Ampex 351 Preamp

Ampex 351 valve/tube preamp for sale. One of two we have here with us in the UK currently (part of a larger collection we are selling on behalf of our New York engineer at Thump).

Originally from an 8-track damaged in transit. Extensive work has been undertaken to produce an excellent standalone preamp. Full details of work completed below.

Note this unit also has a modification to bypass the tape transport electronics and improve signal path – further details below.

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Detailed information on the work completed by Thump NYC:

Modification added that we now call the “thump mod.” This mod essentially bypasses the tape transport electronics allowing for a slightly cleaner signal path. We are left with a much more direct signal path and only parts of the circuit that are dedicated to the mic/line preamp itself remain. Since the tape transport electronics are disconnected, we took that opportunity to hardwire the record indicator lamp to be permanently on to add a bit of extra vibe.

Work done:

• Replaced all electrolytics
• Replaced all passives that commonly leak DC
• Replaced all power resistors
• Replaced any other resistors or otherwise out of spec components
• Re-tension tube sockets
• Cleaned all mechanicals including every edge crimp connection
• New #47 lamps
• Assemble / Test / Burn in

When restoring our Ampex 351s, we began with replacing all electrolytics throughout the circuit. Every single component is changed on the power supply board to insure the circuit is fed exactly what it was intended to receive. This includes all passives (resistors and ceramics) and actives. A common failure point on these units is the old selenium rectifier for the DC heater supply. This too is pulled from the unit and replaced with a pair of 5402 diodes and dropping resistors to provide a perfect 12.6 Vdc heater supply in the circuit. Once our blanket parts swap is complete we clean every interconnecting point within each unit and resolder weak traces to make sure there is no fear for intermittent edge card crimp connections. We tighten all hardware and clean all mechanicals until the unit feels good to operate. The unit is then brought up on a variac slowly to help form the new capacitors and all power is checked over throughout the circuit. Tubes are loaded and power is checked again. Mic check, we’ve got another Ampex!

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Consignment sale on behalf of a client. If you have gear that you want us to look at selling on your behalf then please look at our Commission & Consignment page for more information and get in touch to discuss your requirements.

This particular unit comes from a good friend of Soundgas, whose expertise and attention to detail matches (and at times exceeds) our own: this will not disappoint.

As a commission sale, payment will be made to us but will be held in escrow for the seller until the buyer confirms satisfactory receipt of the item. The buyer has 14 days from receipt to raise any concerns, after which we will release funds to the seller. Full terms available on request.