I have this vintage tube amp with schematic that uses a 6J7 tube.
The socket on the chassis is wired per the schematic which matched the 6J7 (6J7-G, 6J7-GT) tube data pinouts.
I discovered that the tube that was installed (I guess as a substitute) was a 6SJ7GT tube. When I looked at the tube data/pinout for the 6SJ7GT it's completely different than a 6J7? It is the same type of tube and the numbers and letters are similar. Do you think someone thought it was the same tube?
And would anyone have any idea what would have happened if this was powered up and what that tube would do to the amp like that?.....
The socket on the chassis is wired per the schematic which matched the 6J7 (6J7-G, 6J7-GT) tube data pinouts.
I discovered that the tube that was installed (I guess as a substitute) was a 6SJ7GT tube. When I looked at the tube data/pinout for the 6SJ7GT it's completely different than a 6J7? It is the same type of tube and the numbers and letters are similar. Do you think someone thought it was the same tube?
And would anyone have any idea what would have happened if this was powered up and what that tube would do to the amp like that?.....
That's exactly what it was!...The schematic is pretty old (1940's) and the 6J7 was in the original schematic drawing, wiring and I'm sure the tube used at one time. The schematic even showed the little square tab off the shell (cap).
and internal connections in the tube, so that added to the confusion.
After posting this I went back and looked more carefully at the pin wiring and it was wired correctly for the newer 6SJ7GT tube!
I did a little further research and found out that the 6J7 tube was discontinued. So that was what happened and I'm an idiot....😕
In my defense, there were other missing parts and info on the schematic too, but all the other tube subs were the same wiring, so I checked them off as OK.
All is well with the world now and it just taught me not to trust old schematic's over the actual wiring.....
Thanks though for the reply!
Well, it's a good lesson... I never trust schematics. Any mods that have been done in production later on won't appear in the service manual. Only outfits like Philips issued errata or new variants (/01, /02...) of a model.
Yes it was a good lesson. I used to have to do "as-builts" back in my youth for commercial drawings, so I know how that goes. It all made sense.
Also one of the reason avionics schematics and wire diagrams are updated and corrected with revisions as they happen....
Also one of the reason avionics schematics and wire diagrams are updated and corrected with revisions as they happen....
Sometimes tube amps will work (sort of) with the wrong tube in.
I had one working when I missed the ground line off a cathode resistor.
It worked but just wasn't as loud as it should be.
I had one working when I missed the ground line off a cathode resistor.
It worked but just wasn't as loud as it should be.
Yeah I could see that, with this it would have been a reverse of the plate and cathode in the circuit!!....and because both the filter caps were bad when I got it apart I sort of thought maybe I had discovered the cause of that.
I rationalized that someone maybe got the wrong replacement, smoked the thing (caps blew) and then put it away in the attic until I recovered it.
I have however tested the transformers (primary and audio output with scope and meters) and as soon as I finish checking installing my new caps, resistors and wire we'll see how well I've done.
Wish me luck!
I once bought a faulty SS amplifier that worked but quietly.
All transistors tested ok out of circuit.
It wasn't until much later I realised someone had put in a PNP instead of an NPN transistor.
With an amplifier of any age the electrolytics probably all need replacing.
Good luck...
All transistors tested ok out of circuit.
It wasn't until much later I realised someone had put in a PNP instead of an NPN transistor.
With an amplifier of any age the electrolytics probably all need replacing.
Good luck...
Funny....it's certainly easy to miss something. This unit is 65+ years old and for fun I am restoring everything I can. It also allows me to learn and understand the ancient technology of tubes which I'm enjoying!
So far it has been a wonderful experience...
So far it has been a wonderful experience...
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