Garnet Herzog questions

[Randall]

Probably the first of many. Regarding the mute/in/out relay, in the non-energized postion, the input is routed to the output jack, but also to the 150K in series with the output pot wiper. Seems like this would load down the signal depending on the postion of the pot? What about the 270R on the wiper?

Also, in the non-energized postion there is a negative voltage apllied to the grid of the output tube so it does not conduct, but in the engergized mode the voltage is removed and the tube operates in cathode bias mode, correct?

Why is there an unlabeled circle at the first filter node after the rectifier diodes? Doesn't seem to be doing anything.

Why are there two AC fuses, one Int and Ext, and what is the circle with the X in it just below them?

https://el34world.com/Forum/index.php?topic=16934.0

[nosaj]

Probably the first of many. Regarding the mute/in/out relay, in the non-energized postion, the input is routed to the output jack, but also to the 150K in series with the output pot wiper. Seems like this would load down the signal depending on the postion of the pot? What about the 270R on the wiper?

Also, in the non-energized postion there is a negative voltage apllied to the grid of the output tube so it does not conduct, but in the engergized mode the voltage is removed and the tube operates in cathode bias mode, correct?

Why is there an unlabeled circle at the first filter node after the rectifier diodes? Doesn't seem to be doing anything.

Why are there two AC fuses, one Int and Ext, and what is the circle with the X in it just below them?

Can you link to what you are looking at? Nsublysses I believe has the Garnet Amplifiers book.

nosaj

[Randall]

Oh yes, my bad. Link is added to post #1.

[g1]

Gar drew some funny symbols that were um unconventional.
For him, a circle with an x is usually a switch.

[g1]

There are a few versions, this seems to be the one you are discussing.

[Justin Thomas]

So we still wanna put the squiggly line before the Xed-out circle when we build our iwn, right?

Justin

[Randall]

So we still wanna put the squiggly line before the Xed-out circle when we build our iwn, right?

Justin

I don't know what that means. I am just looking for answers to my questions. And, yes I think I may build one.

[Enzo]

Yes, cathode bias.

I interpret the empty circle as an unused B+ node. They left it in the drawing.

Two fuses like on many AMpegs. One is external, as in you can change the fuse from the outside. Note the internal fuse is slightly larger. It is mounted inside. They do this so that the dummy who replaces the 1A fuse with a 30A fuse doesn't eliminate the fuse protection. The circled X is the power switch.

The output jack is a line/instrument level signal. In bypass mode input is wired to output. In through mode the very hot speaker level signal is padded down by the 150k resistor.

[Justin Thomas]

It's considered safe practice for the fuse to be the first thing in line at the power switch rather than the switch itself. The schematic has the switch first then the fuse(s). But at least they're all on the same line instead of fuse on one side & switch on the other.

Justin

[Randall]

My biggest question remains, in bypass mode the input is routed to the output, but also connectected to the 150K resistor and then the output pot. Wouldn't this load down the input/output signal?

[g1]

It's considered safe practice for the fuse to be the first thing in line at the power switch rather than the switch itself.

It seems to go both ways on this, I don't know if there is a legal requirement. Modern Fenders have the switch first. I've seen some people argue that this way, if someone forgets to unplug the amp to change the fuse, they will usually at least turn the power switch off.

[g1]

As far as I know, the loading is not considered significant.

[mhuss]

My biggest question remains, in bypass mode the input is routed to the output, but also connectected to the 150K resistor and then the output pot. Wouldn't this load down the input/output signal?

In the schematic linked in the first post, the switch connects the input directly to the output when in bypass mode, and connects the amp in line when 'on.' The 150k is only connected in the latter case.

(This schematic is also the one in the 'As "GAR" Sees It' book, which I have.)

[Randall]

"In the schematic linked in the first post, the switch connects the input directly to the output when in bypass mode, and connects the amp in line when 'on.' The 150k is only connected in the latter case."

That's not the way I read it. I see a direct connection to the input/output junction in bypass mode to the 150K. Correct me.

[Tony Bones]

"In the schematic linked in the first post, the switch connects the input directly to the output when in bypass mode, and connects the amp in line when 'on.' The 150k is only connected in the latter case."

That's not the way I read it. I see a direct connection to the input/output junction in bypass mode to the 150K. Correct me.

The schematic posted by g1 uses a DPST relay and does have the 'feature' that you describe. And, yes, it probably would load down a passive guitar pickup in the off/bypass position.

The schematic on the EL34 website uses a DPDT switch that fully bypasses the entire circuit when in off/bypass mode.

When you build yours, use a DPDT switch or relay.