Stagger Tuned AM IFs - UK Vintage Radio Repair and Restoration Discussion Forum

'LIVEWIRE?' · 1st May 2008, 10:59 am

Not sure if this should go here, or in the 'Components & Circuits' section, but, whilst repairing a Philips P3G38T Car/Portable radio Inoticed from the Makers Service Maual that the IFTs are peaked at 468Khz(L14),472Khz(L18), and 470Khz(L20-3rd IF/Detector). If I'm not mistaken this would result in a (-6dB)Bandwidth of ca. 13kHz, plus a 'lumpy' response with 3 peaks. The sensitivity/selectivity of this 40 year old radio is(are?)O.K., and I'm not about to adjust the IFTs.-I just wondered if anyone knows the reason for the staggered tuning 'cos I've forgotten (The fault by the way was the dreaded{haven't you guessed.....??}AF117s, especially the mixer/oscillator, all 3 of which have now been replaced with AF127s.)

Darren-UK · 1st May 2008, 11:45 am

It was done to give a wider frequency response curve and supposedly reduce the effects of feedback and give an overall softer tone. I don't know if this was another Philips oddity originally but I seem to recall coming across it on a Cossor a long time ago. That may, of course, been on a radio produced after Cossor came under Philips jurisdiction.

There is a brief mention of staggered tuning in post #8 of this thread.

Sideband · 1st May 2008, 11:51 am

Just found this whilst googling. I'm a bit rusty on this now so maybe someone else can elaborate.

'In the stagger-tuning method, the resonant frequencies of the various stages combine so that to- gether they pass the frequency band to be amplified. The product of each stage’s amplitude response curve forms the overall response curve'.

Rich.

geofy · 1st May 2008, 12:42 pm

Staggered IF's where also used to prevent microphony positive feedback between stages or howl-round which some early transistors where prone to, if the set was retuned to have all the same IF's it would start to howl.

Tuned coils should be left alone unless there is reason to retune them as they seldom go out of tune.

Geof

wireful3 · 1st May 2008, 12:46 pm

I think this is intended to get a wider passband but with the same sharp edge as a single tuned circuit with a narrow passband. The effect is to give good selectivity against adjacent stations but still give a good audio response.

Herald1360 · 1st May 2008, 1:19 pm

Attached is an illustration of stagger tuning-

Dark blue is response of single circuit tuned to 500kHz
Green is single circuit tuned slightly lower
Red is single circuit tuned slightly higher

Olive green is 3 cascaded circuits all tuned to 500kHz
Light blue is 3 cascaded circuits tuned to slightly lower, 500kHz and slightly higher.

The overall effect is a response with a 6dB bandwidth for three staggered stages which is about the same as for one stage on its own, but with a much steeper roll off than the single stage would have.

Just what is stated much more succinctly in the previous post which beat me to it!

Chris

1st May 2008, 10:59 am	#1
'LIVEWIRE?' Rest in Peace Join Date: Mar 2006 Location: N.W. Oxfordshire(Chipping Norton) Posts: 7,306	Stagger Tuned AM IFs Not sure if this should go here, or in the 'Components & Circuits' section, but, whilst repairing a Philips P3G38T Car/Portable radio Inoticed from the Makers Service Maual that the IFTs are peaked at 468Khz(L14),472Khz(L18), and 470Khz(L20-3rd IF/Detector). If I'm not mistaken this would result in a (-6dB)Bandwidth of ca. 13kHz, plus a 'lumpy' response with 3 peaks. The sensitivity/selectivity of this 40 year old radio is(are?)O.K., and I'm not about to adjust the IFTs.-I just wondered if anyone knows the reason for the staggered tuning 'cos I've forgotten (The fault by the way was the dreaded{haven't you guessed.....??}AF117s, especially the mixer/oscillator, all 3 of which have now been replaced with AF127s.)

1st May 2008, 11:45 am	#2
Darren-UK Retired Dormant Member Join Date: Apr 2003 Location: Blackpool, Lancashire, UK. Posts: 4,061	Re: Stagger Tuned AM IFs It was done to give a wider frequency response curve and supposedly reduce the effects of feedback and give an overall softer tone. I don't know if this was another Philips oddity originally but I seem to recall coming across it on a Cossor a long time ago. That may, of course, been on a radio produced after Cossor came under Philips jurisdiction. There is a brief mention of staggered tuning in post #8 of this thread.

1st May 2008, 11:51 am	#3
Sideband Dekatron Join Date: Oct 2003 Location: Croydon, Surrey, UK. Posts: 7,566	Re: Stagger Tuned AM IFs Just found this whilst googling. I'm a bit rusty on this now so maybe someone else can elaborate. 'In the stagger-tuning method, the resonant frequencies of the various stages combine so that to- gether they pass the frequency band to be amplified. The product of each stage’s amplitude response curve forms the overall response curve'. Rich. __________________ There are lots of brilliant keyboard players and then there is Rick Wakeman.....

1st May 2008, 12:42 pm	#4
geofy Retired Dormant Member Join Date: Jun 2006 Posts: 1,798	Re: Stagger Tuned AM IFs Staggered IF's where also used to prevent microphony positive feedback between stages or howl-round which some early transistors where prone to, if the set was retuned to have all the same IF's it would start to howl. Tuned coils should be left alone unless there is reason to retune them as they seldom go out of tune. Geof

1st May 2008, 12:46 pm	#5
wireful3 Retired Dormant Member Join Date: Sep 2003 Location: Bristol, UK. Posts: 808	Re: Stagger Tuned AM IFs I think this is intended to get a wider passband but with the same sharp edge as a single tuned circuit with a narrow passband. The effect is to give good selectivity against adjacent stations but still give a good audio response.

1st May 2008, 1:19 pm	#6
Herald1360 Dekatron Join Date: Feb 2007 Location: Leominster, Herefordshire, UK. Posts: 16,535	Re: Stagger Tuned AM IFs Attached is an illustration of stagger tuning- Dark blue is response of single circuit tuned to 500kHz Green is single circuit tuned slightly lower Red is single circuit tuned slightly higher Olive green is 3 cascaded circuits all tuned to 500kHz Light blue is 3 cascaded circuits tuned to slightly lower, 500kHz and slightly higher. The overall effect is a response with a 6dB bandwidth for three staggered stages which is about the same as for one stage on its own, but with a much steeper roll off than the single stage would have. Just what is stated much more succinctly in the previous post which beat me to it! Chris Attached Thumbnails