Novachord #346 Inspection & Initial Wakeup

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Re: Novachord #346 Inspection & Initial Wakeup

Post by Automatic Gainsay » Sat Oct 17, 2009 2:08 am

Amazing. That looks great!
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Re: Novachord #346 Inspection & Initial Wakeup

Post by HideawayStudio » Sat Oct 17, 2009 10:14 pm

Automatic Gainsay wrote:Amazing. That looks great!
Thanks... I'm quite happy with the results - can't wait to get the new transformers and test it! :)

Hammond At Work on the Novachord:
HammondAtWork.jpg
Last edited by HideawayStudio on Sat Oct 24, 2009 12:36 am, edited 2 times in total.

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Re: Novachord #346 Inspection & Initial Wakeup

Post by HideawayStudio » Sat Oct 17, 2009 10:45 pm

THIS MORNING'S TASK WAS SERIOUSLY MESSY!!!

This morning was spent restuffing the two (2x1uF) multi-caps in the preamp channel in the Generator Chassis. It was suspected that these were the primary cause of the PSU failure. There is no doubting they'd suffered some sort of trauma as they'd leaked gunk all over the chassis. I was told this was bitumen and I can now confirm that it is.

This involved removing the two cans from the preamp channel chassis and taking them outside for some serious heat treatment! The two cans were placed on a wooden board and their phenolic end caps levered off. They were then placed on their sides over an old soup can and heated with a hot air gun set at maximum. After a few seconds the bitumen started to melt and flow out into the can. When the cans were hot enough I managed to slide a large screwdriver into the gunk and lever out the entire contents in one horrible gloopy lump into the can.

PreAmp Multi-Cap Gloop!
MultiCapYuck.JPG
The emptied cans were cleaned up with WD40 which dissolved the remaining bitumen a treat.

The new 400 volt polyester caps were soldered together in pairs, terminated in PTFE wire and sleeved.

The New Caps Ready To be Potted:
NewMultiCapGutsSleeved.JPG
The new caps were then placed in the original cans and resin based potting compound poured in. Now the resin has cured the new multi-caps are ready to go!

The Rebuilt Preamp Multi-Caps:
FinishedMultiCaps.JPG
Last edited by HideawayStudio on Sat Oct 17, 2009 11:21 pm, edited 2 times in total.

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Re: Novachord #346 Inspection & Initial Wakeup

Post by HideawayStudio » Sat Oct 17, 2009 11:19 pm

This evening has been delightful! Having redone the multi-caps I switched my attention to the mains wiring in the main Generator Chassis. I decided to sleeve some of the wires in heat shrink as the larger gauge wire is rubber under cotton, and it has a habit of cracking if flexed too much. Having made the mains cabling safe, I checked over the heater transformer, and made sure there weren't any shorts to ground. This transformer, unlike the HT transformers, is a real brute, as it's powering all 144 tube heaters in the oscillator and divider channels, and the two tubes in the preamp channel!!

I connected the main umbilical from the Novachord base to the Generator Chassis, and performed a cold check. For the first time I connected my nice new vintage look cloth mains cable to the isolation transformer and variac....

I connected the power and slowly wound the mains up and to my delight, as I approached 115 volts, all of the tube heaters started to light!! I checked each and every tube and, sure enough, all 146 tube heaters are running!

This evening I have had the tube heaters running for over an hour at full voltage in the Generator Chassis. This is quite a thing to see in the dark! I really wish my digital camera was up to taking such a beautiful site.

I noted a number of surprising things when I ran up the tube heaters for the first time. Firstly, everyone has been poking fun at me about how this thing was going to pour out tons of heat. Marco in Italy said his Novachord doesn't and, sure enough, he's right!! After an hour of running the heaters the transformer was hardly even warm and the tubes themselves produce surprisingly little overall heat. To be honest, it's nothing like the heat that pours out of my vintage amplifier - and that's got less than 10 tubes in it! I put this down to two things. Firstly, the 144 tubes are not power output devices but simply low power non-linear signal amplifier tubes which probably don't need much in the way of heaters. Secondly, the Novachord runs it's tubes at 5 volts, not 6.3 volts, to reduce power consumption and vastly increase tube life.

I took some piccies of the Novachord's amazing Generator Chassis while I was at it.

A Portion of Generator & Keying Circuits:
DW_NovaKeyingAndGenerator.JPG
Tubes by the Bucket Load!:
DW_NovaGenTubes.JPG
This Picture Doesn't Do The Sight Of A Sea Of Tube Heaters Justice!!
GeneratorHeaters1.JPG
Tomorrow I will refit the cured multi-caps to the preamp.........
Last edited by HideawayStudio on Fri Oct 19, 2012 12:47 am, edited 2 times in total.

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Re: Novachord #346 Inspection & Initial Wakeup

Post by pflosi » Sat Oct 17, 2009 11:36 pm

that's seriously awesome mate! congratulations!

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Re: Novachord #346 Inspection & Initial Wakeup

Post by HideawayStudio » Sat Oct 17, 2009 11:37 pm

Mooger5 wrote:#-o You collect vintage tubes and here was I with all the audiophile blurb. I´ll stop now :lol:
Impeccable arrangement there, with the Teflon wiring and heatshrink. The PSU looks fantastic :)
The resistors look so tiny compared to the old ones :o 1 Watt?
Ahhh... you're the second person to ask mention the size of the new resistors. This is because the new ones are metal film, not carbon, like the old ones. The new resistors are rated at 2 Watts at 500 Volts.

It's the size of the new caps that makes me laugh - they are tiny compared to the old ones and are of higher voltage spec in many cases!

Speaking of caps... there is a real irony here. I have just restuffed the horrible bitumen potted multi-cap cans in the preamp BUT the 4uF pcb oil cap next to them is in perfect condition - it still reads 4uF and hasn't leaked a bit of oil over the past 70 years! It also faired well after a leakage test performed at 70V DC where the voltage on the plates just sat there until discharged with a resistor.

The Pristine Oil Cap from the Preamp Chassis:
GoodPA_Oil.JPG
Last edited by HideawayStudio on Sat Oct 24, 2009 9:36 am, edited 1 time in total.

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Re: Novachord #346 Inspection & Initial Wakeup

Post by Automatic Gainsay » Sun Oct 18, 2009 5:41 pm

Call me biased, but this is one of the best threads on VSE.
It's extremely educational!
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Re: Novachord #346 Inspection & Initial Wakeup

Post by dr funk » Sun Oct 18, 2009 8:30 pm

Automatic Gainsay wrote:Call me biased
With all those tubes, I think it's only appropriate... :lol:
Automatic Gainsay wrote:but this is one of the best threads on VSE.
It's extremely educational!
And that is very true. I'm checking in daily to see the progress!

Frank

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Re: Novachord #346 Inspection & Initial Wakeup

Post by HideawayStudio » Sun Oct 18, 2009 10:09 pm

dr funk wrote:
Automatic Gainsay wrote:Call me biased
With all those tubes, I think it's only appropriate... :lol:
Automatic Gainsay wrote:but this is one of the best threads on VSE.
It's extremely educational!
And that is very true. I'm checking in daily to see the progress!

Frank
Thanks for everyone's kind comments on this thread - this encouragement is really driving me to return this beast to working order with the dedication it really demands.

This morning was spent refitting the newly restuffed and repotted 2x1uF multi-caps back into the preamp channel. This was a relatively easy task and left me thinking that overall this thing is delight to work on. Despite the sheer amount of vintage electronics inside this beast, access to most things is excellent and clearly a lot of thought was put into servicability.

Yet again, when I've been reminded of the Novachord's amazing build quality. There are two large round shield caps in the preamp. It turns out these are made of solid brass and after attacking them with copious amounts of Brasso metal polish they've come up like mirrors!

On closer inspection it looks like someone has done some not so great repair jobs on my preamp channel so I set about removing various poorly fitted components, cleaning up the wiring and sleeving several wires for improved insulation with black heat shrink. I then refitted some new components, in particular, any caps wired directly across supply rails.

I connected the PSU and expression pedal umbilicals, replaced the shield caps and then started work fitting my line output modification. Very fortunately, the Novachord has a centre tapped output transformer on the tail end of the preamp channel thus offering a balanced, isolated audio output. This normally feeds a Hammond power amp and the two speakers in the enclosure. The transformer outputs appear on the bottom right hand three screw terminals on the main terminal block (see photo). I sleeved some balanced cable and fitted terminal spades. I connected the new cable in place of the PA terminals and routed the line output cable along the umbilical to the rear cabinet. I then fitted my XLR socket on a metal bracket to rear edge of the bottom shelf of the rear cabinet. At present the PA chassis is not fitted as it's in very poor condition and I've only plans to use the instrument at line level for the timebeing. This is by far the highest quality method of audio output.

The new line output reads correctly on my meter so fingers crossed.

The Revamped Preamp Channel:
DW_Nova Preamp XLR Mod.JPG
The New Line Output on an XLR Connector
DW_Novachord_XLR_Line_Out.JPG

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Re: Novachord #346 Inspection & Initial Wakeup

Post by rjd2 » Mon Oct 19, 2009 4:11 am

wow.....im blown away. your work looks SOOOO clean. wow. this is just awesome.

i can tell that you are the kind of guy that probably has 10 sizes of heatshrink and 10 gauges of wire on hand at all times, dont you? i am impressed.....

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Re: Novachord #346 Inspection & Initial Wakeup

Post by madtheory » Mon Oct 19, 2009 9:36 am

Beautiful work. I love your approach. It seems to me that the research you've done in advance, and your knowledge of vintage electronics has made the task easier for you, compared to Phil's restoration. You're not trying to impove on an already perfect design. Everything is big a well laid out so it's straightforward, it's almost more of a mechanical job than pure electronics, in the modern sense. Some might be inclined to not bother potting the caps, for example, but you've gone to great lengths to keep it as original as possible. Well done!

If I remember rightly, I think Phil hadn't spotted how easy it was to make a line out! That's a seriously hefty bracket you have there for the XLR socket :)

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Re: Novachord #346 Inspection & Initial Wakeup

Post by HideawayStudio » Mon Oct 19, 2009 7:27 pm

madtheory wrote:Beautiful work. I love your approach. It seems to me that the research you've done in advance, and your knowledge of vintage electronics has made the task easier for you, compared to Phil's restoration. You're not trying to impove on an already perfect design. Everything is big a well laid out so it's straightforward, it's almost more of a mechanical job than pure electronics, in the modern sense. Some might be inclined to not bother potting the caps, for example, but you've gone to great lengths to keep it as original as possible. Well done!

If I remember rightly, I think Phil hadn't spotted how easy it was to make a line out! That's a seriously hefty bracket you have there for the XLR socket :)
Again.... thank you all for your kind comments. I'm driven by the fact that I simply must hear it work! :)

Novachord Ad From 1941:
Novachord_Ad_June_1941.JPG
Last edited by HideawayStudio on Sat Oct 24, 2009 12:41 am, edited 1 time in total.

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Re: Novachord #346 Inspection & Initial Wakeup

Post by HideawayStudio » Mon Oct 19, 2009 8:39 pm

TODAY'S TASK: Checking The Vibrato Module

The Novachord has a very special 6-channel electro-mechanical Vibrato system. It works by energising 6 leaf relays which are wired in a positive feedback arrangement much like a doorbell or buzzer. When a current is applied to each of the six coils it pulls in the relay contacts which break the connection to the coil and hence it lets go of the contacts and the cycle is repeated. The mechanisms are weighted so their action is damped and quite slow.

As each contact opens and closes a second contact on each relay switches in an out either one or two capacitors depending on the front panel setting which are momentarily introduced and then removed from each oscillator's LC tank circuit. This has the effect of slightly lowering the oscillator frequency each time the contacts close. When the vibrato circuits are enabled the steady state oscillator frequency is tweaked slightly so that when the vibrato contacts are in their open position the frequency is slightly shifted to normal and when they are closed and the extra capacitance switched in, it is slightly shifted the other way. The mean frequency is thus centred about the tuned position rather than just below it.

Each of the six mechanisms have been arranged to run very slightly out of time with it's adjacent one. Each vibrato then works on each pair of adjacent oscillators (ie. two semitones) thus creating a wonderfully unique vibrato effect across all 12 oscillators! This gives sustained voices, in particular, a wonderfully wide and natural sound.

This evening I applied power to the Vibrato Rail for the first time using a current limited bench supply. Sure enough, as I wound the voltage up to 50V DC at 120mA the Novachord's trademark ticking noise began. It's wonderful noise - you could almost imagine six tiny woodpeckers sitting inside the metal box.

The Vibrato module is situated on the right hand side of the instrument in between the preamp channel and the oscillators.

The 6 Channel Vibrato Unit:
DW_NovaVibratoUnit.jpg
The Oscillator Schematic along with a single Vibrato Channel:
fig14.jpg
The next task is to apply the bench PSU to each terminal pin on the PSU connector in order to check for shorts prior to connecting the rebuilt PSU for the first time in a couple of weeks. It is -vitally- important that I check, as carefully as possible, each rail for excessive loads as I could end up burning out the rebuilt PSU due to missing the original fault!! This will be performed with the heaters off and the bench supply set to < 50mA and then the voltage wound up from 0 to 70 volts DC. The load on each HT rail should be very low indeed as their nominal loading in normal run conditions is set by each tube running at around 0.2mA quiescent current. This is fairly low for a tube design but I suspect the aggregate HT loadings would have been horrendous if it set were any higher! Clearly Hammond were quite concerned about power consumption and keeping the value/size/cost of the capacitors down which has lead the Novachord being a generally very high impedence design.

ERROR: "Some of the resistors in the Novachord are crazy - the envelope/keying circuits make use of several 500MOhm resistors!!" Many thanks to Marco Bacigalupo, who has undertaken what must be one of the finest and most authentic Novachord restoration jobs in the world, for pointing out an error in the Playing Key Schematic (fig.19 in the Service Manual) whereby RN10 should read .180 to .450M (ie. 180K to 450K) and not 180M to 450M.

It remains to be seen how 70 year old caps are going to affect the characterisics of the envelope generators. It also remains to be seen just how well 70 year old caps will hold up to being applied with 270 volts! (I am performing some high voltage tests with a few caps removed from the instrument first!)

Speaking of caps, I have rescued a few caps from the preamp of the same type as the main divider array as I wish to perform some high voltage testing on these to determine how well the insulation has survived and just how leaky and off spec they have become. This type of cap is notorious for absorbing moisture. I am therefore very interested to know what happens if I bake these components whilst energised for several hours before and after testing. There has been some evidence that unrestored Novachords can sometimes improve in functionality with run time - this just might be an explanation. In terms of basic spec, one is reading within 5% of it's original value (not bad for a 70 year old cap!!) and one is around 35% out - and typically for this type of cap construction - it's reading high.

For those who wonder where I'm going with all of this the general plan is as follows:

Cold check all supply rails (WC: 19th Oct Mon-Wed)
Replace last few caps directly across supply rails behind main control panel (WC: 19th Oct Wed-Sun)
Build dummy load for testing PSU (WC: 26th Oct)
Fit new HT transformers and choke to rebuilt PSU and load test with dummy load (WC: 9th Nov)
Fit PSU to Novachord and attempt to power for first time!! (WC: 9th Nov!)
Make recordings of whatever is operational (including waveforms) using DC blocked safety attenuator box at raw oscillator, divider and filter stages. (WC: 9th Nov)
Carry out detailed audit of Novachord Generator Chassis condition (WC: 16th Nov)

From this point onwards I can't speculate on timing until I know the exact condition of the beast!
Last edited by HideawayStudio on Fri Oct 30, 2009 6:49 pm, edited 5 times in total.

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Re: Novachord #346 Inspection & Initial Wakeup

Post by HideawayStudio » Tue Oct 20, 2009 8:46 pm

A quick update....

Yesterday evening I applied 0-70V DC to each HT rail in turn, checking for signs of excessive loading. With the exception of one capacitor, which I can't find!, (probably) situated behind the front panel in the envelope control, all supply decoupling caps have been replaced.

On applying voltages to some rails - eg. the keying circuits - I was able to check the function of the envelope generators and the vibrato circuits. In both cases the loadings look sensible and I could see that the keys are indeed triggering decay curves. All of the key contacts appear to work and the voltage is finding it's way where I'd expect. On removing 70V DC from some circuits there must be precious little leakage as the rails take a significant time to drop back to zero. The 34 volt divider chain situated on the end of the keyboard is working correctly. The oil cap in the preamp appears to be in very good condition too.

Before my new HT transformers turn up there is less work I can do on the beast than before now. I need to replace the wirewound ceramic 2 ohm inrush limiting resistor on the main HT recitifier tube in the PSU as it's showing signs of cracking around it's terminations.

I have had some feedback from the company winding the transformers regarding the gauge of wires in the burnt out choke - this is very thin at 41swg and has been necessary to measure as the known good DC resistance and the wire's resistivity are instrumental in determining the number of windings and hence the inductance of the original. It's been estimated this is somewhere around 100H. Fortunately, it's value in this application, is not that critical.

Very frustratingly the schematics sufficiently detail cap and resistor specs but not inductances. This is of particular concern in the main resonant low pass filter network where, although the chances of failure are low, if a choke were required, it would be difficult to determine it's original characteristics. I would feel happier if these chokes were characterized sooner rather than later for the record by either myself or another Novachord owner.

The Novachord's Wonderful LC Based Resonant Low Pass "Formant" Filter Network:
fig20.jpg
This is all well before the days of Gyrator and diode ladder based filters. The use of multiple LC tanks with variable Q is an important feature of the Novachord in defining it's unique sound.
Last edited by HideawayStudio on Fri Oct 30, 2009 6:49 pm, edited 2 times in total.

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Re: Novachord #346 Inspection & Initial Wakeup

Post by dr funk » Wed Oct 21, 2009 6:00 am

HideawayStudio wrote: Very frustratingly the schematics sufficiently detail cap and resistor specs but not inductances. This is of particular concern in the main resonant low pass filter network where, although the chances of failure are low, if a choke were required, it would be difficult to determine it's original characteristics. I would feel happier if these chokes were characterized sooner rather than later for the record by either myself or another Novachord owner.
Have you asked Mike Fulk if he has this info? You never know, he just might...

Frank

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