Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: prs_matt on February 16, 2011, 11:14:19 am
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What would (or could) the consequences be of plugging in a 6V6 without regard for the octal key? It seems like this one got plugged in with pin 1 in socket 8, so one hole clockwise as seen from the top of the socket.
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Not too much.It may kill the tube.It obviously wouldn't make sound or make a nasty sound.Could blow a fuse.Try another tube and see what happens.
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tube pin 1 is N/C to socket pin 2 is filament
tube pin 2 filament to socket pin 3 is plate
tube pin 3 plate to socket pin 4 is screen
tube pin 4 screen to socket pin 5 is grid
tube pin 5 grid to socket pin 6 is N/C or sometime tie point for grid drive or screen ckt.
tube pin 6 N/C to socket pin 7 is filament
tube pin 7 filament to socket pin 8 is ground or cathode resistor
tube pin 8 cathode to socket pin 1 is N/C or sometimes tie point for grid or screen ckt.
tube pin 1 N/C to socket pin 8 ground or cathode resistor
tube pin 2 filament to socket pin 1 is N/C or sometimes tie point for screen or grid ckt.
tube pin 3 plate to socket pin 2 is filament
tube pin 4 screen to socket pin 3 is plate
tube pin 5 grid to to socket pin 4 is screen
tube pin 6 N/C to socket pin 5 is grid
tube pin 7 filament to socket pin 6 is N/C or sometimes tie point for screen or grid ckt.
tube pin 8 cathode to socket pin 7 is filament
the tube filament must be powered in order for remaining electrodes to flow current IF the remaining electrodes are (or sometimes are not) connected in a ckt.
the power tube filaments are a low(er) value resistor - that is of most concern - now with the chart ( more possibilities omitted - i assume you at least have some idea of where the key was and you missed by one hole to the left or to the right) provided above, what do you think would happen?
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What would (or could) the consequences be of plugging in a 6V6 without regard for the octal key?
How is this possible? The key prevents you from sticking it in wrong. How did you "disregaurd" it?
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How is this possible?
It's not uncommon for the octal key to break off. Once that happens it's easy to plug it in wrong.
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This one was forced into a Belton socket. Not sure how but it has a worn spot now where the owner forced the key.
I have been pondering and cannot come up with an explanation for how the amp sounds now based on the possible outcomes of wrong insertion of the power tube. It did just come to my attention that it may be important to consider that this is a BF Princeton Reverb so it has a Push-Pull output and one of the tubes was inserted incorrectly. Is there a potential for the OT to be damaged by one being tube inserted wrong?
The output is weak and strangely distorted--a sound that I have heard recently with a Silvertone 1484 that had a bad OT...
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On my TOS I inserted my kt77 wrong some how and when I took it off standby it made a really loud noise blew the speaker and took out my channel switching relay. Guess it depends on how you put it in. believe me I can't figure out how that tube slipped into that socket so easily but it did. I put the tube in rotated it until it fell into place and pushed it went in easy just wrong. Good news no permanent damage and I got a new speaker cab out of the deal too. Told the wife it was junk and needed replacing and she bit, I set the hook and bought myself a new cab.
Tony
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Kind of a cool little puzzle question. Let's assume it's simply a traditional wiring with none of the empty pins being used as tie points. I've attached a little drawing. Fig 1 shows correct wiring. The key is broken so I consider the tube a beater, fine for experimentation but not something I'd put in a customer's amp. I consider the tube ruined and in some of these scenarios, it'll probably be 100% ruined. The bigger concern is what might happen to the amp itself. The only pins we need to be concerned with are pins 2 & 7 which appear as a dead short in a cold tube. Everything else is open until the tube starts conducting.
Fig. 2:
Looks real bad. You've shorted the plate to ground. Of course B+1 is supplied through the OT so the OT and PT are getting hot real fast.
Fig.3:
Looks like no harm is done, but.... quite often pin 1 is tied to pin 8 in which case you've now shorted the screen supply to ground. PT suffers, OT should be fine.
Fig. 4:
Neg bias is shorted to 1/2 filament. You've now put a DC bias on your filaments which should already have a ground bias. 1/2 your filament supply is competing with the bias supply. Filaments have more available current, bias supply loses. 100 ohm virtual center tap resistors explode.
Fig. 5:
Looks cool unless pin 6 is used as a tie point.
Fig. 6:
Screen supply shorted to ground.
Fig. 7:
Bias supply shorted to ground.
Fig 8:
No harm done.
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On my Little Bear SE EL84 amp I plugged the 12AX7 in the EL84 slot and the EL84 in the 12AX7 slot one time----the first main power rail resistor started smoking, I shut it down quickly and discovered the problem. The resistor survived and is still in there today. Platefire
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Thank you Butterylicious. I was doodling out such a diagram but made some errors in my doodling. This made it clear. The position the tube was plugged in was unfortunately Fig. 2 so so one leg of the OT was grounded across the heater. I replaced the OT and got back almost all the volume loss but there is still a strange distortion as I turn the amp up louder. It also is more pronounced as I turn up the treble pot. I have tried switching out the preamp tubes for new ones but the distortion remains so it is something wrong inside the circuit. I can't find anything obvious wrong inside the amp so I could use some fresh leads.
Thanks guys for the fabulous comments.