Simple stable triode BFO - UK Vintage Radio Repair and Restoration Discussion Forum

rubicon · 17th Mar 2023, 1:53 am

I have not seen this before, maybe unique, thort to pass it on.
Developed this to use the triode section of the ECH81 product detector in my Deltahet.
Any triode will work, The .01 anode cap is to isolate the HT from the resonator, they hate voltage gradients. One caveat, the filter will oscillate about 5kC above the nominal, use a 450 kC to get 455, a 455 will resonate at 460. Small freq changes , as in very small can be coaxed by fiddling either resistor values or capacitor values. All the 3 terminal ceramic filters I tried worked similarly.
Output can be taken from anode or grid.

Radio Wrangler · 17th Mar 2023, 3:59 am

There were ceramic resonators made specifically for BFO/CIO use. They're fairly stable and a lot more pullable than quartz. Construction/applications articles appeared in the usual radio magazines in the 1980s.

David

rubicon · 17th Mar 2023, 4:31 am

These resonators are designed for use in low Z SS circuitry, never seen them used with valves, but maybe im sheltered. My attempts to find 455kc quartz at reasonable prices failed. To build vacuum state projects is really getting quite difficult now, and does require some innovative thinking....

Radio Wrangler · 17th Mar 2023, 10:51 am

An impedance transforming network would likely be needed and that would put back in the parts that the ceramic device was replacing. But if letting one modern, out-of-period component in, then you might as well do a transistor BFO.

David

rubicon · 17th Mar 2023, 11:32 am

A TRANSISTOR? Heresy. Using a ceramic filter is bad enough, but a semiconductor?

Jon_G4MDC · 17th Mar 2023, 11:46 am

Murata CSB430 is only 2 terminal but it's drawn showing 3.

Is it perhaps a ceramic filter of some sort and that is why it is 3 terminal?

trh01uk · 17th Mar 2023, 12:50 pm

Quote:

Originally Posted by Jon_G4MDC

Murata CSB430 is only 2 terminal but it's drawn showing 3.

Is it perhaps a ceramic filter of some sort and that is why it is 3 terminal?

Looks like it is a filter since the OP said ".All the 3 terminal ceramic filters I tried worked similarly"

Richard

Radio Wrangler · 17th Mar 2023, 6:47 pm

Measure capacitance from the signal pins to the (centre) earth pin. Measure C from signal pin to signal pin.

This will sort out whether you have a single resonator with a screen, or whether you have a two-pole filter with commoned ground electrodes.

Transistor technology was quite old by the time ceramic filters came to prominence.

David

rubicon · 17th Mar 2023, 10:28 pm

Yes, these are ceramic FILTERS , most older cheap single chip AM/FM transistor radios use these, the signal enters one side, exits the other, the center pin then grounded. These are marked CSBxxx, CFSxxx, CFUxxx , SFUxxx etc, depending on manufacturer, where xxx is 400, 450, 455, 460, 470, or 500, they all appear to work the same and all oscillate happily as above.

rubicon · 17th Mar 2023, 10:37 pm

https://www.aliexpress.com/item/3301...d=XdQpF99yzWWr

rubicon · 17th Mar 2023, 10:39 pm

And, if I read that correct, 50 will cost only a few of your british pounds...

17th Mar 2023, 1:53 am	#1
rubicon Triode Join Date: Mar 2017 Location: Greymouth, New Zealand. Posts: 15	Simple stable triode BFO I have not seen this before, maybe unique, thort to pass it on. Developed this to use the triode section of the ECH81 product detector in my Deltahet. Any triode will work, The .01 anode cap is to isolate the HT from the resonator, they hate voltage gradients. One caveat, the filter will oscillate about 5kC above the nominal, use a 450 kC to get 455, a 455 will resonate at 460. Small freq changes , as in very small can be coaxed by fiddling either resistor values or capacitor values. All the 3 terminal ceramic filters I tried worked similarly. Output can be taken from anode or grid. Attached Thumbnails

17th Mar 2023, 3:59 am	#2
Radio Wrangler Moderator Join Date: Mar 2012 Location: Fife, Scotland, UK. Posts: 22,874	Re: Simple stable triode BFO There were ceramic resonators made specifically for BFO/CIO use. They're fairly stable and a lot more pullable than quartz. Construction/applications articles appeared in the usual radio magazines in the 1980s. David __________________ Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done

17th Mar 2023, 4:31 am	#3
rubicon Triode Join Date: Mar 2017 Location: Greymouth, New Zealand. Posts: 15	Re: Simple stable triode BFO These resonators are designed for use in low Z SS circuitry, never seen them used with valves, but maybe im sheltered. My attempts to find 455kc quartz at reasonable prices failed. To build vacuum state projects is really getting quite difficult now, and does require some innovative thinking....

17th Mar 2023, 10:51 am	#4
Radio Wrangler Moderator Join Date: Mar 2012 Location: Fife, Scotland, UK. Posts: 22,874	Re: Simple stable triode BFO An impedance transforming network would likely be needed and that would put back in the parts that the ceramic device was replacing. But if letting one modern, out-of-period component in, then you might as well do a transistor BFO. David __________________ Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done

17th Mar 2023, 11:32 am	#5
rubicon Triode Join Date: Mar 2017 Location: Greymouth, New Zealand. Posts: 15	Re: Simple stable triode BFO A TRANSISTOR? Heresy. Using a ceramic filter is bad enough, but a semiconductor?

17th Mar 2023, 11:46 am	#6
Jon_G4MDC Nonode Join Date: Nov 2015 Location: Welwyn Garden City, Hertfordshire, UK. Posts: 2,015	Re: Simple stable triode BFO Murata CSB430 is only 2 terminal but it's drawn showing 3. Is it perhaps a ceramic filter of some sort and that is why it is 3 terminal? Attached Thumbnails Last edited by Jon_G4MDC; 17th Mar 2023 at 11:52 am. Reason: add data

17th Mar 2023, 6:47 pm	#8
Radio Wrangler Moderator Join Date: Mar 2012 Location: Fife, Scotland, UK. Posts: 22,874	Re: Simple stable triode BFO Measure capacitance from the signal pins to the (centre) earth pin. Measure C from signal pin to signal pin. This will sort out whether you have a single resonator with a screen, or whether you have a two-pole filter with commoned ground electrodes. Transistor technology was quite old by the time ceramic filters came to prominence. David __________________ Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done

17th Mar 2023, 10:28 pm	#9
rubicon Triode Join Date: Mar 2017 Location: Greymouth, New Zealand. Posts: 15	Re: Simple stable triode BFO Yes, these are ceramic FILTERS , most older cheap single chip AM/FM transistor radios use these, the signal enters one side, exits the other, the center pin then grounded. These are marked CSBxxx, CFSxxx, CFUxxx , SFUxxx etc, depending on manufacturer, where xxx is 400, 450, 455, 460, 470, or 500, they all appear to work the same and all oscillate happily as above.

17th Mar 2023, 10:37 pm	#10
rubicon Triode Join Date: Mar 2017 Location: Greymouth, New Zealand. Posts: 15	Re: Simple stable triode BFO https://www.aliexpress.com/item/3301...d=XdQpF99yzWWr

17th Mar 2023, 10:39 pm	#11
rubicon Triode Join Date: Mar 2017 Location: Greymouth, New Zealand. Posts: 15	Re: Simple stable triode BFO And, if I read that correct, 50 will cost only a few of your british pounds...