It's indeed a fairly large undertaking, but you'll find that it accelerates over time. Your mind will quickly grow to like certainty over uncertainty, if it's anything like mine.
You could break it down some, for example, by getting a layout diagram and confirming that the physical parts placement is identical to the one shown in the dwg. At that level, you're not checking any connections, you are just checking that the physicality of the parts placement is correct. In fact, I would start there. When you replaced "all the parts" did you replace numbers of them at a time, or, part-by-part...? You're on top of your resistor color code? If you replaced only one part at a time, parts placement errors are far less likely, but still possible. It's also possible that an under-board wire came out of an eyelet the prior time you heated up a solder joint. Thus a connection that was good might have become unmade, yet is invisible.
I am working on my 1965 Pro Reverb at the moment and I am reminded that the pale yellow cloth-covered wire Fender used to connect from the parts board to most tube-socket pins has a way of tricking your eyes when those wires cross. (Your amp could use different-era wire colors, or it could be the same if it's an early AA1165) If you disconnected multiple wires from the parts board all at once during your replacement-festival it would be trivially easy to get them mixed. Really, really easy. Insanely easy. Use a needlenose to grasp one end of various wires and be super-sure it goes where it supposed to. This has bonus of checking the soundness of your solder connections, which I am of course assuming are all good. Heh. Again, most techs tend to replace one part at a time, although when replacing the twin 100K plate resistors on Fenders that are arranged in a "V", you can do both of those at once. But if you pulled off half a dozen caps and resistors, or ALL the resistors, or "everything to the right of this eyelet", you gotta get back to perfect certainty. If you replaced every single wire and every single part you MUST go through this or something very close to it.
If this amp dropped onto my bench, I think I would proceed:
1: Check physical parts placement against parts layout diagram. At the end of that check the DIAGRAM has a red dot on both ends of every component and every physical component has a magic-marker dot on both of its ends. But be careful: In my last post I referred to that central 7025 in the schematic. The 3 individual parts that connect to that tube's pin 6: That pin 6 does not "earn" its fully-fledged red pencil marking until ALL those parts are checked. This is why you use pencil and go lightly, because you WILL have to erase things in your redlining. You also have to figure out how you are going to show that you have checked TWO of those connections but have not yet checked the third one. Some folks like to have a bare alligator clip, or, one end of one of those cheesy alligator-alligator jumpers to mark which end of a wire they are working on.
2: Check "intra-board" connections. Jumpers under the board, the chained B+ connections, all ground connections.
3: Tube pins to parts board. STRONGLY PREFER starting at the tube socket. Start at pin "1" and confirm that a connection is made to the right spot on the parts board. If you start at the parts board end, I promise you that everyone on this board has mis-read a tube pin number 4, 5, 8, 10, 15 times in a row. "Oh, OK, that goes to pin 3. Oh, OK, that goes to pin 3. Oh, OK, that goes to pin 3. Oh, OK, that goes to pin 3. Oh, OK, that goes to pin 3. Oh, OK, that goes to pin 3." CRAP! NO! It's going to pin 7!!
As it happens, pin 1's are all plates on the little tubes, as are all pin 6's. Maybe you take an excursion "sideways" and check to see that "ALL" your pin 1's go to one of the 100K resistors usually arranged in a "V" shape. Does it matter which of the 100K's each plate goes to? Better believe it. That would be a VERY EASY re-wiring mistake to make. VERY EASY, to take off two of them and flip them around. With that eye-fooling yellow wire? Oh yeah.
Likewise, all pins 3 & 8 are cathodes. Most of them go to resistor-capacitor bypass pairs.
Does everything that is supposed to connect to ground measure "zero ohms" (or very small ohms) with everything else that is supposed to go to ground?
Except for that central 7025, every 12A_7 pin 1 should measure 200K ohms to the same tube's pin 6. The plate load resistors.
Every cathode (pins 3 & 8) on every 12A_7 (except for the last PI) should measure 1000-2000 ohms to ground.
Take sorta frequent breaks and come back with fresh eyes, this is a job that takes lots of concentration, uninterrupted. If there are distractions going on, put it away and come back another time. It's a zen-like process.
The amp is like a tube of toothpaste, full of uncertainty. Your job: Squeeze it all out.
Topic: 67 Bassman head pin voltages (Read 8718 times)