Assistance with modulator design
 

Hi everyone,

I rebuilt an old Soviet KVN-49 tv from the 50’s, and whilst I can run it by directly injecting a PAL signal into the video amplifier, my preference is to run it as intended.

One option is to feed a PAL signal into a pair of MC1374 chips using the design found here http://www.earlytelevision.org/405_modulator.html

Is there a knowledgeable soul who can suggest how I can modify this circuit to one of the frequencies below (and change it for FM sound modulation)? In particular the correct values for the coils and capacitors in the RF section?

best regards,
Matt

The Russian D system is:
Lines: 625
Frame rate: 25
Channel bandwidth: 8 MHz
Video bandwidth: 6 MHz
Vision/Sound separation: +6.5 MHz
Vestigial sideband: 0.75 MHz
Vision modulation: negative
Sound modulation: FM

Channel 1
Vision: 49.75 MHz
Sound: 56.25 MHz

Channel 2
Vision: 59.25 MHz
Sound: 65.75 MHz

Channel 3
Vision: 77.25 MHz
Sound: 83.75 MHz

Re: Assistance with modulator design
 

I think the modulator I have can output with a 6.5 MHz sound separation.

https://www.amazon.co.uk/dp/B07M8WGL..._t2_B07MDKXHM8

The same basic model is available from a few places under different brand names.

Re: Assistance with modulator design
 

Thanks Richard,

Unfortunately these modulators don’t cover the correct frequencies for System D.

Re: Assistance with modulator design
 

Hi, if you look for the data sheet for the mc1374 then it should show you how to add in the FM components to get the sound carrier. The design above uses two ic's one for the video and the other for the am sound.

Re: Assistance with modulator design
 

There should be no difficulty in using MC1374 for this - it was designed for exactly this application - AM vision + FM sound - you will require only one IC - two were only required in applications using AM vision and sound such as 405 line system ‘A’ or 819 line system ‘E’ - application note in data sheet provides a suitable template with only vision carrier and sound intercarrier frequencies requiring adjustment for required system

Re: Assistance with modulator design
 

OK I thought so.

The Eastern European countries seemed to take a time to settle which frequencies to use, I know East Germany eventually aligned their's with the system B ones.

Re: Assistance with modulator design
 

Hi,
I don't know if the mt47 modulators would cover these channels ? ( mentioned elsewhere on this forum ) I am thinking of getting one as they claim to be able to do system L
If I can find a list of the channels they cover I will check.
certainly one of a similar modulator may only cover band 3... and some uk modulators only do 6 mhz and uhf channels

Re: Assistance with modulator design
 

Thanks Peter,

the specs for the MT47 indicate it covers System D with the correct frequencies and modulation. They quite flexible units.

Best regards,
Matt

Re: Assistance with modulator design
 

Hello Autozavod, any chance of a picture of your KVN-49, please? How did you come by it?

That's a model that I would one day very much like to have an example of. It's a classic of its time and place and of quite an advanced design. I saw an early example of one (1951) working in Moscow some years ago (when analogue TV was still around) picking up the transmissions from Ostankino with just 6" of wire in its aerial socket. For the age, it was well-focused, quite bright and had good geometry.

Good luck with the modulator - it shouldn't be too difficult.

Best regards,

Paul M
www.becg.org.uk

Re: Assistance with modulator design
 

Hi Paul,

Photo attached, the cabinet is still under restoration.

Bit of a long story, I have a soft spot for Soviet electronics and a tv was an obvious hole in my collection.

There are a few eBay-style websites such as olx based in Ukraine. This unit came via a Ukrainian friend of mine from a seller in some remote village via L’viv.

The photo doesn’t do justice to the quality of the image the set produces.

Cheers,
Matt

Re: Assistance with modulator design
 

Hi Matt,

I would use a TDA5660 chip (see attachment). This was designed to deliver AM vision with negative modulation and FM sound. Since the FM sound is generated by an LC tank circuit it can deliver the 6.5 MHz OIRT sound-vision spacing easily. The RF channel frequency can be run with an LC circuit also, so any frequency can be generated, or you can try to find a suitable crystal for the vision carrier. I have found though that an LC circuit is absolutely fine and does not drift. I have had such a circuit in operation here on channel E3 at around 56mc and it has been running fine over many years.

I might still have an empty PCB board around here that I had designed for this chip years ago if you are interested send me a PN. I can also build a modulator and send you the board. This might take a few weeks though. I can also send you the project data it was made with the Eagle CAD software.

Cheers

Semir

Re: Assistance with modulator design
 

Hi everyone,

I just wanted to let you know that I am in the process of designing a modulator with PLL that can be tuned accurately to any frequency in 250kc increments. It will use an old Motorola MC145106 PLL chip that can be set up with a simple dip switch -no processor or programming required.

After reading Matts post I am now thinking of making a combination of this PLL and the TDA 5660. This would give any audio-vision spacing with FM carrier and can be tuned to any frequency in the VHF bands.

Semir

Re: Assistance with modulator design
 

Paul,

The KVN-49 would be a good set to get. I knew a fellow with one who had gone to great lengths to restore it and it worked very well. The thing I noticed about them is their Pyrex non aluminised 7" CRT, which I had considered would make a great replacement for the one used in the HMV905. When I got my HMV904, it had no CRT, so I considered fitting this Russian CRT and making it into a 905. In the end I found the 5" 5FP4 that did the job.

The KVN-49 is essentially like a pre-war set in its overall architecture except for having extra channels and FM sound. Not at all dissimilar to RCA's 621TS in that respect, which was designed mostly pre-war and released in 1946, which produced and astonishingly bright high contrast picture .As you noticed the KVN49 has a good picture too.

A possible replacement CRT for the KVN-49, if it needed one, could be RCA's 7DP4 which still turns up from time to time on American eBay. Spare CRT's for the KVN-49 were common eBay a few years ago, but there appears to be less around now.

Hugo.

Re: Assistance with modulator design
 

THese could be modified and as noted the IC is up to the task, but there may be better IC's. I'm not 100% sure but as I recall the supplied PCB for this modulator does not have a ground plane. When I was testing one on the scope I found the measurements were difficult because of the residual RF at different points on the tracks that were ground or common. But the PCB may have been modified since it was first introduced by the ETF and despite not having a ground plane the PCB worked well and as far as I know many people have used these without difficulty. As noted you would just need the one and modify for the addition of FM sound according to the IC's data sheet.Since its L/C and not Xtal tuned you could just adjust it to suit the existing set tuning.

Re: Assistance with modulator design
 

Dear Semir,

Thank you very much for your kind offer. I cheated by taking up the suggestion of purchasing an MT47 modulator.

Cheers,
Matt