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 > Specific Vintage Equipment > Vintage Radio (domestic)

Notices

Vintage Radio (domestic) Domestic vintage radio (wireless) receivers only.

Closed Thread
 
Thread Tools
Old 15th May 2019, 10:09 pm   #1
Keith
Heptode
 
Keith's Avatar
 
Join Date: Jan 2003
Location: Tewkesbury, Gloucestershire, UK.
Posts: 690
Default Fenman II VHF tuning hysteresis

Owners of this set will know that the VHF permeability tuning is implemented by a spring loaded plate in contact with a cam on the tuning shaft. Despite numerous attempts at cleaning/re-greasing, mine has always suffered from hysteresis (i.e. backlash), making tuning difficult. I wonder if other owners have experienced this and if a fix has been found.
__________________
Keith Yates - G3XGW
VMARS & BVWS member http://www.tibblestone.com/oldradios/Old_Radios.htm
Keith is offline  
Old 19th May 2019, 4:22 pm   #2
Keith
Heptode
 
Keith's Avatar
 
Join Date: Jan 2003
Location: Tewkesbury, Gloucestershire, UK.
Posts: 690
Default Re: Fenman II VHF tuning hysteresis

Looks like I'm the only one experiencing this problem!
__________________
Keith Yates - G3XGW
VMARS & BVWS member http://www.tibblestone.com/oldradios/Old_Radios.htm
Keith is offline  
Old 19th May 2019, 7:09 pm   #3
Reelman
Octode
 
Reelman's Avatar
 
Join Date: Aug 2008
Location: Rotherham, South Yorkshire, UK.
Posts: 1,701
Default Re: Fenman II VHF tuning hysteresis

Just noticed your thread Keith, I also have noticed the same issue. I bought the set as "restored" and assumed that the drive cord was just a bit loose. I didn't realise that it was permeability tuning. I find your have to go past the tuned spot and then back up, a bit of a nuisance.
Peter
Reelman is offline  
Old 19th May 2019, 7:51 pm   #4
Radio_Dave
Nonode
 
Radio_Dave's Avatar
 
Join Date: Jun 2004
Location: Norwich, Norfolk, UK.
Posts: 2,543
Default Re: Fenman II VHF tuning hysteresis

All of mine do the same. One in particular is really bad and although it's never bothered me enough to investigate I've always suspected it was the cores binding inside the permeable tuner?


Regards
David
Radio_Dave is offline  
Old 19th May 2019, 8:07 pm   #5
Nickthedentist
Dekatron
 
Nickthedentist's Avatar
 
Join Date: Jan 2005
Location: Oxford, UK.
Posts: 17,820
Default Re: Fenman II VHF tuning hysteresis

Mine too! Often little happens when the tuning knob is rotated, then "clunk!" and something in the permeability tuner frees itself and normal service is resumed.

Not got to the bottom of it yet...
Nickthedentist is online now  
Old 26th May 2019, 3:33 pm   #6
Takapuna
Tetrode
 
Join Date: Jul 2009
Location: Derby, Derbyshire, UK.
Posts: 57
Default Re: Fenman II VHF tuning hysteresis

It must be a design feature! The cam follows the tuning knob without any backlash and the plate to which the cores are attached appears to do the same but I still have to "home-in" on the best tuning point.
Holding the plate against the spring at its high travel limit exposes the top end of all cores and they are a very loose fit inside their formers in my radio. A gentle flex of the rods to which they attach shows the cores can be moved across the inner diameter of the coil formers.

Phil.
Takapuna is offline  
Old 26th May 2019, 4:52 pm   #7
Keith
Heptode
 
Keith's Avatar
 
Join Date: Jan 2003
Location: Tewkesbury, Gloucestershire, UK.
Posts: 690
Default Re: Fenman II VHF tuning hysteresis

Thanks for your replies. I can't see any reason why the plate shouldn't follow the cam. In fact I have moved the spring mounting to give more pressure, without any effect. I hadn't thought of the possibility of the cores moving "across" the coil former but this would presumably affect the inductance, so may be the mechanism. I shall investigate further, as the problem detracts from what is otherwise an excellent receiver.
__________________
Keith Yates - G3XGW
VMARS & BVWS member http://www.tibblestone.com/oldradios/Old_Radios.htm

Last edited by Keith; 26th May 2019 at 4:54 pm. Reason: Punctuation
Keith is offline  
Closed Thread

Thread Tools



All times are GMT +1. The time now is 5:23 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.