Ampex 601 - Keepin’ it runnin’

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Ampex 601 - Keepin’ it runnin’

Post by heavenorlasvegas »

Greetings :sos: !

I was hoping to find some information on this legendary microphone preamp as recently, I was lucky enough to score one for a very reasonable price :D

What should I be looking for in terms of upkeep and maintenance as it relates to this unit?

I’m hoping to keep it running for the long haul. Please chime in with your experiences :bouncy:

Thanks again!

Posts: 154 Joined: Mon Feb 22, 2021 2:41 pm

Re: Ampex 601 - Keepin’ it runnin’

Post by Hugh Robjohns »

I'm assuming you're talking about the electronics associated with the ancient Ampex 601 tape recorder?

The mic input was designed for an unbalanced high-impedance mic — typical of the time — but a multipin plug can be replaced with a bespoke transformer to allow use with balanced low impedance mics.

So hopefully your preamp came with the optional plug-in transformer.

The preamp itself is a pretty straightforward circuit design, and any competent tech familiar with valve amps will be able to service it easily. There are loads of pages on the web detailing the schematics, servicing, as well as worthwhile upgrades and modifications to reduce noise.

A number of valves handle the tape playback (& EQ) and record stages which are redundant if you just want a mic preamp. Those valves can be removed without affecting the mic preamp or output driver, although you would need to modify the power supply to maintain correct voltages on the remaining circuitry.

Like all vintage valve preamps, there are very high anode voltages and, if it hasn't been serviced recently, a number of electrolytic capacitors could well be failing and need replacement. So take care...
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Hugh Robjohns
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