Fringe TV and Aurora - UK Vintage Radio Repair and Restoration Discussion Forum

oldticktock · 29th Oct 2010, 3:01 pm

Hi,

bit of advice required, as I've worked my way slowly through the RF stage of a Fringe TV the signal is obviously getting stronger as the circuit conditions improve. I guess with the Aurora there really is no concept of a Fringe TV now.

The picture quality is excellent but the level of the signal makes the picture jumpy, it's not SOV. I found I could make it better by adding in attenuators 18db, 9db & 6db and setting the sensitivity making it better but not fully. Is there a rule of thumb for working out the correct attenuation or combo of attenuators or is it add until it goes

Chris

p.s. mods put it in this section as it's related to the output strength of the Aurora, if should be in the TV section soz

ppppenguin · 29th Oct 2010, 3:41 pm

We are certainly feeding our 405 sets with better signals than the vast majority could ever receive off air.

Suck it and see with attenuators. 12-18dB seems a good starting point with an Aurora. If you have a Domino this has a much more powerful output and you'd want to use 18dB all the time unless you needed to shout at a very deaf set.

A powerful output is also ideal for splitting to feed multiple sets.

murphyv310 · 29th Oct 2010, 3:46 pm

It all depends on the set, some fringe sets had an extra stage of IF amplification flywheel sync and all sorts of goodies. Later sets may also have gated AGC.
A good set should resolve a lockable picture with 10 microvolts on band 1 but should be happy with 500 microvolts without attenuation.
The aurora gives a lot more signal than that so a 12db should be about right but again it depends on the age of the set and its design.

ppppenguin · 29th Oct 2010, 5:03 pm

I think the Aurora gives about 6mV. So you need 20dB or so to get 500uV. It's not going to be critical so 12-18dB should be fine.

A Domino gives about 18dB more than an Aurora. So do the published stand alone modulators based on 1496 chips. That covers all the common sources.

oldticktock · 29th Oct 2010, 5:20 pm

Thanks chaps, although I did have 18db in-line there was still a bit of overload, perhaps I will wait and see once i've finished replacing the final leaky caps before making the final call.

Chris

murphyv310 · 30th Oct 2010, 9:12 pm

Chris,
Is this the PAM you are talking about?
The set is well designed with a very good RF/IF stage. Although fringe it still wasn't as sensitive as later designs that utilised the likes of a a PCC89, 30L17 or a PC97 frame grid valve in the tuner.
They normally are quite impervious to strong signals, but one thing to remember the aurora along with the domino produce a double sideband signal not a vestigial sideband signal that the PAM will be aligned to, that in itself can cause some disturbance with good signals.

oldticktock · 30th Oct 2010, 10:11 pm

Hi Trevor yes the Pam which is in fact a PYE CTM21F chassis. Thanks for the info, I have no idea what your talking about with regards to VSB an area I have neglected, I shall however rectify that and do some reading.

29th Oct 2010, 3:01 pm	#1
oldticktock Retired Dormant Member Join Date: Nov 2009 Location: Weardale, UK. Posts: 1,981	Fringe TV and Aurora Hi, bit of advice required, as I've worked my way slowly through the RF stage of a Fringe TV the signal is obviously getting stronger as the circuit conditions improve. I guess with the Aurora there really is no concept of a Fringe TV now. The picture quality is excellent but the level of the signal makes the picture jumpy, it's not SOV. I found I could make it better by adding in attenuators 18db, 9db & 6db and setting the sensitivity making it better but not fully. Is there a rule of thumb for working out the correct attenuation or combo of attenuators or is it add until it goes Chris p.s. mods put it in this section as it's related to the output strength of the Aurora, if should be in the TV section soz Last edited by oldticktock; 29th Oct 2010 at 3:25 pm.

29th Oct 2010, 3:41 pm	#2
ppppenguin Retired Dormant Member Join Date: Dec 2003 Location: North London, UK. Posts: 6,168	Re: Fringe TV and Aurora We are certainly feeding our 405 sets with better signals than the vast majority could ever receive off air. Suck it and see with attenuators. 12-18dB seems a good starting point with an Aurora. If you have a Domino this has a much more powerful output and you'd want to use 18dB all the time unless you needed to shout at a very deaf set. A powerful output is also ideal for splitting to feed multiple sets.

29th Oct 2010, 3:46 pm	#3
murphyv310 Dekatron Join Date: Sep 2006 Location: Kilmarnock, Ayrshire, UK. Posts: 5,422	Re: Fringe TV and Aurora It all depends on the set, some fringe sets had an extra stage of IF amplification flywheel sync and all sorts of goodies. Later sets may also have gated AGC. A good set should resolve a lockable picture with 10 microvolts on band 1 but should be happy with 500 microvolts without attenuation. The aurora gives a lot more signal than that so a 12db should be about right but again it depends on the age of the set and its design. __________________ Cheers, Trevor. MM0KJJ. RSGB, GQRP, WACRAL, K&LARC. Member

29th Oct 2010, 5:03 pm	#4
ppppenguin Retired Dormant Member Join Date: Dec 2003 Location: North London, UK. Posts: 6,168	Re: Fringe TV and Aurora I think the Aurora gives about 6mV. So you need 20dB or so to get 500uV. It's not going to be critical so 12-18dB should be fine. A Domino gives about 18dB more than an Aurora. So do the published stand alone modulators based on 1496 chips. That covers all the common sources.

29th Oct 2010, 5:20 pm	#5
oldticktock Retired Dormant Member Join Date: Nov 2009 Location: Weardale, UK. Posts: 1,981	Re: Fringe TV and Aurora Thanks chaps, although I did have 18db in-line there was still a bit of overload, perhaps I will wait and see once i've finished replacing the final leaky caps before making the final call. Chris

30th Oct 2010, 9:12 pm	#6
murphyv310 Dekatron Join Date: Sep 2006 Location: Kilmarnock, Ayrshire, UK. Posts: 5,422	Re: Fringe TV and Aurora Chris, Is this the PAM you are talking about? The set is well designed with a very good RF/IF stage. Although fringe it still wasn't as sensitive as later designs that utilised the likes of a a PCC89, 30L17 or a PC97 frame grid valve in the tuner. They normally are quite impervious to strong signals, but one thing to remember the aurora along with the domino produce a double sideband signal not a vestigial sideband signal that the PAM will be aligned to, that in itself can cause some disturbance with good signals. __________________ Cheers, Trevor. MM0KJJ. RSGB, GQRP, WACRAL, K&LARC. Member

30th Oct 2010, 10:11 pm	#7
oldticktock Retired Dormant Member Join Date: Nov 2009 Location: Weardale, UK. Posts: 1,981	Re: Fringe TV and Aurora Hi Trevor yes the Pam which is in fact a PYE CTM21F chassis. Thanks for the info, I have no idea what your talking about with regards to VSB an area I have neglected, I shall however rectify that and do some reading. Last edited by oldticktock; 30th Oct 2010 at 10:33 pm.