12-13-2018, 09:09 PM
Thanks for the input Terry - I appreciate it. Based on this I decided to take a step back. I recalled that when I tried to complete the FM tests on this page:
step 2 actually failed. I've attached a different copy of the schematic so you can see the test points called out in the tests. Test point A is the control grid of the 7R7 and test point B is the plate of the 6BA6. I was able to get a signal through but it wasn't the same signal strength as in step 1. In fact it was a fair amount lower. I guess I chose to ignore it since I did get a signal through, but I think this may be where the problem is. So I tried to do an alignment again and this time I noticed that adjusting C301A has virtually no effect. If I go back from there and inject into Z300 I can adjust C300A, C300B and C301B and all react as you would expect...I can peak up the output. But C301A has no affect. I think I need to remove Z301 and check C301A...perhaps the mica has failed. Thoughts?
By the way, I did check the plate voltage on the 7F8 and I got about 110 for AM and about 120 for FM. The schematic says I should have 95 and 105, but I measured with a Fluke 77 so I would think that's ok. And I don't have a 100mc scope...I have a Tektronix 2215, so just 60mc.
Thanks!
Rich
step 2 actually failed. I've attached a different copy of the schematic so you can see the test points called out in the tests. Test point A is the control grid of the 7R7 and test point B is the plate of the 6BA6. I was able to get a signal through but it wasn't the same signal strength as in step 1. In fact it was a fair amount lower. I guess I chose to ignore it since I did get a signal through, but I think this may be where the problem is. So I tried to do an alignment again and this time I noticed that adjusting C301A has virtually no effect. If I go back from there and inject into Z300 I can adjust C300A, C300B and C301B and all react as you would expect...I can peak up the output. But C301A has no affect. I think I need to remove Z301 and check C301A...perhaps the mica has failed. Thoughts?
By the way, I did check the plate voltage on the 7F8 and I got about 110 for AM and about 120 for FM. The schematic says I should have 95 and 105, but I measured with a Fluke 77 so I would think that's ok. And I don't have a 100mc scope...I have a Tektronix 2215, so just 60mc.
Thanks!
Rich