NAD 1975 Vox AC30

dudu · October 2023

I struck gold once before. That was a while back. I bought this on a whim based on a couple of low-res pictures on an auction website. It was priced not too much above what the speakers alone would cost. They looked good so I thought if nothing else I would keep them and bin the rest.

What I didn't expect to get was a near-museum condition piece. As far as I can tell, the only changed bits are the cut knob and the power valves. Preamp valves are the stock (I think) RFT/Mazda of the time. Oh, and the flight case was included

It sounds wonderful, especially in a wet-dry setup with my JMI 30/6 and the Geckoplex.

The only thing left to sort out is explaining to my better half why I now need both

Alex2678 · October 2023

That is insanely clean. The panel looks factory fresh

theatreanchor · October 2023

Colour me jealous.

dazzajl · October 2023

Wha a gorgeous pair, they are both subzero cool.

dudu · October 2023

It has been great having both and comparing an actual Vox (factoring in the solid state rectification) and the JMI replica made in 2007. They could have easily been made by the same outfit, absolutely nothing separates them in terms of build quality, tone and vibe. Any difference would fall within the variation margin between any two different units.

ICBM · October 2023

That’s incredibly clean.

I think the speaker cabling and possibly the mains cable has been replaced too, but that’s just sensible maintenance. Being ultra-fussy I would prefer the red/black speaker wire to be wrapped through the terminal hook and not just tacked to it with the solder though

.

The solid-state rectifier makes a surprisingly small difference in my opinion - just a tiny bit tighter, but AC30s don’t actually have much sag even with the GZ34.

Supportact · October 2023

It almost looks new! That wet /dry set up is lush.

ecc83 · October 2023

ICBM will surely put me right on this but I have heard that AC30s ran the bllx off the EL84s? Might be an idea to look for 'red plating' in a dim room?

If you have the gear and the technicals, measure the cathode voltage and HT then, together with the value of the cathode resistor, work out the anode dissipation. The old EL84s would stand the extra heat, not sure about modern ones. The fix is to slightly increase the cathode resistor value, about 22 Ohms seems to sort it.

Dave.

ElectricXII · October 2023

Very nice. Pretty much among the last of the original hand wired AC30s if I'm not mistaken.

ICBM · October 2023

ecc83 said:

ICBM will surely put me right on this but I have heard that AC30s ran the bllx off the EL84s?

Yes, typically around 16W at idle.

The stock cathode resistor is 50 ohms. Going up to 62 or 68 ohms is usually about right for modern EL84s. Higher than that starts to affect the sound - AC30s are always a balancing act between sounding great and cooking themselves

.

Danny1969 · October 2023

I've just done 2 AC30's and used 68R resistors for the cathodes as I thought they were running way too hot. Normally all the AC30's I see have all kinds of botch jobs done, mainly with the large filter caps. The dual filter cap on the right doesn't look stock compared to all the one's I've see but I could well be wrong.

cathodyne · October 2023

Wow, gorgeous! Perhaps the perfect excuse for keeping both might be to run some stereo delay or trem?

Cirrus · October 2023

I prefer lowering the b+ voltage to biasing them colder, but that's much more invasive than a simple resistor change.

That's a beautiful amp there! Those will be some of the last alnico silvers produced.

ICBM · October 2023

Cirrus said:

I prefer lowering the b+ voltage to biasing them colder, but that's much more invasive than a simple resistor change.

You can actually just add a series resistor after the diodes if it’s a solid-state rectifier one - that both drops the voltage a bit and simulates the valve rectifier sag. From memory 47-ohm 10W is about right, although I’d be more inclined to use a 15W chassis-mount one for safety.

JezWynd · October 2023

dudu said:

The only thing left to sort out is explaining to my better half why I now need both

One for each ear of course.

What a great score, you must have been astonished on unpacking it.

dudu · October 2023

cathodyne said:

Wow, gorgeous! Perhaps the perfect excuse for keeping both might be to run some stereo delay or trem?

I have a Geckoplex and an Effectrode Delta-Trem just for that!

Dodge · October 2023

I'm totally biased as mine is in the same livery, but the dark diamond grillcloth is SO much nicer than the "classic" brown IMHO.

AC30 = Greatest amp of all time. Enjoy.

Ozzie744 · October 2023

Very Nice Score!!

Musicman20 · October 2023

What a pair!

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NAD 1975 Vox AC30

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