In article <35F9B94B.5...@urlfor.addr>, Mike <ch...@urlfor.addr> wrote:
> Michael Black wrote: > Radio station CFRB was local when I was fixing these radios. In > fact, it was just down the road. It served as a convenient strong > signal source while troubleshooting radios that appeared completely > dead - if CFRB showed up, at least the power supply, local > oscillator, IF, and audio stages were working. If so, it was usually > a bad RF tube or a broken center conductor in the antenna coax.
I've put some great stuff in the archives that I hope you'll appreciate, including RealAudio clips from days gone by, and some incredible pictures, dating back to 1927 when we went on-air.
Take care.
Iain Grant Executive Producer CFRB Radio, Toronto, Canada
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> In article <35F9B94B.5...@urlfor.addr>, > Mike <ch...@urlfor.addr> wrote: > > Michael Black wrote:
> > Radio station CFRB was local when I was fixing these radios. In > > fact, it was just down the road. It served as a convenient strong > > signal source while troubleshooting radios that appeared completely > > dead - if CFRB showed up, at least the power supply, local > > oscillator, IF, and audio stages were working. If so, it was usually > > a bad RF tube or a broken center conductor in the antenna coax.
> I've put some great stuff in the archives that I hope you'll > appreciate, including RealAudio clips from days gone by, and > some incredible pictures, dating back to 1927 when we went > on-air.
One of them is the Chevrolet Model 986067 (Brazil), a car radio that uses permeability tuning and 262 KHz IF. It uses a 6SK7 for the rf and a 6SA7 for the mixer.
I don't have my books available, so I had to do a web search. There are some tube specs at
The 6SJ7 spec shows a grid 1 to plate capacity of 0.005 pf maximum.
This has a reactance of 58 megohms at 540 KHz, which is high enough to eliminate oscillations using a permeable core and 30 or 40 pf to resonate at 540 KHz. Of course, the wiring and layout needs care.
This explains why the RF stage would not oscillate in a permeability-tuned radio.
The 12BE6 shows a grid to anode capacity of 0.3 pf.
There are two signal grids. If this spec is the capacity from the rf signal grid to the plate, it means the feedback from the plate is sixty times higher for the mixer than it is for the rf stage.
If this is true, it explains the higher susceptibility to oscillation in a mixer using a 455 KHz IF. Moving to 262 KHz would solve it.
If someone who has manuals could confirm this, it may explain why.
"DAVID KATZ" <DAVEK...@prodigy.net> shared these priceless pearls of wisdom:
->
->Michael F. Coyle wrote in message <6tbtuu$ms...@winter.news.erols.com>...
->>..."262.5 KHz" -- double ->>that and you get 525 KHz, near the bottom end of the AM BCB. -><(Hmmm. Half of 530 KHz is 265 KHz -- why not use that?) ->Excellent thought. Rectifying the IF to detect AM produces much 2nd ->harmonic
Actually, much more 3rd, 5th, 7th, etc. 455 only had two birdies in the AM band, 910 and a 5 kc birdie at 1360/1370. 262 has birdies at 790, 1050, 1310, and 1570. And they WERE real.
On Sun, 13 Sep 1998, Alan Peake wrote: > In article <05BBwxAgvX+1E...@jmwa.demon.co.uk> John Woodgate <j...@jmwa.demon.co.uk> writes:
> >Such receivers were particularly good on the h.f. bands, for they could > >receive every station at two places on the dial(;-).
> They probably called this a "feature" :)
I don't know about in those days, but just this year I saw someone talking about an amateur radio transceiver, and he mentioned that it could receive the cellular frequencies by tuning to the image frequency. He acted like that was a feature. Meanwhile, other people are complaining because their transceivers are prone to a lot of out of band junk, precisely because the front end ot he receiver is broadly tuned.
I really don't know the TRUE reason why 262.5 khz was chosen, BUT let's look at the rest of the components and the capacitance effects side of the design of tube gear in harsh environments.
1) Larger value capacitors were needed to resonate the coil inductance values to resonate at 262.5 Khz as opposed to 455 Khz used today which use higher inductance and lower capacitance. Today's 455 Khz systems are higher "Q" for better adjacent channel rejection. This would mean that the -/+ coeficient of capacitors in a 262.5 Khz system would not detune circuits very much since a few picroFarads of change was not a problem with temperature changes. ie: summer/winter
2) Tube grids operate at really high impedances. Suttle changes in tube interelectrode capacitances from wear/microphonics from road vibrations along with stray capacitance caused from moisture across tube sockets would NOT detune the LO and I.F. system L/C circuits much at all.
3) Adjacent channels were not a problem back then. So lower "Q" resonate circuits offered an auto radio a more stable tuning during varying temperatures and humidity conditions, including all those back seat fornications that caused steaming up the inside of the vehicle/radio. Would you not be peed-off if you were involved in one of those scenes and the radio drifted off station????
> One of them is the Chevrolet Model 986067 (Brazil), a car radio that > uses permeability tuning and 262 KHz IF. It uses a 6SK7 for the rf > and a 6SA7 for the mixer.
> I don't have my books available, so I had to do a web search. There > are some tube specs at
> The 6SJ7 spec shows a grid 1 to plate capacity of 0.005 pf maximum.
> This has a reactance of 58 megohms at 540 KHz, which is high enough > to eliminate oscillations using a permeable core and 30 or 40 pf to > resonate at 540 KHz. Of course, the wiring and layout needs care.
> This explains why the RF stage would not oscillate in a > permeability-tuned radio.
> The 12BE6 shows a grid to anode capacity of 0.3 pf.
> There are two signal grids. If this spec is the capacity from the rf > signal grid to the plate, it means the feedback from the plate is > sixty times higher for the mixer than it is for the rf stage.
> If this is true, it explains the higher susceptibility to > oscillation in a mixer using a 455 KHz IF. Moving to 262 KHz would > solve it.
> If someone who has manuals could confirm this, it may explain why.
I really don't know the TRUE reason why 262.5 khz was chosen, BUT let's look at the rest of the components and the capacitance effects side of the design of tube gear in harsh environments.
1) Larger value capacitors were needed to resonate the coil inductance values to resonate at 262.5 Khz as opposed to 455 Khz used today which use higher inductance and lower capacitance. Today's 455 Khz systems are higher "Q" for better adjacent channel rejection. This would mean that the -/+ coeficient of capacitors in a 262.5 Khz system would not detune circuits very much since a few picroFarads of change was not a problem with temperature changes. ie: summer/winter
2) Tube grids operate at really high impedances. Suttle changes in tube interelectrode capacitances from wear/microphonics from road vibrations along with stray capacitance caused from moisture across tube sockets would NOT detune the LO and I.F. system L/C circuits much at all.
3) Adjacent channels were not a problem back then. So lower "Q" resonate circuits offered an auto radio a more stable tuning during varying temperatures and humidity conditions, including all those back seat fornications that caused steaming up the inside of the vehicle/radio. Would you not be peed-off if you were involved in one of those scenes and the radio drifted off station????
Alan Peake (Alan.Pe...@dsto.defence.gov.au) wrote:
> Well, I can add to the noise too. I seem to recall that there was yet another > IF frequency at one time - around 90 KHz - presumably to get higher > selectivity. No idea if this was a single or double conversion thing.
When superhets were first invented, an IF of ~60kHz was common. The term 'supersonic heterodyne' makes much more sense when you consider that originally the IF was at what we would now refer to a 'ultrasonic' frequencies.
Also there was originally no standard IF, so different manufacturers would use whatever frequency they felt like. It took quite a number of years before 455kHz became universal. I understand 175kHz was quite common in the '30s.
> In article <35F62034.6...@urlfor.addr>, Mike <ch...@urlfor.addr> writes > >I don't recall seeing the solid dielectric versions until they > > came out in transistor radios. I have never seen the 'pip' type > > you mention. Wouldn't the studs wear and change the gap over > > time? > They appeared in the 70s in Europe. No, they don't wear out: > nylon/polished aliminium is a 'non-wearing' combination.
> I thought I had actually given the reason for the 262 kHz IF; mixer > stability. > -- > Regards, John Woodgate, Phone +44 (0)1268 747839 Fax +44 (0)1268 777124. > OOO - Own Opinions Only. You can fool all of the people some of the time, but > you can't please some of the people any of the time.
--
Non wearing?
Polished aluminium VS nylon?
Al2O3 always wins.
--
John Fields, Austin Instruments, Inc. El Presidente Research, Design, and Development "I speak for the company" Austin, Republic of Texas
In article <36045AA6.1...@fc.net>, John Fields <jfie...@fc.net> writes
>> They appeared in the 70s in Europe. No, they don't wear out: >> nylon/polished aliminium is a 'non-wearing' combination. [snip]
>Non wearing?
>Polished aluminium VS nylon?
>Al2O3 always wins.
I reported what I was told by the manufacturers. If they don't know, who does? Is A1203 a grade of nylon? If so, maybe they use another grade. The friction properties of different nylons are rather complex. -- Regards, John Woodgate, Phone +44 (0)1268 747839 Fax +44 (0)1268 777124. OOO - Own Opinions Only. You can fool all of the people some of the time, but you can't please some of the people any of the time.
> In article <36045AA6.1...@fc.net>, John Fields <jfie...@fc.net> writes > >> They appeared in the 70s in Europe. No, they don't wear out: > >> nylon/polished aliminium is a 'non-wearing' combination. > [snip]
> >Non wearing?
> >Polished aluminium VS nylon?
> >Al2O3 always wins.
> I reported what I was told by the manufacturers. If they don't know, who > does? Is A1203 a grade of nylon? If so, maybe they use another grade. > The friction properties of different nylons are rather complex. > --
John,
I agree with you that the frictional properties of the various nylons can be rather complex.
For example, a graphite loaded nylon will generally exhibit lower starting and running friction than will a glass loaded grade.
Al2O3 is aluminum oxide, and it will always form on the surface of unprotected aluminum, whether the aluminum surface is polished or not, in the presence of atmospheric oxygen.
Being the second hardest material known, (next to diamond) if it it placed in frictional contact with nylon, the nylon will wear.
--
John Fields, Austin Instruments, Inc. El Presidente Research, Design, and Development "I speak for the company" Austin, Republic of Texas
In article <3605D85B.2...@fc.net>, John Fields <jfie...@fc.net> writes
>Al2O3 is aluminum oxide, and it will always form on the surface of unprotected >aluminum, >whether the aluminum surface is polished or not, in the presence of atmospheric >oxygen.
Well, that's the limitations of ASCII. I interpreted that as A followed by the number 1203.
>Being the second hardest material known, (next to diamond) if it it placed in >frictional >contact with nylon, the nylon will wear.
Well, *some forms* of aluminium oxide are very hard indeed, but hardness is not the arbiter of whether wear takes place. Glass is quite hard, but few things wear as a result of contact with it. The molecular-level smoothness of a surface, and the 'stickiness' of any free chemical bonds at the surface are important factors. -- Regards, John Woodgate, Phone +44 (0)1268 747839 Fax +44 (0)1268 777124. OOO - Own Opinions Only. You can fool all of the people some of the time, but you can't please some of the people any of the time.
John Woodgate wrote: > Well, *some forms* of aluminium oxide are very hard indeed, but > hardness > is not the arbiter of whether wear takes place. Glass is quite > hard, but > few things wear as a result of contact with it. The > molecular-level > smoothness of a surface, and the 'stickiness' of any free chemical > bonds > at the surface are important factors.
--
I'm in general agreement with you, but for the specific case at hand; an aluminum oxide / Nylon interface, the aluminum oxide surface formed as a result of oxidation will, I believe, be porous, rough, and harder than the Nylon.
In this instance I believe the rheology of the interface will involve only mechanical forces, with the result that particles of Nylon will be scraped from the suface by the "hills" an will be embedded in the "valleys" of the Al2O3 surface.
Thus the Nylon, and not the Al2O3 will wear.
When the valleys fill, the interface will be mainly Nylon/Nylon, and the frictional characteristics of the interface will change to the point where analysis would probably become a nightmare!
-- John Fields, Austin Instruments, Inc. El Presidente Research, Design, and Development "I speak for the company" Austin, Republic of Texas
I did a lot of wear testing when I worked for the late Dr. Philip Stein (an expert tribologist) at the Stein Seal Co, and can say that nylon/aluminum wear is not as simple as all that. Other significant factors: the long molecular chains of nylon have considerable flexibility to ride over small irregularities. The aluminum oxide layer will become polished by wear. Particles of dirt will embed in the softer material and cause wear in the harder material (probably the predominant wear mechanism). The wear interface is not unlubricated! The moisture in even the driest air a car is likely to encounter will provide a layer of water molecules on the surface of the aluminum, which are believed to act like tiny ball bearings in the interface. If you take away the trace of water vapor (not easy but often done in chemical process systems), friction will increase *drastically*! All in all, I have no difficulty believing that nylon on aluminum is essentially "non-wearing" in this application; that is, wear over service life will be less than elastic preload of the nylon nubs.
Glen Walpert
In article <36066147.68612...@fc.net>, John Fields <jfie...@fc.net> wrote:
>> Well, *some forms* of aluminium oxide are very hard indeed, but >> hardness >> is not the arbiter of whether wear takes place. Glass is quite >> hard, but >> few things wear as a result of contact with it. The >> molecular-level >> smoothness of a surface, and the 'stickiness' of any free chemical >> bonds >> at the surface are important factors.
>--
>I'm in general agreement with you, but for the specific case at >hand; an aluminum oxide / Nylon interface, the aluminum oxide >surface formed as a result of oxidation will, I believe, be porous, >rough, and harder than the Nylon.
>In this instance I believe the rheology of the interface will >involve only mechanical forces, with the result that particles of >Nylon will be scraped from the suface by the "hills" an will be >embedded in the "valleys" of the Al2O3 surface.
>Thus the Nylon, and not the Al2O3 will wear.
>When the valleys fill, the interface will be mainly Nylon/Nylon, and >the frictional characteristics of the interface will change to the >point where analysis would probably become a nightmare!
> > p.p.s. Owning a 75A4 does have a practical side -- it's all tubes. > > After the "big one", when radiation has zapped all the Kenwoods > > out there, with their semiconductor guts, performance of the > > 75A4 will not even be dented! ;->
> Who will have a working transmitter you can listen to?
--
Say again?
--
John Fields, Austin Instruments, Inc. El Presidente Research, Design, and Development "I speak for the company" Austin, Republic of Texas
There are many good points made below but I think that they mostly miss the mark. I have seen 2nd harmonic of the 455 kc IF frequency cause interference in the old 5 tube house radios at 910 kc. It causes annoying beats as the dial is moved slightly from proper frequency. The 2nd harmonic of the 262.5 kc IF appears at 525 kc which is below the lowest AM frequency of 540 kc.
In addition the lower IF frequency simplifies accurate tracking and allows greater selectivity for reduced IF bandwidth. This is important for reception of weak distant stations as you drive thru various towns with strong local stations.
trojancow...@gmail.com wrote:
> There are many good points made below but I think that they mostly miss the mark. I have seen 2nd harmonic of the 455 kc IF frequency cause interference in the old 5 tube house radios at 910 kc. It causes annoying beats as the dial is moved slightly from proper frequency. The 2nd harmonic of the 262.5 kc IF appears at 525 kc which is below the lowest AM frequency of 540 kc.
> In addition the lower IF frequency simplifies accurate tracking and allows greater selectivity for reduced IF bandwidth. This is important for reception of weak distant stations as you drive thru various towns with strong local stations.
> WB0KVV
Cannot say about modern car radios, but in the tube daze, the 262KC IF was not common.
If one has a beat problem at 910KC, it is simple to re-align the IF so harmonic is off-station; a good tech could do that in a few minutes with no extra electronic aids.
Your beef seems to be almost pointless.
> trojancow...@gmail.com wrote:
> > There are many good points made below but I think that they mostly miss the mark. I have seen 2nd harmonic of the 455 kc IF frequency cause interference in the old 5 tube house radios at 910 kc. It causes annoying beats as the dial is moved slightly from proper frequency. The 2nd harmonic of the 262.5 kc IF appears at 525 kc which is below the lowest AM frequency of 540 kc.
> > In addition the lower IF frequency simplifies accurate tracking and allows greater selectivity for reduced IF bandwidth. This is important for reception of weak distant stations as you drive thru various towns with strong local stations.
> > WB0KVV
> Cannot say about modern car radios, but in the tube daze, the 262KC
> IF was not common.
>> trojancow...@gmail.com wrote:
>>> There are many good points made below but I think that they mostly miss the mark. I have seen 2nd harmonic of the 455 kc IF frequency cause interference in the old 5 tube house radios at 910 kc. It causes annoying beats as the dial is moved slightly from proper frequency. The 2nd harmonic of the 262.5 kc IF appears at 525 kc which is below the lowest AM frequency of 540 kc.
>>> In addition the lower IF frequency simplifies accurate tracking and allows greater selectivity for reduced IF bandwidth. This is important for reception of weak distant stations as you drive thru various towns with strong local stations.
>>> WB0KVV
>> Cannot say about modern car radios, but in the tube daze, the 262KC
>> IF was not common.
> It was, in Delco car radios, and it was 262.5 KHz
Interesting.
What was that bit about base and collector, when the subject implied tube daze?
I quote from part of a response:
"Now, if you have a permeability-tuned mixer stage (whether or not there
is an RF stage before it), with the IF at 455kHz, it tends to go
seriously unstable when tuned to the lower frequency end of the MF band
(520 kHz?), because base and collector circuits are tuned to near-enough
the same frequency. The use of a 262 kHz IF prevents this. I suppose 262
kHz was chosen to minimise problems (whistles) due to image reception
and IF harmonics."
> Interesting.
> What was that bit about base and collector, when the subject implied >tube daze?
> I quote from part of a response:
>"Now, if you have a permeability-tuned mixer stage (whether or not there
>is an RF stage before it), with the IF at 455kHz, it tends to go
>seriously unstable when tuned to the lower frequency end of the MF band
>(520 kHz?), because base and collector circuits are tuned to near-enough
>the same frequency. The use of a 262 kHz IF prevents this. I suppose 262
>kHz was chosen to minimise problems (whistles) due to image reception
>and IF harmonics."
