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AI & ENTERPRISE

RTX 4090

48GB

Twice the memory, all the power.

The first dedicated RTX 4090 VRAM upgrade service in the United Kingdom.

From £1,000.

Blackstone Repair is the first dedicated provider of RTX 4090 24GB to 48GB VRAM upgrade services in the United Kingdom, to the best of our knowledge at the time of launch. This service is not endorsed by or affiliated with NVIDIA Corporation.

From £1,000 when the original 12 memory chips are healthy and can be transplanted. Final price depends on parts required and is always agreed before work begins.

Your original core, clocks, and power limit are unchanged: only memory capacity increases. Every card is tested before it ships and the results are recorded on the test report we send with it. Full detail in our upgrade terms.

AI models, 8K timelines, and production renders all run out of memory before they run out of compute.

The RTX 4090 has the speed for all of it, but NVIDIA gave it only 24GB.

OFF THE CLOUD

AI that runs in the room with you.

A 48GB card turns a desktop into a serious AI workstation, with the models running on the machine in front of you.

The bigger the model, the smarter it is, and the more memory it needs.

Check what fits in 48GB →

A private assistant that reads everything you give it.

Legal contracts and case files, patient records, unpublished university research, client code under NDA. It answers from those documents without a single word leaving the machine.

Image and video generation with no meter running.

Flux at full precision and local video generation both outgrow a stock 24GB card. On 48GB they run without offload, overnight if the job calls for it, and the only cost is the electricity.

A coding assistant with the whole codebase in view.

48GB holds a capable model and enough context to keep a whole repository in view at once, not just the file you have open.

70B-class models, the tier where answers get good.

At Q4 quantisation a 70B model needs around 43GB. That tier never fits in 24GB, which is the reason this upgrade exists.

Why local beats the cloud for this

Private by physics

Nothing is uploaded, logged, or retained by a provider. Data cannot leak from a server it never reached.

A single cost

No per-token billing, no monthly tier, no invoice spike after a heavy week. Buy the memory once, run it flat out.

No terms attached

No rate limits, no model deprecations, no usage policies shifting underneath the work. The models you choose, configured your way, available offline.

Built to multiply

These are 2-slot blower cards, made for dense systems. Four in one workstation is 192GB of VRAM, for a fraction of the price of a single 48GB workstation card.

If everything you run fits in 24GB, you do not need this. The fit checker below tells you honestly.

What happens to your card

  1. 1

    Register and get your quote

    Tell us about your card. We reply personally with a fixed quote, split into parts and our work, plus the full terms.

  2. 2

    Ship it or drop it off

    A deposit covering the parts secures your build. Then tracked, signed-for Royal Mail shipping with the cover figure shown in pounds before you book, or drop off in Milton Keynes by appointment.

  3. 3

    Teardown and validation

    We photograph everything on arrival and check your core first. If it cannot take the upgrade, your deposit comes straight back, before any parts are committed to the build.

  4. 4

    The transplant

    Hot air on a controlled preheat curve lifts your core and memory from the old board, with thermocouples tracking every stage. Cleaned and reballed, they move to the new clamshell board alongside the additional modules that double the capacity. The rebuilt card then goes through the full test protocol below.

What can go wrong and what we do about it →

5

TEST PROTOCOL

Tested before it ships

Test protocol v1.0, June 2026

  1. 5.1

    Driver recognition

    Standard NVIDIA drivers, no special configuration. The system sees 48GB or the card does not ship.

    nvidia-smi reports 48GB at full PCIe link width
  2. 5.2

    Memory validation

    Chip-level fault isolation across every populated memory channel, run at stock and again above stock. Zero errors tolerated at either setting.

    every memory channel validated, zero errors tolerated
  3. 5.3

    Sustained burn-in

    Sustained AI generation workloads at full power draw, with rest and cool-down periods, across a 48-hour test window.

    AI workloads across a 48-hour test window
  4. 5.4

    Thermal mapping

    Front and rear module temperatures measured at equilibrium. The clamshell design puts 12 modules on the rear, so we check them all.

    memory junction temperatures within spec under sustained load
  5. 5.5

    The report

    Every card ships with its own test report. It doubles as the warranty baseline: if the card ever comes back, that report is what we measure against.

    signed, dated, ships in the box
6

Balance and tracked return

Your deposit covered the parts. The balance, our work, is due only when your card has passed everything. It returns tracked and signed-for, with the cover figure shown in pounds before dispatch, in plain unmarked packaging, and we share the test results we recorded at completion.

Every report carries the date, the test versions, and the signature of the engineer who ran it.

As builds complete, their test reports, thermal captures and bench data publish here, card by card. First builds land autumn 2026.

It stays your card. Same core, same silicon, twice the memory.

Will it fit and is it worth it

13B class

A capable assistant at full precision · 32GB and up

Quant

FP16

Needs

~26GB

16GBdoes not fit
24GBdoes not fit
32GBfits
48GBfits

30B class

Strong reasoning and document analysis · tight at long context on 24GB

Quant

Q4

Needs

~18GB

16GBdoes not fit
24GBfits
32GBfits
48GBfits

30B class

higher precision, needs 48GB

Quant

Q8

Needs

~32GB

16GBdoes not fit
24GBdoes not fit
32GBdoes not fit
48GBfits

70B class

Near-frontier quality, the best on one card

Quant

Q4

Needs

~43GB

16GBdoes not fit
24GBdoes not fit
32GBdoes not fit
48GBfits

70B class

needs multi-card

Quant

Q8

Needs

~75GB

16GBdoes not fit
24GBdoes not fit
32GBdoes not fit
48GBdoes not fit

70B-class at Q4_K_M quantisation, 8K context, needs about 43GB: fits with headroom on 48GB, does not fit on 24GB. Figures cross-checked against three published 2026 VRAM guides, as of June 2026.

All roads lead to 48GB

The 48GB upgrade

VRAM

48GB

Bandwidth

~900 GB/s

Cost

From £1,0001

Warranty

90 days, modules included

Note

send a card in, or buy one ready-built1

Stock RTX 4090

VRAM

24GB

Bandwidth

~900 GB/s

Cost

~£1,700 used market3

Warranty

out of warranty, returns vary by seller

Note

70B-class will not load2

RTX 6000 Ada 48GB

VRAM

48GB

Bandwidth

960 GB/s

Cost

£7,172 new, ~£6,300 used6

Warranty

manufacturer terms

Note

ECC, pro drivers

Cloud rental, 48GB class

VRAM

48GB, rented

Bandwidth

960 GB/s class4

Cost

~£590 a year at 4h/day4

Warranty

not applicable, rented

Note

data leaves the building

DIY kit route

VRAM

48GB, if the build works

Bandwidth

~900 GB/s, same design

Cost

~£420 kit, plus modules, plus £2,000+ rework gear5

Warranty

none5

Note

slow, demanding work, one slip can end the core

  1. From £1,000 on a send-in RTX 4090 with healthy memory. Ready-built units on donor cards we source are quoted per build. The final quote is always agreed before work begins.
  2. See the fit checker above for what fits where.
  3. PriceSpy UK best price, eBay UK sold listings, June 2026.
  4. RunPod RTX 6000 Ada hourly rate, about £0.59 an hour, June 2026.
  5. One kit vendor’s published price, about £420, June 2026. Their terms state: “PCB Kits are not covered under warranty of any kind.”
  6. NVIDIA RTX 6000 Ada Generation 48GB: £7,172 new (PriceSpy UK best price) and about £6,300 used (eBay UK sold listings), June 2026. The RTX 6000 Ada is a professional workstation card with ECC memory and certified drivers, differing from this upgrade in other respects.

Published third-party figures, as of June 2026. Our own measured numbers replace these as our builds complete.

Not for gaming. Games do not use 48GB.

Not for workloads that already fit in 24GB. The extra memory would sit idle.

The full honest list

Built in the UK

No borders, no customs

Your card never leaves the country. No import VAT on the service, no duty, no seizure risk.

UK consumer law applies

The Consumer Rights Act 2015 covers this work. Your statutory rights survive everything in our terms.

Covered both ways

Shipping cover is shown in pounds at the point of booking, before you commit, with the cover figure for the return leg shown the same way before dispatch.

You talk to the engineer

The person who quotes your card is the person who builds it and signs its report.

Sending your card abroad, or buying a ready-modified one from overseas, typically costs hundreds of pounds more once shipping, VAT, duty and the markup are added. It also means weeks of waiting while the card sits in transit and at customs checkpoints.Ours is a tracked Royal Mail parcel, there and back.

PRICING

What the price includes

From £1,000.

Two ways to get one: send a 4090 in for the upgrade, or have us build one on a donor card we source and test. Ready-built units are quoted per build.

A £500 deposit covers your parts and starts the build. The £500 balance is for our work, due only when your card passes.

  • Teardown, core and memory validation, photographed on arrival
  • New clamshell board, the latest 3.0 revision, in a 2-slot blower form factor built for multi-card systems
  • 12 additional Micron D8BZC modules fitted alongside the original 12
  • Firmware configured for the doubled memory
  • The full test protocol and a signed report in the box
  • 90-day warranty covering our work and the modules we fit

The only thing that can add to the price is replacement memory, at our published chip prices, added to the parts deposit, and only with your agreement after diagnosis.

Because we are new, reputation matters more to us right now than margin, so this price is lower than it will be once our work speaks for itself.

Card faulty? Most faults live on the board rather than the core, where failures are rare. The upgrade moves your core and memory to a new board anyway, so a faulty card is often a perfect candidate. We repair and upgrade in a single job.

Warranty at a glance

Our rework: solder joints, board assemblyCoveredour work, our responsibility
Memory modules we fitCoveredtested before the card ships
Your original core and memoryNot coveredthey are your original parts, so their underlying health sits outside the warranty
User damage, overclocking, liquidNot coveredstandard exclusions
Read the full upgrade terms and warrantyWhat can go wrong and what we do about it

Returned tracked and signed-for, in plain unmarked packaging.

Register your interest

We reply personally as soon as we can, usually within two working days.

Condition
How many cards?
How did you hear about us? (optional)
I have read and accept the Policies and Terms.

They cover pricing and parts, shipping and transit cover, the 90 day warranty, and how we photograph and record work on your device, including footage we may publish on YouTube.

Read the Policies and Terms ›

Also available: the RTX 4080 SUPER 16GB to 32GB upgrade.

See the 4080 SUPER upgrade

Questions, answered properly

No. The card runs on standard NVIDIA drivers and reports 48GB out of the box.

No. Your core is untouched and the memory runs at stock speeds, so compute and bandwidth are unchanged. Your signed report shows your own card’s measured numbers, since real-world results vary by workload.

The 48-hour burn-in exists to answer this. For business-critical deployments we recommend a spare card, as we would with any hardware.

We do not have one yet, honestly, because we have just started. Nor will we invent a number before the builds add up. What stands behind every card instead: every memory channel validated, the 48-hour test window before shipping, and the 90-day warranty. Real figures publish here as they accumulate.

Often ideal, oddly enough. Most faults live on the board, which is replaced anyway, while core failures are rare. If diagnosis finds something deeper, we tell you first and your deposit comes back in full.

Yes, any board-level shop with the right tooling can. We are the best placed though, since we built the card and hold its baseline test report.

You can. The comparison above prices that route too. It needs the board, twelve matched modules, BGA rework equipment, and the skills to use them, with no warranty if it goes wrong. If you have all four, you do not need us.

No. Games rarely use anywhere near this much VRAM. The upgrade is for memory-bound AI and compute work.

Yes, it is your card. Our terms ask one thing: describe it accurately as a modified card when you sell it. The test results we recorded help your sale, since the next owner gets the same record you did.

Cover figures are shown in pounds next to every shipping option before you book. For a high-value return we agree the service and its cover figure with you before anything ships. Full details are in the shipping section of our terms.

Three or more cards quote as a batch with scheduled build slots. A £500 reservation deposit secures the slots and comes off the final invoice. Use the form below and tell us how many.

Only a bad core can stop it, since memory just gets replaced. If your core cannot take the upgrade, your deposit comes back in full and you choose between a return at your shipping cost or donating it to us.

Twice. A parts deposit when you accept the quote, then the balance for our work once your card passes testing. If we cannot proceed after diagnosis, the deposit comes back in full.

Heat, mainly: the transplant takes controlled heat cycles, with a small but never-zero risk to the core and the memory. We publish the honest picture, risk by risk, on its own page:

What can go wrong and what we do about it

Same approach, 16GB to 32GB, from £850. The full page is linked at the bottom.