Cossor 500 poor on LW - Page 2 - UK Vintage Radio Repair and Restoration Discussion Forum

kalee20 · 10th Sep 2009, 1:00 pm

I'd be surprised too that SW didn't work properly when it left the factory - except that that's the conclusion I came to with mine also!

Mine works at the high-frequency end of the SW band, but oscillator amplitude drops like a stone as you tune across the band (tuning capacitor becoming more fully meshed).

MW and LW performance are satisfactory though - except that RF and oscillator circuits don't track particularly well on MW. And there are design inelegancies I could comment on, like the tone control inside the negative feedback loop, which consequently tries to nullify the effect of the control... at least it's a well spaced-out layout, not cramped, no hot spots, and sounds quite good!

YT2095UK · 14th Sep 2009, 7:00 pm

I came across my old 1950`s valve Sig-gen and wondered what would happen if I clamped the output to the longwire in lead, turns out it Can pick up a signal below 8MHz, but not Much below it, so I clamped it on Directly to the wire conductor and Wow! I can get a signal down to about 6.5.
And I can use the sig-gen to tune channels in (prabably like some sort of BFO?).
so after I had a play (it was kinda fun!), I disconnected and got a belt of the Sig-gen output and the antenna going into the radio, not enough to spark, but Easily feelable and uncomfortable to hold (stings!).
now the sig-gen is all switched off, I`m still listening to radio Bulgaria just below the 7MHz mark on the dial, And held it there for a while now.
coincidence and the skip is just right? or did that uncomfortably high voltage "lubricate" aging parts of the radio?
the only other thing that`s changed since trying SW the last time was changing "That" capacitor, and I can`t see how the Audio/Out side of things would have any effect?
I can tune way off that end and back again and it`s still working!

anyone?

YT2095UK · 20th Nov 2009, 12:17 pm

Update:

after my extraordinary good fortune finding the fault on my Ekco A144, I thought I`d give my old Cossor 520 another go on the bench and try an fix the problems (outlined in this thread) once and for all.
Cleaning the Wave changer switch brought the SW back to 100% in no uncertain terms, leaving the LW still only just about able to pick up R4 with plenty interferance and a whistle when off channel.
I remember reading a Pamphlet on I.F that Station X provided about a week ago and worked out that it Must be Antenna coupling coil(s), so I had a look down inside the little tube that holds these coils in the day light and saw a broken wire on L4, after a continuity check to establish which end wasn`t connected (it`s not made very clear with these sets), it`s now repaired and working perfectly as well

so now All my radios are working perfectly... time to get some More in I think

10th Sep 2009, 1:00 pm	#21
kalee20 Dekatron Join Date: Feb 2007 Location: Lynton, N. Devon, UK. Posts: 7,082	Re: Cossor 500 poor on LW I'd be surprised too that SW didn't work properly when it left the factory - except that that's the conclusion I came to with mine also! Mine works at the high-frequency end of the SW band, but oscillator amplitude drops like a stone as you tune across the band (tuning capacitor becoming more fully meshed). MW and LW performance are satisfactory though - except that RF and oscillator circuits don't track particularly well on MW. And there are design inelegancies I could comment on, like the tone control inside the negative feedback loop, which consequently tries to nullify the effect of the control... at least it's a well spaced-out layout, not cramped, no hot spots, and sounds quite good!

14th Sep 2009, 7:00 pm	#22
YT2095UK Retired Dormant Member Join Date: Sep 2009 Posts: 487	Re: Cossor 500 poor on LW I came across my old 1950`s valve Sig-gen and wondered what would happen if I clamped the output to the longwire in lead, turns out it Can pick up a signal below 8MHz, but not Much below it, so I clamped it on Directly to the wire conductor and Wow! I can get a signal down to about 6.5. And I can use the sig-gen to tune channels in (prabably like some sort of BFO?). so after I had a play (it was kinda fun!), I disconnected and got a belt of the Sig-gen output and the antenna going into the radio, not enough to spark, but Easily feelable and uncomfortable to hold (stings!). now the sig-gen is all switched off, I`m still listening to radio Bulgaria just below the 7MHz mark on the dial, And held it there for a while now. coincidence and the skip is just right? or did that uncomfortably high voltage "lubricate" aging parts of the radio? the only other thing that`s changed since trying SW the last time was changing "That" capacitor, and I can`t see how the Audio/Out side of things would have any effect? I can tune way off that end and back again and it`s still working! anyone?

20th Nov 2009, 12:17 pm	#23
YT2095UK Retired Dormant Member Join Date: Sep 2009 Posts: 487	Re: Cossor 500 poor on LW Update: after my extraordinary good fortune finding the fault on my Ekco A144, I thought I`d give my old Cossor 520 another go on the bench and try an fix the problems (outlined in this thread) once and for all. Cleaning the Wave changer switch brought the SW back to 100% in no uncertain terms, leaving the LW still only just about able to pick up R4 with plenty interferance and a whistle when off channel. I remember reading a Pamphlet on I.F that Station X provided about a week ago and worked out that it Must be Antenna coupling coil(s), so I had a look down inside the little tube that holds these coils in the day light and saw a broken wire on L4, after a continuity check to establish which end wasn`t connected (it`s not made very clear with these sets), it`s now repaired and working perfectly as well so now All my radios are working perfectly... time to get some More in I think