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Homebrew Equipment A place to show, design and discuss the weird and wonderful electronic creations from the hands of individual members. |
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27th Apr 2023, 4:46 pm | #1 |
Tetrode
Join Date: Mar 2022
Location: Chippenham, Wiltshire, UK.
Posts: 71
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MBFB or BBFM
Some years ago I built an Octal superhet 3 x EF39, ECH35, EBC33, 6V6 loosely based on an article in RC of September 1948. The original design used hand made coils for which I substituted a set of Wearite P3 series coils (14 - 47 metres) as I was only really interested in this range, it acquits itself pretty well, is stable (even with EF39s!) and boringly reliable so has seen much use.
I have a shed load of Wearites covering 12 - 2000 metres and before either I shuffle off or am radio dies completely I thought it would be nice to install a switch and add a few more ranges. As I am sure you all know suitable, shafted switches with separate wafers offering sufficient shafting to install screens are like hens teeth, so I planned to bite the bullet and order some shafting and wafers from RS or Farnell. That is when my Catch 22 moment arose, I have always assumed RF switching needs to be MBFB, but the NFS Controls wafers offered by RS and Farnell are (at least in the range I need) BBFM. Put simply does it matter whether I use MBFB or BBFM, I can't think of anything likely to be an issue, but I am not a technically qualified person as many of you are, just an ancient bodger, so your thoughts would be very welcome before I shell out my cash. As always, many thanks in anticipation of your help. |
27th Apr 2023, 4:55 pm | #2 |
Dekatron
Join Date: Apr 2012
Location: Wiltshire, UK.
Posts: 13,998
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Re: MBFB or BBFM
I wouldn't worry. Have used both options in the past.
My bigger issue has been the one of wanting to short-circuit the unused coils in a coilpack to stop stray resonances of the unused coils causing 'suck out' of the wanted signals in the active coils. Finding wafer-switches with the necessary shorting-sectors is nowadays not easy.
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27th Apr 2023, 7:35 pm | #3 |
Dekatron
Join Date: Jan 2004
Location: Newcastle upon Tyne, Tyne & Wear, UK.
Posts: 8,194
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Re: MBFB or BBFM
Hi Gents, keep a look out for the Plessey Switch Kit, occasionally seen on ebay and invaluable for this as a custom shorting wafer can be fitted to the rear of each rotor.
It may be possible to find suitable wafers if you have a good spares box of stuff salvaged from old coilpacks The switch mech should not be a problem and 6BA studding is easily bought for the wafer supports Ed |
28th Apr 2023, 12:01 am | #4 | |
Moderator
Join Date: Mar 2012
Location: Fife, Scotland, UK.
Posts: 22,876
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Re: MBFB or BBFM
Quote:
Getting shorting discs is pretty much impossible, inserted screens may also be needed but are more within reach of DIY. David
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30th Apr 2023, 2:01 pm | #5 |
Tetrode
Join Date: Mar 2022
Location: Chippenham, Wiltshire, UK.
Posts: 71
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Re: MBFB or BBFM
Thank you for your replies, order placed with RS for wafers, spacers, inter wafer screens and a switch assembly, had to put the dog on the streets with a begging bowl to pay for it, but looking forward to the project nonetheless.
Best wishes to you and thanks again. |