Issues with 5E3amp

[alkuz1961]

Yes. A short is fine. Open is bad.

um... it looks a little weird. I'll keep that in mind for the future. But I always used a dummy load on the switchable connector.
Thanks

[pdf64]

Maybe you’re used to pentode amps?
The ‘shorting output jack’ arrangement is more common with (and suited to) beam tetrode amps.

[martin manning]

Perhaps alkuz1961 is thinking of the case where the speaker cable becomes disconnected at the other end?

[pdf64]

But a switchable dummy load, ie as per the photo but a resistor rather than a wire link that only connects into circuit when the switching contact in the jack socket is closed, is of no benefit in that scenario?

[sluckey]

I've seen schematics that used a 250Ω high watt resistor connected to the tip of the speaker jack. That resistor is always there even if the speaker cable does become disconnected at the speaker cab. A 250Ω load is better than an open load. I don't remember where I saw that idea. Could have been a commercial amp or some boutique.

[martin manning]

I believe some AX84 amps had that feature.

[pdf64]

I’ve seen some Traynors with that, but the earliest example I’m aware of is JMI Vox AC50
https://el34world.com/charts/Schematics ... master.pdf
https://el34world.com/charts/Schematics ... x_ac50.pdf

It’s certainly worth doing something, and the ‘back up load’ may be seen to have benefits over the shorting jack method, which sometimes just isn’t feasible, eg an output jack per secondary tap.
Also, the Fender BF NFB resistors (820+100 or 47ohms) may be low enough in value to kinda act as a back up load.

[guile]

Do you have more preamp tubes to try? Failed heater-cathode insulation can cause hum like that.

I swapped all the tubes, but only swapping V2 for 12AT7 yielded less hum. A 12AU7 even less.
Could this be a lead?

Moving and redressing the heater wires does not alter the hum in any way..

[pompeiisneaks]

Not necessarily, it means the source of the hum is likely either in the first stage or that stage and you're putting in lower gain tubes so the hum is being amplified less.

At least it helps narrow down the location of the hum itself.

I'd check the components and solder connections around V1 and V2 for issues, or lead dress around those tubes.

~Phil

[pdf64]

...Same voltage here in the Netherlands (240 max). It's common here that wall outlets are not grounded. They're protected with an earth leakage circuit breaker system. Wall outlets in kitchens, bathrooms etc. are of course grounded...

Thanks for the insight, I (naively) assumed that the whole EU area would have grounded wall outlets

...I got the kit from a reputable source...

What guidance did the kit supplier provide regarding circuit 0V to chassis connection arrangements?

Are the input jack switching contacts wired up properly, ie so as to mute the inputs when nothings plugged in?
From the video, it kinda sounds as if the inputs are being left wide open.