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Old 26th Apr 2021, 5:40 pm   #1
matspar
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Default Philips 663A combined radio/television 1948

Hi all,

Currently restoring the above set which so far has been very successful. Power supply chassis completed and a healthy looking raster has been obtained.

No sign of any signals however. The aerial input is a twin feeder arrangement via a two pin socket. I have connected my Aurora via the matched balum type adaptor shown which I have used on another Philips set of this era.

Before I delve deeply into the front end and risk a wild goose chase could any kind soul confirm this is indeed a suitable way of connecting the set?

Probing around V2 frequently changer (ECH35) will produce noise and white spots on the raster, suggesting the forward stages are functioning to a degree. HT appears to be perfectly adequate!
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Old 27th Apr 2021, 9:52 am   #2
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Default Re: Philips 663A combined radio/television 1948

I don't know this set, but are you sure this is the way the TV aerial would be connected? I would have expected a connection via a user accessible socket of some sort - that is, a connector that the viewer would use without requiring the back to be taken off. Rather like that 2 pin socket attached to the main chassis in your second picture...

BTW where is aerial input for the radio section of this set?
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Old 27th Apr 2021, 10:04 am   #3
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Default Re: Philips 663A combined radio/television 1948

Its certainly the correct TV aerial input socket - it gets a mention in the service book although it describes it as a 4 pin. On my set it is only a two pin.

The tuner aerial & earth sockets are in fact the ones you mention (2 pin sockets to the right on the vertical bracket) This is responsive when the tuner is selected.

I can't help thinking I'm doing something wrong here hence the request for advice.
With an ear firmly pressed to the speaker I can get the merest suggestion of an Aurora test tone on CH1.

There are no signs of any previous Band III conversions or any mods or bodgery, and everything looks original.
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Old 27th Apr 2021, 10:16 am   #4
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Default Re: Philips 663A combined radio/television 1948

Thanks for the info. A 1948 set that is a Superhet (you mention V2, a frequency changer) and not a TRF is interesting as there was only Ally Pally on Air - unless Philips were getting prepared for Tv in the Midlands due to come in 1949.
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Old 27th Apr 2021, 12:44 pm   #5
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Default Re: Philips 663A combined radio/television 1948

Philips weirdness at it's best! Crazy early flyback EHT generation with TWO B4 based HVR2 EHT rectifiers in voltage doubler circuit with their 4V heaters fed from a separate mains transformer 6.3v primary, 2 X 4v secondaries. From whatI I can remember, three heavy mains transformers into the bargain. EBL31 video output valve! Crazy!

Yes a superhet using Mullard red E radio valves in the front end and a LOPT that looks like a PP9 battery.. There were a lot of superhets in early TV circuits including pre war. HMV 904, 1804, Murphy A56V and 114, plus the Vidor range and many more.
Good luck with that one Matt. Watch yer back when moving it! better to hire a crane. Regards, John.
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Old 27th Apr 2021, 2:17 pm   #6
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Default Re: Philips 663A combined radio/television 1948

ECH35 as a TV frequency changer The mind boggles! How good was that at 45Mhz? I thought they struggled at 20Mhz shortwave but at low VHF......?
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Old 27th Apr 2021, 3:30 pm   #7
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Default Re: Philips 663A combined radio/television 1948

I know! The I.F. is 10/14mc/s as were a lot of the early post war superhets. I think this is the only series that used an ECH35 as a frequency changer. Like all Philips products no matter how odd, this model performs very well as no doubt Matt will support.
John.
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Old 27th Apr 2021, 5:17 pm   #8
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Default Re: Philips 663A combined radio/television 1948

I have the TV only version of this chassis which is more or less identical to yours. Just connecting the aerial co- ax and not even bothering with a balun produces good results results. I suspect the frequency changer might not be oscillating. I presume you have got the contrast turned well up?
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Old 27th Apr 2021, 6:41 pm   #9
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Default Re: Philips 663A combined radio/television 1948

Does sound like the ECH35 isn't oscillating,
I had one in an old radio of that period
and it would work at lower frequencies
but just stop as one went higher up
the shortwave band, a new valve
brought things back to life.
Presumably the rf amp valve is OK?
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Old 27th Apr 2021, 7:38 pm   #10
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Default Re: Philips 663A combined radio/television 1948

Doesn't the frequency changer employ two ECH35 triode-hexodes? The local oscillator is common to both vision and sound with the triode sections working together in a cross coupled arrangement.
I believe the pre-war model 2405 employed a similar circuit using ECH3 triode-hexodes.

DFWB.
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Old 27th Apr 2021, 7:38 pm   #11
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Default Re: Philips 663A combined radio/television 1948

Hi Matt,
please see the attached info.
The manual seems to suggests it has two ECH35 valves, one for vision and one for sound, so if you have neither then it would point to the RF amplifier or the sensitiivity link.

Cheers
Andy
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Old 27th Apr 2021, 10:44 pm   #12
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Default Re: Philips 663A combined radio/television 1948

Hi everyone,

Many thanks for your suggestions! here is the relevent bit of circuit.

There are a pair of ECH35's as frequency changers, one sound one vision. My first thought was something not right early on in the V1 area as there is no sound or vision, however I can't find anything amiss here. I have replaced the 0.004uf decouplers which were originals. All windings intact. Slowly adjusting S2 will produce some very slight noise with a signal applied.

Touching the anodes and grids of V1 & V2 will cause disturbance and HT is well up to spec. Could both ECH35's be low I wonder. My valve tester has thrown its toys out of the pram so I'm currently unable to test. The EF50 (V1) is a known good one.
I haven't explored the contrast circuit fully apart from the obvious. Pot intact but it doesn't have much of an effect on the raster when adjusting. The sensitivity link is in place.
Bit of a mystery this one but a fantastic set to restore. Any more thoughts gents?
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Old 28th Apr 2021, 4:08 am   #13
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Default Re: Philips 663A combined radio/television 1948

Quote:
Originally Posted by Sideband View Post
ECH35 as a TV frequency changer The mind boggles! How good was that at 45Mhz? I thought they struggled at 20Mhz shortwave but at low VHF......?
In the immediate post-WWII period, some of the standard AM frequency changer valves were claimed to be satisfactory for use up to 100 MHz, and so suitable for use in FM receivers. This group included the 6BE6 (X77) and X79 (6AE6). Both the ECH42 and ECH81 were used in this way, although a better FM application for the ECH81 was with the triode as a self-oscillating frequency changer, and the heptode as IF amplifier (pentode-strapped). In advertising, if not in the data sheets, the ECH81 was described as being suitable for use up to 100 MHz. The X81 and X79 were both used as frequency changers in a BBC FM receiver design; Lowther used essentially the same circuit in its first FM tuner, but with a 6AH8. Nonetheless, the realizable performance on FM with these valves was not very good, and in the case of the 6BE6, reputedly rather poor. Thus they were soon eclipsed by other solutions, typically the 6AT6 (ECC81) frequency changer preceded by an RF amplifier in the USA, and the ECC85 RF amplifier and frequency changer in Europe, the latter evidently an “economy” solution.

In that context, it is not so surprising that there would have been one or two applications from this valve group in Band I-only TV receivers, on the basis that “good for 100 MHz” implied “good for around 50 MHz”. Evidently Philips saw the ECH35 as being suitable.


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Old 28th Apr 2021, 5:38 am   #14
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Default Re: Philips 663A combined radio/television 1948

Quote:
Originally Posted by Synchrodyne View Post
Lowther used essentially the same circuit in its first FM tuner, but with a 6AH8.
No, that was a 12AH8.
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Old 28th Apr 2021, 7:03 pm   #15
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Default Re: Philips 663A combined radio/television 1948

I wonder what the noise floor was like? I didn't think they were particularly good at high shortwave....quite acceptable for normal broadcast bands.
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Old 29th Apr 2021, 12:32 am   #16
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Default Re: Philips 663A combined radio/television 1948

I imagine that the noise floor was quite high. I think though that the use of the ECH35 (and like valves) at VHF was predicated on their being preceded by a suitably high gain, low noise RF amplifier, such as an EF50 or an EF42, which would diminish the effect of the mixer noise. To some extent, that approach, noisier-than-ideal mixer preceded by high-gain, low-noise RF amplifier soon returned with TV front ends. Something like the ECC81 (6AT6) would have been a very good low-noise frequency changer for TV use at Band III, and would not have made undue demands on the RF amplifier. And in fact GE developed the 6AT6 for TV as well as FM (and FM-AM) frequency changer use. But the upward shift in TV IFs, which put the IF channel very close to the lowest Band I channels, created a potential regeneration problem that was most easily solved by using a pentode mixer. But that created a potential noise problem at Band III, where without any other constraints a triode mixer would be the logical choice. That problem was solved by the development of a very high gain, very low noise RF amplifier, namely the cascode. RCA had started that development programme in the late 1940s for other reasons, but it moved from being a desirable target to a very necessary target, and in the event arrived at the same time as the TV triode-pentode frequency changer.

At HF too, a good RF amplifier would have been highly desirable with the ECH35 and its ilk, both for front end selectivity and noise reasons. And it was not uncommon in the later 1940s to use a high-slope pentode for the RF amplifier. As far as I know, the early version of the Weyrad bandspread front end was based upon an EF50 RF amplifier and an ECH35 frequency changer.


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Old 29th Apr 2021, 4:34 pm   #17
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Default Re: Philips 663A combined radio/television 1948

Some progress over the last couple of days.

I didn't have any replacement ECH35's so I swapped the pair over to see if this would make any difference. To my surprise doing so has put a test card on the screen, with terrible line linearity and a curious white line to the left!

Still no audio so a pair of new ECH35's are on order, along with an EA50 signal diode which I found has an o/c heater. Work can then recommence once they arrive.
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Old 29th Apr 2021, 7:44 pm   #18
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Default Re: Philips 663A combined radio/television 1948

That is a very impressive set! The underside of the chassis is a bit daunting... well to me anyway!
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Old 30th Apr 2021, 8:20 am   #19
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Default Re: Philips 663A combined radio/television 1948

What a chassis and in such good condition! Pre war in appearance. The tube appears to have been changed for the MW31-16 with ion trap. I think the original was a MW31-7. Maybe a line drive fault causing that severe fold over. Good luck with it! John.
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Old 2nd May 2021, 11:56 pm   #20
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Default Re: Philips 663A combined radio/television 1948

I'm thinking exactly that John. The line and frame oscillators are both ECH35's also, so I shall try replacing both with new items to see if this corrects the line non-linearity. Both chassis although having required extensive cleaning are in remarkably good condition. The 663A has never been anywhere damp in its life by the look of it.
I've fitted a 31-74 as the 31-16 (itself a replacement from the original 31-7) was completely flat. I suspect this set had quite a life back in its day.
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