Input and Output Jacks

[CraigGa]

This is a retirement project so I'm taking my time with it but this is the current state of play.

Craig

[CraigGa]

I need to get that heater rectifier straightened up

[Stevem]

What are the rca jacks for?

[Colossal]

I need to get that heater rectifier straightened up

I was gonna say...please straighten that rectifier

Looks like a fun project!

[CraigGa]

What are the rca jacks for?

They are the reverb send and return.

[CraigGa]

I need to get that heater rectifier straightened up

I was gonna say...please straighten that rectifier

Looks like a fun project!

I'm glad I got in there first now

[pdf64]

The output jack you typically want to be grounded to the chassis…

Just to note that given the context of the Benson Monarch, which doesn’t have a global NFB loop’, there’s no conflict with RG’s advice about best practice.
Certainly the OT secondary needs a good solid reference back to the HT 0V, as a safety measure in case the OT shorts primary to secondary.
So it’s fine to use non-isolated jacks here. Perhaps even add a wire back to the main amp 0V, in case the jack’s nut gets loose.

[R.G.]

One last question, R.G. mentioned the AC safety ground, would that typically be the same chassis bolt as the ground connections or a seperate one?

Separate bolt/stud on the chassis for just the safety ground, nothing else. The safety inspectors who do type certifications for manufacturing (UL, CSA, TUV, etc.) insist that the right way to do this is with a hole through the chassis for a single bolt. The area around the bolt hole is to be sanded down to bright, shiny metal. With the bolt in place, the stack up on the nut side is (1) star washer (2) ground wire ring terminal (3) another star washer (4) nut.

The safety guys insist that the ground wire should be set up so that using enough force to pull the power cord out of the chassis will cause the line and neutral wires to break first. That only counts if you use an AC cord through a grommet in the chassis. For me, it's simpler to put in an IEC power inlet socket so the AC cord would pull out of the socket. Another advantage of the IEC is that they can be bought with an internal fuse holder in the AC hot wire, so it makes the issue of mounting a separate fuse holder and how to wire it a non-issue as well.

[Stevem]

Keep a eye out for oscillation problems by having that reverb send jack back up near the input jack and the first gain stage area.

[pdf64]

Keep a eye out for oscillation problems by having that reverb send jack back up near the input jack and the first gain stage area.

Bear in mind that the design takes the reverb send from a cathode follower after the input stage.
So with respect to the input, the reverb send only has a voltage gain of maybe 60, and is in opposing polarity.
So as I see it, there’s no stability consideration / mitigation required there.
A schematic for the amp in question would be a useful addition to the thread.

[CraigGa]

A schematic for the amp in question would be a useful addition to the thread.

Sure

[Stevem]

So in that case I would use shielded wire from the reverb pot to pin 7 of V1A to nip that in the Bud!

[ChopSauce]

7D26950A-1CD6-47A8-8314-AB0DC1EE4CDD.jpeg

This arrangement will shunt radio interference.

Now (lately) I'm all confused. I thought R.G. mentionned a (few 100pF) cap between the sleeve and ground and now I see both a (ten times larger) cap plus a resistor between the tip and ground?

Moreover the resistor value seems pretty low, in comparison with the 1M grid leak ...

... can anyone confirm either or both solutions, please?
(I'd like to try that and see if that solves what might be an RF catching issue)

[pdf64]

7D26950A-1CD6-47A8-8314-AB0DC1EE4CDD.jpeg

This arrangement will shunt radio interference.

Now (lately) I'm all confused. I thought R.G. mentionned a (few 100pF) cap between the sleeve and ground and now I see both a (ten times larger) cap plus a resistor between the tip and ground?

Dunno where that diagram was dug out from. I don’t think it’s relevant to our application. It’s context may be in regard of piezo transducer type signal sources?

RG mentioned a small ceramic cap if using an insulated jack. By small, my understanding is physically small, eg 50V 10 - 100nF.

I thought you were using non insulated ‘open’ jacks?

A properly implemented input grid stopper, ie mounted at the socket terminal, is usually plenty to stop whatever RFI can be stopped.
Maybe consider ferrite beads on the wires at the input jacks if it’s still a problem.
If still a problem after that, move away from the transmitter

[ChopSauce]

I am using open jacks, yes, but insulated with a pair of shouldered washers.

So, the cap should be connected between the tip and the ground, right?