Philips TV set for 441 lines

[FERNSEH]

This evening I turned my attention to the frame timebase, and again it's bad news. Blocking oscillators are employed in both timebases. In the case of the frame timebase the triode section of an UCH21 serves as the oscillator valve and the heptode is triode connected (grids 1,2 3 and 4 connected to the anode) and operates as a frame sync pulse clipper.

The bad news is that the blocking oscillator transformer has OC windings.
However, I'm sure I have a spare transformer somewhere.

DFWB.

[wiwior]

Hello David,

In french ouille ouille ouille

So is it the same Blocking oscillators as on the tf390 ?.

kind regards

wilfrid

[FERNSEH]

Hello Wilfrid,
Some good news. I have found a genuine Philips frame blocking oscillator transformer, it was fitted into a scrap HMV 1807 chassis.

The transformer has been fitted into the TF384 and it works! So now we have a working frame oscillator but I find that the sawtooth waveform is not apparent at the UL41 control grid, I'm sure that will be easy enough to fix.
The oscillator is running at the correct frequency, 50Hz,(20mS). With regard to the TF390 frame oscillator transformer. I'm sure that the transformer is similar to the TF384. Also, the TF390/TX390 is very similar to the UK Philips model, the 385U.

The cathode bias resistor of the UL41 frame output valve started to burn, seems that the valve has gone bad. That's a pity as it was the earliest version of the valve. Early Philips rimlock valves had a metal base similar to those fitted to UK Mazda B8A base valves. Also, the early UL41 had a reduced diameter near the the top of the bulb.

Information on the development of valves can be found on:
www.radiomuseum.org/

DFWB.

[FERNSEH]

The frame timebase is now fully working. The problem with the output stage was nothing more than dry solder joints at the base of the UL41. The UL41 valve is mounted on a metal plate above the chassis along with the two UL44s and the UB41 double diode.

Now comes the next the stage of the restoration. This will be to check out the line timebase oscillator and output. The line blocking oscillator uses the triode section of an UCH21, the heptode section serves as the sync separator. The two UL44s are conected in parallel as a single UL44 cannot deliver sufficient scanning power in a circuit that does not employ an efficiency diode. The UL44 has a max Pa of only 5 watts.

The later TF390 and 385U models employ one UL44 and an UY41 operating as the efficiency diode.

DFWB.

[FERNSEH]

Things are really going well. All the valves have been fitted into their sockets, but before the full mains was supplied to the set I decided this time to use the variac. The frame oscillator started to work with a supply of only 125volts and the line blocking oscillator came to life at 150V.

The line oscillator employs mica capacitors and as these have a good reputation I did not bother to test them.
The line output stage is out of action at the moment, the common screen resistor to the UL44s was disconnected just in case the line oscillator was running at the wrong frequency. Actually the line oscillator can be adjusted to run at 10Kc/s (100 micro-seconds)

The next stage of the restoraton is to check the vision TRF amplifier and video output. The set will accept a standard 405 signal for test purposes.

DFWB.

[FERNSEH]

On Saturday evening I decided to reconnect the screen grid resistor of the UL44s and thus activate the line output stage.

My old RANK-BUSH-MURPHY EHT meter was connected to the CRT connector to measure the EHT voltage. The EA40 damper diode was refitted into it's holder above the line transformer can.

Again, the variac was employed to bring the mains supply up in stages starting at 150 volts. The first indication of EHT voltages was with a supply of 190 volts.
No problems this time, no bangs of flashes and the mains supply was finally set to 220volts.
The highest EHT voltage available so far is a rather disappointing 3.5KV.
However, when the damper diode is removed the EHT rises to 6KV.
The EA40 heater is supplied from a winding on the line output transformer just like an EHT rectifier.
The line output transformer lives in an oil filled can along with the EHT rectifier valve(s) I have no idea what arrangement exists in the can, allthough Philips did seem to favour an EHT voltage doubler in their early sets.
The 383A employed two HVR2 valves with the heaters supplied from a special high insulation transformer supplied from the 6.3V heater supplies.

In the TF390 the two EHT rectifiers are inside the oil filled can. In the 385A the two EY51 valves are outside the can.

DFWB.

[Jac]

Hello David,

I think that the correct EHT should be 7 kV.
The transformer in the TF384 is, as I see it, similar to the TX/TF390 transformer but with the addition of taps for the EA40 efficiency diode.
2x EY51 will be inside the can for voltage doubling.
I expect different windings (as the TX390 transformer), since there will be no booster-configuration, and enough energy has to be stored despite the lower supply voltage.
The EA40 setup is used during a very short period only. The (relatively) low supply voltage does put a high load on the dissipation of the line output pentode. Which is much improved with a higher supply voltage. The configuration with the EA40 called for an EL38 (or 2xUL 44 in parallel) for higher line frequencies (as during the experimental period of 567 lines).
Philips soon changed over to the use of a boosterdiode (on the HV-end of the winding or on a tap).
The EHT is of course depending on the line frequency. But in that case, setting it for 405 lines should give an even higher EHT than 441 lines.
(Due to the fact that the built up voltage during scan is higher, resulting in a higher flyback voltage.)
The coil of these transformers is not known to be all-bad. But (especially as the transformer oil level is below the capacitors) the capacitors in the doubler could be leaky. It is always possible to replace them by ceramics.
I hope this helps a bit.

Best wishes, Jac

[FERNSEH]

Originally Posted by Jac

The EHT is of course depending on the line frequency. But in that case, setting it for 405 lines should give an even higher EHT than 441 lines. The line frequency for 441 lines is 11,025hz.
(The coil of these transformers is not known to be all-bad. But (especially as the transformer oil level is below the capacitors) the capacitors in the doubler could be leaky. It is always possible to replace them by ceramics.
I hope this helps a bit.

Hello Jac,
I think that you are correct about the possiblity of the EHT capacitors in the line output transformer can are leaky. Now comes the messy job of opening the oil filled can.
The MW22/7 CRT has no external graphite coating to serve as the final THT capacitor, so it is likely that the capacitor will be installed inside the can.

DFWB.

[FERNSEH]

Originally Posted by Jac

I think that the correct EHT should be 7 kV.

My reportage of Saturday evenings work on the set is mainly good news.

The CRT has been refitted into the cabinet and long extension leads have been connected to the focus coils and the scanning yoke. The EHT lead was also extended.
In an earlier report I mentioned that the EHT voltage was too low and the correct voltage should be 5 to 7KV. Possibly the low EHT voltage could be the result of faulty capacitors in the EHT doubler circuit?

Anyway, I decided to connect up the focus and scanning coils along with the extended EHT lead.
The first results were not encouraging, just a dull blob on the CRT screen. After the brightness control was turned fully down the EHT rose to 10KV!
The EHT supply was overloaded by eccessive beam current.
The line frequency was checked and found to at 405 rate, 10,125hz. After resetting the line frequency to 11,025hz, which is the correct figure for 441 lines the EHT became 7KV.
It turns out if the line scan coils are disconnected the EHT will be low.
The cathode voltage of the CRT was checked and found to be only 15 volts, that's the reason why the raster is too bright.

One thing is sure, the original Philips MW22-7 is excellent, it's the same type of tube which is employed in the Pye D and B16 TV receivers.

Pictures of the latest results will appear tomorrow.

DFWB.

[FERNSEH]

The attached picture shows the first results of the TF384 restoration.
The next stage is to sort out the frame timebase and find out why the anode voltage of the video amplifier is so low.

DFWB.

[FERNSEH]

The TF384 is now back on the workbench and this stage of the restoration is to attempt to display a picture on the CRT.

On switch-on it was always noticed that the video output valve lights up very brightly, this is not a desirable condition because the UF42 valve is difficult to find.
The set employs four valve heater chains which are supplied from a 120 volt winding on the mains transformer. Three of the heater chains add up to the correct voltage, but one does not. The offending heater chain adds up to 86 volts, 45 volts for the UL44, 20 volts for the UCH21 and 21 volts for the UF42 video amplifier. I've inserted a 240 ohm resistor into the heater chain to correct the problem.

On Saturday evening my attention was drawn to the video output stage.
This set does not employ a vision detector diode. Instead the video OP valve is biased to cutoff and operates an anode bend detector. Radio receiver enthusiasts will be familiar with this type of detector.
The valve only conducts on the positive cycles of the RF signal.

The only other television receivers that I know of to employ the anode bend vision detector are the pre-war Marconi and HMV models; 706, 707, 904 and 905.
The video waveform at the anode of this type of detector is negative going and is connected to the CRT cathode.

The TF384 should operate on the 45 mhz channel B1 frequency.

DFWB.

[Jac]

Hello David,

Carrier frequencies for the TF384 are 42 and 46 MHz.

Best wishes,
Jac

[FERNSEH]

Originally Posted by Jac

Hello David,

Carrier frequencies for the TF384 are 42 and 46 MHz.

Best wishes,
Jac

Hello Jac,
I passed my 441 "Eiffel Tower" modulator on to a Continental collector. I'll use a signal generator to test the TRF vision and sound circuits.
Bad news. The EA40 line timebase damper diode has failed, No direct replacement exists for this valve and I doubt if an EA40 can be found anywhere.
I have two options: The first is to employ an EY81 with the 0.9 amp heater supplied from an additional transformer or from the CRT 6.3 volt heater supply. This might overload the mains transformer.
The other option is the Brimar R10. In some respects the R10 is similar to the EA40 except the heater is 4 volts @ 0.5 amp. The EA40 has a 6.3 volt 0.2 amp heater.

A damaged tag strip has been found in the second vision RF amplifier and the connections to an RF transformer will require tracing.

The picture shows the EA40 damper diode.

DFWB.

[Jac]

Hello David,

Yes, the EA40 is a rare bird. Only used for a very short period of time by Philips.
The heater supply comes from a series winding on the LOPT.
If you feed the heater of the (replacement) tube from a separate transformer, the capacitance (to GND or mains) will be connected to the LOPT. That is not desirable.
Feeding from the CRT 6.3V heater is also not feasible for the same reason and the voltages at which the cathode of the EA40/EY... is, when connected to the LOPT.
Maybe the best temporary solution is to use a solid state diode (or in fact several diodes in series, the EA40 can take 6500V) if required in series with a resistor (representing the series resistance of the EA40).
If eventually ;-) everything works as it should be, you can substitute that by an original EA40.

Do you know why the EA40 has failed? The heater voltage has the same 'fly-back'-shape and if the output stage is not working properly, the heater voltage might become too high (if the EHT is also >7kV). On the other hand, a heater does not fail lightly.

A nice set! I could only wish it was mine....

Best regards, Jac

[Ed_Dinning]

Hi David, a small auto transformer perhaps as the wattage rerquirements are about the same?
I take it there is no chance of modify in the LOPT winding or adding a few turns to the appropriate tap?

Ed

[FERNSEH]

Originally Posted by Ed_Dinning

I take it there is no chance of modify in the LOPT winding or adding a few turns to the appropriate tap?

Ed

Hi Ed, The line output transformer is installed into a sealed oil filled can so there is no chance of modifying the windings.

Hello Jac, The EA40 valve has lost it's vacuum.

I can report some good news. After further examination of the 2nd UF42 valve vision amplifer stage it turns out that the set is in fact a superhet.
I've replaced the missing components associated with the 2nd stage and now it it a mixer-oscillator similar to the circuit employed in the later TX390.

The IF frequencies are quite low, being 1.5Mhz for the sound and 5.5Mhz for the vision, this means that the oscillator frequency is 40.5Mhz for the 441 line Eiffel Tower frequencies of 42Mhz sound and 46Mhz vision.

The sound circuits are now working well and a video waveform can be observed on the oscilloscope at the anode of the video amplifier

The get the line timebase working I'll follow Jac's suggestion and use silicon diodes as a substitute for the EA40 line TB damper tube.

Tomorrow, there is a good chance I will able to display a picture on the CRT.

DFWB.

[Ed_Dinning]

Hi David, you will need to use a fast diode in this position, possibly with some snubbing (C&R) in parallel to reduce ringing.

Ed

[wiwior]

Hello David,

Many thanks for all this job I can search an ea40 ? Unfortunately I don't have it in my stock actually.

kind regards

wilfrid

[FERNSEH]

Hi Wilfrid,
Tomorrow I will try the Brimar R10 as a subsitute for the EA40.
The filament watts of the R10 are 1.75 more than the EA40, otherwise the two valves similar.
I believe that the EA40 was developed for the TF/TX384. No oher set has ever employed this valve.

DFWB.

[Jac]

Hello David,

The EA40 indeed was used for a very short period, only a couple of years.
I have two sets in which the EA40 is also present:
an (experimental) Philips projection set (567 lines) and the Philips TX594U (also 567 lines).

Best regards, Jac