HMV model 2401 "Stereomaster" restoration
 

Hello,

Just before Christmas, my brother donated an HMV model 2401 Stereomaster (in teak veneer) to my collection. Now, I already have a very nice Ferguson model 3322 “Transistagram” (their first all transistor stereogram and quite highly specified for a Ferguson), so I wasn’t sure that I would keep the Stereomaster.

However, it is much smaller and lower than my Ferguson gram and it does look rather nice (the cabinet is very good). So, with permission from “the management”, it is to be restored. It dates from 1968.

Several models under the “Stereomaster” banner were made by the British Radio Corporation (BRC) over the years. Some only had a record player, whilst others also had VHF radio.

The 2401 model features a side facing bass/mid range speaker and forward facing tweeter (all made by EMI). The speakers are in their own sealed enclosures, with foam sealing strip around the removable rear panels and foam plugs in the holes for the speaker wiring, from the amplifier.

The record deck is a BSR MA70 unit, which is one of their better offerings from that era (fitted with a BSR C1 ceramic cartridge). The all-metal turntable is driven by the motor via an intermediate drive pulley and is of a larger diameter than found in their cheaper units.

The amplifier part uses a mixture of plastic silicon transistors in the preamp stages and AD161/162 output pairs. The radio section uses silicon transistors in the RF stages and AF12x in the IF amplifier section. The 24V dc power supply is (AD143) series regulator stabilised (mainly, I suspect, for the benefit of the radio tuner’s varicap tuning circuitry).

The VHF radio has with five presets and an AFC defeat switch. There is also provision for external (mono) radio and (stereo) tape recorder connections. This unit has provision for retrofitting a multiplex stereo decoder and luckily, I have found the correct item (a BRC type SD1 unit) in my loft. The SD1 plugs into a B7G socket, which currently has a B7G plug in it, containing a capacitor, resistor and some links between pins, to enable correct mono operation. It has a stereo transmission indicator lamp, which fits onto a bracket behind the red “stereo” indicator bezel on the control panel. There was a factory fitted stereo decoder version under model number 2402.

The unusual thing is that access to the electronics is from underneath; the rear is all teak veneer. The electronics (three PCBs) is mounted on a sheet of hardboard and at the top, is a metal rail which carries the rotary controls and VHF preset tuning pushbuttons.

CURRENT FAULTS

1. The BSR deck is missing its knob for “off/play/reject” and will doubtless benefit from a thorough clean and re-lubrication.

2. One of the preset VHF tuning station selector buttons is broken (the unit is made by “Preh” of West Germany).

3. A wire to one of the five pins of the “tape recorder” DIN socket has never been soldered.

4. The left hand channel’s tweeter has been replaced in the past by a BRC supplied part, but it hasn’t been fitted very well and one of the four 4BA studs is missing its spring steel securing clip and nut/washer. I’d like to obtain and fit the correct EMI tweeter.

5. The two Hunts 2uF 25V reversible electrolytics that feed the tweeters are open circuit (surprise!). One has been bridged in the past by a 22uF polarised electrolytic.

6. There are a lot of “Callins”, TCC and Hunts electrolytics on the PCBs and most are likely to be out of spec by now.


Another Forum member has kindly donated a complete BSR MA70 deck for parts and I have found an identical but undamaged “Preh” preset VHF tuning unit in my loft.

I have a lot of electrolytics on order from Farnell.

To be continued……………..

Re: HMV model 2401 "Stereomater" restoration
 

Some more pictures.

Re: HMV model 2401 "Stereomater" restoration
 

Nice to see someone who's preserving these. They're a bit too new and "ordinary" for many of us to bother with, and there are an awful lot to be seen on eBay with no bids whatsoever.

One of our neighbours in the 1990s was a fairly famous classical musician and had a vast collection of mint LPs. I expected to discover that they had an upmarket, esoteric hifi system. But no, it was one of these!

I had the "separates" tuner/amp that your radiogram incorporates, housed in a 3-sided teak case with silver fascia. It was very reliable and the presets were a boon, but I was a bit disappointed with the build quality, the highish level of hiss, and the fact that it didn't have an input for magnetic pickup. The styling and construction also seemed rather old-fashioned for its date.

The speakers on your radiogram look really rather good compared with what's to be found in many similar-looking machines.

Keep up the good work,

Nick.

Re: HMV model 2401 "Stereomater" restoration
 

Hello Nick,

My HMV 2401 sounds pretty good on VHF (mono), for a "radiogram" (assisted in no small way, by the EMI speakers - also fitted in my larger Ferguson Transistagram, which also sounds rather good). I was quite impressed and that, together with its appearance, convinced me to restore and retain it.

If your similar tuner/amp was hissy (on radio, I presume?), I expect it was because it used the original Thorn/BRC SD1 mux decoder, a discrete components multiplex decoder, rather than the later Phase Locked Loop IC types.

Regards,

Dazzlevision

Re: HMV model 2401 "Stereomaster" restoration
 

I think you're right about the tuner and decoder. It did the job, but my slightly newer Japanese receivers (Trio, JVC etc.) were in a different league entirely - perfect reception with just a finger touching the aerial connection, and dozens of other distant stations that the Ferguson didn't even resolve.

I do have a soft spot for these "bread and butter" BRC systems though, and was intrigued to find out from this forum recently that the rather more upmarket Goodmans Module 80 receiver that I had at about the same time was also a BRC product.

Here's a pic of one similar to mine, found via Google. Same control layout, same chassis no doubt, but mine looked more old-fashioned with transparent plastic skirts around the knobs etc.

Nick.

Re: HMV model 2401 "Stereomaster" restoration
 

Hello Nick,

After Thorn acquired the Radio Rentals group (which included Goodmans Loudspeakers Ltd) in 1968, the Radio Rentals TV factory in Bradford stopped making HiFi for the Goodmans business (e.g. The Maxamp amplifier and Stereomax tuner units). Thereafter, Goodmans electronic HiFi was designed and (I'm pretty sure) made by Thorn in their factories at either Chigwell in Essex or Newhaven in Sussex. You can see the close similarity between various Goodmans HiFi units and the other Thorn brands (HMV, Marconiphone, Ferguson & Ultra). This carried on well into the 1970s but Thorn EMI sold off Goodmans later (early 1980s, I think).

Your HMV branded tuner/amplifier was the model 2404 (I have an HMV catalogue of that era) and included a stereo mux decoder. It also had inputs for magnetic and ceramic phono cartridges. I think it was the next chassis after my model 2401, as it now uses pushbuttons for input/function selection, has greater output power, mag cart premap, etc.

It's going to be interesting to hear how well the BSR MA70 and C1 cart sound, when that part is operational.

Regards,

Dazzlevision

Re: HMV model 2401 "Stereomaster" restoration
 

Hello,

I have now replace all of the electrolytic capacitors on the three PCBs. For maximum reliability, I have used radial leaded plastic film types where the compactness of modern components allows (e.g. 2.2uF 50Vdc working). Several of the removed components were defective in one way or another.

I also replaced a 2.2uF 3V large green "CRL" branded disc ceramic, on the VHF/IF PCB, as it was quite leaky. There were two similar 470nF 3V “Erie” disc ceramics on the amplifier PCB, so I also replaced them (I’ve had these large value, low voltage disc ceramics give problems in Grundig transistor radios).

There were two blue sleeved Mullard axial electrolytics at the rear of the “function” selector switch, which I also replaced with plastic film types.

I then noticed that several of the “Erie” PCB “pluggable” type carbon composition resistors had cracks/splits in their end caps, which could result in noise/intermittency. Most of these had soldering “posts” on them, allowing external wires to be directly soldered to them (or indeed, select on test components – but not relevant in this case). I have used standard 0.25 or 0.5W leaded replacements, with a loop made at one end for any wiring to be connected.

The VHF preset station selection unit was rather intermittent and one button was broken off. In addition, the 24V 2.8W MES pilot lamp fitted just above it had rather discoloured the white plastic part. Luckily, I had a good, undamaged spare, which I partially dismantled, in order to clean the rather tarnished contacts on the five tuning sliders, the AFC defeat switch and the five “printed” carbon tracks. Access to the sliders is achieved by removing the five spring clips that hold the slider’s metal worm gear rods in place; the white plastic moulding then slides off.

Upon reassembling the VHF preset unit, I reconnected the wiring, connected temporary test loudspeakers to the amplifier PCB and switched on (in radio mode). I firstly checked the stabilised supply line was correct, which it was.

There was plenty of hiss from the speakers, so I connected an aerial and was rewarded with good quality mono radio, including Classic FM. The frequency range coverage marked on the control panel is only up to 100MHz, so I was lucky to be able to tune a little above this (the service manual spec says it tunes up to 101MHz).

The 24V MES pilot lamp was not lit, although the filament was intact on a cold Ohms test. So, I removed it and fitted a new spare. However, as it is likely to scorch the new VHF preset tuning unit, I will try to source an LED screw-in replacement for it.

There were a few modifications printed in a “BRC Bulletin” for this model, so I have incorporated them. This includes a 10nF mains rated capacitor across the mains transformer primary, in order to reduce “on-off switching noise” and adding a resistor onto the copper side of the 24V series regulator PCB (presumably to reduce output voltage drift).

I am lucky with this particular example, as there are AF126s fitted in the IF strip, although AF116s are shown in the BRC service manual. So, now tin whisker growth to deal with.

The next step will be to fit wires and a B7G plug onto my BRC SD1 stereo decoder unit and fit it in the space provided.

To be continued……………..

Re: HMV model 2401 "Stereomaster" restoration
 

A few more pictures..

The third picture shows the "dummy" factory fitted plug in the multiplex stereo decoder socket, to enable correct mono operation.

Re: HMV model 2401 "Stereomaster" restoration
 

Again, nice to see someone spending some time and doing a proper restoration on one of these.

Yes, I remember the "on-off switching noise" well, a loud pop, especially on switch-off.

Nick.

Re: HMV model 2401 "Stereomaster" restoration
 

Hello,

I had to replace a few more of those Erie PCB mount carbon composition resistors, due to split end caps.

The next step was the provision of a stereo decoder for the radio part of my Stereomaster. The correct unit is a BRC type SD1, which uses discrete component (PCB reference PC155). I do not have one but I do have a very similar unit from a Goodmans Module 80 stereo tuner-amplifier (made by Thorn/Ferguson), with PCB reference PC169.

Comparing the circuitry, the two units are of essentially the same design, but with a few component value variations:-

The series connected dc supply input dropper resistor is lowered in value due to the 24V Stereomaster supply, rather than 65V in the module 80.

The filter circuitry in the L and R channel detector stages and the coupling to the 19kHz doubler stage.

The “stereo radio” indicator lamp driver stage.

The input coupling low pass filter (from the FM detector).

Luckily, I have the service sheet for the Module 80 and the BRC Bulletin detailing the circuit and component changes in the Schedule B version of the BRC SD1 unit.

I made up a list of items to be changed in order to convert the Goodmans Module 80 PCB into a “Schedule B” (the “schedule” letter signifies changes made during production) BRC type SD1 unit. I had to replace one resistor with a wire link, remove one capacitor and change the values of several resistors and capacitors. I also had to replace a silicon transistor (Texas Instrument TIS91) with a germanium type in the stereo beacon lamp driver stage (Mullard AC128).

I then made up the wiring loom and B7G plug and soldered the free ends to the solder posts on the PC169/SD1 board. I was now ready to mount the unit onto the hardboard base, which already has a strip of wood with a rebate cut into it, for locating one end of the PCB. At the other end, there is a hole provided in the PCB which allows the fitting of 4BA countersunk screw, large flat washer, spacer, nut and shakeproof washer. I had to drill a 4BA clear hole on the hardboard base.

The next step was to plug in the B7G connector and switch on. I was rewarded with an illuminated stereo beacon and good stereo radio. I have a Philips VHF/FM multiplex stereo signal generator, which I haven’t used for years. I will connect it up at some point to see if the tuned circuits on the decoder board need adjusting.

Finally, I inserted a 2A (T) 20mm fuse (in an in-line fuse holder) into the secondary output wiring of the mains transformer (a factory production modification). I used a “Bulgin” type, which can be seen in the attached pictures.

The next step will be to refit the electronics into the cabinet and test it. After that, the mechanical overhaul, re-lubrication and adjustment of the BSR MA70 record deck.

To be continued……………..

Dazzlevision

Re: HMV model 2401 "Stereomaster" restoration
 

Nice work, thanks for sharing the pictures of your progress.

Funny to think that in the early 1990s, I had a Goodmans Module 80 in my bedroom and my brother had one of these Thorn tuner-amps in his, but I didn't realise they had something in common.

N.

Re: HMV model 2401 "Stereomaster" restoration
 

Hello,

The BRS MA70-A-1 deck fitted in my Stereomaster looks better cosmetically than the spare deck I have, so I will use parts from the spare to restore it.

The first thing needed was to remove the broken off/play/reject knob, which involves removing the plastic trim that is embossed with the control knob functions. This is held in place by several plastic barbs that latch onto the underside of the metal deck plate. Once this was done, a self tapping screw has to be removed in order to free the remains of the off/play/reject knob. The spare was then fitted and the whole thing re-assembled.

I then felt that excessive force was required to operate the off/play/reject knob and this is probably what caused the original knob to break. On the underside of the deck, the knob is coupled in one direction to the on-off switch for the deck motor and the idler wheel (turntable rim drive) engage/disengage mechanism. In another direction, it is coupled to a sliding plate that is part of the complex mechanism that links the tone arm to the trip pawl, etc. I removed the sliding plate, cleaned it and applied some ”Molykote” grease. Now, much less force is needed to operate the off/play/reject knob.

I then removed as much dust and fluff from the mechanism as I could see, re-lubricated the motor bearings with some sintered bearing oil and checked the large die cast gear wheel (I am uncertain as to the correct name for this part) under the turntable that controls the auto-reject system. It was very stiff, due to hardened grease used on the mounting post that is riveted to the deck plate and in the groove in the die cast gear. So, I removed the old grease and applied fresh.

Everything then seemed to operate freely and smoothly, so I refitted the deck into the cabinet. I also refitted the electronic unit and reconnected all the wiring.

Tomorrow, I will apply power and checked for correct operation of all parts. I will also use a jeweller’s loupe to inspect the stylus, to ensure it wasn’t worn excessively. The final step will be to check the deck adjustments: tracking weight, bias force, set down position, etc.

To be continued………..

Dazzlevision

Re: HMV model 2401 "Stereomaster" restoration
 

Some pictures of the deck before cleaning and relubrication of the most affected areas.................

The second picture shows the sliding part secured by the large relatively diameter blackened metal disc/washer, with a "Starlock" fixing at the top of the assembly. In the bottom left hand corner of this picture is the linkage from the off/play/reject knob.

Re: HMV model 2401 "Stereomaster" restoration
 

Hello,

Somewhat later on than planned, I have recently returned to this project.

I fitted an exact replacement second hand EMI tweeter in the left speaker compartment. I also removed the other three speakers ands checked that their voice coils weresn't binding against the magnet (luckily, they were all OK).

After refitting the speakers, I turned to the BSR MA70 record deck. It wouldn't move to the correct point on the record when used in "auto" mode (it only moved slightly towards the record before descending). I checked the adjustments, but they didn't make much difference, so I stripped down the remainder of the deck that I hadn't already attended to and removed old grease and applied fresh. After reassembly, the same fault persisted. After spending some time studying the operation of the mechanism, I couldn’t see any obvious cause, so I fitted a complete sub chassis from a spare MA70 (that I had already stripped, cleaned and relubricated) and that did the trick!

I then set up the usual adjustments and it plays various sized records correctly in manual and auto mode, producing a very pleasing sound. I had problems ascertaining the correct wiring connections to the BSR C1 cartridge, but after posting on this forum (in the last few days: https://www.vintage-radio.net/forum/...d.php?t=115618), I was able to establish the correct terminations (mainly a phasing issue).

The Stereomaster now works very well on VHF/FM stereo radio and disc. It also gives a good account of itself when a good quality tape recorder is connected via the 5-pin DIN "tape" input socket.

Altogether, I have found this to be a very pleasing and informative restoration job, especially as I haven't completely stripped down, cleaned up and relubed a BSR record deck before.

I like the compact appearance of these Stereomasters and the side facing bass/mid speakers still seem to produce a good sound when listening from the front of the unit. The user manual recommends the unit be placed in the corner of the rooms, to allow sound to reflect off the hard walls near them.

The only other thing that I have noticed is a loud click when the deck switch makes or breaks. I am considering fitting a C-R series snubber network or VDR across it.

Regards,

Dazzlevision

Re: HMV model 2401 "Stereomaster" restoration
 

Well done!

I was beginning to wonder what had become of this, so it's nice to hear its conclusion.

I didn't realise the later BSRs were modular like this; the early ones (e.g. UA6) were too. You must find the cause of the mystery fault when you have time, I'm intrigued.

Nick.

Re: HMV model 2401 "Stereomaster" restoration
 

Hello Nick,

I don't like leaving a fault unresolved, but "the boss" wanted her kitchen table back, so expediency was the order of the day! It would be nice to track the fault down to a specific component, but whether I will ever have the time to do so is another matter.... The only thing that didn't seem quite right was the position of the "stud" fixed to the large metal plate on the underside of the deck (see second image - by the big single coil spring), that is driven by following the groove in the big diecast cam/gear wheel on to top side of the deck. It didn't seem to travel quite as far as the one in the correctly working mechanism. This then failed to move sufficiently the metal plate with several "steps" on one side (see first image) that is connected to the rod that rotates the tonearm.

Regards,

Dazzlevision