Thank you Max, I will indeed revisit the 6BL8. I checked all the tubes and they seemed fine on my Philco 7052 (which is a re-badged Hickok 533A). However, it may have been marginal. Too, I have ran across too many tubes that look good on the tester, yet fail to work properly in some Tek circuits.
All the tunnel diodes are in place (I looked to make sure they had not been made off with). However, They have not been checked. Will check the tube first, then address the condition of the TD's.
Thanks again.
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On 5/31/22 07:42, unclebanjoman wrote:
Hi Jerome,
I read only now your post.
The symptoms you describe are different faults.
The first, trace moving backwards at very low time/div is due to the miller run-up not working properly. The culprit is in the V161 tube: If the gain of the pentode section drops due to aging, the Miller run-up shows exactly this behavior.
Put in a new 6BL8 (replaceable with a ECF80 also) and the sweep section will return fully functional.
Regarding the second problem (no sweep triggering): check first if all tunnel diodes are present.
Due to their rarity, they are often plundered. It happened to me with my 3B4: fully functional but the tunnel diodes had been removed. Result: a very poor and insensitive trigger.
If they're in place trace the trigger signal path starting from V13. On the schematics there are some waveforms that will help.
I hope I have given you useful information.
With instruments of such type you need to be prepared for the fact that sooner or later there will always be one (of tubes) to replace.
Max
