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Old 21st Jun 2022, 12:24 pm   #21
Lucien Nunes
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Default Re: Compton Amp Circuit

Quote:
the work of updating service information
Service information?!

In the early days, instruments were supplied direct from the company as a pipe-organ would be, and serviced only by them. At one time they were offering a 21 year warranty (20 years was standard on pipe organs) subject strictly to holding a maintenance contract, so it is unlikely that many outsiders ever looked under the hood.

Take model 347, for example; about 190 units were sold over a decade at a price equivalent to £30-40,000 in today's money. No service manual appears to have been issued. Someone partially reverse-engineered serial No. 13 and made something resembling a service manual, although lacking in most of the juicy detail that one might want. I have five copies of this retrospective effort, sourced from different directions, but no trace of an official one. I have since done a bit more in this direction, see: http://www.electrokinetica.org/d8/3/3.php

Once sales volume increased in the early 50s and dealers started to come into the equation, a manual was issued which was updated over time to become a generic guide to servicing the popular models. You can chart the updates by the change in typewriter font (they were stencil duplicated) and the appearance and subsequent correction of errors introduced by the typist working from a variably legible manuscript. The large and custom instruments are not covered, again probably because they were only serviced by the firm's personnel who knew them inside-out. For the amplifier, the original version of this manual shows the pentode-connected KT66 chassis that was in use from 1952 - 1965 or so. If you happened to have an instrument with one of the three later valve amp designs, you might or might not have got a relevant circuit for the amp. I have never seen one for either of the single-channel units.

The problem of most technical information about the organs remaining in-house was compounded in 1966, when it is thought that some of it was sent to Rushworth by mistake and was skipped. There had already been a much more serious loss of important factory records especially about the cinema organs, in a factory fire during the war as a result of bombing. No original data about the prewar electronics seems to have survived at all; what we know today is mainly from the few semi-complete instruments that exist.

Everything that remained in 1971 when the later company was wound up, went to Compton-Makin, a company formed by a former customer to buy the inventory from the receivers. It was moved to an old mill in Rochdale along with a few of the men. They built 36 organs over the next ten years some of which where superlative behemoths, still using 1930s generator technology but pushed to the very limit of practicality (215 63-pole relays switching DC analogue control voltages, anybody?) In about 1980 they got with the times and soon flourished in solid-state organs. Much of what remained for the electrostatics was purged at a later date, to the chagrin of the service manager who had been away at the time.

So I think I have painted a picture of what might seem to be a peculiar situation by comparison to say radio and TV. In 1968 a church could buy an organ for £7,000 (£86k in today's money), that would come with a very smart specifications sheet with embossed paper and whatnot, but the technical data showing how that spec was implemented might not have gone beyond Fred Allen's desk.

BTW see one of the 10W amps in use in my HE/3: http://www.electrokinetica.org/d8/6/4.php
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Old 22nd Jun 2022, 10:52 am   #22
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Default Re: Compton Amp Circuit

Just to add a little more on this amp, I am trying to put the circuit of the amp I got from pamphonic back to how I think it would have been wired, reason is I think it is a great pity that there is a valve ECC83 not doing anything, will place a picture on my progress later.

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Old 22nd Jun 2022, 10:56 am   #23
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I found your posts absolutely fascinating, Lucien, thank you.
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Old 22nd Jun 2022, 12:54 pm   #24
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Hi folks

Here is that picture of what I have done to the amplifier, I have used that circuit diagram I posted earlier in this thread. I am not sure of what value electrolytic caps I should used on the cathodes of the Ecc83 though, in the circuit diagram there are two pots which were not marked with a value so I have used two 100k lin pots and where there is two 220k resistors that come off the center of these I have used 250k and like wise for the anodes of the double triode as nearest value I had was 100k instead of 220k. But here is picture.

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Old 22nd Jun 2022, 6:12 pm   #25
Lucien Nunes
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Unfortunately I am not near either of my two chassis of this type to check any values.

Because the first stages constitute a preamp for the generators, the input sensitivity is very much higher than a normal power amp chassis would be. It's something like a few mV into 470k for full output*.

The function of the two pots after the first stages is to trim the gains of the separate bass and treble channels. Each of the 12 rotary electrostatic generators has two outputs, one for signals below 250Hz and one for signals above. As I mentioned elsewhere, this was to minimise intermodulation of the higher pitches by large-amplitude bass tones. Because the generated signal levels and the total shunt capacitance of the parallel-connected generator outputs depends on the mechanical setup, discrepancies can occur between the levels of the two channels which the mixing pots correct.

Clearly a difference between the channel levels would cause a step in loudness between tenor B and middle C either side of the divide, but the effect is further-reaching. The organ uses additive synthesis; different timbres are created from a fundamental and a palette of harmonics**, which for many notes below middle C are divided between the two channels. Therefore a mismatch in channel levels would result in such notes having some or all of their harmonics reproduced at the wrong intensity, giving them the wrong tonal character.

* On some Compton amp models possibly including this one, the input resistances of the two channels are different, to strike a different compromise between noise voltage and frequency response, as the generator outputs look like a few nF and it's much more important not load the bass side. The coupling capacitors are also different values, to roll the channels off at different points.

** Actually in the small Compton models (and in Hammond organs) these are not true harmonics but equivalent notes of the even-tempered scale. Since no scale notes lie close enough to the 5th and 7th harmonics to be used instead, the synthesis of many timbres is only an approximation. The lack of higher harmonics especially limits the quality of available reed voices. In the larger models Compton incorporated palettes of pre-mixed harmonics into some of the generator waveforms to use alongside the additive synthesis. Makin went further and equipped their generator racks with five sets of 12 generators, one set dedicated to the 5th and another to the 7th harmonics. As time went on and generators were in short supply, it is said that during major overhauls Makin technicians would silently remove one of these two sets of generators and rewire the harmonics to run with four sets, returning the harvested generators to stock for repair jobs. Of the two known surviving Makin generator systems, mine (S/No.8) has all five sets but the other one only has four.

</ramble>

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Old 28th Jun 2022, 4:05 pm   #26
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Originally Posted by Lucien Nunes View Post
@Techman

Please do not modify or re-purpose this amplifier. There is a strong chance that it is the only surviving example of a non-organ electronic product from this stable. I have been collecting and researching all things Compton for many years and have never seen its like. Before coming to any conclusions, please could you get the date codes from the capacitors. I see half a dozen that will have codes.

Now onto how the 'gramophone amplifier' might have come into existence.

First I will say that I do not have proof that these chassis were completely made in Minerva Road.

Compton would build anything your heart desired.

If you want two, you get the prototype and a production run of one. But who would think to order a PA amplifier from Compton?

Possibility #1. It was a special for a church, for their meeting rooms etc. Perhaps as a sweetener, or just because it seemed like a good idea at the time..."can you make us a little PA system?"

Again the reason I go into this at length is to set the scene for the day when some contact from the EPTA side of things asks the Colonel if his chaps wouldn't mind making up an amp for their village hall / language lab / destroyer / whatever. Why would they use a valve amp at this late stage? Because they could.

Possibility #2: It was supplied to or via EPTA, despite being past its theoretical technical obsolescence by then.

And of course
Possibility #3: It was made by a subcontractor who was doing chassis for the J.C.O.C. at the time.

E2A I have also thought of
Possibility #4: It was a 'home office' job made in Acton out of Compton bits but not officially supplied by them. I can well imagine foreman Fred Allen doing that, he had a propensity to build amplifiers on Compton chassis.

Let's have those cap date codes and I will ramble on at more length soon. Also are the legends on the control panel engraved? If so I need to look at the font carefully and see if it matches any of Compton's normal engraving.
I hadn't forgotten about this, but due to having been side tracked with a host of various other different things I haven't done anymore with it since my last post other than to extend the three brown wires from the secondary that were all linked together within the shroud, out of the shroud with different colour coded wires for further possible investigation - it can all be put back to original at some future date if desired. I've come to the conclusion that there's unlikely to be any easy way of getting a suitable low impedance winding from this transformer as it stands, although there may be space to wind one on the outside of the windings at a push, however, looking at where the various tapings enter the bobbin, it looks like those original secondary windings are probably interleaved. I did remove the other shroud just in case there were any other capped off connections on that side, but as expected there were none - other than the expected primary ones (photo shows).

I'm not intending to re-purpose this amplifier I'm not exactly short of amplifiers, and you asked about the front panel, yes, it is professionally 'engraved'. I was very interested to read your posts regarding Compton, and, as it happens, a day earlier I'd spent a while with 'Google' doing some of my own research and I'd been on various websites, including ones you've mentioned and looked at a lot of pictures of these amplifiers and organs and I've come to the conclusion that there's a strong possibility that these amplifiers were made for Compton by a third party. I say this because they're all coloured with this same identifying cream paint - nothing else in the organs has this cream coloured paint on its chassis. Of course, there's the possibility that the chap you mentioned at Compton built these amplifiers and decided that they'd all be painted the same colour, although I've also seen a green one somewhere on the 'net, and also some other different types, particularly those built on two chassis that are silver metal coloured. It's as you say, a lot of information is lost and so there's a lot of 'unknowns'. All the cream ones have fairly low chassis numbers (where they can be seen), I think I remember seeing a number 338 as one of the highest on a picture I was looking at somewhere, although it was over a week or so ago when I was looking.

I said in an earlier post that I thought that the mains transformer was a replacement on mine, due to it not being painted cream. Well, now I'm certain that it's original after all because of the coloured paint seal on the soldered connections that can be seen in the photos, also I've seen pictures of others with silver, and not cream transformers. It's interesting how all the laminations are externally covered with that black tape...they all seem to be like that. Also, the smoothing can has its top half covered in the same tape, hence on this it would have to be removed to reveal a possible date. although a picture below shows the date codes on the paper Hunts type.

I've been thinking some more about the language lab thing and although that's a possibility, I've got absolutely no memory of where this amplifier came from. The language lab thing was sometime in the late 80s (I think), but I thought I'd had this amplifier longer than that, but I honestly can't remember. I used to have a large speaker (now long gone) which had an upstand from the centre magnet with the supporting spider going from it across the front of the speaker to the outside of the cone surround, the likes of which I've never seen before or since - I seem to possibly associate this speaker with the amplifier, but I really can't remember.

Many thanks for your very interesting input, Lucien - looking forward to your further thoughts, comments and information.
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Old 28th Jun 2022, 7:18 pm   #27
Lucien Nunes
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IYI on the Moldseals is a good start: Week 30 of 1963, which puts it before the EPTA era. Any other codes gratefully received. I am very interested to research what level of subcontracting might have gone into these and have a few lines of enquiry to pursue.

The colour of the chassis is an interesting point and it ties-in to a degree with some other characteristics. The very first post-war units were the rack-mount type and at first they were cream-painted, but by the early 50s were grey. The generator support frame also changed from black crackle-finish to grey but maybe not at the same time. So few survive that it is hard to make any sense of the chassis serial numbers, although the cabinet numbers are consecutive.

Chassis with separate PSUs, types PA352 (fixed g2) and PA661 (UL) were used in models with external speakers. These were normally zinc plated, although there was at least one production run, of which I know of two surviving units both from the 'Palladium' model of which maybe a dozen were made, that had grey painted chassis. The two versions had consecutive serial number sequences,

The single channel chassis like the subjects of this thread were used in 1960s models with integral speakers and these are all cream, both the EL84 type seen here and the larger one with octal bottles. These also had chronological serials independent of the dual-channel ones although I have not yet determined whether the two sizes had separate sequences.

The transistor amps, both the transformer-coupled germanium 40+40W and the DC-coupled silicon units which existed in three versions up to 70+70W were all plated. So in chronological order of model introduction, chassis finish went cream / grey / plated / cream / plated but with overlaps.

You mention green chassis. These are all aftermarket reworks by Fred Allen, fitted with a variety of bought-in solid-state modules, either discrete-transistor or in a few cases ILP hybrids. After Fred left Makin, he traded from his base in Hertfordshire as the 'Compton Organ Maintenance Co.' and travelled the country keeping Electrones working. He was of the opinion that valve amps were fundamentally obsolete and probably soon to become unmaintainable, so during overhauls and in the event of failure, he recommended replacing the original valve amp with solid-state on an exchange basis.

Fred must have stripped down a hundred or more valve chassis and probably weighed the transformers in for scrap. He sprayed the bare original Compton chassis green and built his various arrangements of amp modules onto them. He also retrofitted ex-works Compton transistor amps in some cases. This is one of the reasons so few organs have original amps; the ones most likely to have survived are the ones he maintained, which are also the ones most likely to have been upgraded to solid-state.

One peculiarity found on all Compton units is the high HT feed for the tone generators (via the voicing circuitry) termed the 'polarising supply.' Different designs derive it in different ways, some with a separate HT chain, some even from a separate rectifier, but it is in the order of 450-500V. The choke seen on certain chassis is just for the polarising supply; it does not and cannot handle the amp's own HT current. I think there is a hole in the 'Gram Amp' chassis where one mounting lug of the polarising supply choke would be. If there are signs that a choke has been there, that might tell us something (I'm not sure what!) Compare the pics of the two amps in this thread.

The polarising feed is needed on organs with solid-state amps too, where it can be a trap for the unwary. E.g. the PSU for the silicon amp in a late model 365 has not only the +/-40V for the amp and +/- 2.5V for the rotor bias but also the +500V ready to bite you. Dereux, one of the two European makers of rotary electrostatic generators, went higher with c. 900V. In my model AB it comes from an EY81 stacked on top of the main HT.

If it's not too O/T I can post pics of some of this stuff I keep rabbiting on about, although as mentioned before it is such a challenge to stop amps being pilfered from these things that I am cautious about raising their profile too much.
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Old 28th Jun 2022, 11:10 pm   #28
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OHH keep rabbiting on!! A facinating story, and you know what you are talking about.
I am waiting for the next installment.

Joe
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Old 28th Jun 2022, 11:32 pm   #29
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Polarising supply is exactly the right term for the DC bias used to make capacitive transducers work. Right for electrostatic microphones, headphones, speakers and accelerometers.

You've already pointed out that many of the organs have been upgraded to transistor power amps, Lucien, so that might have cooled the ardour of many valve aficionados.

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Old 3rd Jul 2022, 3:22 pm   #30
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As mentioned above, the EL84 chassis only saw use in the very smallest instruments. The next tier up in the Electrone range were the compact consoles with a 30-note pedlaboard and integral speakers. In principle there were four models, CH/2 and HE/2 being the 2-manual classical and entertainment versions respectively, and 3M/C and 3M/E being the 3-manual equivalents. Of these, only the CH/2 sold in quantity, maybe a thousand or so. The others were probably made in dozens rather than hundreds. I have all four models; my 3M/C is the only example I have ever been aware of, and while I knew of two other examples of the 3M/C and one other example of the HE/2, all of those have been broken up. I recall trying to verify whether my 3M/E was the one used in the Beatles movie or not; IIRC there is some visible constructional difference that proves not.

Attached PDF has the circuit and a general view of the chassis. Never having found an original Compton drawing, I drew the circuit from an example amp so the component IDs won't match if the original ever turns up. Searching my picture archive for some reason I can't find any under-chassis views nor any of the associated reverb spring unit, but can add them when I am next near examples to take pics.

It starts with the customary separate input stages V1A & B for the two generator channels. Bass channel grid leak R6 is deliberately high to avoid the generator effective source capacitance rolling off the low notes. Note also the different values of coupling capacitors C2 and C5, to roll off the rumble from the treble channel where, unlike the bass channel, it's out of band. VR1 & 2 set the generator levels as described previously, VR3 taps off some of the treble channel to send to the reverb. V2 drives the swell pedal pot if fitted.

The subject of swell (expression) controls as used by Compton and others is worthy of a post of its own. Many different types of controls were used, each with pros and cons, including integral or remote variable control voltage, integral or remote light gate, differential variable capacitor and potentiometer. For now, suffice to say that Compton used audio potentiometers only on smaller models. This amp was equipped for an external pot, but the model of organ shown in the the pic of the amp in the attached PDF does not employ one, using variable control voltage instead; I will return to this subject later.

Returning to the amp circuit, the reverb driver consists of two halves of an ECC83 paralleled, with a matching transformer mounted in the spring tank housing. This device is worth seeing, I will take some new pics. It consists of two loudspeakers drive units minus cones and baskets, mounted side by side magnet-upwards with a necklace of three different springs strung between their coils. It worked, but did not have the response of the best of the era such as the Accutronics spring lines. The reverb recovery amp is interesting in probably being Compton's first use of a transistor and only use of a hybrid circuit. The reverb is remotely switched by controlling the screen voltage of V102.

The power amplfier is entirely conventional and was the only circuit for which Compton chose that particular output valve. Contrary to one of my earlier posts, this chassis does include CLC smoothing for the amp main HT. However it will be seen that the amp rectifier runs from taps in the HT secondary, with the higher HT from the winding ends taken through a separate smaller rectifier and CLC to supply the polarising voltage. AFAIK this was the only Compton chassis to include adjustable humbucking.

Construction-wise the preamp and power amp sections are built on turret board but the reverb section is on a PCB, oddly with the components mounted on the track side. I don't know why this was done other than to avoid the need to remove the PCB for repair.

This chassis was replaced by a germanium transistor one during production of the CH/2. The latter have proved quite reliable and amongst the few CH/2's that can still be found working in a churches, one is likely to find either the Compton transistor amp or more likely a Fred Allen green silicon replacement. I'm struggling to recall whether Compton themselves fitted silicon amps in any of these models, logic tells me they did in the late 60's but I can't think of an example.
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Old 4th Dec 2022, 8:22 pm   #31
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Update! I have found the original Compton circuit diagram for the 10W EL84 amp.

I commented earlier that Compton's service manuals were a bit thin on the ground and never seemed to detail certain models and chassis. For much of the 1950s and 60s, there was a generic manual covering all the popular stock models, updated from time to time in line with the introduction of new models and features. Over 15 years of searching, I have amassed a dozen copies of editions from 1952 to 1969, plus some additional drawings and data sheets. Amongst all the above, only one valve amplifier was ever shown, that of the 15+15W PA352. Only with the introduction of the 40+40W transistor amp did a new set of circuit diagrams appear in any of my documentation.

Finally, last week, another copy of the 1966 edition arrived, with many extra pages that include some of the missing links. Included are the 10W and 20W chassis including the latter's reverb driver subassembly, and some model-specific details that I have not previously seen.

A pic of the 10W circuit is attached below. I see a few minor differences from Ken's:
* First stage anode loads 100k
* Step network in V2's anode circuit
* EL84 grids have 10k stoppers
* Coupling caps are 0.1uF, although IIRC I have seen both 0.05 and 0.1 in production amps.

This circuit shows a few of the component values that Ken's drawing does not have, although it omits the first HT dropper (15k in Ken's) and voltage amp coupler (0.1 in Ken's) and incorrectly shows the bass input grid leak as 3.3k (it must be 3.3M)

I am launching further enquiries into non-organ Compton products with a hope that we might discover more about how this particular amp came into being.
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Old 8th Dec 2022, 12:49 pm   #32
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I must say it looks like an amp from the ROGERS stable. J.
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Old 8th Dec 2022, 2:26 pm   #33
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Interesting comparison. I looked at it side-by-side with a Cadet, and there are some stylistic similarities actually more so with the larger 20W chassis. But also, some important differences in components and construction technique. I'm still no further towards discovering whether any subcontractors were involved in building amps for Compton. I am fairly sure they had the resources to do it all themselves, but they did use subcontractors for various other things and in turn they did make parts for other organ builders.

The 10W EL84 unit used in the little home spinets, on which this is based, was by far the smallest fitted to a Compton organ, so it doesn't give us as many clues as its larger brethren. The proper church models of the 1950s had four channels each with a pair of octal output bottles, built on five 19" rackmount chassis - two PSUs, two 2-ch power amps and a preamp - and there is quite a lot about it that says Compton-made. They had been making equipment for RADAR during the war and it seems plausible that it boosted some of their manufacturing resources such as chassis-making. But again there are other quirks, such as the different serial numbering format on the 'box-chassis' amps compared to the rackmount ones, and the variety of paint finishes that I mentioned upthread, that suggest different origins.

For comparison, here are some views of the 4-channel setup of the 1950s used in the 'full-size' organs. It's bi-amped, each chassis has one bass and one treble channel, and feeds one speaker cabinet. The output stages are tetrode-connected with a gasfilled stabiliser reducing the screen voltage, driven by 6J7s. The preamp is common to both power amps, using EF37As and 6J5s/ L63s.
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Old 8th Dec 2022, 11:12 pm   #34
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Its certainly beautifully made !!!. Thats an extremely professional setup. I work on a lot of Hammond organs, and they are nothing like that.

Joe
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Old 9th Dec 2022, 12:45 am   #35
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The comparison between Compton and Hammond is an interesting one that rewards close study. As far as electronic organs were concerned, despite setting out to do much the same thing at the same time, their products ended up about as different as they could possibly be. It's all completely understandable when the relevant factors are taken into account, and I might do a separate thread about it.

Compton stuff was very nicely built and no expense was spared on the larger models. But as you might expect with small manufacturing volumes of highly priced products, for which extensive customising was available, quite a lot of quirks and eccentricities tended to creep in. Value-engineering was non-existent and some of the implementations were a bit OTT for what they were aiming to achieve. By contrast, Hammond was much more geared to mass production, had better engineering design in some aspects, and a reasonable amount of bean-counting that did not impact on reliability. Indeed golden-age Hammonds have an enviable reputation for reliability.
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Old 9th Dec 2022, 12:54 am   #36
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Thats very true Lucien.
Most of the Hammonds I work on are 1940's or 1950's, and providing the "starter motor " hasnt been burnt out, virtually go forever. Lots of capacitor changes are required, but as yet I have never changed a paper waxy in the filter circuits. The same goes for the Leslie units, pretty much bullet proof. but they too are manufactured using "ugly " chassis tecniques.
Alas, most of the units I have seen have been "hotted up " with inexplicable modifications that sometimes take weeks to diagnose. Especially in the mixer circuits.

Joe
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Old 9th Dec 2022, 1:31 am   #37
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I would say that the amplifiers in post 33 have all of the traits of Vortexian Ltd. Wembley.

Same tray design method as some of the big Vortexians I have.
Same cabinet side perforations for ventilation. Same colour paint. Same professional well engineered layout and construction.

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Old 9th Dec 2022, 4:58 pm   #38
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Default Re: Compton Amp Circuit

A very interesting insight Mike, which deserves further investigation. As it happens there is some Vortexion kit in the Bedford warehouse, such as the rackmount 200W unit, just 50 feet away from the nearest Compton generator cabinet. I'm looking forward to doing a comparison the next time I go up, but being in the midst of chemo and not getting out very much it won't be this weekend.

Apart from a few units made at the start of post-war production, these rackmount Compton amps and the dual-channel box-chassis ones use transformers made by AEE - Associated Electronic Engineers, of Stanmore, Middx. It would be interesting to know whether Vortexion ever used AEE transformers, I can't picture them until I go look in person.

But I just made another interesting discovery. There is an ad for AEE transformers in Grace's guide, where I have just noticed for the first time that the company claimed to make complete amplifiers. They are just up the road from Compton and might have been behind more than just the transformers.
AEE advert in Grace's Guide

OTOH, against the idea of subcontractors and in favour of in-house manufacture, I note that Compton had a test station in the Acton factory specifically built for testing these chassis that have AEE transformers. I have seen an acceptance test form IIRC on Compton stationery, with the test point voltages, distortion etc filled in. If the amps were made by a subcontractor, would they have gone to the bother of doing this themselves?

The single-channel chassis such as the OP's and the later transistor ones that are generally different in construction, tend to have Albion transformers.

Here are some pics of a tone generator cabinet from the late 1940s, when the amp chassis were cream (before changing to grey around 1950.) It is a smaller model of organ with a smaller cabinet, as there is much less apparatus for the tone generators themselves. Unless ordered otherwise, the large model came with four channels of power amp and this one with only two, but it could be upgraded with the addition of extra PSU and PA chassis in place of the blank panels. The wiring loom is prepared for that option, with the unused Jones connector parked on a dummy on the blank panel. Note the little paper labels stuck on the tagstrips identifying the circuit nodes, not the components. These match the circuit diagram and I wonder whether that is a clue to its maker?

You will note that the hinged rack frame carrying the amps swings right out for access and might wonder whether the cabinet would tip over, especially with two PSU and PA chassis fitted. Fear not - a support leg for the rack frame swings down as you open it!
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Old 9th Dec 2022, 6:37 pm   #39
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Default Re: Compton Amp Circuit

Quote:
Originally Posted by murphymad View Post
I would say that the amplifiers in post 33 have all of the traits of Vortexian Ltd. Wembley.
Vortexion were in Wimbledon
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Old 12th Dec 2022, 1:55 pm   #40
Lucien Nunes
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Default Re: Compton Amp Circuit

I think we have the answer to the origin of the EL84 amp: Probably made by Associated Electronic Engineers, aka Astronic, of Stanmore, Middx. See this similar unit:

Astronic amp at Radiomuseum

This also suggests that at least the 10W and 20W single-channel amps used by Compton were made for them by Astronic. @Techman's gramophone amplifier, although based on the same chassis, probably has nothing to do with Compton themselves.

The clue was the AEE logo on the transformers used on the older 2-channel Compton amps. Somewhat paradoxically, the transformers on the Compton 10 & 20W amps don't have the same finish or AEE branding, but those on the Astronic-branded amp have the same distinctive varnish treatment.

There are enough differences in construction details between the single and dual channel amps to suggest they might have been made by different companies. Compton or another subcontractor might initially have bought just the transformers from AEE; then, when new models were introduced the early 1960s and two additional chassis types were needed, these were subbed out to AEE complete. As they weren't selling the transformers separately, AEE didn't feel the need to apply branding (although, they don't have the paxolin cover on which the other transformers are engraved.

I am going to study more closely, the similarities and differences between all of the above, to see if there is anything conclusive to tie the dual channel units to Astronic or not.

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