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Vintage Radio (domestic) Domestic vintage radio (wireless) receivers only. |
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3rd Jul 2018, 4:29 pm | #21 |
Banned
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Re: Ferranti A1016 bluetooth project
1:1 RS transformer.
I doubt the heater winding will have any problem supplying 50mA extra, all the valve filaments together could be that far out anyway. |
3rd Jul 2018, 4:41 pm | #22 |
Heptode
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Re: Ferranti A1016 bluetooth project
If you use a half wave rectifier, you will retain a common ground and not need a coupling transformer?
Ken |
3rd Jul 2018, 10:51 pm | #23 |
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Re: Ferranti A1016 bluetooth project
I don't think I could get enough DC out of a 1/2 wave on the heater supply. I reckon on 6.3 x 0.45 = 2.8V (less allowing for diode fwd drop?). My full wave gives (6.3 x 1.414) - (2 x 0.7) = 7.5V and I just about get enough headroom to drive a regulator with some decent smoothing capacitor.
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3rd Jul 2018, 11:03 pm | #24 |
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Re: Ferranti A1016 bluetooth project
Thanks, I have ordered similar. I note most are 600 ohm. Not sure if that matters for my application, but I'll see how I get on with it.
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3rd Jul 2018, 11:16 pm | #25 |
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Re: Ferranti A1016 bluetooth project
one of these will contain 2 line-level audio transformers.
http://cpc.farnell.com/unbranded/b07...op%20isolator# The beauty is that the plastic casing can either be retained or split open as it's only held together by its sticky labels.
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Kevin |
4th Jul 2018, 11:09 am | #26 |
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Re: Ferranti A1016 bluetooth project
The half wave rectifier will actually give a higher peak rectified voltage (one less diode) but of course will need about 4 times the smoothing cap because of the higher ripple at 50Hz versus 100Hz. You might also consider a low dropout regulator, several good chips or diy !
Ken |
4th Jul 2018, 2:16 pm | #27 |
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Re: Ferranti A1016 bluetooth project
hmmm not convinced. Anyway, I don't want to have a large smoother as it will increase switch on surge current. I already have 500 uF on the full wave to keep the rail from dipping and I'd need even more on half wave. Thanks - Paul
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4th Jul 2018, 2:30 pm | #28 |
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Re: Ferranti A1016 bluetooth project
Yes, half wave will be fine, say 6.3V RMS, that's nigh on 9V peak, less diode drop and using 1000uF of smoothing and you will have at least 8V to feed a 7805 regulator. Do put 10nF or so across the diode to stop switching noise.
A quick simulation at 50mA gives a minimum voltage of just over 7V, more than enough for a low drop out 7805 type of regulator. And a whole 1/2W extra from the transformer, no problem there either. |
4th Jul 2018, 3:22 pm | #29 |
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Re: Ferranti A1016 bluetooth project
Switch-on surge will be a second or so and unlikely to cause problems. It will prob be limited by the transformer winding rather than the esr of the cap.
Of course, go with whatever you are comfortable with, it’s your radio ! Ken |
5th Jul 2018, 9:40 am | #30 |
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Re: Ferranti A1016 bluetooth project
You are using full wave rectification? The trick here is to use Schottky diodes. A 1N5819 as an example has a forward voltage of <0.45V.
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5th Jul 2018, 9:49 am | #31 |
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Re: Ferranti A1016 bluetooth project
Yes I am using full wave (1N4001) components I had to hand but I may change these for Schottky diodes to get more head room even though the regulator seems to be coping ok - thanks for the heads up. I may also try 1/2 wave in light of other posts here to see if that works out ok. It's fun to refresh my basic electronics. Thanks to all ideas here! Paul
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7th Jul 2018, 10:22 am | #32 |
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Re: Ferranti A1016 bluetooth project
I'm now satisfied with how it works and with little impact on the original circuit. I couldn't get the 1/2 wave idea working (#22) as there was still the problem of the heater line being grounded to the sets signal ground and I didn't want to change that so I used a small 1:1 coupling transformer and it works a treat. I think it has given the set a useful technology update and I can now stream internet radio, phones and any other bluetooth source to the set simply by pressing the 'Gram' button on the set. All 3 radio bands work as before so I can still use them too. I will put a removable bluetooth symbol on the front panel glass as a talking point. Thanks for all who helped with suggestions. Paul
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7th Jul 2018, 12:20 pm | #33 |
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Re: Ferranti A1016 bluetooth project
Paul, glad you got it working, it is a good way to update a vintage set. I am curious though as to why a half wave rectifier did not work. This retains the original connection of the heater supply (one side grounded) and therefore the Bluetooth negative supply line and signal common grounded too. Perhaps a hum loop or excessive ripple caused the problems. I would have expected that “floating” the Bluetooth module off the sets ground would have caused more problems but clearly not, given the signal transformer.
I am just (technically) puzzled but great if your solution works. It does have the advantage of keeping the mains transformer balanced. Regds Ken |
9th Jul 2018, 11:06 am | #34 |
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Re: Ferranti A1016 bluetooth project
It goes something like this:- I am deriving a new DC supply (5V) from a heater winding, and that heater winding is connected to the sets chassis and signal ground rail in the set. In isolation this is fine to power my module, but between the ground (0V) of my new supply and the ground of the set it is effectively "modulated" by the 6.3V AC of the heater supply. If I connect my oscilloscope between my 0V and the sets chassis i "see" the heater supply AC. In other words, my 0V is at the heater potential at all times. When I first connected the o/p of my module to the gram i/p of the set it blew the module - in fact I saw a spark when I connected the signal screen to ground. ouch! RIP module. Take 2 and with a tiny little coupling transformer all seem happy.
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9th Jul 2018, 11:16 am | #35 |
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Re: Ferranti A1016 bluetooth project
There's a difference between a half wave rectifier and a full wave bridge rectifier, in your receiver and with no isolation a full wave bridge rectifier will blow something, a half wave rectifier won't.
Lawrence. |
9th Jul 2018, 11:33 am | #36 |
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Re: Ferranti A1016 bluetooth project
I tried it and got the same result. Perhaps with hindsight I needed to make sure I used the correct side of the heater winding for 0V? One side goes to chassis the other the heater chain. I didn't think about that as it's just A/C and so just connected a diode to one side...may have been the wrong side? Oh well I'm still living and learning.
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9th Jul 2018, 11:38 am | #37 |
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Re: Ferranti A1016 bluetooth project
Yes, rectifier connected to the wrong side from the sounds of it.
Lawrence. |
9th Jul 2018, 12:17 pm | #38 |
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Re: Ferranti A1016 bluetooth project
This thread may be useful info. for anyone contemplating such a conversion. I will stick with the full wave solution as the module load varies quite a lot and getting a stable supply wasn't achieved without significant smoothing (currently 660uF) and I didn't want to use even bigger smoothing cap. I am waiting for the Schottky diodes to arrive to see how that works out, hopefully improving my DC headroom and making the regulators job at bit easier. I'd like to try this conversion on one of my AC/DC sets with a dropper. Where to derive the supply? A future project.
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9th Jul 2018, 1:30 pm | #39 |
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Re: Ferranti A1016 bluetooth project
I guess I just don't understand but you have a working solution so well done. Schottky diodes should certainly help the voltage headroom.
Ken |
9th Jul 2018, 4:27 pm | #40 |
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Re: Ferranti A1016 bluetooth project
Thanks Ken. Looking at the attached circuit snippet, you can see the heater winding labelled (C) connects to C on the heater feed and is shown bridged across to the sets ground. I think it's important NOT to put the diode on that side. I haven't gone back and tried it on the (A) side but it seems likely it was the problem, as it should work on 1/2 wave as you say.
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