yewneek
Active Member
I got a pair of good condition KEF Reference 104/2 from e*ay for 280GBP, and paid another 100GBP to have them couriered to me.
While playable, they were untouched from new, (May 1986) so needed to be fully restored. Which I completed at 230am this morning, totalling 20 or so hours work over 4 days or so. I built on the previous experiences I've documented here, and with other speakers I've not mentioned. Possibly 10-15 pairs in total over several years, usually listened to for a while then flipped for cost.
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• Removal of all drivers and crossover assemblies for inspection and servicing.
• Noted perished mid–bass coupler foam donuts, aged electrolytic capacitors, and one woofer with a potential surround bond issue.
• Identified crossover mounting using hard washers; replaced with rubber grommets to improve vibration damping and prevent PCB stress.
• Removed degraded ferrofluid from magnetic gap.
• Cleaned pole pieces and gap with isopropyl alcohol, noting that brown staining was cosmetic only.
• Refilled with generic ferrofluid for tweeters supplied by Blue Aran.
• Cleaned bonding surfaces to bare substrate using xylene as a solvent.
• Installed new foam donuts sourced from a correct, application-specific supplier for KEF 104/2 restoration.
• Bonded in place with T-7000 adhesive.
• Applied an additional bead of T-7000 around outer rims, pressed into place to ensure full adhesion and air-seal integrity.
• One unit exhibited abnormal noise in comparative testing; unglued surround using xylene, re-centred coil with PET shims, re-glued with T-7000.
• As a preventative measure, re-glued rim of surrounds of all B200 drivers with T-7000 adhesive to ensure uniform compliance and eliminate asymmetry risk. They were then replenished with PlatenClene, (hexane based cleaner/lubricant which preserves the butyl rubber and acts as an oxidation inhibitor).
• Installed Falcon Acoustics capacitor kit – like-for-like Alcap replacements in correct values and voltage ratings.
• Verified values against originals and schematic at each stage.
• Secured large parallel capacitors with hot-melt glue to prevent vibration damage.
• Cleaned solder side with isopropyl alcohol.
• Applied Servisol Super 10 to solder side, inductor ferrite core, and all contact points to inhibit oxidation.
• All soldering carried out using high-quality 60/40 tin–lead rosin core solder to match original joint characteristics and ensure long-term reliability, avoiding the brittleness and fatigue issues common with lead-free alloys.
• Replaced woofer mounting grommets where degraded with like-for-like or superior material equivalents.
• Ran 20–400 Hz sweep tones at moderate SPL – no parasitic resonances detected.
• Conducted subjective listening tests with classical music – confirmed improved bass clarity, definition, and overall system fullness.
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**Total Cost:** £644
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Scope: Complete mechanical and electrical service — tweeter ferrofluid replacement, donut refoams, crossover recap, driver mechanical checks, full surround re-glue, cleaning, oxidation protection, reassembly.
Analytical Basis: Degraded ferrofluid increases HF damping, reducing extension and clarity.
Improvement: Clearer high frequencies, better transient definition.
Consideration: No further cleaning required; staining is cosmetic.
Analytical Basis: Donuts act as acoustic resistors between B200 cones, controlling coupled-cavity bass response.
Improvement: Restored correct LF damping, tighter bass, reduced lower-mid masking.
Consideration: Foam chosen to match KEF’s original compliance; extra T-7000 applied at edges to improve sealing and adhesion.
Analytical Basis: Ensures uniform compliance, eliminates partial bond failures, and removes any asymmetry risk.
Improvement: All four B200 surrounds now have identical adhesive and curing history.
Consideration: T-7000 chosen for its flexibility, adhesion to both paper and rubber, and long-term stability.
Analytical Basis: Prevents long-term edge lift and ensures airtight coupling.
Improvement: Enhanced mechanical stability and acoustic consistency over service life.
Analytical Basis: Ageing electrolytics increase ESR, affecting tonal balance.
Improvement: Restored tonal accuracy, tighter bass response.
Consideration: No cosmetic reflow to avoid thermal stress on large copper planes.
Analytical Basis: Prevents oxidation, maintains low contact resistance.
Improvement: Slows long-term corrosion in woofer cavity.
Consideration: Chosen over conformal coating for ease of future servicing.
Analytical Basis: Reduces PCB bowing and vibration transmission.
Improvement: Less mechanical stress on solder joints.
Analytical Basis: Maintains acoustic integrity.
Improvement: Consistent driver coupling and sealing.
Analytical Basis: Confirms mechanical stability in intended operating range.
Outcome: LF performance restored; no mechanical faults present.
Summary: All mechanical and electrical wear points replaced or serviced. HF restored via ferrofluid service; LF damping corrected with new donuts; all B200 surrounds re-glued; donut edges sealed; one woofer re-centred; all capacitors replaced; contacts cleaned and protected; mounting points upgraded. Projected service life: decades under normal use.
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REW files to follow, prior and following. I need to set up a post-restoration analysis, and I'm enjoying the music for now!
GB
www.bluearan.co.uk
www.thepolishingshop.co.uk
af-net.com
www.falconacoustics.co.uk
www.richersounds.com
While playable, they were untouched from new, (May 1986) so needed to be fully restored. Which I completed at 230am this morning, totalling 20 or so hours work over 4 days or so. I built on the previous experiences I've documented here, and with other speakers I've not mentioned. Possibly 10-15 pairs in total over several years, usually listened to for a while then flipped for cost.
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KEF 104/2 – Formal Service Record
This document records the full refurbishment and restoration of the KEF Reference 104/2 loudspeakers, carried out to a standard meeting or exceeding professional practice in mechanical and electrical service for vintage loudspeakers. All work was completed with suitable, application-specific materials and methods, restoring original performance and ensuring long-term reliability.Work Summary
• Full disassembly of both loudspeakers.• Removal of all drivers and crossover assemblies for inspection and servicing.
• Noted perished mid–bass coupler foam donuts, aged electrolytic capacitors, and one woofer with a potential surround bond issue.
• Identified crossover mounting using hard washers; replaced with rubber grommets to improve vibration damping and prevent PCB stress.
Tweeter Service
• Disassembled KEF T33 tweeters.• Removed degraded ferrofluid from magnetic gap.
• Cleaned pole pieces and gap with isopropyl alcohol, noting that brown staining was cosmetic only.
• Refilled with generic ferrofluid for tweeters supplied by Blue Aran.
Mid–Bass Coupler Donut Replacement
• Removed all original, perished foam donuts.• Cleaned bonding surfaces to bare substrate using xylene as a solvent.
• Installed new foam donuts sourced from a correct, application-specific supplier for KEF 104/2 restoration.
• Bonded in place with T-7000 adhesive.
• Applied an additional bead of T-7000 around outer rims, pressed into place to ensure full adhesion and air-seal integrity.
Woofer Surround Re-glue
• Inspected all KEF B200 bass drivers.• One unit exhibited abnormal noise in comparative testing; unglued surround using xylene, re-centred coil with PET shims, re-glued with T-7000.
• As a preventative measure, re-glued rim of surrounds of all B200 drivers with T-7000 adhesive to ensure uniform compliance and eliminate asymmetry risk. They were then replenished with PlatenClene, (hexane based cleaner/lubricant which preserves the butyl rubber and acts as an oxidation inhibitor).
Cabinet Internal Foam Re-adhesion
• Inspected and re-adhered internal cabinet acoustic foam using appropriate spray adhesive to restore original fit and damping.Crossover Refurbishment
• Removed all original capacitors.• Installed Falcon Acoustics capacitor kit – like-for-like Alcap replacements in correct values and voltage ratings.
• Verified values against originals and schematic at each stage.
• Secured large parallel capacitors with hot-melt glue to prevent vibration damage.
• Cleaned solder side with isopropyl alcohol.
• Applied Servisol Super 10 to solder side, inductor ferrite core, and all contact points to inhibit oxidation.
• All soldering carried out using high-quality 60/40 tin–lead rosin core solder to match original joint characteristics and ensure long-term reliability, avoiding the brittleness and fatigue issues common with lead-free alloys.
Mounting Hardware
• Replaced hard washers between crossover PCB and cabinet with large rubber grommets, superior to original in vibration damping and longevity.• Replaced woofer mounting grommets where degraded with like-for-like or superior material equivalents.
Reassembly & Testing
• Reinstalled all drivers and crossover assemblies, ensuring even torque and correct gasket seating.• Ran 20–400 Hz sweep tones at moderate SPL – no parasitic resonances detected.
• Conducted subjective listening tests with classical music – confirmed improved bass clarity, definition, and overall system fullness.
Materials Statement
All replacement parts and consumables used were suitable for the application, matched or exceeded original specification, and sourced from reputable suppliers. Donuts were sourced from a specialist supplier for KEF 104/2 restoration; ferrofluid was generic tweeter-grade fluid supplied by Blue Aran; capacitors from Falcon Acoustics (Alcap brand); adhesives included T-7000 for driver and donut bonding; and appropriate spray adhesive for internal foam. Where hardware was replaced, like-for-like or superior quality parts were used. Cleaning of bonding substrates was performed using xylene where appropriate. All soldering performed with 60/40 tin–lead rosin core solder to ensure electrical and mechanical integrity over time.---------------------------------------------------------------------------------------------------------------------------------
KEF 104/2 Refurbishment – Cost Breakdown
| Item / Description | Cost (£) |
| Speakers (initial purchase) – Private sale / original acquisition | £280 |
| Carriage – Courier transport from seller | £115 |
| Ferrofluid – Generic tweeter-grade ferrofluid, Blue Aran | £10 |
| Speaker cable – 14 AWG OFC cable | £22 |
| Banana plugs – Gold-plated banana plugs | £10 |
| Cable boots – Insulating boots for banana terminations | £6 |
| Capacitors – Falcon Acoustics capacitor kit – Alcap brand | £144 |
| Custom feet – Self-made cabinet feet | £5 |
| Mid-bass donuts – Correct specification foam donuts from specialist supplier | £25 |
| T-7000 adhesive – High-strength adhesive for driver/donut bonding | £10 |
| Mounting grommets – Like-for-like/superior replacements for degraded originals | £7 |
| Xylene – Solvent for removing old adhesive and cleaning bonding surfaces | £10 |
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KEF 104/2 – Full Restoration Record (Updated)
Total work time: ~15–20 hoursScope: Complete mechanical and electrical service — tweeter ferrofluid replacement, donut refoams, crossover recap, driver mechanical checks, full surround re-glue, cleaning, oxidation protection, reassembly.
1. Tweeter (T33) Ferrofluid Service
Disassembled T33 tweeters, removed degraded ferrofluid, cleaned pole pieces and gap with isopropyl alcohol (brown staining noted as harmless cleaning artefact), refilled with measured ferrofluid quantity.Analytical Basis: Degraded ferrofluid increases HF damping, reducing extension and clarity.
Improvement: Clearer high frequencies, better transient definition.
Consideration: No further cleaning required; staining is cosmetic.
2. Mid–Bass Coupler Donut Replacement
Removed perished foam donuts; cleaned cone edges; installed new foam using B-7000/T-7000 adhesive, ensuring concentric placement.Analytical Basis: Donuts act as acoustic resistors between B200 cones, controlling coupled-cavity bass response.
Improvement: Restored correct LF damping, tighter bass, reduced lower-mid masking.
Consideration: Foam chosen to match KEF’s original compliance; extra T-7000 applied at edges to improve sealing and adhesion.
3. Woofer Surround Inspection and Full Re-glue
Initially detected anomaly in one B200 during comparative testing; shimmed, unglued, and re-glued that unit with T-7000. As a final safety measure, re-glued rims of surrounds of ALL B200 drivers with T-7000 prior to reassembly. PlatenClene to clean, preserve, and, ensure elasticity of butyl rubber.Analytical Basis: Ensures uniform compliance, eliminates partial bond failures, and removes any asymmetry risk.
Improvement: All four B200 surrounds now have identical adhesive and curing history.
Consideration: T-7000 chosen for its flexibility, adhesion to both paper and rubber, and long-term stability.
4. Additional Donut Edge Sealing
Ran a secondary bead of T-7000 around the outer rim of each donut, pressing down with a rounded tool to ensure complete adhesion and eliminate any flaps or gaps.Analytical Basis: Prevents long-term edge lift and ensures airtight coupling.
Improvement: Enhanced mechanical stability and acoustic consistency over service life.
5. Crossover Recap & Mechanical Securing
Full recap using Alcap replacements (black), like-for-like values; parallel caps hot-glued; multiple verification passes before, during, and after assembly.Analytical Basis: Ageing electrolytics increase ESR, affecting tonal balance.
Improvement: Restored tonal accuracy, tighter bass response.
Consideration: No cosmetic reflow to avoid thermal stress on large copper planes.
6. Cleaning & Oxidation Protection
Servisol Super 10 applied to solder side, inductor ferrite core, and contacts.Analytical Basis: Prevents oxidation, maintains low contact resistance.
Improvement: Slows long-term corrosion in woofer cavity.
Consideration: Chosen over conformal coating for ease of future servicing.
7. Mounting Isolation Upgrade
Replaced hard washers with large rubber grommets.Analytical Basis: Reduces PCB bowing and vibration transmission.
Improvement: Less mechanical stress on solder joints.
8. Final Reassembly
Drivers remounted; woofer grommets replaced; cabinet screws evenly torqued.Analytical Basis: Maintains acoustic integrity.
Improvement: Consistent driver coupling and sealing.
9. Post-Restoration Performance Verification
20–400 Hz sweeps and classical music listening; no parasitic resonances at ~70 dB SPL.Analytical Basis: Confirms mechanical stability in intended operating range.
Outcome: LF performance restored; no mechanical faults present.
Summary: All mechanical and electrical wear points replaced or serviced. HF restored via ferrofluid service; LF damping corrected with new donuts; all B200 surrounds re-glued; donut edges sealed; one woofer re-centred; all capacitors replaced; contacts cleaned and protected; mounting points upgraded. Projected service life: decades under normal use.
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REW files to follow, prior and following. I need to set up a post-restoration analysis, and I'm enjoying the music for now!
GB
Sonitus Audio :: Sonitus Audio FF05
Sonitus Audio :: Ferrofluid :: Sonitus Audio Ferro Fluid 0.5ml :: Sonitus Audio Ferro Fluid 0.5ml - 4.99. Sonitus Audio Ferro Fluid 0.5ml
www.bluearan.co.uk
Xylene 1 litre Tin | The Polishing Shop
Xylene 1 litre Tin, Solvent that can be used for many cleaning applications.
www.thepolishingshop.co.uk
Platenclene - Printer Roller Cleaner/Restorer - 100ml Spray PCL100 - Technical Cleaning Products for Offices | AF
Key points: Printer roller cleaner and restorer available in 100ml spray and 1L bulk Restores roller flexibility by dissolving ink stains, oil and grease Helps to reduce paper jams Alcohol -free cleaning solution
af-net.com
KEF 104/2 Replacement Capacitor Set
REPLACEMENT CAPACITOR SET FOR KEF 104/2. Each set comprises 2 pairs of 16 no. ALCAP 150/100V and Low Loss electrolytic capacitors as specified by KEF.1 set is needed per pair of KEF 104/2 loudspeakers. Available in 5% Tolerance.
www.falconacoustics.co.uk
ExcellaElite T7000 Super Glue, 50ml Black Multi-Function High Precision Industrial Adhesive for Phone Jewelry Glass Wood Tyre Fabric Crafts : Amazon.co.uk: DIY & Tools
ExcellaElite T7000 Super Glue, 50ml Black Multi-Function High Precision Industrial Adhesive for Phone Jewelry Glass Wood Tyre Fabric Crafts : Amazon.co.uk: DIY & Tools
www.amazon.co.uk
260 Pcs Rubber Grommets Assortment Kit – Durable Rubber Grommets for Holes – Ideal for Electrical, Automotive, and Home DIY Projects : Amazon.co.uk: DIY & Tools
260 Pcs Rubber Grommets Assortment Kit – Durable Rubber Grommets for Holes – Ideal for Electrical, Automotive, and Home DIY Projects : Amazon.co.uk: DIY & Tools
www.amazon.co.uk
Chord Company Trousers Leyline2X / RumourX
Shop for Chord Company Trousers Leyline2X / RumourX Cable Termination (Single) with Richer Sounds for expert advice and Lowest Prices Guaranteed
www.richersounds.com
Isopropanol Alcohol IPA 99.99% 1L : Amazon.co.uk: Business, Industry & Science
Isopropanol Alcohol IPA 99.99% 1L : Amazon.co.uk: Business, Industry & Science
www.amazon.co.uk
951 10ml Soldering Rosin Flux Pen Low-Solids Non-Clean Solar Cell DIY Panel Flux | eBay UK
10ml pen applicator with specially designed felt tip. Capacity: 10ml. Exhibits improved soldering performance to minimize solder bridges (shorts) during rework operations. 100% new high quality. Color as shown.
www.ebay.co.uk
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