Tube amp schematics 101, etc: NEW NEWER UPDATE: Biasing tutorial!

[Fiddy]

See when I first read this I thought the champ showed two 12AX7's on this schematic. I now think, that the schematic shows only one 12AX7. The two separate triode icons threw me off.  Am I safe to assume that all 9 pin tubes are dual triodes then? So does the tube work by allowing current to flow through the anode to heat the filament,  then releasing electrons that the grid traps,  grid opens up slightly when an audio signal passes through exiting through the cathode? Will that signal go out directly to the speaker?  What is the center tap on a dual triode then? the ground?  :-\ 

[Fiddy]

There is a low-voltage current that heats the filament just like in a light bulb.  This part of the circuit is separate from the audio portion.  The only job of the filament is to get the tube hot.  The filament (or heater) is not usually drawn on the schematic, since it functions similarly for all tubes.  There is a separate low-voltage winding on the power transformer... it's really not connected to anything else in the amp.  Its sole function is to heat the tube.  The cathode is NEAR the filament, and when the filament gets hot, it boils electrons off the cathode.

Awesome! So in this case is the 6.3 V winding at the bottom of the schematic, I guess.

The anode has high voltage on it, called the B+ voltage or "plate supply," etc.  The anode is also called the "plate."  The high positive voltage on the plate/anode has a very, very strong attractive charge to the electrons that were boiled off the cathode.  Remember that electrons have a negative charge and opposites attract.

Is the voltage supplied by the middle winding on the transformer. Then is the job of the caps is to maintain the proper voltage in case of a drop or a spike?

Remember as I said that the stream of electrons travels through the vacuum because opposites attract.  Well you may also know that like charges repel.  By applying a negative charge on the grid, you can slow down the stream of electrons somewhat, as the negative charge applied to the grid repels the electrons a little bit back toward the cathode.  The charge on the plate will still be strong enough to overcome this negative charge, but the grid's charge will influence the stream of electrons somewhat nonetheless.

So this would be when a resistor comes in handy? To control the negative charge that the grid gets?


On the transformer on this 5F1 schematic is there polarity only on the middle winding of the transformer?

Dude your explanations rock!! 

[Fiddy]

Cool, it is starting to make sense. How do you id the taps on a tranny? Multimeter? 



On a somewhat related note..
I got a .05 cap @ 400VW that I want to replace on the ELK. All I can find is an orange drop cap .05 @ 600 V. Will that do? (actually I unscrewed the turret board and there were 5 Atlas Oil caps underneath that are bubbling up, so Im going to replace them all.


Thanks dude!!

[Fiddy]

Awesome, I knew that about the caps I just wasn't sure if the drop shape made a difference on but I guess a cap is a cap after all. 

Cool, that clears it about the transformers. I think that as soon as I come up w/ some extra cash (I don't know if there is such a thing as extra tho') I might do a tweed champ....

You wouldn't happen to have a pics of a 5F1 guts anywhere on your HDD there, do u Brad?

[Fiddy]

BUT the 12xxx tubes can often have their filaments wired humbucking, in which case the center tap of the filament is utilized and they run off of 6.3v.  They can be wired either way, but usually they are wired humbucking.  This reduces noise and allows a single filament winding to supply the heater voltage for the power AND preamp tubes.  Gibson amps tended to use 6EU7s instead, which is similar to a 12AX7 but can only be wired conventionally as far as the heaters go.

Sorry quick question about a 12AX7's that's wired humbucking...

Wiring said 12AX7 to the tranny....

Will a single 6.3  supply on either pin 4 or 5 plus wiring pin 9 to the trannys center tap do? Or do you wire to either 4 or 5 then short them, then wire your pin 9 to the tranny's center tap?   :ph34r:

[Fiddy]

I just looked inside the ELK and answered my own question. Pins 4 and 5 are shorted. On the ELK is the blue cable supplies the 6.3 v to pins 4 and 5 the white wire goes to the center tap.

[øøøøøøø]

Right.  Pin 9 is the center tap. 

[Fiddy]

See, I think I get the picture as a whole but there is little gaps of info here and there that confuse me a bit.

See an example here....

Then we get to power transformer D.  You can see that the wall power hooks to the coil on the left side.  This is called the "primary" of the transformer.  The coils on the other side put out all different voltages.  The one on the bottom is for the 6.3v filaments in all the tubes and connects to them all.  The other two are the 5v rectifier filament and the high voltage winding, and connect to the full-wave rectifier tube E .  The tube is a 5Y3.  Back up for a second to the power transformer and notice that the middle winding is center-tapped, with the center tap grounded.  This means that the winding is "zero" in the middle, making the voltage on one end positive and the voltage on the other end negative.

In this example if the bottom winding of the tranny is negative/ground, the middle winding is Positive/Center Tap/Negative then what is the 5 V filament heater winding on top? Shouldn't it also have a ground? Or is the ground to the rectifier supplied by the center tap of the high voltage winding? If so then is the top winding both Negative?



See on my Elk I got heater wires going to pins 4 and 5, and high voltage going to pins 1 and 7.  I looked up an 6CA4 (EZ81) and got some vague info pins 1 and 7. I believe are anode and cathode and 4 and 5 im going to assume are the filaments. (Freaking info is in German I think.. >)   >:(   So does that mean then that a 6CA4 is also a dual triode?

Sorry dude, Im trying here, So... I'd rather look dumb asking than to never learn. (Or I can just Google it and not look dumb...but then is much cooler having it all here in one place)   ???


     

EDIT:
Found out an EZ81 is a Dual Anode Rectifier... So I guess pins 1 and 7 are Anode and Anode. Ok but the first question about the top wiring I still don't know...

http://www.tubebuilder.com/images/tubed ... 1specs.pdf

[Fiddy]

Am also confused cuz see...

The anode has high voltage on it, called the B+ voltage or "plate supply," etc.  The anode is also called the "plate."  The high positive voltage on the plate/anode has a very, very strong attractive charge to the electrons that were boiled off the cathode.  Remember that electrons have a negative charge and opposites attract.

I f I Google anode an cathode

http://www.google.ca/search?client=fire ... gle+Search

The second entry there says that the flow of electrons is from Anode to Cathode. Yet you are telling me that the plate is attracting electrons boiled off the cathode meaning the flow of electrons is going from Cathode to Anode. What you explained makes sense but it just confuses me to see that on Google.

I knew I should have not dropped out of Electronics on my second day!! ARGHHHHH..........   

[Fiddy]

On this pic..
If the yellow lines represents the now rectified and an unconstant DC power that will be smoothed out by our filter caps then what does the red line represent? Why do those meet at that point?   8)   



PS that was a pretty good post there dude!

I want to build an amp sooooo bad!!

On the 12AX7 symbol what is represented? Plate, Grid and Cathode? From top to bottom.

[Fiddy]

Sorry, I think you've reached the point where my expertise ends.     I'm sure I'll learn some day.  It's probably really basic.

Hahahaha.... Awesome. I think I've crammed enough for the weekend. Thanks for all your help. This is interesting yet mind numbing stuff.

What was really cool was reading and understanding your last post. It felt good. 

[Fiddy]

I agree, nothing beats hands on training. I'd love to maybe in the future become an amp tech!   :ph34r:

[mezcalhead]

Would anybody have some clear nice shots of the guts of a champ?

The first page of this thread might be helpful .. the circuit on that one is 5F1 (mostly, thanks Brad).

[Fiddy]

The first page of this thread might be helpful .. the circuit on that one is 5F1 (mostly, thanks Brad).

Perfect, that's exactly what I was looking for. I knew I'd seen those gut pics somewhere.   :)

[Fiddy]

Found this really neat schematic and layout for the champ. Makes it a easier to understand what's going on in there.

http://www.dockeryamps.com/web/Docs/5f1 ... ematic.pdf


http://www.dockeryamps.com/web/Docs/5f1 ... layout.pdf