Kolster-Brandes HV40 TV set.

[FERNSEH]

The attachment shows the underside of a Kolster-Brandes HV40 TV set.

Note the valve among the components.

DFWB.

[FERNSEH]

According to the Radio and Television servicing book the KB HV40 was released February 1953 being a development of the HF40 which was introduced the previous year.
The 14" rectangular CRT is a Brimar C14BM which has a triode gun assembly. The tube has an ion trap magnet fitted on the neck although this device is not needed for this tube type.

DFWB.

[German Dalek]

Hi,
That is a nice set and seems to be in good shape.

It is told, that Triode CRTs have a weak picture compared with Tetrode CRTs.
Isn´t it recommended to swap these CRTs?

Regards,
German Dalek

[FERNSEH]

Hi German Dalek,
I believe the Brimar C14BM and the C17BM were the first rectangular CRTs to be marketed in the UK. Design of the tubes might well be of American origin.
Brimar replaced the triode CRTs with the types C14FM and C17FM, both having tetrode gun assemblies. The C14FM can be considered to be an equivalent for the Philips/Mullard MW36-24.
Today, I applied mains supply via a variac to the KB. So far the maximum EHT voltage is only 7KV, half the figure quoted in the service manuals.

DFWB.

[beery]

Hi David,
It is nice to see any early KB set. They are quite rare.

I've got a spare LOPT which was lined up for my KV35. The transformer in that set has a bad holder for the R19 EHT rectifier, so it is currently fitted with a silicon diode.
The LOPT is the horizontally mounted type, with a movable core for the width adjustment (using the back of a wander plug as a knob). The LOPT molding supports the socket for the R19. Is that similar to yours?

Cheers
Andy

[FERNSEH]

Hi Andy,
the line output transformer has a ring type of core.
Last night the coupling capacitor between the control grid of the 6CD6G and the line oscillator was replaced. It had a slight leak. With the 6CD6G removed there was +45volts on the grid connection.
Replacing the capacitor actually reduced the EHT. Line oscillator is running a bit slow, repetition rate is 120uS.

DFWB.

[FERNSEH]

Circuit diagram of the line timebase. This is the version that uses a 12AU7 for the line oscillator. The set which is the subject of this topic has a Brimar 8D3/6AM6 as a line blocking oscillator. Said to give better immunity to degraded sync pulses.
Note the values of the boost capacitors, 0.08uF and 0.06uF.
It's likely the line output transformer is faulty.

DFWB.

[FERNSEH]

"It's likely the line output transformer is faulty."

Evidently not. The set was switched on today and the first thing I observed was the EY51 EHT rectifier valve heater was glowing. A 5mm spark at the anode of the valve. Later on it was noticed a TCC waxie capacitor connected across the width control coil was very hot. The capacitor is C76 (0.01uF 1000V) and is fitted in later production sets. See attached circuit diagram.
The EHT is now 14KV.
No raster though. The C14BM CRT is completely useless. Found a Mullard MW36-24 tetrode tube upstairs. Whether or nor it is usable we'll find out tomorrow.
370 volts boosted HT is available across C79 (0.06uF)

DFWB.

[FERNSEH]

Well, that's disappointing, the replacement CRT is gassy. I'll re-box the set and put it on the waiting for spare parts pile.

DFWB.

[FERNSEH]

A good CRT has been found for the KB HV40. The replacement tube is a Brimar C14FM which has a tetrode gun and a 12.6volt heater.
In order to use this tube the existing 6.3volt CRT heater winding on the mains transformer has been connected in series with one of the other 6.3volt windings. A 400 volt first anode supply is required for the C14FM tube, this is available across C79, refer to post No.8 for the circuit diagram.
Additional components required are a 470Kohm series resistor and a 0.001uF capacitor connected between the CRT AI and the HT line. The information for establishing a CRT A1 supply was found in the 1953/54 Radio and Television servicing book.
Late production 17" KV60 models were supplied with a Brimar C17FM CRT in lieu of the C17BM. KV60 receivers had a 12.6volt winding on the mains transformer to allow the fitment of the tetrode CRT.
Not so lucky with the HV40, this receiver was designed to use a 6.3volt CRT. Fortunately the tube heater winding is isolated from the the other heater supplies so it was an easy matter to wire it is series with another 6.3V heater supply.

DFWB.

[FERNSEH]

Good progress this afternoon. The focus coil HT supply fault was caused by the 64uF smoothing capacitor and the RM3 rectifier needing replacement. See pic No1.
The receiver now displays a bright well focussed picture but the frame timebase needs attention.
The replacement Brimar C14FM CRT looks absolutely correct in this KB set.

DFWB.

[German Dalek]

WELL DONE!

Regards,
German Dalek

[FERNSEH]

Yesterday evening two capacitors in the frame timebase were replaced.
The coupling capacitor between the blocking oscillator and the grid of the 6BW6 output valve. The other was the sawtooth forming capacitor in the oscillator.

DFWB.

[Heatercathodeshort]

Very nice picture David.
Yes the early KB receivers are very rare. Many moons ago I did a write up on my earlier EV30L employing the Cintel 12" aluminised 10kv tube. The cabinet is 20" deep to accommodate this long neck CRT. It has many similarities including the ferrite ring LOPT.

https://www.vintage-radio.net/forum/...light=KB+EV30L

The picture is still super bright and very stable.

KB were very popular 'up North'. Pic taken a few moments ago. It has not been powered up for years. John.

[Heatercathodeshort]

Pics added. J

[FERNSEH]

The KB HV40 had only sufficient picture height to fill the screen. More picture height would be desirable. The 820Kohm grid resistor of the 6BW6 output valve was found to be open circuit. Replacing the resistor has secured more vertical amplitude. See attachment. The camera has captured only one picture field, hence the very noticeable line structure.

No sound fault. For starters the Brimar 8D3/6AM6 valve output was found to be gassy. All the valves in the sound receiver are OK, hum at volume control tags.
With the contrast control advanced fully there was a trace of vision on sound.
It was found all the sound IF transformers were mis-tuned. The sound intermediate frequency is the old industry standard of 19.5Mc/s.
Sound IFs realigned and peaked up. More than enough sound now, especially when one considers the type of sound output valve, a small RF pentode.

This set is fix tuned to BBC channel 5. Retuning to another Band 1 channel isn't an easy task. The service manual informs us that all the RF and local oscillator coils must be changed in order to receive another BBC transmitter.
In this TV receiver the Brimar 6BW7 makes it's debut. Better VHF performance than the miniature 6AM6. In terms of sensitivity this set is even better than the Pye FV1

The set might keep company with a Bush TV22, if that is the case it is a simple matter to retune the Bush to channel 5.

DFWB

DFWB.