29-06-2013, 10:50 PM
Back on the job at long last.
I hate leaving things because no matter how many Pictures I take and Notes I write it still takes time to catch up.
Anyway, everything looked OK so switch on, wait 90 seconds, and ...... nothing. What now? A quick poke round with the AVO showed no ht, and lo, two of the HT fuses were blown. How's that happened? Don't know, but replacing them brought it back to life as before with a bright little lissajou figure on the screen. So far so good.
Having pondered on the problem during the gap I decided to change my mind and work backwards. After all, that's what I do with Radios. So, I applied a nice big Sine Wave from my trusty Advance 81A to the X Amplifier and was rewarded with a stretched out figure on the screen. Why was it like that? It looked supsiciously like hum, and my Tek 475 confirmed it. So where was it coming from? I'd changed all the main Electrolytics and most of the Supplies are regulated. A quick poke around showed that the +150v was down at about 80v and there was 5v of hum on it. Now I'd been here before, and it turned out to be dirty valve pins. Sure enough, cleaning the pins of V607 fixed it. I then decided, rashly perhaps, that I should have cleaned all the valve pins to start with, so I did. Switch on again and the +150v says 80v. This was getting a bit wearing. So, what's on the 150v line? Easy answer, an ancient Plessey double Electrolytic - 8 + 8. Must be them, mustn't it? Tacking a spare across them made not one iota of difference. Now what? While poking about with an AVO I managed to get a bang off the aforementioned Electrolytic and no amount of valve wiggling and cleaning would get the 150v back. Next candidate was the 2M2 Anode load, which indeed measured about 2M7, as did the one in the +300v circuit, but changing them made no difference. All the other Resistors measured OK. In desperation I also changed a couple of Hunts lurking in there, but to no avail.
After a lot of pondering and measuring I swapped the ECC83s - V606 and V607. That got the +150v back but killed the +300v. Not good. Later on I had a look on ebay for ECC83s. There's strange phrases like 'Blackburn Code', 'Square Getter', 'Yellow Print' and 'Matched Pair', all of which seem to multply the prospective price by about 50. I was sitting there in a state of gloom and despondency when it dawned on me that there was one in a Black Box Amplifier that I have. Lo and behold I could even locate it, and when fitted everything, at least as far as the PSU was concerned, worked fine.
So, I'm back to square one, ish. There's nothing on the screen now, but the Trace Locate button puts a nice bright spot in the middle. I hope to get back to some proper testing and diagnostics shortly.
One last sting in the tail: when I switched on there was a faint ticking from the EHT Generator. This, I think, was a bit of damp 'cause a gentle waft from my Hot Air Gun at long range fixed it.
Alan
P.S.
That took three goes over 3 days
I hate leaving things because no matter how many Pictures I take and Notes I write it still takes time to catch up.
Anyway, everything looked OK so switch on, wait 90 seconds, and ...... nothing. What now? A quick poke round with the AVO showed no ht, and lo, two of the HT fuses were blown. How's that happened? Don't know, but replacing them brought it back to life as before with a bright little lissajou figure on the screen. So far so good.
Having pondered on the problem during the gap I decided to change my mind and work backwards. After all, that's what I do with Radios. So, I applied a nice big Sine Wave from my trusty Advance 81A to the X Amplifier and was rewarded with a stretched out figure on the screen. Why was it like that? It looked supsiciously like hum, and my Tek 475 confirmed it. So where was it coming from? I'd changed all the main Electrolytics and most of the Supplies are regulated. A quick poke around showed that the +150v was down at about 80v and there was 5v of hum on it. Now I'd been here before, and it turned out to be dirty valve pins. Sure enough, cleaning the pins of V607 fixed it. I then decided, rashly perhaps, that I should have cleaned all the valve pins to start with, so I did. Switch on again and the +150v says 80v. This was getting a bit wearing. So, what's on the 150v line? Easy answer, an ancient Plessey double Electrolytic - 8 + 8. Must be them, mustn't it? Tacking a spare across them made not one iota of difference. Now what? While poking about with an AVO I managed to get a bang off the aforementioned Electrolytic and no amount of valve wiggling and cleaning would get the 150v back. Next candidate was the 2M2 Anode load, which indeed measured about 2M7, as did the one in the +300v circuit, but changing them made no difference. All the other Resistors measured OK. In desperation I also changed a couple of Hunts lurking in there, but to no avail.
After a lot of pondering and measuring I swapped the ECC83s - V606 and V607. That got the +150v back but killed the +300v. Not good. Later on I had a look on ebay for ECC83s. There's strange phrases like 'Blackburn Code', 'Square Getter', 'Yellow Print' and 'Matched Pair', all of which seem to multply the prospective price by about 50. I was sitting there in a state of gloom and despondency when it dawned on me that there was one in a Black Box Amplifier that I have. Lo and behold I could even locate it, and when fitted everything, at least as far as the PSU was concerned, worked fine.
So, I'm back to square one, ish. There's nothing on the screen now, but the Trace Locate button puts a nice bright spot in the middle. I hope to get back to some proper testing and diagnostics shortly.
One last sting in the tail: when I switched on there was a faint ticking from the EHT Generator. This, I think, was a bit of damp 'cause a gentle waft from my Hot Air Gun at long range fixed it.
Alan
P.S.
That took three goes over 3 days
