Tweet
I was sent this amplifier from a person in the UK that as he wasn't confident enough to get this amplifier going, I undertook the repair at the cost of parts only. It is too valuble to get destroyed or lost.
The story was that it went wrong back in the early 70s and was stored away in the loft until a few weeks ago.
I suggested it was not powered up as the electrolitycs will need reforming. That was a slow process. I removed the valves except the rectifier, checked for any electrical issues and then fitted a 100k resistor between the output of the EZ80 rectifier and the first tank capacitor. This is very important as it stops any inrush of current that will damage any old electrolyte until it has been reformed, a lot like an old lead acid battery with a similar process but usually more success with electrolitycs.
The whole process took about 24hours before the leakage current was reduced to uAmps and then I check and replace the faulty components.
There was a few components that were out of tollerance and were replaced. The original fault was a faulty EL84. Intermittant Screen grid short to Supressor grid. Not that unusual but the valve looked original, so I forgive Mr Mullard.
I enclose a few photographs for interest and still carry out 'hospital jobs' at cost. Another interesting part of our history.
Thank you for looking and hope you find this interesting.
The story was that it went wrong back in the early 70s and was stored away in the loft until a few weeks ago.
I suggested it was not powered up as the electrolitycs will need reforming. That was a slow process. I removed the valves except the rectifier, checked for any electrical issues and then fitted a 100k resistor between the output of the EZ80 rectifier and the first tank capacitor. This is very important as it stops any inrush of current that will damage any old electrolyte until it has been reformed, a lot like an old lead acid battery with a similar process but usually more success with electrolitycs.
The whole process took about 24hours before the leakage current was reduced to uAmps and then I check and replace the faulty components.
There was a few components that were out of tollerance and were replaced. The original fault was a faulty EL84. Intermittant Screen grid short to Supressor grid. Not that unusual but the valve looked original, so I forgive Mr Mullard.
I enclose a few photographs for interest and still carry out 'hospital jobs' at cost. Another interesting part of our history.
Thank you for looking and hope you find this interesting.
Attached Files
Comment