Having owned my FL2000B for around 8 years and used it on rare occasions but more so when I had the FT990 to get a bit of power out when needed, I decide it was time to give it its monthly warm up and also give it a good clean as it was pretty dusty inside the cabinet.
Once unplugged and after removing the top cover I decided to delve deeper and check out the tubes. So I removed the PA cage and released the safety interlock switch and proceeded to clean. All complete I put everything back together making sure the safety interlock was back in place. I turned on the amp and let it warm up and then there was a loud bang…………..Oops something was not right!!
Well of course I inspected fearing the worse that the tubes and everything else had blown up. Further investigation showed the main fuse had blown and that the parallel parasitic choke containing two resistors over one of the 572B valves were both burnt and also a resistor on the safety interlock switch had also gone.
The burnt out resistor on the safety interlock switch
Thankfully from correspondence with fellow hams from my local club and on QRZ.com agreed that it was unlikely I had damaged the tubes. So the first thing to do is order some new resistors which I have done for the parasitic choke but am still trying to find out what the value is of the resistor on the safety interlock switch is. Of course I may well have damaged other parts but there is nothing visible to see and only further testing once I have the new resistors will show anything further.
One tube removed and the offending parallel resistors and safety lock removed
Further updates will follow as I continue with the repair, I have to admit although I was devastated when it went bang, I'm actually quite in to fixing it as I'm learning loads about old valve equipment!