Reviews and Recollections - The Germanium Transistor Era

I have divided the transistor designs into two ‘eras’. This page looks at the ‘Germanium Transistor Era’ and covers the 400 and 500 ranges which used germanium transistors in the output stages of their power amplifier sections.

Note that all the magazines and books referred to below were United Kingdom publications unless otherwise specified. In some cases I don’t know the exact date of publication because I only have a reprint that omits the date. I indicate these with a “?” mark.

The last valve units that Armstrong designed were the 200 range and its associated 100 range. The 100 range units were essentially the same as the 200’s. However their power amps omitted an output valve to make them cheaper to manufacture so they could be sold at a lower price. In later decades some Hi Fi enthusiasts have come to regard “single ended” valve power amps as being the designs that deliver the highest possible sound quality. It is a curious quirk of history that an approach that was once seen as a cheaper and poorer arrangement is now sometimes sold at high prices as providing the ultimate in quality!

There never was an Armstrong 300 range. Their first all-transistor range of units were the 400’s. The 400, 500, (and 600) ranges were all ‘modular’. i.e. The tuner-amplifier units (receivers) used the same amplifier and tuner circuit boards as were sold separately in the stand-alone tuners and amplifiers. As a result, Armstrong tended to send an AM/FM receiver (tuner-amplifier) for reviews unless the magazine specifically requested a tuner or am amplifier to test.

400 Range

1968 October “Hi Fi News” 426 Receiver (Amp + AM/FM tuners) rev. by George Goodall

The review began by explaining that the performance and features of the amplifier and tuner sections of the 426 were essentially the same as those of the relevant functions in the 421 amplifier and the tuners in the range. However there was an exception which George Goodall then pointed out:

“...that the separate amplifier unit has two treble filter switches and the tuner-amplifiers have one. Also, when the AM/FM tuner-amplifier is operating on medium and long wavebands, the filter comes in at a lower frequency than on other functions, the purpose being to reduce noise and heterodyne whistles which sometimes spoil AM reception. The two separate filters on the amplifier unit correspond with the different operations on the tuner-amplifiers.”

The review then outlined aspects of the constructional details, mentioning that the circuits were on a set of plug-in circuit boards and that the circular tuning display was controlled via an epicyclic gear from the tuning control. The reviewer also explained that:

“The circuit design is straightforward throughout, the standards of electrical performance being maintained by use of selected transistors in the power amplifier and regulated power supply sections. Armstrong can, of course, supply these components should they ever need replacement, but it as well to point out that in some cases off-the-shelf semiconductors should not be used for servicing.”

The output devices in particular were selected germanium AL102’s. At that time the variations between individual examples of a given type of transistor were often far greater than today. The devices were also much less robust than modern silicon transistors. Hence the devices needed to be individually tested and selected. By modern standards, these devices were virtually ‘hand made’.

The 400 range amplifier section had a number of facilities that would surprise many modern Audio enthusiasts. Not only did the units have treble and bass tone controls, they also included a “loudness” switch which contoured the frequency response to avoid low and high frequencies becoming relatively inaudible at low volumes. The reviewer added that:

“A useful feature for tape recordists is the tape monitor switch which makes possible direct comparison between original and recorded signal. The tape recorder must be fitted with "off the tape-monitor" facilities, of course. The balance control can reduce the sound in either channel to zero level and remains in the recording circuit together with tone controls when the tape monitor facility is in use.”

Measurements made by the reviewer during his tests showed that the 426 met the specifications published by Armstrong.

Unfortunately, the 400 range units didn’t sell very well. From feedback at the time Armstrong felt this was for two reasons.

Firstly, in their adverts and publicity material Armstrong tended to simply describe the 400’s amplifier as rated at “15 Watts per channel, 4 to 16 Ohm loads”. However other makers at the time had begun advertising higher powers by being more selective about the loudspeaker load specified. In fact the 400 could deliver around 25 Watts into 8 Ohm loads. As a result, the initial advertising tended to present a unfair impression when readers simply compared adverts in terms of the ‘rated power’ because the values were given on a different basis.

Secondly, the ‘futuristic’ styling of the 400 range was disliked by many prospective users. Armstrong had originally though that the brushed aluminium facia with purple trim and tuning dial would be attractively ‘modern’ for the trendy 1960’s buyers. But many people felt it would look weird in their homes! So – after a relatively short interval – Armstrong revamped and restyled the 400 range and launched it as the 500 range. Internally, the changes were minor, but the presentation and styling had a positive impact on reviews, and on sales...

500 Range

1969 April “Hi Fi Sound” review of 521 Amplifier by Fred Judd

In his review Fred Judd seems to have been very impressed with the 521. His comments included:

“This transistorised unit is designed primarily for use with 8 ohm speakers but performs well with those having an impedance of 15 Ohms.”

“There is nothing pretentious about the styling and finish which are neat and businesslike, with controls all labelled with symbols. The outer case of matt-finished wood can be removed quickly, leaving the entire chassis exposed for service or for installation in a large cabinet.”

“Layout and construction of the 521 have been well thought out. The preamplifiers, for example, are all assembled on plug-in printed circuit modules which enable the dealer or manufacturer to provide faster service should one of the modules develop a fault. The transistor output stages have very large heat sinks to ensure cool running even at high power levels, and each stage is fully protected against accidental short circuiting across the output sockets by means of fuses in the ht lines. ”

“An outstanding feature of this amplifier is the output power: the unit is rated by the makers at 25 watts rms per channel for an 8ohm load. This came out at 25.9 watts for the sample sent for review and with distortion not exceeding 1%. With a 15ohm load each stage yielded 15.15 watts rms per channel. The power output is also well maintained over a wide frequency range and at 25 watts (per channel) reference 0dB at 1,000Hz, was measured at -1.5dB at 12Hz and -2dB at 25,000Hz. With power of this order available the Armstrong 521 is merely 'cruising' at around 20 watts output and, as it were, 'idling' at average listening levels.”

Before concluding:

“As one would expect, any worthwhile product of this nature cannot be very cheap. But this example is not unduly costly when one takes into account its extreme flexibility, a genuine high fidelity performance and excellent engineering. The Armstrong 521 sets a high standard.”

1969 ? “Audio and Record Review” review of 521 Amplifier by Frank Roberts & Donald Aldous

This review contained the following comments:

“Forty years on! Yes, it is that period of time since the first Armstrong radio receivers were produced and over this span the Armstrong organisation has deservedly built up a reputation for good performance allied to exceptional value for outlay. Now comes their latest 500 series of units, which can only enhance their established name. This new range covers amplifiers, FM tuners, AM tuners and Tuner-AmpIifiers, but, whatever the configuration, each uses the amplifier of the Model 521 which is the subject of this review.

The fact that all Armstrong models have been selected by The Council of Industrial Design for inclusion in The Design Index comes as no surprise, as the new 521 is at once elegant in its simplicity with an attractive appearance that will grace any room.”

“Our 'road' tests proved that the 521 is a delight to operate, accepting programme material of many types into the various inputs and producing sounds fully up to the expectations raised by our experience and knowledge of the particular pickup, tape or radio signals provided for the amplifier to perform on.”

“The several dynamic loudspeakers we attached to the 521 performed to the best of their capabilities - even the 15 ohm models - but we must exclude the Quad electrostatic which, we found, produced low-frequency instability with a sustained note and, in any case, the upper frequency response was obviously being limited.”

“Verdict : As we have said before in reviews of many Armstrong products, the performance, standard of construction and appearance contradict their reasonable price. Good to look upon and even better to hear, the Armstrong 521 stereo amplifier is a genuine hi-fi design.”

The measured results obtained were in line with other reviews.

It is perhaps worth noting the cautional comment about using the original QUAD electrostatics as views on their use with the 500 range amplifier clearly varied from one reviewer to another as we can see below in the “Luister” review...

1969 ? “Luister” [Dutch] review of 521 Amplifier by Jan Kool

(This review was translated into English by Tera Phillips .)

The review contained the following comments:

“The Armstrong brand has had, particularly in the last few years, a very good reputation in England, its country of origin. It has been represented in our country before, but has never really become very well known. Recently, the very active firm Naho, has taken up this English name (which reminds us more of trumpeters than amplifiers). We hope with success, because the first representative, the 521, 2 x 25 watt amplifier has left a very good impression.”

“The squarewave measurements illustrated the ample frequency response. The steep sides and limited rounding off, even at 10 kHz, confirmed the sound quality which had already indicated a very praise reproduction of low and high frequencies. One can call the stability excellent. Maximum power into an unloaded output had no other effect than that the square wave at 10 kHz rounded off a little more with no ringing apparent. This is an amplifier which we find suitable for electrostatic loudspeakers.”

Which shows a difference of option with the Audio and Record Review comments! However it should be borne in mind that Armstrong recommended adding 1·8 Ohm series resistors when driving QUAD electrostatics with a 500 series amplifier. The reviewer continues with:

“An excellent well-considered design that can deliver equally excellent music reproduction, even in very large rooms. The understatement of the specification and the simple appearance are very nice. The very practically designed and steep working filters and the evident stability are extra attractions. The good figures for the signal/noise ratio help to make this amplifier a real quality product.”

1970 April “Which” – A large survey of stereo equipment including the 521 Amplifier.

The 1970 review of Hi Fi equipment in “Which?” magazine turned out to be a very significant event for Armstrong. Sales of the 500 range were already fairly healthy by this point. But the effect of this publication was to lift the demand for Armstrong equipment though the roof!

For those who are unfamiliar with “Which?” it is worth making a few points about the magazine.

It was produced by an independent body called the Consumer Association (CA). Member of the public interested in consumer goods could join the CA, and in return would get the magazine. Its approach to reviews was different to most commercial magazines. Usually, a magazine would request items for review direct from the manufacturer. However “Which?” would buy the items in retail shops anonymously. This was to ensure they did not get equipment that might have been given special treatment by the maker. Also, “Which?” tended to carry our ‘surveys’ that tested and compared many competing units. The magazine then presented the results in terms designed to be understandable by a general audience with no previous knowledge or expertise. The survey in the April 970 issue actually covered amplifiers, tuners, loudspeakers, and the other items that members of the public might buy as ‘separates’ to combine into a complete home ‘stereo’ or Hi-Fi system.

The result tended to be lists or tables of models which gave ratings in a format which were often described as “the more blobs the better!” These were then followed by picking out some models as “best buys”. Readers of the magazine could simply look for the units that had “the most blobs” in the charts and were mentioned as a “best buy” without needing to understand the technical tests or their measured results.

In general, specific models or manufacturers weren’t discussed in the text. The emphasis was on a explanation of the (then novel for a mass-market!) field of ‘stereo’ or Hi-Fi. However a few specific comments were made. For example the CA had sent out questionnaires to its members and analysed just under 1,000 responses on stereo equipment. This led to a mention that:

“In their comments, a number of members complimented the [repair] service from Armstrong, Goldring, Heathkit, Leak, Quad, and SME.”

At that time Armstrong had established a reputation for being swift at fixing any faults. This was aided by the plug-in cards used for the electronics in the 500 (and previous 400) range. Most faults or problems could be dealt with quickly by simply removing a faulty board and plugging in a working replacement. Armstrong retailers were happy to accept sets to send back for repair. But customers who could get to Holloway in London soon realised that if they had a problem with a 500 range set they could bring it to the factory and it was often repairable whilst they went and had a cup of tea! One result of this was that those who worked at Armstrong became used to customers walking down the road and into the factory, carrying their precious item.

For Armstrong, the most significant results and remarks in the “Which?” survey were probably those relating to “Value for money”. On that topic the review said:

“Amplifiers -

The Leak Stereo 70 (£69 10s) and the Quad (£98) amplifiers were excellent in all respects. The Quad had a wide range of adjustments for different equipment and different source material — but you pay a lot more for this. We think the Leak better value for most people. However, unless you have a very sensitive ear and all your other equipment is of the highest quality, you would probably be perfectly happy with the amplifiers rated ••• for sound quality — Armstrong 521 (£52), Cambridge P 40 (£75), Goodmans Maxamp 30 (£54), Leak Stereo 30 Plus (£59 10s), and Rogers Ravensbrook (£49). Of these the Ravens- brook was the least powerful, and didn't have a headphone socket; and the Cambridge was considerably more expensive. So the Armstrong 521, Goodmans Maxamp and Leak Stereo 30 Plus would be best value.”

And the brief recommendations at the end of the survey featured the 521.

At that time “Which?” was sent out to over 600,000 subscribers. Copies would also have gone to many public libraries, and its content tended to be picked up by newspapers and broadcasting. So what was said in the survey would have reached a far wider audience than a review in a specialist magazine for Hi Fi enthusiasts. The 521 was the cheapest amplifier mentioned as “good value for money” so became the primary choice for many people wanting to put together their first stereo system. Sales rose dramatically!

The rapid rise in demand for the 521 coincided with a change that was happening in the consumer goods retail market. Until the mid-1960’s the retailers tended to be specialist dealers. They usually offered a personal service advising and helping customers, and were often technically skilled as well as being audio enthusiasts themself. These retailers tended to become ‘franchised’ for given makes, and each established maker of audio equipment had their own set of franchised dealers around the UK who they felt would treat the customers well.

However by 1970 a totally different approach to retail was growing rapidly. These were the ‘warehouse’ or ‘discount’ outlets. The biggest example of these at the time was ‘Comet’. These warehouses simply sold units in unopened boxes on the basis of offering a low price. It was assumed that the buyer preferred the lower price in exchange for having to make their own choices and be able to put together the items they bought into a stereo system. This approach was proving very popular with the increasing number of consumers who wanted a decent ‘stereo system’ that was as good as their neighbour’s.

As a result the retail warehouses started to order 521’s in larger and larger quantities. At one point they were trying to order more sets than Armstrong could actually make. In addition, at one time Comet started selling the 521’s they obtained at a lower price than they paid Armstrong wholesale! At one point the director/owner of Comet visited Armstrong and said he wanted to buy the firm’s entire output, but at a lower wholesale price so he could cut his retail price still further.

They were doing this because they realised that their customers tended come and to buy a system of associated items. So the amplifiers became what was known as a ‘loss leader’. The customers saw the low price for the 521 and came to the warehouse. Having chosen the 521 they then wanted loudspeakers, a record deck, etc. Since they were now in the retail warehouse they bought these other items there during the same visit. Hence the warehouse made its profits from the other items having drawn in the customers with the ‘bargain price’ 521. Nowdays this practice might be regarded as “predatory pricing” because smaller retailers wouldn’t have the resources to compete. But back then it was perfectly legal and regarded as acceptable.

Alas, this presented a dilemma for Armstrong. It was great to be selling so many units, but they realised that if they agreed it might well kill off the many small specialist retailers. The result might then become a quasi-monopoly retailer. Consumers would lack choice and Armstrong would only have one dominating retailer who could virtually dictate terms. What then would happen when the ‘boom’ prompted by the 521 ended? So they decided to continue to supply their franchised dealers and sell the rest of what they could make to the warehouses. As a result, following the “Which?” survey the Armstrong 500 range was a best seller, but the sales were divided between the specialist franchise retailers and the warehouses.

1970 May “Hi Fi Sound” review of 526 by Fred Judd

This review begins with a description of the 526 before going on to say:

“This unit has the same audio preamplifiers and power output stages as the model 521 amplifier which I reviewed in the April 1969 issue of Hi-Fi Sound. (The 524 tuner was the subject of a report in October 1969). However, one or two modifications have since been made to the 521 and included in Model 526. One modification is the use of silicon transistors for the driver modules of the power output stages, resulting in slightly lower distortion. The 526 is supplied in a neat wood case but can be mounted in a larger cabinet.”

Unfortunately, I don’t currently have the details of the 524 tuner review so can’t comment on that at present beyond noting that the above indicates it appeared in the magazine as mentioned. However the above is interesting for the comment made on the driver transistors.

The 521 continued to use Germanium AL102 transistors in the output stage of its power amplifiers. But Armstrong had a long tradition of ‘continuous development’. This meant that they tended to tweak or improve the circuity in their units to improve performance or reliability. This was generally done without any public announcements or change in model numbers, appearance of units, etc. So in general, sets made during that last period of manufacture might have been better than ones made near the start. They all met the initial specifications, but tended to exceed those specifications by a larger margin for later examples. The mention above shows an example of this.

When the 400 range was designed and released, the available silicon transistors were not able to provide the required power output. And the 500 range was – electronically – similar to the 400 range, so inherited the same choice of transistors. But by mid 1970 better silicon transistors had become available which could be used to improve the performance of the 500 range. So they were incorporated into the sets.

Regarding the amplifier performance Fred Judd wrote:

“Testing model 526 has provided the opportunity to compare the amplifier section performance with that of the 521 which I reviewed. My general impression is that the 526 has a slightly better overall performance, at least as far as bench tests show. The small modifications that have since been incorporated into the 521 and of course included in the 526 may well account for this. For instance, distortion was well below 0.5% for 25 watts rms output over the specified frequency range of 20 to 25,000Hz. At lower power—at 1 watt output—the performance was especially good with distortion at less than 0.1% at 1,000Hz. There was no evidence whatsoever of crossover distortion at any volume setting.”

And regarding the tuner he wrote:

“The radio section has exceptional sensitivity and excellent FM stereo reception was possible with an indoor FM aerial at about 25 miles from the BBC transmitters at Wrotham.”

“Accurate tuning is assisted by a centre reading tuning meter and stereo transmissions are indicated when a small light on the front panel becomes illuminated. There is also an inter-station noise muting control for use on FM reception.”

1970 October “Hi Fi Sound” 525 included in a comparison of 10 tuner-amps. by Gordon King and Clement Brown

This review gave a very brief report on each of the ten tuner-amplifiers (receivers) included. The models compared were all in the price range from 76 to 188 UK Pounds. The units covered were: Heathkit AR-14, Armstrong 525, Lafayette LR-500-T, Pioneer SX440, Warfedale 100.1, Beomaster 3000, Trio TK-140X, Lux HQ555, Scott 3141, and Sony 6060FW. The only unit in the comparison which cost less than the 525 was the Heathkit AR-14 which had a lower technical specification – e.g. only 10 Watts per channel output power. The review does indicate that the Armstrong 500 range was seen at the time as being excellent value in terms of performance versus price.

3800 Words
Jim Lesurf
28th Sep 2015