Complete 124 Schematic

[odourboy]

It's been done before, and it'll be done again, but I haven't been able to find a complete schematic of #124, I decided to take a shot at it myself. I've gone through all the discussions that have occurred in the last while and poured over the photos Gil presented and I've attempted to document #124 in as completely and accurately as possible. Here it is for your consideration.

If you notice any errors, please let me know so we can get an accurate picture.

Cheers!

EDITS:
1.2- OD/PAB reversed on XLR; Legal Size PDF
1.3- OT xformer taps, PS cap, 50W mode tubes
1.4- switched speaker jack, added some notes
1.5- move the B+1 to other side of standby switch, courtesy plug
1.6- reversed diode in power LED circuit
1.7- corrected Send/Return network connection

[butwhatif]

Question, where are the photos located that are providing this info, are they on the site?

[odourboy]

Question, where are the photos located that are providing this info, are they on the site?

Look here:

https://tubeamparchive.com/viewtopic.php?t=1118

[Structo]

Hey guys, help an old timer that grew up fiddling with electronics though not necessarily tube amps.
There is a lot of slang thrown around here that I can guess at sometimes.
But particularly the CL1, CL2 terms.
Why do we call them that rather than say, V1a, V1b?
I understand that V1 is the clean stage.
Does CL mean clean and so what would you call the V2 stage in the same vein?
Thanks for any edification on these terms?

[mlp-mx6]

CL1 = first clean stage
CL2 = second clean stage
OD1 = first overdrive stage
OD2 = second overdrive stage
PI = phase inverter

I actually find the "CL" and "OD" terms to be more accurate. HAD sometimes rotated the preamp tubes so that V1B was CL1. V1B refers to pins 6, 7, 8 specifically. So describing the function is more accurate than describing which side of the triode.

[Structo]

Thanks!
So CL1 is the stage where the guitar signal enters the tube?
And Cl2 is the other half of V1?

[butwhatif]

You're all over it Structo-

[ic-racer]

Nice schematic. I had just put an update on the other thread but I also put a note to move any discussions over to this thread as your schematic is more detailed.

The only things (other than my lack of a relay circuit) I could see different between the two are these:

1) I believe the original output x-former has just the 4 ohm output
2) The #124 pictures seem to indicate that one of the speaker output jacks is a 'switched' jack
3) I drew in the fifth capacitor in the power supply as the 10uf/10uf 500v Can
4) It looked to me like the 50w switch takes out tubes 1 and 3 but the wires are hard to follow in the #124 pictures. (the yellow wires from the switch seem to go to 1 and 3, or 4 and 2, which ever way you want to count them)

Again, nice work odourboy!

[JimiB]

nice work odourboy

+1!

[nickt]

++1 odourboy

[odourboy]

Thanks all. Trying to pay it forward.

Nice schematic. I had just put an update on the other thread but I also put a note to move any discussions over to this thread as your schematic is more detailed.

The only things (other than my lack of a relay circuit) I could see different between the two are these:

1) I believe the original output x-former has just the 4 ohm output
2) The #124 pictures seem to indicate that one of the speaker output jacks is a 'switched' jack
3) I drew in the fifth capacitor in the power supply as the 10uf/10uf 500v Can
4) It looked to me like the 50w switch takes out tubes 1 and 3 but the wires are hard to follow in the #124 pictures. (the yellow wires from the switch seem to go to 1 and 3, or 4 and 2, which ever way you want to count them)

Again, nice work odourboy!

IC - thanks for taking a close look. My replies,
1) I only had the 4/8/16 xformer in my library. Gotta do a custom component at some point with just a single tap for the 'final'.
2) I disagree. Nothing suggests this to me - wiring, they appear to be in parallel. Labeling o the back panel also indicates this. But I'm open to discussing this further.
3) I believe you are right. I should show it as 10 + 10 like you did. Are you sure of it's position in the chain or was that an educated guess? (I agree with the guess but wondered if this was 100%)
4) I'd already made that change for the next revision - but good catch! I think the cathodes that are lifted are on V5 and V7.

Also:
What do you make of the Boost (PAB) rear panel switch wiring? Based on the photos and Billy's schematic, in 'manual' mode the switch isn't grounded (unlike the OD switch) and as such, wouldn't work. This puzzles me - what am I missing?

What are your thoughts on the pre-OD network fixed resistor (120K versus 220k)? Despite Gil's insistence, the evidence seems to favor the 120K value.

Updated version (1.3) posted.

[ic-racer]

Check out this picture and see what you think.

This is how I interpret it:

A - I think this shows that the green wire from the OT goes BOTH 'tip' connections of the two jacks and they are shorted together. I think the smaller orange wire also connects there and it is the NFB wire.

B- I think this shows the black wire from the OT looping around and connecting with the middle 'switched' part of the RIGHT jack

C - I think this shows a jumper shorting the 'sleeve' lug to the 'switched' lug of the right jack.

[ic-racer]

Here is a composite showing what I believe to be the connections for the can cap. It looks like the white wire (from the last resistor and last 20uf cap on the board) goes to the can cap. The two leads of the can cap are shorted together and then the red wire heads over to the side of the chassis to meet up with the last resistor/cap in the chain.

[odourboy]

Here is a composite showing what I believe to be the connections for the can cap. It looks like the white wire (from the last resistor and last 20uf cap on the board) goes to the can cap. The two leads of the can cap are shorted together and then the red wire heads over to the side of the chassis to meet up with the last resistor/cap in the chain.

Yep! I 100% agree.

[odourboy]

Check out this picture and see what you think.

This is how I interpret it:

A - I think this shows that the green wire from the OT goes BOTH 'tip' connections of the two jacks and they are shorted together. I think the smaller orange wire also connects there and it is the NFB wire.

B- I think this shows the black wire from the OT looping around and connecting with the middle 'switched' part of the RIGHT jack

C - I think this shows a jumper shorting the 'sleeve' lug to the 'switched' lug of the right jack.

I think I misunderstood your original post. I agree with you. I should have looked at that part of your schematic before responding. I thought you were suggesting that the extension switched out the main, but I think we both see that the switch simply grounds the OT in the case that there is no main plugged in.