18Watt.com

yello wrote: ↑

Wed 09/28/22 12:05 pm

Currently I'm creating a new layout for this amp circuit, so it can be built on a turret board in a typical amp chassis, not in the original projector enclosure which is crowded and convoluted. That means I'm not recreating what I see in person in my layout, but rather translating the original schematic and original layout, into a totally new (better) layout. Its a great learning process.

That's great! And it also means you can do whatever you want.

JMPGuitars wrote: ↑

Wed 09/28/22 8:01 pm

yello wrote: ↑

Wed 09/28/22 12:05 pm

Currently I'm creating a new layout for this amp circuit, so it can be built on a turret board in a typical amp chassis, not in the original projector enclosure which is crowded and convoluted. That means I'm not recreating what I see in person in my layout, but rather translating the original schematic and original layout, into a totally new (better) layout. Its a great learning process.

That's great! And it also means you can do whatever you want.

I will likely mimic the layout sections of the 18w, as that worked out great when I built my ef86 Lite 2p.

Here is a question, as I draw up my own new layout for this circuit:

There isn't anything that connects to filter cap C216B - it is connected to filter cap C216A and C216C via a 350 ohm 3w resistor on either side (R240 and R228). What is the point of that? Can I just eliminate C216B and just up the resistor size between C216A and C216C? Would the resistor be 700 ohms 5w? Or 1k or 1.5k 5w? Or does cap size need to change too?

In other words, can I redesign this filter stage to work better and without (what seems to my inexperienced eyes as) extraneous parts?

Bieworm wrote: ↑

Wed 09/28/22 10:07 am

Looks correct to me..

I'm circling back to reviewing this tone circuit (been awhile since we discussed it). This tone control affects various changes in a preamp negative feedback loop.



What does the dotted line going from s201a to s201b represent? A connection between those points done by the switch? Or is it just showing the unison movement of the switch positions between two independent switch portions? are s201a and s201b separate or connected?

Calm down, no need to yell.

It's showing you the common terminal on each half of a 2 pole 5 position switch. The poles move together, but are isolated.

What Josh said

JMPGuitars wrote: ↑

Fri 09/27/24 5:38 pm

It's showing you the common terminal on each half of a 2 pole 5 position switch. The poles move together, but are isolated.

Thanks, that is what my staring at the circuit and multimeter seemed to be showing, but I'm not familiar with these switches and that dotted line in a schematic, so an extra set of eyes or two is always helpful!

yello wrote: ↑

Sun 09/29/24 1:15 pm

Thanks, that is what my staring at the circuit and multimeter seemed to be showing, but I'm not familiar with these switches and that dotted line in a schematic, so an extra set of eyes or two is always helpful!

The more schematics you see, the more new things you'll see. The dotted line is a standard thing for multi-pole switches, but it gets more confusing when the poles are farther apart like that. Here's a basic 2 pole switch symbol:

JMPGuitars wrote: ↑

Sun 09/29/24 2:58 pm

yello wrote: ↑

Sun 09/29/24 1:15 pm

Thanks, that is what my staring at the circuit and multimeter seemed to be showing, but I'm not familiar with these switches and that dotted line in a schematic, so an extra set of eyes or two is always helpful!

The more schematics you see, the more new things you'll see.

And another interesting schematic/switch thing: there is a switch to select between the 8 ohm internal speaker, or the 16 ohm remote speaker cabinet output jack that lifts/moves the ground wire to accomplish the task. I don't think I've seen that before, is that common on a combo amp (as opposed to a selector switch that chooses between OT secondary wires as seen on most heads)?

yello wrote: ↑

Wed 10/02/24 10:26 am

I don't think I've seen that before, is that common on a combo amp (as opposed to a selector switch that chooses between OT secondary wires as seen on most heads)?

The wire may be grounded, but is it a ground wire? Do your speaker terminals say + and Ground, or do they say + and -?

JMPGuitars wrote: ↑

Wed 10/02/24 1:13 pm

yello wrote: ↑

Wed 10/02/24 10:26 am

I don't think I've seen that before, is that common on a combo amp (as opposed to a selector switch that chooses between OT secondary wires as seen on most heads)?

The wire may be grounded, but is it a ground wire? Do your speaker terminals say + and Ground, or do they say + and -?

Ah, yes, forgot to think of it in terms of the OT. So it is muting the speaker by not completing connection with both sides of the OT secondary, is that the right way to say/think about it?

yello wrote: ↑

Wed 10/02/24 1:30 pm

Ah, yes, forgot to think of it in terms of the OT. So it is muting the speaker by not completing connection with both sides of the OT secondary, is that the right way to say/think about it?

Pretty close. It's swapping the negative speaker connection to the external speaker, which disconnects it from the internal speaker. The OT is still connected to something.