NAD - Fender 57 Custom Deluxe with Hum

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NAD - Fender 57 Custom Deluxe with Hum

Post by Dano_NZ »

Finally managed to get a 57 Custom Deluxe (longish story). Sounds great although haven't really cranked it yet. Problem is I get a low 60/50hz cycle hum when idling. Nothing plugged in. Pulled the V2 and it's gone, also touch the chassis and it reduces. I have a pretty old house (1929) and I suspect the wiring is not great. Tried different outlets around the house and same issue. Tried different amps, Carr Rambler same plug very quiet and the 57 Champ not silent but very close.

Worth getting it looked at post lockdown? I'm Wellington based.

Thanks in advance amp techs.

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Re: NAD - Fender 57 Custom Deluxe with Hum

Post by Slowy »

Swap V1 and V2. Or try a tube from the Rambler and see if it makes a difference.
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Re: NAD - Fender 57 Custom Deluxe with Hum

Post by robthemac »

Looks hot, even if it does hum. Would make a great support for a leanin' guitar.

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Re: NAD - Fender 57 Custom Deluxe with Hum

Post by sizzlingbadger »

Its fucked, send it to me and I'll make sure its disposed of in an environmentally friendly manner.
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Re: NAD - Fender 57 Custom Deluxe with Hum

Post by Dano_NZ »

sizzlingbadger wrote: Thu Aug 26, 2021 1:06 pm Its fucked, send it to me and I'll make sure its disposed of in an environmentally friendly manner.
:rofl:

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Re: NAD - Fender 57 Custom Deluxe with Hum

Post by Dano_NZ »

Thanks for the tips. Tried a few 12AX7's just the same then a 12AT7 (quieter). I'll run with that for now for home use. Anyone had luck with "low noise" preamp tubes?

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Re: NAD - Fender 57 Custom Deluxe with Hum

Post by RectifiedAmps »

Does it do it *with* a guitar plugged in? And what effect on the hum does turning down the amp’s volume and tone controls?

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Re: NAD - Fender 57 Custom Deluxe with Hum

Post by calling card »

Is it a reissue? looks new. The originals had a ground switch.
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Re: NAD - Fender 57 Custom Deluxe with Hum

Post by Dano_NZ »

RectifiedAmps wrote: Thu Aug 26, 2021 1:48 pm Does it do it *with* a guitar plugged in? And what effect on the hum does turning down the amp’s volume and tone controls?
Hum is there without the guitar plugged in and changing the volume and tone makes no difference. Thanks.

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Re: NAD - Fender 57 Custom Deluxe with Hum

Post by Dano_NZ »

calling card wrote: Thu Aug 26, 2021 1:57 pm Is it a reissue? looks new. The originals had a ground switch.
It's a new reissue of the 57 Deluxe.

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Re: NAD - Fender 57 Custom Deluxe with Hum

Post by RobRoyMcCoy »

Dano_NZ wrote: Thu Aug 26, 2021 1:26 pm Thanks for the tips. Tried a few 12AX7's just the same then a 12AT7 (quieter). I'll run with that for now for home use. Anyone had luck with "low noise" preamp tubes?
A "low noise" pre-amp tube is probably not the solution if you have tried a few. The 12AT7 has lower gain so will amplify the hum less. Is often difficult to diagnose via the interwebz so taking it to a tech once lockdown is over is certainly a good option. Particularly so if you are not confident in poking around inside a high voltage device.

Hey, you may get lucky, there are lots of smart people on here and hopefully it is something simple and/or obvious.
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Re: NAD - Fender 57 Custom Deluxe with Hum

Post by RectifiedAmps »

There’s nothing in the circuit between the volume and tone controls and the first grid of V2, so the problem must be V2 itself or something inbetween V2a and V2b. If other 12ax7s still hum then it can’t be the tube itself, so you’re left with capacitor C7, which may be leaking DC voltage through to the grid of the phase inverter (V2b). If you have a multimeter and you’re comfortable with electricity, you could put the negative probe on pin 8 of V2 and the positive probe on pin 7 and see what the DC voltage reading is. It should be a few volts negative. If it’s zero or positive then that tells us C7 is leaking DC from the anode of V2a.

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Re: NAD - Fender 57 Custom Deluxe with Hum

Post by jeremyb »

Try tying a knot in the power cord, acts as a poor mans variac.
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Re: NAD - Fender 57 Custom Deluxe with Hum

Post by MikeC »

Dano_NZ wrote: Thu Aug 26, 2021 1:26 pm Thanks for the tips. Tried a few 12AX7's just the same then a 12AT7 (quieter). I'll run with that for now for home use. Anyone had luck with "low noise" preamp tubes?
12AT7 = less gain than a 12AX7 so you would expect that the hum would reduce if the hum source is before that tube in the pre-amp. Could be heater wiring (lead dress). Does the hum change if you plug a guitar in?

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Re: NAD - Fender 57 Custom Deluxe with Hum

Post by RectifiedAmps »

Forgot to add the schematic to my post…
57_deluxe.pdf
(656.27 KiB) Downloaded 7 times

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