05-06-2011, 06:06 PM
Hi All,
I think that this is more or less complete now so I thought that it was about time the I wrote this one up and posted it on the forum.
This was the 2nd valve radio I bought and like all things it was left on the 'round to it' pile for a very long time before starting work on it. This was the condition as it arrived to me.
[attachment=1885][attachment=1886][attachment=1887]
The inside wasn't too bad although it had a crumbling mains dropper and the someone appears to cut the case to one of the IF units for some reason. It also had the full compliment of waxies!
[attachment=1888][attachment=1889]
An examination of the smoothing cap shows that an additional 8uF cap had been added to the 16uF side of the double cap and it was assumed that this was to deal with mains hum especially if this side of the cap was breaking down under load.
[attachment=1890]
Everything that could be cleaned was cleaned. The case was initially washed in soapy water and polished with Greygate No5. The chassis was spreaded with Car Pride Instant Valet (£1 a can from the Factory Shop) - this is foam cleaner that really appears to attack and dissolve the build up of old grease and the associated dust bunnies that have accumulated over many years! I also learned that this will dissolve bakelite too as I tried it on a small area inside the case. I was sweating that I had not caused too much damage but as it was a very small area inside its not noticable!
The dropper and smoothing cap was replaced with ones supplied by Rob T (thanks very mush for these) and the waxies were all replaced by axials obtained from Just Radios in Canada. There is much debate whether to change all waxies or just the ones that have failed. In this instance, I decided to replace them all.
[attachment=1893]
I replaced 'that cap' with an X2 275V cap - perhaps 275V is a bit near to the knuckle but its in now!
I had a great deal of problems getting this to work and for a while I though that perhaps I had reached my limit as a 'radio engineer' (ho ho - I should be that lucky to have this title) as I could get a simple DAC90a set to work. I spent several hours on the phone to Alan (Shaman) whose help was invaluable (thank you).
I discovered that I had connected the base of the UY41 rectifier valve through the R17 (the 150R dial lamp resistor) to the 250v side of the mains dropper which I'm sure could not have helped. Whilst talking to Alan on the phone I could smell burning only to see R15 smoking badly (as well as the new mains dropper - poo, what a pong). Also, I noted that the oscillator valve V1 (UCH42) needed replacing having tested the values of all of the valves using my Mk 1 Avo VCM tester think that I could have a faulty valve (the UL41 was spot on!!). I 'killed' a couple of UCH42 triodes when in my eagerness to test them I forgot to change the anode and screen volt values for testing the additional triode section using the A2 setting on my Mk1 VCM (the valves glowed very brightly and died very quickly too!!). Thanks to Brian C who can to the rescue with some replacements for me.
R17 was replaced with a new 3w wirewound resistor from Maplins and I ensured that the base of V5 rectifier valve was connected to the 210v side of the mains dropper.
[attachment=1892]
Finally, the tone cap C19 was replaced with a 390pF cap kindly supplied from David (Yorkie).
The radio appears to be working well although the dial lamps are very dim. I bought 10x 3.5v 200ma MES bulbs but there is not enough current to get these to light at all. Currently, the set has 6v 150ma bulbs in it that work and give a low but pleasing glow as it would have done when it was initially made (adds to the charm I suppose).
So its finished albeit it needs a replacement back cover as this one thing I do not have just yet!
Rob
[attachment=1894][attachment=1895]
I think that this is more or less complete now so I thought that it was about time the I wrote this one up and posted it on the forum.
This was the 2nd valve radio I bought and like all things it was left on the 'round to it' pile for a very long time before starting work on it. This was the condition as it arrived to me.
[attachment=1885][attachment=1886][attachment=1887]
The inside wasn't too bad although it had a crumbling mains dropper and the someone appears to cut the case to one of the IF units for some reason. It also had the full compliment of waxies!
[attachment=1888][attachment=1889]
An examination of the smoothing cap shows that an additional 8uF cap had been added to the 16uF side of the double cap and it was assumed that this was to deal with mains hum especially if this side of the cap was breaking down under load.
[attachment=1890]
Everything that could be cleaned was cleaned. The case was initially washed in soapy water and polished with Greygate No5. The chassis was spreaded with Car Pride Instant Valet (£1 a can from the Factory Shop) - this is foam cleaner that really appears to attack and dissolve the build up of old grease and the associated dust bunnies that have accumulated over many years! I also learned that this will dissolve bakelite too as I tried it on a small area inside the case. I was sweating that I had not caused too much damage but as it was a very small area inside its not noticable!
The dropper and smoothing cap was replaced with ones supplied by Rob T (thanks very mush for these) and the waxies were all replaced by axials obtained from Just Radios in Canada. There is much debate whether to change all waxies or just the ones that have failed. In this instance, I decided to replace them all.
[attachment=1893]
I replaced 'that cap' with an X2 275V cap - perhaps 275V is a bit near to the knuckle but its in now!
I had a great deal of problems getting this to work and for a while I though that perhaps I had reached my limit as a 'radio engineer' (ho ho - I should be that lucky to have this title) as I could get a simple DAC90a set to work. I spent several hours on the phone to Alan (Shaman) whose help was invaluable (thank you).
I discovered that I had connected the base of the UY41 rectifier valve through the R17 (the 150R dial lamp resistor) to the 250v side of the mains dropper which I'm sure could not have helped. Whilst talking to Alan on the phone I could smell burning only to see R15 smoking badly (as well as the new mains dropper - poo, what a pong). Also, I noted that the oscillator valve V1 (UCH42) needed replacing having tested the values of all of the valves using my Mk 1 Avo VCM tester think that I could have a faulty valve (the UL41 was spot on!!). I 'killed' a couple of UCH42 triodes when in my eagerness to test them I forgot to change the anode and screen volt values for testing the additional triode section using the A2 setting on my Mk1 VCM (the valves glowed very brightly and died very quickly too!!). Thanks to Brian C who can to the rescue with some replacements for me.
R17 was replaced with a new 3w wirewound resistor from Maplins and I ensured that the base of V5 rectifier valve was connected to the 210v side of the mains dropper.
[attachment=1892]
Finally, the tone cap C19 was replaced with a 390pF cap kindly supplied from David (Yorkie).
The radio appears to be working well although the dial lamps are very dim. I bought 10x 3.5v 200ma MES bulbs but there is not enough current to get these to light at all. Currently, the set has 6v 150ma bulbs in it that work and give a low but pleasing glow as it would have done when it was initially made (adds to the charm I suppose).
So its finished albeit it needs a replacement back cover as this one thing I do not have just yet!
Rob
[attachment=1894][attachment=1895]
if all else fails...read the instructions!
