraft. Andrew.
I am nearly sure this is basically the same chassis that was in the Bush 21inch TV my parents bought in 1958
That might be the TUG59 model that is listed in the Trader Sheet data. It is a console with doors though.
To understand the black art of electronics is to understand witchcraft. Andrew.
Something at the back of my mind is saying "TV79"... IIRC the advertising almost went along the lines of "we can't imagine why anyone would want a table set this big".
I might see if I can find an appropriate catalogue.
