KB QF80 Majestic.

[FERNSEH]

This receiver appeared on an earlier thread.
The KB QF80 is a 21" console TV set which also incorporates three switched FM radio positions: Home, Light and Third.
The set employs an eighteen position turret tuner, possibly made by Brayhead.

The set was easy to get going, the usual frame timebase faults were solved by re-capping. A strange line sync fault was traced to a wierd modification in the line oscillator, perhaps someones idea to improve line sync.
All the valves in the IF amplifier were low emission. They are a Brimar 9D7 vari-mu pentode in the common IF amplifier and two Brimar 6BW7s which serve as the vision and sound IF amplifiers.
I found a good 9D7, a NOS Mazda 6BW7 (made by Brimar) and a NOS Mazda EF80. The EF80 and 6BW7 are not direct replacements but as the set was going to be realigned the slight inter-electrode capacitances will not be a problem.

The realignment of the vision and sound IFs was completed resulting a dramatic improvement in performance. Before the IF amplifier job was done, even the high RF output from the Aurora was bearly sufficient to produce a contrasted picture.
The CRT was bad, a Mazda Re-Life CME2101. A replacement Mullard AW53-88 was found and fitted. The picture quality is now excellent. Thanks John.

The set has FM radio and the the performance was hopeless. One tends to expect FM radio equipped TVs to produce poor reception.
The QF80 employs a dual channel sound IF amplifier, 38.15Mc/s for TV and and the correct 10.7Mc/s for FM radio. I decided to realign the FM IF transformers and coils according to the infomation in the 1960/61 R & T book.
The results turned out to be impressive, first class reception on BBC radios 2 3 4. Switching back to TV the sound was was found to be missing, no trace of the test tone generated by the Aurora. The fault was finally traced to one of the 38.15Mc/s IF coils having been mis-tuned during the FM realignment.

Pictures 1 shows the rather odd line sync mod. The second picture shows the tidied up wiring.

DFWB.

[Heatercathodeshort]

That certainly looks like a Brayhead David with those one piece coils biscuits. Repair guys found flywheel sync difficult to deal with when the faults were probably down to simple diodes or capacitors. This was the start of the decent K.B. series and led on to the famous VC1 series a couple of years later. Put the back on and leave it at that. Looks very good to me. John.

[FERNSEH]

Originally Posted by Heatercathodeshort

Put the back on and leave it at that. Looks very good to me. John.

Hi John,
Just one job needs to done on the chassis. The CRT has to be repositioned to fit into the mask properly.

The original HT rectifier was a contact cooled type FC31 and was fitted on the right side of the chassis next to the sound IF stage. Not good.
It must have been replaced sometime in the sixties or early 70s by a Lucas made silicon diode. Instead of the usual series resistor a VA1015 thermistor was fitted. I have not replaced this component because it works very well.
The thermistor can be seen on the under chassis picture. It's near the smoothing choke L72.

DFWB.

[chipp1968]

Thats very nice indeed. Iwish i had some room for one .

[Heatercathodeshort]

I like the thermistor arrangement. Sounds of the RBM A823! J.

[brianc]

Were all the KB sets of that vintage so untidily wired? It looks a real mess. What part was the PCB? There looks to be a screened cable going to the pots so is it the sound section? More likely to be the LOP stage, I would have thought.

[Hybrid tellies]

Looks nice that tube looks very good as well.

[FERNSEH]

Hi Brian,
The under chassis wiring is untidy, but that's how those KB sets were built.
The PCB carries the PCL82 sound output valve and a 12AX7/ECC83 double triode which operates as the sync separator and vertical sync amplifier.

The QF80, QV70 and QV30 110 degree CRT receivers are a development of the 1957 model OV30 which also employed a similar PCB.

Two Brimar PCL82s are employed in the QF80. They are marked as "foreign made" and are made by Lorenz in Germany. The interesting feature of these valves is that they are beam tetrodes, unlike Philips or Mullard PCL82s which are real pentodes.

Hi Simon,
All the 405 only KB TV sets made between 1960 to 1962 are good looking and are well worth looking out for. Model types starting with Q are the 1959/60 series followed by RVxx, SVxx, and TVxx receivers. The later 405 only models have a long thin chassis which is not unlike in appearance to the VC1,2,3,4,51 dual standard receivers.

DFWB.

[Tazman1966]

Nice set David. Was there much to do to the cabinet?

[FERNSEH]

Originally Posted by Tazman1966

Nice set David. Was there much to do to the cabinet?

Hi Taz,
The cabinet is in very good condition which is just as well because it is finished in a high gloss polyester lacquer. Not easy to repair.
The handles on the folding doors need tidying up, that'll be an easy job.

Regards,
David.

[murphyv310]

Looking good David.
The finish must be very similar to the Bush TV128C that I picked up yesterday from Cheeky Bobby!