21-04-2012, 02:31 PM
I thought I'd provide more detail of my work to restore this set. My original post here http://www.golbornevintageradio.co.uk/fo...p?tid=2029
I removed the chassis from the cabinet yesterday. This involves removing the four soldered connections to the speaker cross-overs, the main speaker, four bolts underneath and of course the knobs.
The chassis was given a quick clean to get rid of the dust while working on it and the cabinet a rub over with scratch cover, basically 'cause I wanted to see how shiny it might be
I then brought it back inside to start work on the electrical side. The person I bought this from had applied power and told me it had made a noise. I've no idea why people do this, I guess ignorance. I was showing Al the other day a true rust bucket of a comms receiver that someone had just plugged in. The thing looked like it had been sitting outside under a hedge for 30 years!
The first item to be replaced was the AF coupling capacitor. I then stuck the set on the lamp limiter and turned on. The bulb dimmed and stayed dim, valve heaters came on and hiss came from the speakers. However, from the sound it was clear the smoothers needed reforming.
I connected one side at a time of the 2 x 50uF electrolytic can to my reformer and while the current leakage went down to 5ma over 15 minutes, it then started to rise to 8ma rapidly and stay there. The reformer was switched off, I waited a while though the can wasn't at all warm to the touch and tried again only to get the same result. 5ma for a 50uF can is not too bad but what worried me was the quick climb back up.
By this time it was 1am so thinking the can may just be getting warm enough to stop the reforming process I closed down and started again this morning. Cold checks with the Megger at 250v showed a paltry resistance on one side of the can, the other side was better. A check on ESR using 'The Yorkie' showed 'Good' on one side and well into the red on the other. As a comparison my commerical Peak ESR meter shows 0.30 ohms on the 'good' side and 'low capacitance/open circuit probes' on the other 50uF. So, it looks like I'll be adding new electrolytics then...hmmmm.
Andrew
I removed the chassis from the cabinet yesterday. This involves removing the four soldered connections to the speaker cross-overs, the main speaker, four bolts underneath and of course the knobs.
The chassis was given a quick clean to get rid of the dust while working on it and the cabinet a rub over with scratch cover, basically 'cause I wanted to see how shiny it might be
I then brought it back inside to start work on the electrical side. The person I bought this from had applied power and told me it had made a noise. I've no idea why people do this, I guess ignorance. I was showing Al the other day a true rust bucket of a comms receiver that someone had just plugged in. The thing looked like it had been sitting outside under a hedge for 30 years!
The first item to be replaced was the AF coupling capacitor. I then stuck the set on the lamp limiter and turned on. The bulb dimmed and stayed dim, valve heaters came on and hiss came from the speakers. However, from the sound it was clear the smoothers needed reforming.
I connected one side at a time of the 2 x 50uF electrolytic can to my reformer and while the current leakage went down to 5ma over 15 minutes, it then started to rise to 8ma rapidly and stay there. The reformer was switched off, I waited a while though the can wasn't at all warm to the touch and tried again only to get the same result. 5ma for a 50uF can is not too bad but what worried me was the quick climb back up.
By this time it was 1am so thinking the can may just be getting warm enough to stop the reforming process I closed down and started again this morning. Cold checks with the Megger at 250v showed a paltry resistance on one side of the can, the other side was better. A check on ESR using 'The Yorkie' showed 'Good' on one side and well into the red on the other. As a comparison my commerical Peak ESR meter shows 0.30 ohms on the 'good' side and 'low capacitance/open circuit probes' on the other 50uF. So, it looks like I'll be adding new electrolytics then...hmmmm.
Andrew
