Little more explanation regarding the Zobel network, its purpose is to make the output appear resistive rather than inductive, without it the back EMF caused by the inductance of the voice coil will cause high voltage spikes which could exceed the breakdown voltage of the output transistors in the TBA820.
I think it'll be pretty sad when they finally turn off radio broadcasts. But it's coming, that's for sure. And to some extent I do 'get' it. But I also have a general objection to internet _only_ broadcasts. It's the same sort of thing that they're doing with phone lines. And that's all fun and games until there's a power cut. I know power cuts are pretty rare these days, but who knows what the future holds and in a disaster scenario the old tech wins by a mile. Of course, we should not expect that the relatively expensive old ways of doing things will be kept going only for that "just in case" scenario, I understand that. But it'll be sad, just the same. There'll be a pretty significant demand for car radios that can accept phone streaming when that happens. I know many of the new cars have that built in, but there are also many that still don't - my 2019 car doesn't.
The LW radio 4 transmission was supposed to be the emergency one I thought. I did read that radio 2 and radio 4 would continue on FM if we had power cuts this winter. I remember in the storms of 87 FM was still on lower power. Yes, ofcom did relax battery requirements for telecoms I remember. I guess all these transmitters cost money to run and cost is important these days. I expect by 2027 the am bands will be pretty dead, but I expect FM to go longer. I wonder if community stations will keep going longer, such as radio Caroline. Thanks Brian. Daz
Happy New Year Daz, and congratulations on breaking your Roberts Duck... Interestingly, the RFM3 is the Roberts Rambler II - same board - the Rambler II evolved into the Rambler-FM (RFM). It would have been called the Rambler 3, but someone at Roberts had a brainwave... To say it's your first Bob, I enjoyed watching and hearing your circuit analysis, I've done many of them over the years, but never gone into the detail of circuit operation as you have. Looking forward to more... Maybe grab another chat at Biggleswade or somesuch, you should be on Roberts repair no. 432 by my reckoning by then 🤣 Ashamed to say I wasn't subbed, but proud to say I am now...
Happy New Year Paul, thanks for the Sub too. I'm sure the naming of the radio was thought too long, so perhaps the sales and marketing thought RFM sounded snappy, LOL. Was good to see you at Biggleswade. I did find the circuit interesting and how it was optimised for compactness and ease of setup in production. Daz
i had a roberts r505 with a random shorting cap in the audio output stage, cant remember if output coupler or bootstrap, quite a while ago, watch out if you get one of these, i dont think they used one of high enough voltage, a 6.3v type was fitted, it had about half supply volts across it when working (4.5 ish) so you'd think ok, but got a short surge overvoltage each time set was switched on,, all other caps were A1, (all blue philips)
@@darrencoe5795 poor quality, cheapened, too much miniaturisation, 'capacitor plague' in the 2000s due to incorrect copying of the low esr electrolyte formula
Hi Daz, usually people shove the wrong polarity 9V up 'em from an external supply :) Seems a popular thing to do. These are nice little radios. HNY to you. Regards - Andrew
certainly wont do them a lot of good, 😉 common issue with zx spectrums, as polarity is centre negative, instead of more common centre positive, usually it blows the top off the 7805 regulator and possibly destroys the +12/-5v oscillator transistor
@@Andrewausfa probably would, not possible, without force, to reverse the internal, battery supply but external very easily done, cant remember what polarity these use, i never had the model shown in the video but had a couple of others with dc in jack.. a discrete transistor output stage may well survive reversal for a short while,
Good news Darren, a quote from the Mail online today: "Big radio switch-off is DELAYED again: AM and FM stations will be available on old devices for another decade as switchover from analogue to digital is put off until 2032" Bad news also in the report "The changes only affect analogue commercial radio services as digital radio is subject to different arrangements. The BBC's radio stations are not subject to the rules." So maybe the BBC will leave analogue soon?
Well the commercial stations can hand in their AM or FM licence's at any time, but continue to have protected status on the D1 national multiplex. So they can switch too. All it means is they can continue to use and AM and FM and that's good news. But they can hand in licences. Luton and Bedford AM licence's for smooth were handed back. When my local smooth am transmitter went off, I contacted them to check if they had shut it down. They said no, there a fault. So always report a AM problem I say so they know it's being used. Transmitter s cost money to run, but because of the net neutrality, carrying on the net is cheap. Also that transmission cost is pushed to the consumer as they have to pay for data. Many thanks, Daz.
@@darrencoe5795 Thanks for additional info. Good to know. It's a bit like right of way on public footpaths, use it or lose it. Or at least let them know you use it.
Well that sounds a lot better now :-D I have to admit that i have never looked close at boot strapping, i would have checked the components around the amplifier, anyway. Thin sounding audio is often poor coupling. I have never liked digital radios, they give you THERE SELECTION of stations, no freedom to listen where you want. You won't be able to listen to other countrys radio. Boxed in with no real choice. They know were they can stick there digital crap!. Can you tell i don't like what they were up to. They pulled the same trick with freeview t.v, low quality crap that wasnt anywhere near as good as analog. Ooow aint i an angry man :-D
surely you mean TBA820M, never heard of a TDA820M? unfortunately the TBA is now discontinued by its original and main manufacturer so i dont know what long term availability will be, these were used in a lot of stuff, i 'think' theres some 'clone' ones around... there used to be a 14 pin version, without the M but much harder to find
@@darrencoe5795 yep, 'modernish' caps dont last as well as the older ones, especially the blue philips ones, they seem to last forever with only occasional bad ones, that said, i never assume caps are bad, like some do, i find most do last pretty well, i wouldnt 'blanket' recap unless signs that more than 2 or 3 of the same brand caps were giving issues, or signs of leak as you found, dont forget these types are not low ESR but standard grade, so may seem a bit 'high' anyway
Little more explanation regarding the Zobel network, its purpose is to make the output appear resistive rather than inductive, without it the back EMF caused by the inductance of the voice coil will cause high voltage spikes which could exceed the breakdown voltage of the output transistors in the TBA820.
Thanks Michael for making that clearer. Daz
HNY Daz. Interesting to see a different perspective on the RFM3. Here’s to 2023!
Thank you . Happy new year. Daz
These were used as a standard equipment for fault finding in REME @ SEE Arborfield in 1970’s. Great fun.
Nice easy repair. Happy new year to you. Keep that soldering iron hot. 👍
Happy new year, Terry. Yes, need to get into that workshop more! Daz
I think it'll be pretty sad when they finally turn off radio broadcasts. But it's coming, that's for sure. And to some extent I do 'get' it. But I also have a general objection to internet _only_ broadcasts. It's the same sort of thing that they're doing with phone lines. And that's all fun and games until there's a power cut. I know power cuts are pretty rare these days, but who knows what the future holds and in a disaster scenario the old tech wins by a mile. Of course, we should not expect that the relatively expensive old ways of doing things will be kept going only for that "just in case" scenario, I understand that. But it'll be sad, just the same.
There'll be a pretty significant demand for car radios that can accept phone streaming when that happens. I know many of the new cars have that built in, but there are also many that still don't - my 2019 car doesn't.
The LW radio 4 transmission was supposed to be the emergency one I thought. I did read that radio 2 and radio 4 would continue on FM if we had power cuts this winter. I remember in the storms of 87 FM was still on lower power. Yes, ofcom did relax battery requirements for telecoms I remember. I guess all these transmitters cost money to run and cost is important these days. I expect by 2027 the am bands will be pretty dead, but I expect FM to go longer. I wonder if community stations will keep going longer, such as radio Caroline. Thanks Brian. Daz
@David Wanklyn I think that's true on the dab. I also think that radio is free, data/broadband incurs a cost.
Happy New Year Daz, and congratulations on breaking your Roberts Duck...
Interestingly, the RFM3 is the Roberts Rambler II - same board - the Rambler II evolved into the Rambler-FM (RFM). It would have been called the Rambler 3, but someone at Roberts had a brainwave...
To say it's your first Bob, I enjoyed watching and hearing your circuit analysis, I've done many of them over the years, but never gone into the detail of circuit operation as you have. Looking forward to more... Maybe grab another chat at Biggleswade or somesuch, you should be on Roberts repair no. 432 by my reckoning by then 🤣
Ashamed to say I wasn't subbed, but proud to say I am now...
Happy New Year Paul, thanks for the Sub too. I'm sure the naming of the radio was thought too long, so perhaps the sales and marketing thought RFM sounded snappy, LOL. Was good to see you at Biggleswade. I did find the circuit interesting and how it was optimised for compactness and ease of setup in production. Daz
i had a roberts r505 with a random shorting cap in the audio output stage, cant remember if output coupler or bootstrap, quite a while ago, watch out if you get one of these, i dont think they used one of high enough voltage, a 6.3v type was fitted, it had about half supply volts across it when working (4.5 ish) so you'd think ok, but got a short surge overvoltage each time set was switched on,, all other caps were A1, (all blue philips)
Thanks for that. I don't think modern capacitors have such a headroom as they used too. Daz
@@darrencoe5795 poor quality, cheapened, too much miniaturisation, 'capacitor plague' in the 2000s due to incorrect copying of the low esr electrolyte formula
Hi Daz, usually people shove the wrong polarity 9V up 'em from an external supply :) Seems a popular thing to do. These are nice little radios. HNY to you. Regards - Andrew
certainly wont do them a lot of good, 😉 common issue with zx spectrums, as polarity is centre negative, instead of more common centre positive, usually it blows the top off the 7805 regulator and possibly destroys the +12/-5v oscillator transistor
@@andygozzo72 No :) Usually blows the TDA amp in these. I put a Schottky diode in-line with the supply now.
@@Andrewausfa probably would, not possible, without force, to reverse the internal, battery supply but external very easily done, cant remember what polarity these use, i never had the model shown in the video but had a couple of others with dc in jack.. a discrete transistor output stage may well survive reversal for a short while,
I wondered about fitting a diode to it to protect it. HYN to you and was good to meet you Andrew, in September. Daz
Good news Darren, a quote from the Mail online today: "Big radio switch-off is DELAYED again: AM and FM stations will be available on old devices for another decade as switchover from analogue to digital is put off until 2032" Bad news also in the report "The changes only affect analogue commercial radio services as digital radio is subject to different arrangements. The BBC's radio stations are not subject to the rules." So maybe the BBC will leave analogue soon?
Well the commercial stations can hand in their AM or FM licence's at any time, but continue to have protected status on the D1 national multiplex. So they can switch too. All it means is they can continue to use and AM and FM and that's good news. But they can hand in licences. Luton and Bedford AM licence's for smooth were handed back. When my local smooth am transmitter went off, I contacted them to check if they had shut it down. They said no, there a fault. So always report a AM problem I say so they know it's being used. Transmitter s cost money to run, but because of the net neutrality, carrying on the net is cheap. Also that transmission cost is pushed to the consumer as they have to pay for data. Many thanks, Daz.
@@darrencoe5795 Thanks for additional info. Good to know. It's a bit like right of way on public footpaths, use it or lose it. Or at least let them know you use it.
Well that sounds a lot better now :-D
I have to admit that i have never looked close at boot strapping, i would have checked the components around the amplifier, anyway.
Thin sounding audio is often poor coupling.
I have never liked digital radios, they give you THERE SELECTION of stations, no freedom to listen where you want.
You won't be able to listen to other countrys radio.
Boxed in with no real choice.
They know were they can stick there digital crap!.
Can you tell i don't like what they were up to.
They pulled the same trick with freeview t.v, low quality crap that wasnt anywhere near as good as analog.
Ooow aint i an angry man :-D
surely you mean TBA820M, never heard of a TDA820M? unfortunately the TBA is now discontinued by its original and main manufacturer so i dont know what long term availability will be, these were used in a lot of stuff, i 'think' theres some 'clone' ones around... there used to be a 14 pin version, without the M but much harder to find
Yes I did mean TBA. My mistake, whoops. Daz.
@@darrencoe5795 hehe 😉 stock up on a few while theres chance, you can use a lm386 in place with a bit of alteration but is lower output
I guessed it was a high ESR cap.
Fun finding it though we knew it would be. Daz
@@darrencoe5795 yep, 'modernish' caps dont last as well as the older ones, especially the blue philips ones, they seem to last forever with only occasional bad ones, that said, i never assume caps are bad, like some do, i find most do last pretty well, i wouldnt 'blanket' recap unless signs that more than 2 or 3 of the same brand caps were giving issues, or signs of leak as you found, dont forget these types are not low ESR but standard grade, so may seem a bit 'high' anyway
Wow thiers nothing to that radio
The IC's and ceramic filters certainly made it a AM size PCB. Daz
Thats a nice radio never seen one like that😯📻📈📉
Yes it's a nice radio I must agree. I don't often work on a radio with IC"s. Daz