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Television Standards Converters, Modulators etc Standards converters, modulators anything else for providing signals to vintage televisions. |
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15th Feb 2015, 4:20 pm | #21 |
Dekatron
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Re: An ITV converter.
I remember in the late-1960s the gruesome patterning=stripes on an elderly[1]-Kiddeminster-residing relative's equally-elderly[2] originally-Sutton-Coldfield-BBC-but-supposedly-"converted-to-receive-Lichfield-ITV" TV.
When she was finally persuaded to get a 'modern' TV she was deeply impressed !! - now she could get both ATV from Lichfield and Granada from "oop-north" ! [1][2] "elderly" to me at the time meaning anyone-over-about-40. |
15th Feb 2015, 4:21 pm | #22 |
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Re: An ITV converter.
My grandfather had one to go with his Regentone TR20 - both of which are now in my possession.
I've never had the opportunity to try the converter, as the only 405-line source I have is a band I channel 1 Domino.
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Mending is better than Ending (cf Brave New World by Aldous Huxley) |
15th Feb 2015, 7:25 pm | #23 |
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Re: An ITV converter.
Hooked the ITV converter up to another set. This time a Bush TUG24 which like the Masteradio is a superhet. Both sets have the pre-BREMA IF frequencies of 16Mhz vision and 19.5Mhz sound. The Band 1 signals are supplied by my own make standards converter. The Aurora supplies the Band 3 signals on channel 8.
The initial tests were not at all promising. The patterning on ITV channel 8 was terrible when the Band 1 converter was connected directly to my standards converter which has a very high level output on channel B1. Inserting an 18db attenuator into the Band 1 input has improved matters considerable, but there is still evidence of some patterning. However, the pictures on band 3 are watchable. What I must do next is try the converter on a TRF receiver. No local oscillator harmonics to cause any possible interference. DFWB. |
15th Feb 2015, 8:31 pm | #24 | |||
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Re: An ITV converter.
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15th Feb 2015, 9:45 pm | #25 |
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Re: An ITV converter.
The type 245 converter has two inputs, one for band 1 for what would have been for the existing BBC only aerial and a band 3 input for the separate ITV aerial. So it follows I have supplied the converter in a similar manner. The output from my own standards converter's modulator is >200mV so in fact the converter is getting a taste of what it would have been like in SE London.
The Aurora delivers less than 200mV on Band 3. DFWB. |
16th Feb 2015, 1:11 am | #26 |
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Re: An ITV converter.
Don't recognise all of those John but the middle one was I believe made by EMI, it also came with a variety of other manufacturers names on it.
Peter |
16th Feb 2015, 9:47 pm | #27 |
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Re: An ITV converter.
The chosen TRF set to try out the 245 converter is the Ekco TSC30.
Just like the superhet TVs the ITV picture exhibits patterning. When the "BBC" input is removed the patterning disappears. The TSC30 has a picture positioning problem and was the subject of discussion last year: https://www.vintage-radio.net/forum/...ght=Ekco+TSC30 DFWB. |
16th Feb 2015, 11:02 pm | #28 |
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Re: An ITV converter.
Perhaps then the next step would be to try a patterning removal unit, if one could be found. Evidently such were made, per the attached item.
Cheers, |
17th Feb 2015, 11:58 am | #29 |
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Re: An ITV converter.
I've seen similar things done with a capacitance bridge and a 'noise' aerial to reduce ignition interference on WWII aircraft radar sets.
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17th Feb 2015, 12:00 pm | #30 | |
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Re: An ITV converter.
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It's very unlikely one will ever turn up, no doubt about that. However, looking at the circuit it appears to be a simple enough device to make. The coil for channel B1 will be the usual twelve turns on a 1/4" former and is tuned by an iron dust core. The other component values will have to determined by trial and error. DFWB. |
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18th Feb 2015, 12:35 pm | #31 |
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Re: An ITV converter.
Well it turns out that the 245 converter was made by Invicta, a company within the Pye group. Information for this unit can be found in the 1957/58 Radio and and Television servicing book. Pages 394 -396.
A year earlier Invicta made another converter, the model DSB/1 for double sideband receivers and the SSB/1 for single sideband receivers. The valves employed in this converter are a PCC84 for the RF amplifier and an ECC81 as the mixer-oscillator. The PCC84 is used in a rather strange circuit, not the usual cascode arrangement found in almost every other TV tuner and some FM tuners as well. The first triode section serves as a cathode follower and the second section as a grounded grid amplifier. The HT rectifier the the EZ90/6X4. Whereas the 245 is fairly conventional in it's circuit design the model DSB/1 is rather different. It is well known that left to their own devices Invicta produced some pretty strange designs. DFWB. |
18th Feb 2015, 10:00 pm | #32 | ||
Nonode
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Re: An ITV converter.
That cathode-coupled (differential) RF amplifier was an interesting departure from conventional practice. The ECC84 was suited to it, though, as the second triode, which had the internal screen connected to its grid, was specifically intended for grounded grid service. In fact one might say that given that the ECC84 could be used in both differential and cascode modes, it presaged (by a decade or so) the CA3005/CA3028 IC, which was similarly endowed. I suspect that Invicta then chose a triode rather than a pentode mixer because the cathode-coupled RF amplifier would have had less gain than a cascode, and so mixer noise could have been an issue. In any event, the rationale for the pentode mixer was to avoid feedback and feedthrough problems at the lower Band I channels with “high” IFs, so it wasn’t really needed for the Band III channels anyway.
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Cheers, |
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18th Feb 2015, 10:16 pm | #33 | |
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Re: An ITV converter.
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The 30L15 is an improved PCC84/30L1. It is not a frame grid valve. I was just about to post up the circuit of the Invicta DSB/1 converter, but Synchrodyne beat me to it. DFWB. |
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18th Feb 2015, 11:01 pm | #34 |
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Re: An ITV converter.
Thinking about that some more, I guess the logical approach would have been to use the ECC84, etc., derrière-backwards so as to speak. That is, with the #2 triode as a grounded-grid RF amplifier, and the #1 triode as the self-oscillating mixer. That way, the internal screen would be grounded. I think that the two triodes have similar properties, but that the pinouts were arranged to best suit their usual orientations. With the #2 triode as a self-oscillating mixer, it probably have worked well enough, but with oscillator voltage on the screen, there might have been quite a bit of feedback through the RF stage to the aerial.
Cheers, |
18th Feb 2015, 11:30 pm | #35 |
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Re: An ITV converter.
In fact I remember that was what I did. Triode 2 "the upper one in a cascade" was employed as the grounded grid amplifier. Triode 1 " the lower one" was the mixer-oscillator.
That was fifty-five years ago, and I guess memories do fade. Would be fun to construct something similar again. Got plenty 30L15 valves. DFWB. |
19th Feb 2015, 7:14 pm | #36 |
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Re: An ITV converter.
I believe you are right! I have one, it works well but it is calibrated for Channel B1 operation, which means a Birmingham set won't be able to receive the lower Band III channels.
I'll have to plug it in again to confirm but I believe Channel B6 could not be received, I think B8 upwards were OK. Not really a problem as my 405 channels are B8, B10, B13 and there's a 625 channel on E5 (B6 is within E5 spectrum) but it would be nice to have the channel numbers line up. That reminds me, I promised someone a high resolution scan of the back cover some time back and promptly lost the scans (my own scanner wasn't working) .. I've now found them so if anyone is missing a back cover I'll find a way of making them available. Think the files are too big to attach here. Brian |
7th Mar 2015, 6:13 pm | #37 |
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Re: An ITV converter.
This is the Pye F124 Band 3 converter that was supplied for the 34/38mc/s IF 'FV' range of superhet five channel receivers. It could be mounted on the cabinet back or freestanding on the top of the receiver.
Conversion took 5 mins! It was only a matter of removing the RF amp EF80 and replacing it with the power supply B9A plug from the tuner. The ECL80 mixer oscillator was also removed but this time it was plugged into the converter adaptor from the tuner turning the mixer section into an additional IF amplifier. An almost identical unit type 47 was supplied for the V4 range with 16/19mc/s IF. This time the mixer oscillator is an EF80 that took up position in the adaptor as in the FV series. Tidy the leads, screw the back on, done! Regards, John |
7th Mar 2015, 6:22 pm | #38 |
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Re: An ITV converter.
This one is the familiar 184 unit supplied to convert all Bush superhet 20 and 30 series models.
These quality units are often removed by restorers, [?] such a shame as they are a real part of the receivers history. Fitting was very easy as a large space existed to the left on the chassis of the RF deck. It was a simple matter to introduce the B5 connector and a couple of additional wires. A very good drift free tuner, the basic design of which continued through to the TV125 series, some ten years later. The valves employed in the Bush and the earlier mentioned Pye unit were the cascode RF amplifier, Mullard PCC84 and the mixer/ oscillator PCF80 introduced for band 3 in 1953/4. John. |
8th Mar 2015, 8:17 am | #39 |
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Re: An ITV converter.
I remember those, you had to cut an 'neat' hole in the back cover to accommodate them, they worked pretty well and were for band 111 only so you had two aerial inputs, very useful where we lived when Crystal Palace opened as you could almost run the lights off the BBC signal.
Peter |
8th Mar 2015, 10:34 am | #40 | |
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Re: An ITV converter.
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As you say, these are a part of the set's history. It would have also left a big hole in the back of the set! |
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