The valve option

[Danny]

Hi has anyone tried using valves in a modulator the old fashioned way a good old hartly should do the job! Watch this space ! i have built the schasis and psu and shall be firing it up tommorow . i know xtal oscilators are the norm but
the old teles are just tuned curcuits so any drift shouldnt be to bad (i hope)
This is to be part of a bigger project and i want an all valve setup but has anyone tried it before ?.
Danny

[FERNSEH]

Hi Danny,
Last year I acquired an all valve Murphy sync pulse and pattern generator, not the more common one unit model,the TPG100. This one is much more advanced. The main unit contains the modulator, the sync & blanking generator and the pattern generator, whatever that that might be.

A quick examination confirmed that the sync generator has proper divider circuits so the correct number of lines can be assured. The moduator can be tuned to any of the five BBC channels.
Unfortunately, the power supply unit is missing. That should not be a real problem to construct when the supply requirements of the main unit have been confirmed.

So your all valve modulator is a real vintage TV project. I look forward to hearing about the results.

Regards,
DFWB.

[Danny]

Hi all ive made the prototype and it does work after a fashion but i have run out of spare time at the moment so it will have to be the weekend before i can do anymore to it.
the thing is quite powerful and will have to be muted a bit as it will produce pictures on a set indoors without to much problem and causes interferance to uhf sets in the house (whoops sorry )the picture is a bit ragged but yes i think it would be a winner for simplicity and cheapness. and work on most channels with a turn of the tuning capacitor! i dont know how the sound is going to be yet as i only had one tuning capacitor which is of the wrong value anyway so i shall order some in the morning.
once its sorted i would think most will have the parts in there junk box and anyone with a little noledge should be able to get some results .
Danny.

[Sean Williams]

Hi Danny,

Would love a circuit

Feels much more "period"

Cheers
Sean

[Danny]

Yes i will draw one out as things are at the moment i should have done it already but ive been tinkering but will get one drawn so if anyone has better ideas thay can tell us and we can make this work! im not a transmitter expert so it might mean a total rebuld but as each modulator has about a dozen parts that wouldnt be the end of the world. the valves im using are EF85s
i have about twenty boxes of these so im using them in most of my experiments!.

[Duke_Nukem]

Chas Miller published an all-valve modulator in a mid-80's Television magazine. IIRC I think it had maybe half a dozen bottles in it ? Probably had enough oompf to drive a number of sets at once - without anything connecting to their aerial sockets ! I'll dig it out if anyone is interested.

TTFN,
Jon

[Sean Williams]

Yes Please Jon!

As if I do not have enough to do already......

Cheers
Sean

[oldeurope]

Yes, schematics are always interesting.
At the moment the valve option makes no sense to me, because my
sources are all solid state.
A valve modulator is like the katode-follower in a cd-player
like the audiophools use it. Only to say :"I have a valve cd player." hi hi.

Kind regards,
Darius

[Danny]

Hi yes the diagram would be handy jon i didnt know about the television article i have been fiddling with a cuircuit from a ham radio book so if it has been done in the past i would be interested in finding a copy. I to have much to get done. this is for a flying spot scanner project i shall be building one unit at a time and want it to be all valves and no three legged beasties .
but it will be time consuming as i have some sets to get restored for any shows comming up this year. this is a drawing of whats been done so far
dont fall down wetting your pants it does seem to work i havent included the psu as its just a common trany and rec setup with a couple of smoothers chuked in for good measure.
Danny

[Duke_Nukem]

Found it. See attached.

TTFN,
Jon

[oldeurope]

Thanks Danny and Jon for the schematics.

In the schematic from Danny I can not see how the vision biasing
is made. The carrier must be switched off at the sync tips.
The carrier must be 30% at black level.
The expected vision bandwidth is nearly 1MHz.
How much vision level is needed at the input?

Chas E. Miller has a DC restorer at the input. Negative going vision
and I think about 10Vpp is needed at the "Video input".
To get full bandwidth at maximum level, the 1K5 at the Kathode of
V5/6 should be connected to a negative voltage source.
The vision bandwidth now depends in the vision level,
I think at high levels it is lower than 1MHz because the 1K5 must be
able to follow the negative slope of the signal and must handle the
current of V4 V5/6 and discharge the 100pF plus stray caps.

For some forum members it may be interesting to see that V3 is
a triode g2=plate. Well designed.

Kind regards
Darius

[Giulio Maiocco]

Hi Guys,

I hate to disturb your thread, but please could you suggest what I should modify to Chad Miller's design in order to use it as a RF modulator for a DVD player with the Italian standards? (7MHz bandwidth, FM audio modulation, different sync pulses waveform).. I fully agree with Darius that a valve modulator is "stupid" compared to the solid state sources, but I deeply hate solid state technology!!

Thanks

Giulio Maiocco

P.S.: About the 27" CRT, Scotty can't rebuild it, but he probably can find another one for me. Wish me luck!!

[oldeurope]

Originally Posted by Giulio Maiocco

Hi Guys,

I hate to disturb your thread, but please could you suggest what I should modify to Chad Miller's design in order to use it as a RF modulator for a DVD player with the Italian standards? (7MHz bandwidth, FM audio modulation, different sync pulses waveform).. I fully agree with Darius that a valve modulator is "stupid" compared to the solid state sources, but I deeply hate solid state technology!!

Thanks

Giulio Maiocco

P.S.: About the 27" CRT, Scotty can't rebuild it, but he probably can find another one for me. Wish me luck!!

Gidday Giulio,
in Italy you have the 5,5MHz FM sound and negative vision modulation.
You need 5MHz vision bandwidh. So you need a very different circuit.
Of course I am able to build one, if you pay me for this job,
but first comes building it and than drawing the schematic!
A lot of TV xmtrs are disassembled because of DVBT.
Maybe you can get one.
If you don't need a perfect quality you can use the RF stages of an old
pattern generator.

Kind regards
Darius

[Giulio Maiocco]

Good day to you also Darius,

Well, if the money sum isn't enormous, I might be interested in your modulator, but I would like to assemble it myself.. Of course, more are the tubes, the better I like it . I could try the RF stages of a pattern modulator, but unfortunately I haven't ever seen one and I don't know where to get one either..

Just a question, if you don't mind: are you anywhere near Ulm in Germany? if so, I have a friend who lives here and if I go to his home, maybe this would be a good occasion to meet in person.

Thank you

Giulio Maiocco

[oldeurope]

Originally Posted by Giulio Maiocco

Good day to you also Darius,

Well, if the money sum isn't enormous, I might be interested in your modulator, but I would like to assemble it myself.. Of course, more are the tubes, the better I like it . I could try the RF stages of a pattern modulator, but unfortunately I haven't ever seen one and I don't know where to get one either..

Just a question, if you don't mind: are you anywhere near Ulm in Germany? if so, I have a friend who lives here and if I go to his home, maybe this would be a good occasion to meet in person.

Thank you

Giulio Maiocco

Hi Giulio,
the money sum will be very enormous, of course. Ulm is far away from Solingen.

I'd like to discuss about the existing schematics. The interest here
is 405, isn't it?

Kind regards
Darius

[Giulio Maiocco]

Hi,

Ok, I have understood that you are interested in the 405 system and my questions are not to be posted here, so I quit

Giulio Maiocco

[Danny]

Hi giulio we are interested in all vintage sistems so please dont quit but start another thread and im sure someone will be able to help if any of us have the answer, but we must keep on topic to keep things tidy on the forum .
I havent been able to play this weekend so i will have to wait until my manding is done during the week!. i know my valve job is a poor design at the moment but i have some new ideas that might work my friend has given me a diagram for a patern generator and the modulator is vary similar to what i have done already so i dont think it will all be bad (it is only for fun though and i dont think i will get as good results as a solid state modulator).
Danny

[oldeurope]

Originally Posted by Danny

i have some new ideas that might work my friend has given me a diagram for a patern generator and the modulator is vary similar to what i have done already so i dont think it will all be bad (it is only for fun though and i dont think i will get as good results as a solid state modulator).
Danny

Good morning, why not? The quality is a question of design and not the
components.
The bandwidth problem can be solved by changing some components.
The cut off from a valve is not that sharp as the cut of from a bipolar
transistor.
This causes that the sync level at the receiver will be smaller than 30%
of peak white. I would solve this problem in the following way.
A sync seperator generates a large sync signal. This can modulate the
g2 of the modulator valve or you add it to the vision signal after
the DC restorer. Now the biasing makes no change in the sync tip level,
because it is always 0. The biasing can now be adjusted for the black-
level at 30%. The rest is linear, so you'll get a perfect vision modulator
this way. The vision signal must be delayed as much as the sync sep.
delays the sync to get no step in the sync edges. This is no problem.

What do you think?

Kind regards
Darius

[Danny]

Hi darius yes the diagram i have been given has separrate sync fed in to g3 of the valve but it uses an ef50 so i will have to do some homework to see if the ef85 will be happy in this project im still working on modern rubbish so the good stuff will have to wait until my pay work is done

[oldeurope]

Originally Posted by Danny

Hi darius yes the diagram i have been given has separrate sync fed in to g3 of the valve but it uses an ef50 so i will have to do some homework to see if the ef85 will be happy in this project im still working on modern rubbish so the good stuff will have to wait until my pay work is done

Hi Danny, in the modulator the EF80 is much better than the EF85.
The EF85 has not a sharp cut off because it is made for automatic gain
control stages.
I would like to see your EF50 schematic, if there is no problem for you to
publish it.

Kind regards
Darius