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Old 22nd Nov 2015, 2:46 pm   #41
Lucien Nunes
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Default Re: 193 valves in 5 days - rescuing the Miller Classic IV organ

I will post some pics of the speaker, which is still in situ as it is an integral part of the building. LF uses two 12" drivers in a folded horn about 10' effective length, built of plywood and cement rendered internally. Two upward firing dual-cone units provided the top end.
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Old 22nd Nov 2015, 2:58 pm   #42
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Default Re: 193 valves in 5 days - rescuing the Miller Classic IV organ

And you have time to post here too!
 
Old 22nd Nov 2015, 3:11 pm   #43
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Default Re: 193 valves in 5 days - rescuing the Miller Classic IV organ

I haven't had a lot of time recently, work averaging 120-130 hours per week. The Miller organ recovery was the only not-strictly-work thing I've done since the BBC TX recovery, although it was a serious project sponsored by the event. Today I'm on site programming / commissioning, so I get to fire off emails and posts while waiting for stuff to compile / verify / upload / restart / fail dismally.
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Old 22nd Nov 2015, 7:00 pm   #44
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Smile Re: 193 valves in 5 days - rescuing the Miller Classic IV organ

Hi,
This is an amazing project and I'm enjoying being able to follow its progress.
It will be wonderful to hear it on BBC Radio 2's 'The Organist Entertains' when it is fully up and running once again.
Cheers, Pete.
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Old 22nd Nov 2015, 10:33 pm   #45
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Default Re: 193 valves in 5 days - rescuing the Miller Classic IV organ

Quote:
Originally Posted by Lucien Nunes View Post
Removal completed
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Old 23rd Nov 2015, 3:17 am   #46
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Default Re: 193 valves in 5 days - rescuing the Miller Classic IV organ

Obligatory YouTube link: https://youtu.be/r5XX9LX2es4
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Old 23rd Nov 2015, 7:20 am   #47
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Default Re: 193 valves in 5 days - rescuing the Miller Classic IV organ

"work averaging 120-130 hours per week"

Watch them hours boss, been there done that and observed some tragic consequences.

Lawrence.
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Old 25th Nov 2015, 2:03 am   #48
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Default Re: 193 valves in 5 days - rescuing the Miller Classic IV organ

Oscillators, pt. 1.

It is often said of electronic organs that they consist only of a very simple circuit repeated a ridiculous number of times. There's slightly more to it than that but first here's the simple circuit.

From Fig. 30 you will see it is a Hartley oscillator based on half an ECC82. Normally quiescent, it runs only when the matrix relay sends it HT in response to a key being pressed. The tank coil is made up of transformer A and variable tuning inductor L. The secondary of A consists of a small number of turns, with selectable taps, from which a fairly pure sinusoid is available. Anode coil C is variably coupled to output coil B, from which a harmonically rich signal is available. These two signals are collected by separate low-impedance summing circuits in which all the oscillator outputs of a rank are connected in series or series-parallel, to feed the input transformers of that rank's voicing filters.

The white box in Fig. 30 outlines one oscillator. Note the rotatable ferrite limb in L, which moves as shown for tuning. Coils B and C will be seen fixed on a laminated bar core. By slackening the clamping nuts, coil B can be moved along to alter the coupling, and hence regulate the output of the complex waveform. In Fig. 31 the same oscillator is seen, with the regulating taps just visible on the side of the bobbin of coil A. The polystyrene tuning capacitor Ct sports a paper label with its value at room temp to 4 s.f. In some of the other oscillators, the multiple parallel caps used to make up the appropriate value can be seen.

Fig. 32 shows how the oscillators are grouped by octave and rank. Each metal panel carries one octave (12 generators) with common heater and output connections. The panels of each rank span between the central post and one of the corner posts of the cabinet, in ascending frequency order. The Diapason and Flute ranks each encompass 8 octaves, the Trumpet 7 octaves and the Twelfth 6 octaves, making a total of 29 panels and 348 oscillators.
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Old 25th Nov 2015, 7:44 am   #49
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Default Re: 193 valves in 5 days - rescuing the Miller Classic IV organ

Transformer A can be viewed as a current transformer sampling the circulating current in the tuned circuit formed by L and the polystyrene capacitor. Working the secondary of A into a low impedance summing network means that the primary of A looks like only a very low impedance in series in the tank circuit. The tank acts as a filter, making this output reasonably sinusoidal no matter what the valve is doing.

Transformer B-C can be thought of as another current transformer, sampling the current which the ECC82 is pumping into the tank. There are books and books written on the business of oscillator circuits and frequency control and frequency drift, but there is very little written on the amplitude control mechanisms, which is a shame because it's also kind of important. To have a stable amplitude, the amplifier's active device must be driven into non-linearity, so that the effective gain falls with increasing amplitude. This allows the circuit to start and to run up in amplitude to an equilibrium point where the gain falls enough to not allow the amplitude to increase any further. In this case, the triode bias will be designed to run it into cutoff over part of the cycle and the self-rectified grid bias automates this. This makes the anode current significantly non-sinusoidal, and harmonic rich.

The amplitude control in this circuit is very important because of the keyed HT. It affects the rate and shape of the attack of the notes.

Polystyrene capacitors have a significant temperature coefficient, but you can pick a grade of ferrite with a similar, but opposite temperature coefficient and you can get a useful reduction in temperature sensitivity. I've used Siemens N28 for this in filters etc in the past.

David
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Old 25th Nov 2015, 11:19 am   #50
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Default Re: 193 valves in 5 days - rescuing the Miller Classic IV organ

Hi,
I think it looks like a most impressive project. I've only worked on a Lowrey Heritage Deluxe Organ, which was much smaller and not nearly as complex.
It took me ages to get it going, lots of keying neons had gone faulty.
Most impressed again, hope you can have some time out ( well deserved ) after this project is finished.

regards Peter B
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Old 26th Nov 2015, 12:47 am   #51
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Default Re: 193 valves in 5 days - rescuing the Miller Classic IV organ

I never did get as far as measuring how much of the tank inductance is contributed by transformer A, nor the effective load presented to the outputs by the filter input circuit. I described this as low impedance, but it is probably not negligible. The tuning range on inductor L is relatively small, and small variations in the reluctance of the core of A have a noticeable effect on the tuning. In order to avoid a plot spoiler I won't say any more about that yet.

Due to time pressure, only measurements needed to complete a specific task were taken. I've never looked at the oscillator waveforms on a scope, nor measured their amplitudes etc. As much as I would have liked to become thoroughly familiar with the beast, it was crucial not to stray from the critical path.

Day 2

Cabinet standing in the workshop, oscillators at the top of the to-do list. The preamps and PSU worked well enough to get started, so a power amp and speaker were connected and troubleshooting began by energising each oscillator in turn from a cliplead fed with HT. The strategy was to start in the (important) middle of one rank and work upwards, fixing each fault, timing each fix. After four octaves, progress was reviewed.

A few of each of the following types of fault showed up:
a) Duff valve, usually O/C heater. Replace, regulate and tune. 5 mins.
b) O/C anode coil C. No time to rewind; borrow coil from relatively unimportant top octave, working back from the top note. Regulate and tune. 15 mins.
c) Duff / badly substituted cap. Replace, some experimentation involved, 15 mins.
d) Tuning inductor partially dismantled / falling apart. Various oddities here e.g. , clamping springs missing, tuning bar wedged open or removed to compensate for faulty cap. Luckily most of the necessary parts were found lying in and around the cabinet during preparations for the move; by the time the bag of bits had been used up, only a few coils remained incomplete. Reassemble, regulate and tune. 20 mins.
e) Dry joint, loose B coil, etc usually from previous repair. 5 mins

Tuning and regulation were only done roughly to prove the repair, pending a full tuning and regulation once all notes were on speech. The results were promising - apart from the few O/C anode coils everything was reparable promptly and effectively - leading to an estimate of 16 hours to complete the oscillators. Work stopped around midnight with two ranks finished and two well underway. The quick faults had been reduced to a minute or two each, while the tuning inductor repairs and coil substitutions had proven impossible to speed up.

Last edited by Lucien Nunes; 26th Nov 2015 at 1:08 am.
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Old 26th Nov 2015, 7:46 am   #52
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Default Re: 193 valves in 5 days - rescuing the Miller Classic IV organ

Polystyrene capacitors are pretty good parts and usually reliable, but they do have one nasty behaviour. If they go above about 70 degrees C, they undergo a value shift of a few percent, and they don't recover when cool. That tower construction looks like it ought to create airflow by the chimney effect so they should be OK on temperature. The shift would be enough to get noticed in a musical instrument.

David
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Old 26th Nov 2015, 10:08 pm   #53
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Default Re: 193 valves in 5 days - rescuing the Miller Classic IV organ

Hi David, can the value shift be "pre-conditioned" in the cap, or is there a shift everytime it is taken over 70C?

Ed
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Old 26th Nov 2015, 10:52 pm   #54
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Default Re: 193 valves in 5 days - rescuing the Miller Classic IV organ

I think it can be pre-conditioned, but the amount is not predictable.

I designed lots of filters with them in, and the equipment was rated for use to 55C max. If anyone overshot a thermal test chamber it was back to square one...

David
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Old 30th Nov 2015, 6:33 pm   #55
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Default Re: 193 valves in 5 days - rescuing the Miller Classic IV organ

Day 3

8am. Work continues on the oscillators, mainly the bottom end. I mentioned polystyrene tuning caps earlier, did I mention paper ones? Because of the larger values required for the lower few octaves, Miller used high quality paper capacitors in the tank circuit. Like the polystyrenes, these had been measured accurately on the bridge and selected / paired up to achieve the ideal value. Unlike the polystyrenes the very largest values had started to fail or go very high in value to the point that the note would not tune. Some had been replaced, some had a larger cap in series to compensate, some notes had the tuning coil fudged to reduce its inductance. I put these rogues right as I went along, ensuring that they would tune to within the necessary range by setting a scale on one octave that I would use henceforth as my reference. Many paper-equipped oscillators would not comfortably tune beyond A4=440Hz concert pitch, nor was it necessary at this stage to achieve concert pitch, so I compromised at classical pitch of A4=330Hz.

2pm. Oscillators 'finished'. Not restored but repaired, 340 out of 348 working, the remaining faults due to open coils having been moved to the top octave of the Clarinet. These can be sorted out when time permits. Admittedly there were a few weird cap combinations, some polyesters sneaking in and the odd note that couldn't quite be regulated, but nothing that would be noticed in the circumstances. Temperature tracking is not terribly important as the whole thing runs very cool inside, as David says it's well designed in this regard and very few valves have anode dissipation at any one time so there's only the heater power to dissipate.

There was now a certain frustration at not being able to test the improvements from the console, as the main cable had yet to be connected up. What main cable, didn't we leave that behind in the church?!
All electric action consoles, except those modernised with a multiplex transmission, have a large multicore cable from console to chambers (for pipe organs) or generator cabinet (for electronics.) The largest theatre instruments might have 1,000 cores or more, this one has a modest 240, consisting of eight 15-pair telephone cables. These had totally refused to budge when we tried to pull them out of their conduits, and the midway inspection point had been floored over years ago, so we abandoned them. A new roll of 15-pair cable was on order but had not yet arrived, so the ability to play tunes in any way other than by poking the matrix relay magnets was a way off. This in turn suggested that although the next most important task was to inspect / adjust / clean the relays, that would be better deferred until the main cable was completed. The next task was therefore to overhaul the preamps, filters, and power supply....
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Old 30th Nov 2015, 8:31 pm   #56
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Default Re: 193 valves in 5 days - rescuing the Miller Classic IV organ

Lucian,

You and your team really do deserve a huge thank you from me and all the likeminded people who love this kind of obsolete but usable technology, very little of which was made, and virtually none of which survives.

It seems a bit of a shame to take it out of its orginal setting, but absolutely incredible that somebody was not only willing, but also able, to save it. And restore it. And play it!

Could I ask where it came from? Was there any associated paperwork surviving?

Nick.
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Old 30th Nov 2015, 10:08 pm   #57
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Default Re: 193 valves in 5 days - rescuing the Miller Classic IV organ

Thanks Nick! You have touched on part of our core philosophy which, if I might be allowed a slight digression to explain, goes like this:

There are lots of vintage electrical and electronic items that have not survived well, or are not being collected nowadays in proportion to their significance or prevalence in their heyday. The heavy, ugly lumps; models with few endearing qualities, devices that have some over-riding disadvantage to ownership such as toxicity or inflated value when dismantled, tend to be under-represented by all but the most comprehensive collections and museums. They get relegated to the bottom of the wants list, derided as 'more trouble than they are worth', or just forgotten entirely. As a result, I started to notice gaps in the current representation of the history of electronic and electrical technology to the interested member of the public.

Knocking this idea around a bit, convinced us that a collection of the peculiar alone could not hope to survive on its own merits, but a museum that gave equal display space to the popular and the unpopular, would bring things to the attention of the average person that he has previously passed by or been shielded from. From this, the Electrokinetica concept developed, an open platform for all electrical technology to have its few moments of fame in a working, hand-on environment. We'll never own Colossus or Faraday's first transformer, but we can show things that you can't see at the Science Museum, and let you play with things that the Smithsonian can't allow people to touch, because our remit is different.

Electric organs are one of my specialisms; they are substantial pieces of work that have embodied a wide range of technologies over the years, plus they are very hands-on and fun to play with. I saw in them an opportunity to illustrate many techniques and inventions from the latter half of the 20th century, so made it an aim to collect a variety of different kinds, good, bad and ugly. We are well along that road now, but the individual-oscillator valve organ had been a stumbling block, because it fell into most peoples' 'not worth the effort' category. Too cumbersome and maintenance-intensive for someone who just wants an instrument to play, too obscure for the average collector of valve stuff, their general intractability and higher value once dismantled condemns the few survivors to the valve-and-transformer hunters.

This one, like many of our more interesting finds, was lucky to have the support of a couple of enthusiastic and constructive people who were convinced that it might have something to offer in historical interest, even if it was no longer prized as a musical instrument. Campbell, an organist at a nearby church who had heard of the imminent need to remove it, did the spadework and made the connection. Once we were hooked (which took all of 3 seconds) Mary at the church did everything possible to facilitate the project and make it all happen on the day. These and others like them, are the people who will deserve much of the credit for making Electrokinetica an interesting place. No amount of capacitor-changing will bring you the sound of a Miller Classic IV, if the only raw material you've got is Hammond B3's, fabulous instruments though they are in their own right.

And thus we return to the subject of capacitors, and the changing of the small number of electrolytics present (not more than a few dozen) in the next instalment.
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Old 30th Nov 2015, 11:37 pm   #58
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Default Re: 193 valves in 5 days - rescuing the Miller Classic IV organ

Waiting eagerly for the next gripping episode as the theme tune, Charles Williams' "Devil's Galop" starts up.

David
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Old 1st Dec 2015, 1:15 pm   #59
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Default Re: 193 valves in 5 days - rescuing the Miller Classic IV organ

Would Cole Porter's "From This Moment On" not be more apposite?

Maybe when it's finished and appears on Youtube
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Old 1st Dec 2015, 1:23 pm   #60
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Default Re: 193 valves in 5 days - rescuing the Miller Classic IV organ

Definitely not the Devil's Gallop yet, and From This Moment On is too sophisticated for a sunny afternoon's re-capping. I would say the mood is more 'Arrival of the Queen of Sheba'; it's day 3 and the oscillators are all working. The signal processing circuits now to be tackled comprise three similar filter chassis and a final preamp / swell control stage. The functioning of the filters deserves a quick description.

Two of the four ranks (Diapason/Dulciana) and (Diapason 12th/Dulciana 12th) belong to the same tone family; the 12th rank merely plays at a mutation pitch which, in the true individual-oscillator scheme, needs its own rank instead of borrowing the close-but-not-exact 12th of the scale of the unison rank. Thus one filter chassis serves for both of those ranks. Another serves the Flute/Clarinet rank and another the String/Trumpet rank. Only one of each pair of tone families has its filter in operation at a time. For example, when you select Flutes instead of Clarinets, no matter which of that rank's stopkeys you have on (which act on the marix relays), the voicing relays shunt the Clarinet filter networks, leaving those of the Flute in parallel with the input transformer secondaries, so all such stops sound as Flutes. Separate transformers are provided for the electrically independent sinusoidal (A coil) and complex (B coil) summing circuits, the signals being mixed within the filter circuit.

In a lesser organ that derives all its waveforms from a set of (harmonically complex) divider outputs, the low-order components must be filtered from them using narrow bandwidth filters handling as small a fraction of the compass as possible. The better the organ, the narrower the bandwidth. For example, the mid-range late 70's Wurlitzer home organ model 630 filters its Tibias in 1-octave groups throughout the compass. The top model of the same range 950 uses instead double the number of 1/2 octave groups in the critical middle section, for better tonal fidelity. Constraints of ths type do not apply to the Miller, since each note is created with its own set of harmonics (or lack of them) and is to a large extent complete in itself. The functions of the filters are therefore to shape the rank's overall characteristics and remove unwanted residual components. The exact details of the filter behaviour I cannot yet give, as much of the work is done by some funny-looking wound components concealed in metal cans, for which I have no information and will need to reverse-engineer in due course.

There aren't many electrolytics in this organ; some in the higher pickup loops to roll them off, cathode bypasses and decouplers in the preamps and filter amps. All of these were changed, perhaps 30 caps in total. Some of the paper caps in these areas had already been changed to Philips C280 or C296 polyesters, these were left along with non-critical papers but all the others for which leakage was a criterion were changed. A few resistors had gone way off, a couple of dry joints and one wrong connection sorted and the passive side of things was sorted.

The active parts turned out to have been letting the side down rather badly. Each preamp uses two B36s a.k.a. 12SN7s - 12V because when you've got 181 valves to feed, up to 7 feet from the mains transformer, it's worth keeping the current to a minimum and all the ECC82s are wired for 12V too. I happily dialed in the settings on the VCM but with the first valve the needle hardly moved. After staring at the bias controls for a few seconds without spotting any error, I moved to the next valve and got a similar result, arousing suspicion. Not having any 12SN7s immediately to hand, I had to click the heater down to 6V and try one of my own 6SN7s which measured fine, before being convinced that they were both completely hopeless. Thus it seemed that the B36s with only a milliamp or so of emission and too low a gm to indicate, were much overdue for replacement. Two had previously been subbed with ECC82s fitted into octal bases, one of which was badly K-H, and the remainder uninspiring, so I made a snap decision to swap the lot to good-as-new 6SN7s and run them off a separate heater supply for the time being, as I could not wait to get my hands on enough 12SN7s.

This done, the sound perked up nicely, with each rank taking on its proper tone character. A similar job was done on the preamp stage - passives changed as required and valve checked (a 6BS7 with its heater ballasted to 12V) but this proved to be in excellent condition and did not need replacement.

Pictures to follow when I have better connection...
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