VOX AD30VT 'valve/tube' amp

[n cook]

Retro look of the 1960s Vox AC30 amp made probably 2004 with lots of SM
digital chippery for effects undreamt of in the 60s.
One 12AX7 , but is it for show only ?
Heaters have an AC supply but the anodes don't seem have any HV components
attached to them. The speaker o/p is a non-retro National Semi LM3886T.
I've not powered up yet as only poking around cold at the moment as I've
never seen the like before, all seems DVM ok for power supplies etc.
Apparently went pop between songs and then no more.

 

[Arfa Daily]

Retro look of the 1960s Vox AC30 amp made probably 2004 with lots of SM
digital chippery for effects undreamt of in the 60s.
One 12AX7 , but is it for show only ?
Heaters have an AC supply but the anodes don't seem have any HV components
attached to them. The speaker o/p is a non-retro National Semi LM3886T.
I've not powered up yet as only poking around cold at the moment as I've
never seen the like before, all seems DVM ok for power supplies etc.
Apparently went pop between songs and then no more.

I had one of these in for repair a while back. As far as I recall, the
triode stage is genuine, but not run from a particularly high HT voltage.
You can get away with some quite low anode voltages on these twin triodes.
Elektor mag have published a few circuits in recent years, where they have
run these at low HT. The digital simulations of various retro amp types, was
actually remarkably good.

Arfa

 

[n cook]

I had one of these in for repair a while back. As far as I recall, the
triode stage is genuine, but not run from a particularly high HT voltage.
You can get away with some quite low anode voltages on these twin triodes.
Elektor mag have published a few circuits in recent years, where they have
run these at low HT. The digital simulations of various retro amp types, was
actually remarkably good.

Arfa

I'll get around to powering up tomorrow but from poking around there are no
capacitors with greater than 50V dc working anywhere on the ps and o/p
board, I've not undone the digital effects board.
I've just noticed a 3.3V v. reg.

 

[n cook]

I had one of these in for repair a while back. As far as I recall, the
triode stage is genuine, but not run from a particularly high HT voltage.
You can get away with some quite low anode voltages on these twin triodes.
Elektor mag have published a few circuits in recent years, where they have
run these at low HT. The digital simulations of various retro amp types, was
actually remarkably good.

Arfa

Damn hybrid O/P devices , -V rail to o/p short on the LM3886T.
Not being abused and no audio troughput at all when it failed.
Is there a learned file on WWW on why these sort of devices fail ,
a loudspeaker wire short or heavy throughput you could understand.

So ten squid to replace rather than just a 3055 or 3773

 

[n cook]

Retro look of the 1960s Vox AC30 amp made probably 2004 with lots of SM
digital chippery for effects undreamt of in the 60s.
One 12AX7 , but is it for show only ?
Heaters have an AC supply but the anodes don't seem have any HV components
attached to them. The speaker o/p is a non-retro National Semi LM3886T.
I've not powered up yet as only poking around cold at the moment as I've
never seen the like before, all seems DVM ok for power supplies etc.
Apparently went pop between songs and then no more.

I will probably use a 100W TDA7294 as I've a couple at hand, pinning swapped
to match the 68W LM3886.
Monitoring phones outlet, all effects and classic amp colourations are
functioning so the valve is presumably an expensive and highly inefficient
indicator, for show only, the maximum DC on any of its pins wrt ground
is -15V

 

[default]

Monitoring phones outlet, all effects and classic amp colourations are
functioning so the valve is presumably an expensive and highly inefficient
indicator, for show only, the maximum DC on any of its pins wrt ground
is -15V

No experience with the VOX amp, but in the 50's I do remember a
pop'tronics article on using tubes "starved for voltage" They had a
radio with a plate supply of +12 volts driving a single transistor
class A transformer coupled output.

I don't remember which tubes they used, but they were standard 6 & 12V
filament parts.

 

[Neil J. Harris]

I seem to remember the was PC motherboard with a 12A?7 on it a few
years ago -for that authentic valve sound -
car radios with valve front ends and no vibrator pack, but, they were
special valves with an extra grid I think.

 

[Michael A. Terrell]

I seem to remember the was PC motherboard with a 12A?7 on it a few
years ago -for that authentic valve sound -
car radios with valve front ends and no vibrator pack, but, they were
special valves with an extra grid I think.

That motherboard was made by Aopen, which is Acer computers.