Last updated: FEB 20th, 2013. Guestbook & feedback

The mathematics of Anti-skating DIY Speakers New REVOX B225, B215, B285 LINK 4

These are items I have bought second-hand, some were in a bad way or incomplete. Some are restoration projects, others just collectibles to love. (Click on image for full sized in new window)

* PHOTOS * Since the collapse of the photo hosting site in January 2013, many of my photographs have vanished from the www. I will re-post & relink them from another host site soon.

My Feedback/Comments is just swamped by Polish spam, (c.f Polish Sausage) so it now is no longer operational. But I'm on AVSA and DIYAUDIO.COM for messaging

Sp10 turntable arty green Building new drive electronics for the Technics SP10 MK2 direct drive turntable motor.

When Jean's Radio & T.V spares sadly closed forever at the the end of 2006, I acquired among a huge pile of components that she gave to me, a new-old-stock motor for the legendary Technics SP10 broadcast turntable.
To become part of a turntable, it needs a 3-phase drive system, and a quartz phase-locked-loop servo control system. This project has a special page here, and web-forum here

ReVox Amplifier painting The non-ReVox "ReVox" Amplifier

A DIY power amplifier built to match the ReVox B250 amplifier and B260 tuner. This drawing on the right is the intended end result (click for large).

Link to page: Project overview and historical notes.

Philips N4520 stereo tape recorder

Phlips N4520 This is reputed to be Philips' best ever domestic tape recorder (the ¼-track version N4520 and the ½-track version N4522). Only a few thousand of the fomer, and a few hundred of the latter were ever made. Both operate at 33/4, 71/2, and 15 IPS, with quartz PLL. The tape tension arms form part of a feedback system that electronically regulates tape tension on both sides, and braking is 'electronic' by motor torque. The VFL counter measures linear tape length calibrated in metres. Curiosly, the transport control buttons are mechanical latching types, there is no logic circuitry involved: auto-stop is achieved by a large solenoid lifting the push-buttons' latching bar as if the stop button had been physically pushed. End of tape sensing is by conductive foil, not optically, but loss-of-counter pulses from the impedance roller will also stop the tansport. Its country of manufacture is not Holland, but Austria.

revox b77

The counter IC was faulty, and impossible to locate as a spare. Fortunately it was not entirely dead, but its internal oscillator had failed. A piggyback oscillator signal, generated using a 7555, injected into the timing pin of the counter IC got the display working again. Concerning my hand-annotation "PLL" on one of the wires to the counter: the display will show five dots ". . . . ." if the capstan PLL fails to lock, so confidence of quartz-accurate speed is always assured.

Phlips N4520 Here is the Philips side by side with a Revox B77. Both were brought into production around the same time - 1979. The Revox is more solidly built, the the Philips is substantially heavier though. The Philips is more akin to the older Revox A700 shown below, as far as features and looks are concerned, but its tape handling is smoother than the A700. The A700 also confirms its quartz-lock status visually like the Philips, but by lighting up the pushbutton correspoding to the selected speed.

ReVox A700 stereo tape recorder

revox A700 The ReVox A700 is quite an uncommon machine outside Europe. Launched in 1973 it was the most advanced home tape recorder you could buy, with a price of US$1800, i.e., very costly. The transport far outclasses the later A77, B77 and PR99. Servo tension control of tape on both sides of the headblock in all modes including braking; electronic braking by the reel motors; quartz PLL capstan, with 33/4, 71/2 AND 15 IPS. Four balanced mic inputs, plus two aux, one radio, and one phono input, with inboard mixer. And solid state control of the reel motors (not by relays) with IC logic supervision (in 1973!). And a real-time counter. And tape motion sensing. Auto-rewind and repeat mode too. The same machine with the IC-based mixer electronics replaced by simpler audio stages became the Studer A67.

The picture above-right is an internet-lifted picture showing the beauty of a new machine. On the left below is the way I got a pair of them.
They stood for years in an abandoned Johannesburg building with the windows smashed out; so the dirt is indescribable - they even had pigeons roosting on them!
Some parts were missing, but by using the two to combine parts, I have got a very nicely working one shown here -> Restoration Photos.

ReVox B77 Mk1 stereo tape recorder

revox b77 The B77 ¼" ½-track reel-to-reel is so famous, a photo is not necessary. This 'Mark 1' version I got for R200 (about $26), and it looked in a sad way. Yet again, I neglected to photograph it before revitalising it - the photo on the right is after I fixed it up. This one had paint splatters across its face (why is that so common with vintage audio - what do people DO with them??), the Record and Monitor knobs were broken off, and the cabinet in front of the handle had been heated to the point of distortion and blistering (a desk lamp perhaps?).

Electrically it seemed to work, but after 10 minutes it started smoking & smelling terrible! No surprises - the Rifa class-X capacitor across the mains had caught fire. Getting to it requires removal of just about everything, so a good opportnty to clean it all out. Someone had replaced the tape-drive-control PCB with the most recent version - which is nice, but also shortsighted, since it isn't directly compatible with the original B77's tape tension switching, it could never have worked properly as I received it! The previous owner must have suffered all kinds of poor starting, and tape snatching. Some rewiring of the reel-size switch and added resistors fixed that.

revox b77

The Record and Monitor switches on all ReVox B7** components are almost always broken when you find them now - a fragile switch dolly - although the switch itself remains fully intact.

Repair here requires drilling a hole directly in the centre of the remainder of the snapped-off dolly (a specially carved wooden centering jig makes this possible), inserting a short steel rod, and fabriating a new dolly. The dollies I machined from strips of acrylic plastic, cut from a cracked tuntable cover. Once painted, they are indistinguishable from the originals (photo above shows my replacements), although not as resistant to finger wear as the genuine metal-coated originals.

The melted cabinet required sanding down, to flatten the warps. I tried filling it with polyester body-filler to restore the dimples, but the polyester reacts with the ReVox plastic and makes it gummy. Instead, I fixed its looks by carving out a rectangular recess along the entire top front, and slotting in a strip of 35mmx10mm aluminium extrusion. Apart from the fact that no other B77 has an aluminium 'fringe', it looks like it came out of the factory like this! All the original Nextel had to come off - easy enough as it dissolves totally in ordinary methylated sprits. Recoating in Nextel is just too costly, so I used satin-black aerolak. Very dark grey would have been preferable, but I could not find any in a matt finish.

I replaced the 1979-vintage red record LEDs: the originals - as with all of that time period - don't have much brilliance, and their colour is rather yellow.

SABC-SAUK broadcast turntable Dok Viljoen Mk3 top

From the 1950s through to the 1980s, the SABC/SAUK built their own broadcast turntables, unofficially known as the 'Dok Viljoen' Mark-1, Mark-2, and Mark-3.

I was given part of one of these several years ago (around 1998) by an acquantance who was a tennant of a building in President Street and found it abandoned in the building. The turntable has since been been in my storeroom until 2010, where some help in the form of parts from other collectors around the country has allowed me to get it back in working order.

The long story, history and photographs on this page: Dok Viljoen Mark 3

Dynaco FM-1 valve FM tuner & SCA-35 amplifier Dynacos

The Dynaco SCA-35 amplifier I have had for about twenty years, bought from the Hi-Fi Exchange in Harrison Street. In November 2011 I bought the matching FM-1 tuner from a classified advert, but this was without the stereo decoder module - Dynaco's FMX-3. So I built a stereo MPX adapter, although not using the original circuit. The transfomers and coils of the original were just too much work to clone. Mine uses a more modern IC-based PLL decoder, but I tried to give it a look that wasn't out of place for a 1961 design. The Texas Instruments IC is hidden inside a screening can that was once a Philips air-velocity sensor. An ECC81 and an ECC83 valve do sub-carrier and audio buffering.

The original volume control was replaced with a switch for setting the MPX mode: mono, blend or stereo. Two rotary switches were used - one providing only its shaft and bush. The second switch's threaded bush is needed to attach the FM1's front panel. The functional switch I wanted to put as close to the circuit board as possible, so the second switch provides an effective means of shaft extension. I added an 'mpx' indicator light, in exactly the position where the power light is placed on the amplifier. (The authentic Dynaco Stereo model used an EMM801 dual beam magic eye tube, the second beam serving to illuminate a 'stereo' stencil on the front panel.)

ReVox G36 tape recorder Future Modification Project: ReVox G36 full-logic tape drive control with electronic braking (=reverse motor torque) and motion sensing.

The ReVox G36 (A736) is unusual (unique?) for a 'domestic' tape recorder of the 1960s for having a three-motor direct drive transport with solenoid activation, and 'almost soft-touch' controls.

When the pushbutton switch assembly on one of mine broke many years ago, I replaced it with a system of eight relays that mimicked the mechanical locking/interlocking safety action of the original pushbutton system, and provided equivalent electrical switching for the motors and solenoids. 'Feathertouch' micro-switches gave it a 'modern' feel and look. In the delirium of my hubris, I also sprayed the entire faceplate black - I was a teenager and wanted a black Teac X2000. Little did I know what I already had.

But now, I like the idea of restoring its looks (original appearance as in the photo above), AND giving it extra performance in the tape drive control circuitry. The aim of this project is to replace the electro-mechanical pushbutton assembly (or my old relay substitute) with original-look buttons, but with microprocessor derived logic, contactless electronic switching of all motors and solenoids, electronic reel braking by means of the winding motors with tape motion sensing, and full IR remote.

Since I have other projects jostling for my time, this one is at the end of the queue. But send me your comments, if you have opinions on the idea. More info on this project here

Nakamichi 550 Dual Tracer Nakamich 550 Dual Tracer portable cassette recorder
Very DIRTY and un-cared for when I received it. The first thing I did was to completely disassemble it for cleaning. For all the reputation Nakamichi has, this one has a spectacularly UN-impressive tape transport. I have better engineered transports in cheap mono portables from JVC and Sanyo. A transplant may be in order one day! A better bet may be to replace the tape transport with a Compact-Flash-based digital transport. The 550's analogue amplifiers and layout are still rather nice.

The reel hubs have been given new rubber tyres - from a Panasonic VCR service kit, and the capstan bush ought to be replaced (a job for a rainy sunday). The belts are still good - I suspect replaced not too long ago by previous owner.

The cassette compartment door is missing, so a replacement will have to be constructed. Also, the plastic of the front panel seems to have some sort of blistering disease. This is easy enough to remove by abraision, but with it will go the printed lettering for the record level controls. So I still need to create a new printed plastic facia to install behind the two rotary knobs.

When I got it, the mic mixing knob was missing and the shaft bent. Curiously, when I opened it up, there was the knob - rattling around inside! The pot shaft was fairly easy to straighten by putting it in a stationary lathe and using the 'back end' of the tool to bend the shaft.

Marantz 6170 shell Marantz 6170 (1978)
2 speed direct drive turntable. (now a 4 speed)
This was in a very bad way - very badly scratched, smashed arm, glue spilled on it. I bough it JUST because I wanted a platter for another project. but when I looked more closely at it I decided it was too special to hack up for donor parts.

So it's been gutted: the injection moulded chassis I filled with lead shot and polyester resin which added a good 3kg to the plinth mass. Then resprayed with "Krylon Champagne Nouveau", which is NOT an exact match for the original, but I like it better. The original was an almost 'pink' metallic. This is now a golden-yellow Champagne.

The original arm was broken - the bearing carrier cracked - and very messily glued. By chance I have an almost identical NOS arm (except without the moulded Marantz logo) in my box of collected spares.

I took out the permanently wired in audio and mains cables and made these both socketed connections. And I added 16.66 & 78 RPM to the DD control system, mainly so I can play my extra-long play CBS 16's. The motor is of Matsushita origin, and seems to be the same as used in the first Technics SL1200. The switch to select 16 or 78 I put under the platter - accssible just by lifting the rubber mat - so the original cosmetics are not altered in any way.

You can see the interior - showing the casting resin - here
And the small piggyback circuit board to enable 16 and 78 RPM here

It came with no headshell, so I made a replacement out of parts I had lying around - DIY headshell construction here

Well it's finally finished - fully revivified, and here are the photographs (click any image to enlarge)

Sansui SM-12A (1963)
AM-Stereo + FM-Stereo (outboard MPX) receiver. 2xECC85 + 2xEL84 SE class-A audio output.
Required general clean-up and a capacitor & valve replacement. I replaced the co-axial volume potentiometer with a dual-mono tone/vol pot from a Sharp car cassette deck. Since the Sharp pot had 2 different resistance track wafers, I disassembled two of these pots, and swapped the wafers.
Sharp is a useful company! Their car cassette deck pinch rollers fit the ReVox B710 & B215 !
Still needs a tuning eye.

I managed to get two 'magic eyes' from Mr Valve. They are not the correct 6GE12A - which is impossible to get NOS. But I did get a 6AF6 and a 6AD6, still quite costly at R400 each. These eyes are unusal in having dual independant shadows. The ones I got lack the triode section, but I will make a simple FET circuit to substitute for that.

Grundig CD 7500 (1984)
Based on a Philips CD-303, but with improved DAC & Decoder board (NO Sony chips in here!), and a special uniquely Grundig grounding layout.
I traded this for an old 20" TV set.
It was broken when I got it, not reading discs at all. But a replaced 6n8 capacitor on the servo board restored it to full functionality. The cabinet was very badly scratched, but is getting re-painted, and new wood side panels (instead of original plastic).
It has the highly regarded Philips CDM-0 mechanism & optical unit, and TDA1540 D/A converters, which are also reputed to sound special. It really does sound GOOD!
The early Philips players have a reputation for slow track searching (20s for a track search I have read), but this one is not particularly slow - it will find any track on a 'long' cd in under 7 seconds. Maybe it has upgraded Grundig firmware in the servo microprocessor?

I replaced the wired-in AC power cord and wired-in audio cable with sockets. Inside there was no space for an AC receptacle, so this went into a die-cast box on the back.

3 RCA sockets? Maybe a hint of getting SPDIF from the SAA7000/SAA7020 !

Below are just more photographs of items I have collected, with no story yet writen. I haven't time to write every items story so far: everything HAS a story & a history, that's why I like the old stff more than the new. Many more to come as I find time to photograph them and upload the pictures.

Teac X-7R tape recorder. 7-inch reels, 3-3/4 + 7-1/2 IPS, switchable bias and equalisation, dual capstan, 1/4 track stereo, auto reverse. 6 heads, 3 commutator DC motors. This came out around 1980. Apart from its 'short' chassis, it is identical in every way to the X-10R. The TEAC X7R has the weight-to-size ratio of a black hole - a complete contrast to the featherweight Fostex below.
Fostex R8. 8 tracks on ¼" tape, 7-inch reels, Dolby C, 3-motor, 2-head, 15ips-only belt drive DC commutator capstan motor. This looked good on the outside, apart from lots of dust. But somebody had 'got' at it, and stuck the tape tension arm idlers onto their shafts with contact adhesive! Inside, the right reel motor pulley had been replaced - but the sleeve that locks it to the motor shaft was missing. All fixed up now. Mechanical contruction isn't its strongpoint - it has all the buld quality and strength of a 1990's VHS recorder. But the firmware and autolocator are rather nicely designed. It gets 10/10 for being the cutest, tiniest multitrack I've seen: the whole front face is only the size of an LP cover, and it weighs less than 10kg!
Saxon brand portable tape recorder. 5-inch reels, 1-7/8 + 3-3/4 + 7-1/2 IPS by interchangeable capstan sleeve, switchable bias and equalisation. This was probably designed for reporters, or film location sound recording. The metal cover for the reels makes it very robust and portable while actually operating. 7-1/2 IPS is an unusually high speed on such small reels, giving quite good quality for a very short recording time. 1/2 track mono only.
Ampex 351 tape recorder. 10.5-inch reels, 7-1/2 + 15 IPS, DD capstan motor. This was THE studio and broadcast tape recorder of the 1950s and early 60s - you'll see them in films like "Cadillac Records" and "Detroit Rock City". The two I have came out of the SABC/SAUK Broadcast House in Commissioner Street, and are therefore full track mono, for 1950s radio use. The amplifier units each had a splicing block attached to them, and show a lot of "razor-blade activity".
Ampex 351 amplifier box: The RECORD LEVEL potentiometer was replaced with a screwdriver-adjustable type - either at the foctory or by the SABC. The RECORD indicator lamp has been removed by me, until I can locate a suitable replacement - the hole is an odd non-metric size. I have a pair of pretty Bulgin panel lamps , but they might look too 1970s.
"Selectomatic" 1960 valve/tube radio/phonograph, made by Tesla Radio Corporation of South Africa. The changer is a Garrard 209. The FM front end and IF cans are from Torotor of Denmark. EL84 SE amp for each side, Philips AD8080 woofers and Isophon LSH85 electrostatic tweeters. My parents were friends of Herbert Silbermann who owned the company in George Goch street, Johannesburg.
Webcor Model 201, made in the USA around 1958 ¼-inch ½-track mono tape recorder, bidirectional record and playback. 9.5 & 19cm.s-1
Studer D740 Compact Disc Recorder, made in Belgium, 1990; actually a rebadged Philips CDR-850, with slightly different firmware and balanced audio + AES/EBU I/O. The wooden side cheeks are my addition instead of the ugly rack ears.
Here's a Selenium rectifier. This came from Jeans Radio & TV spares; I have no idea what it was intended for - it's interesting because it's SO big! Next to is it a Philips Miniwatt EZ80 rectifier.
This Pilot model B3-T3 Broadcast/Shortwave Radio was given to me by U235 on the AVSA forum. It's a USA built live-chassis, modified for 220V by two large dropper resistors. These photos show it "un-cleaned". The logo below I drew based on the label stuck inside.
Pilot radio corporation logo trademark

Also from "U235" comes this Koninklijke Philips Gloeilampenfabrieken EL3541-RK14 tape recorder. 7-inch reels, and 33/4 IPS only, ¼-track. All valve circuitry, but for one Germanium diode, it was made in 1962. No work required at all, it was in pristine condition. Remarkably, the rubber drive belt and rubber brake pads are in a good condition still. It is basically mono, but has a socket for an add-on amplifier / speaker module to enable stereo playback. This is a stardard DIN socket that also puts out +30v DC for the amplifier. Pity the hapless user that plugs it into an ordinary integrated amplifier by this socket!
SW/BC Table radio made by Royal Dutch Philips. This comes from Moçambique, and all the dial labels are in Portuguese. The 'magic eye' is an EM70, but all the other valves are of the E*8* series. It's very well preserved and well looked after: I bought it from The Museum Store, when that still existed.
SW/BC Zenith table radio, made in the USA but with a 220V power transformer.The valves are a mix of loctal and octal types. This needs much work still - the rubber insulated wiring is spontaneously disintegrating.
Telefunken Gavotte radio, LW/BC/SW/FM. This German AM/FM radio has the 'usual' German FM band that goes from 87.5MHz up to only 100MHz. On each side of the cabinet is an electrostatic tweeter, to aid the 6"x9" moving coil, so sound quality is very good. Mice had chewed up the Long-Wave coils, but I haven't sought replacements since there is nothing in that band to receive. The photo left was taken the day I got it, before it was cleaned.

This is one of my most prized toys: A Soundcraft-Magnetics multitrack tape recorder. Soundcraft-Magnetics was a short-lived sister of the British company that made the incredible Soundcraft mixing consoles, and a child of Brennel engineering, renowned for remarkable tape recorders. This model 381 puts 8 tracks on 1-inch tape at 30 inches per second! And it's built like a Studer: even though it's only 19" wide, it needs two people to move it. The pics are - for now - from a catalogue. It cost me nothing: a gift from a friend who grabbed it from a studio (The VideoLab) that was upgrading.

Tannoy "Little Gold Monitors". 12-inch "dual concentric" bass reflex. These came from the EMI's Johannesburg studios - one still has the EMI inventory sticker. They were re-coned at EMI, so the cones are in excellent condition - probably the 'new' low-compliance surrounds. Manufactured December 1987. I wanted to replace the single electrolytic in each crossover, but on one some moron had glued the crossover into the cabinet - a good few hours required to remove & clean that mess.

My first real Studer! A-80 ¼-inch mastering tape recorder, made December 1980. 7½ & 15 IPS. From EMI's Johannesburg cassette duplication plant. Butterfly heads. A bad photo, but it is IMPOSSIBLE to move on my own - it weighs more than I do, so I cannot move it to better light for a nice photo.

Colibri portable gramophone. In the mid 1930s, most portable gramophones were about 60 x 40 x 20cm, and weighed 10kg or more. This was almost a pocket version, and it can play a 12-inch record. The Compact Disc, and compact cassette in the photo show how tiny it is when packed into its leather case. This was given to me by a family friend who bought it for himself, new, when he was a pupil at boarding school.
The soundbox comes off, and the arm telescopes, to fit into the lid, which has a movable flap to form the horn.

Philips GM2307 audio signal generator, from 1946. This I bought from a second-hand dealer, and still use it as a piece of functional test equipmemt. The 'magic eye' is an EFM-1 (elephant foot base).

Trek shellac 78. I have many 78s, but this one is particularly interesting and valued, both because of the cultural & historical content of the music (Afrikaner folk music), and also the record label. Looks like it is new old stock, never been played. Side 1 is "My Vader Weet" (My Father knows), side 2, "Geen silwer of goud" (No silver or gold). By 'Die Oorsporonklike Vos Broers' (The Original Vos Brothers).

Philips N4415 stereo tape recorder, from Gmaestro on the AVSA forum.
This Austrian-made Philips is a light-weight machine (9kg) compared to the N4520 above. The case is plastic, and the mechanism of pressed steel. It is a genuine 3 motor transport with FG servo capstan. All three motors are belt-coupled to their loads, and the belts had become a sticky mess - which was very laborious to clean out. Two heads only - ¼-track, and speeds of 33/4 & 71/2, but it bears the High Fidelity International logo, meaning it achieves the DIN specifications for hi fi performance.
The two tape tension arms are part of a feedback path that adjusts reel motor tension, although unlike the infinitely variable torque of the N4520, the N4415 has only two torque levels. All operational control is electrical with heavy-duty solenoids doing the moving - what Philips call 'magnocontrol'. There is no motion sensing, so it is possible to go from FF to playback immediately and ruin a tape.
It includes twin power amplifiers and loudspeakers, so very nice for portable entertainment in a single package.

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