UK Vintage Radio Repair and Restoration Powered By Google Custom Search Vintage Radio and TV Service Data

Go Back   UK Vintage Radio Repair and Restoration Discussion Forum > General Vintage Technology > General Vintage Technology Discussions

Notices

General Vintage Technology Discussions For general discussions about vintage radio and other vintage electronics etc.

Closed Thread
 
Thread Tools
Old 10th Feb 2020, 10:42 pm   #1
Aub
Nonode
 
Aub's Avatar
 
Join Date: Mar 2005
Location: Nuneaton, Warwickshire, UK.
Posts: 2,034
Default What were Transfilters?

Hi all,

I've just remembered something I'd forgotten all about. In ( I think )Practical Wireless, in 1967, was a project to build a "Transfilter Portable". What were they? An IFT with an inbuilt filter?

Cheers

Aub
__________________
Life's a long song, but the tune ends too soon for us all.
Aub is offline  
Old 10th Feb 2020, 10:47 pm   #2
barrymagrec
Octode
 
Join Date: Dec 2017
Location: Morden, Surrey, UK.
Posts: 1,552
Default Re: What were Transfilters?

I have a vague memory that they were ceramic filters that could be used in place of tuned IF transformers - could be wrong though.
barrymagrec is offline  
Old 10th Feb 2020, 10:52 pm   #3
Aub
Nonode
 
Aub's Avatar
 
Join Date: Mar 2005
Location: Nuneaton, Warwickshire, UK.
Posts: 2,034
Default Re: What were Transfilters?

Ah ok. Thanks. That sounds likely.

Cheers
Aub
__________________
Life's a long song, but the tune ends too soon for us all.
Aub is offline  
Old 11th Feb 2020, 12:46 am   #4
Radio Wrangler
Moderator
 
Radio Wrangler's Avatar
 
Join Date: Mar 2012
Location: Fife, Scotland, UK.
Posts: 22,800
Default Re: What were Transfilters?

They were early piezo-acoustic ceramic filters made by Brush-Clevite. I think it was their brand-name. Makes them sound a bit grander than they were. Toko and Murata took over the market.

David
__________________
Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done
Radio Wrangler is offline  
Old 11th Feb 2020, 1:32 am   #5
Nuvistor
Dekatron
 
Nuvistor's Avatar
 
Join Date: Aug 2013
Location: Wigan, Greater Manchester, UK.
Posts: 9,427
Default Re: What were Transfilters?

Enjoy.
https://www.americanradiohistory.com...PW-1967-07.pdf
__________________
Frank
Nuvistor is offline  
Old 11th Feb 2020, 9:33 am   #6
Aub
Nonode
 
Aub's Avatar
 
Join Date: Mar 2005
Location: Nuneaton, Warwickshire, UK.
Posts: 2,034
Default Re: What were Transfilters?

Thanks Frank. I wondered if someone would do that. Love those plastic covered batteries.

Aub
__________________
Life's a long song, but the tune ends too soon for us all.
Aub is offline  
Old 11th Feb 2020, 10:14 am   #7
Nuvistor
Dekatron
 
Nuvistor's Avatar
 
Join Date: Aug 2013
Location: Wigan, Greater Manchester, UK.
Posts: 9,427
Default Re: What were Transfilters?

They improved selectivity by using a bypass filter in the emitter circuit of an IF amp instead of just a capacitor. I understand how that works, just never thought about it before. Or if I have seen it I have forgotten all about it which is very possible.
__________________
Frank
Nuvistor is offline  
Old 11th Feb 2020, 3:32 pm   #8
G6Tanuki
Dekatron
 
G6Tanuki's Avatar
 
Join Date: Apr 2012
Location: Wiltshire, UK.
Posts: 13,953
Default Re: What were Transfilters?

There were at least two styles of 'Transfilter' - one was a 2-terminal device which replaced the normal emitter-resistor-bypass-capacitor. The idea being that at the series-resonant frequency of the transfilter the emitter was essentially grounded at the intermediate frequency so gicing good gain, but at other frequencies when the Transfilter wasn't resonant the gain of the transistor was reduced by the degenerative-feedback from the emitter resistor.

The other type was a 3-terminal device used as a replacement for the 'traditional' IFT between the collector of an IF amp and the base of the next-amp-in-the-chain.

Their big selling-point to the receiver-manufacturers was that - unlike wound-component IFTs, there was no alignment needed, so cutting production-costs.

Several Heathkit receivers of the 1960s used them.

Attached is a section of the schematic for the GC1-A "Mohican' that shows both the inter-stage-coupling Transfilters and the emitter-resistor-bypass variety.
Attached Thumbnails
Click image for larger version

Name:	heath.jpg
Views:	111
Size:	15.9 KB
ID:	198809  
G6Tanuki is online now  
Old 11th Feb 2020, 4:14 pm   #9
'LIVEWIRE?'
Rest in Peace
 
'LIVEWIRE?''s Avatar
 
Join Date: Mar 2006
Location: N.W. Oxfordshire(Chipping Norton)
Posts: 7,306
Default Re: What were Transfilters?

Those three-terminal filters wiere used by Blaupunkt (and possibly others) in car radios both at AM and FM(VHF). They were made in 455, 460, 465, and 470kHz versions for AM, and nominally 10.7Mhz (which could be between, IIRC 10.65 & 10.75Mhz) for VHF. If replacing a ceramic filter (They did fail occasionally), obviously one of the correct frequency had to be used.. I may still have some somewhere)
'LIVEWIRE?' is offline  
Old 11th Feb 2020, 5:32 pm   #10
radioman
Heptode
 
radioman's Avatar
 
Join Date: Apr 2003
Location: Ayr, Ayrshire, UK.
Posts: 630
Default Re: What were Transfilters?

Yes, here's some pictures of one I repaired from a Mohican - it had become 'intermittent' and responded to cleaning of the disc and contacts with IPA then reassembly with the disc rotated by 90°.

Andy
Attached Thumbnails
Click image for larger version

Name:	Transfilter1.jpg
Views:	103
Size:	43.8 KB
ID:	198819   Click image for larger version

Name:	Transfilter2.jpg
Views:	110
Size:	47.4 KB
ID:	198820   Click image for larger version

Name:	Transfilter3.jpg
Views:	99
Size:	43.9 KB
ID:	198821  
__________________
G-QRP #12697
radioman is online now  
Closed Thread

Thread Tools



All times are GMT +1. The time now is 10:00 pm.


All information and advice on this forum is subject to the WARNING AND DISCLAIMER located at https://www.vintage-radio.net/rules.html.
Failure to heed this warning may result in death or serious injury to yourself and/or others.


Powered by vBulletin®
Copyright ©2000 - 2024, vBulletin Solutions, Inc.
Copyright ©2002 - 2023, Paul Stenning.