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Ampex 350 Preamp

Ampex 350 Preamp

Brand: Ampex

Regular price £2,000.00 GBP
Regular price Sale price £2,000.00 GBP
Sale Sold out
Shipping calculated at checkout.

No longer in stock. If you're interested in something similar, please make an enquiry below.

Classic Ampex valve/tube preamp overhauled to an extremely high standard – ready to go to work as a standalone unit.

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Product Description

Ampex 350 valve/tube preamp for sale. This unit is part of a collection we are brokering on behalf of our New York engineer at Thump.

Extensive work has been undertaken to produce excellent standalone preamps. Full details of work completed and additional optional modifications below, as well as shipping arrangements.

The seller had this to say about this unit:

A single channel unit that we purchased in order to compare the 351 to out of curiosity.  This too is rebuilt completely stock and could find a soulmate transport.  The 350 is a different animal all together from the power supply through the circuit itself.  The build even is drastically different.  No boards and all point to point wiring. Very neat piece.

At the time of writing, some units are available with a modification to bypass the tape transport electronics.

See all the Ampex units we have available here.


  • JLM phantom phase pad (very helpful for these as the first V1 stage is quite hot)

  • Output termination (600 ohm load)

  • Meter defeat (lowers distortion levels in the unit)

  • Output attenuator

All of these modifications are to be mounted on a simple 1U rack space panel to maintain the original aesthetic of the unit. Price £600. If the buyer doesn't require all these options, this can be discussed after purchase.


Detailed information on the work completed by Thump NYC:

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!


SHIPPING: This item is located in the USA. Brokerage sale so shipping is arranged between the buyer and seller direct (but we can usually help with access to trusted couriers etc). If you need an estimate then get in touch.

Brokerage Sale Information:

Brokerage 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 item is not at Soundgas and we have (sadly) not had a chance to test it ourselves yet. We only work in this way with trusted clients who understand their gear. 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.

It remains the buyer’s responsibility to confirm details provided in the listing by the seller are to their satisfaction – if you have any questions at all please let us know before we arrange shipping.

As a brokerage 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.


<p class="p1">In excellent cosmetic condition for its age with only minor signs of wear. See photos for more information on cosmetic condition.</p>

Voltage Information

Switchable voltage for use anywhere in the world - it will be set up ready for you to use before we ship.


Zero rated for VAT.

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