Herculean DIY Autoformer wiring.

 They say a picture is worth 1000 words... well how about how about around 180 wires and 820 solder connections?  Brad from the Boston contingency wired 6 of the 28 position autoformers up for Caroll's home theater system.  I often joke that more than half of the $200 autoformers I have sold sit partially wired in a box on a shelf and this picture might explain why.

Another Early Strain Gauge

 I came across this cart on the 'bay and it is from an Admial 6F10

One interesting thing about it is the way the cantilever and stylus appear to be formed from a single piece of bent metal.

The other quirk is that it has three terminals with rather high resistances.

The end to end resistance is 150kΩ and the center pin is 100kΩ and  50kΩ to the outers. "Tweaking" the stylus makes the resistance change by 1-10kΩ+ so it really seems to be a strain gauge  and with a date of "Pre-1952" that would make it an early one.  The idea that the three terminals all seem to be connected to gauges has me puzzled an I haven't fully digested the schematic so have at it.

Unsafe At Any Speed

Apologies in advance to Ralph Nader for a wee bit of appropriation.  

 

Garrard 301

 I know the inerwebs are filled pictures of beautiful Garrard 301's and by that standard this one is a bit pedestrian.

If you take a step back and see that it is partnered with a vacuum tube based phono stage and amplifier things get a bit more interesting

another 20 steps back reveal that this is then paired with a pair of Tannoy Westminsters in a Japanese restaurant in NYC and suddenly that first picture isn't so pedestrian any more.

Makes me really want to exit my bubble and be one of the lucky folks who gets a table during the 25% seating capacity phase of the pandemic.

Doc Hoyer's garage door opener.

 It would seem that something as trivial as a garage door opener would never find its way to these pages but often it is the trivial that gives a glimpse into who a person really was.

This seemingly Rube Goldberg approach to automatically opening a garage door is a testament to the cleverness that was Dennis R. Hoyer.  I have no idea when this was constructed but given that they date back to 1926 my guess is going to Sears was not an acceptable option for Dennis.

The key to the operation is the drive mechanism and when I first looked at it I simply thought motor pulled the door open and the casters and gravity did the trick to lower the door with the motor providing some resistive force.  Upon further inspection I realized something different was going on since the casters were pointed in the wrong direction.

A closer look at the casters quickly refuted my first idea and for a second I though that the outside collar would spin around but when I realized that it was fixed it became clear that this simply operated like a ball screw on a CNC machine.

The motor turns the shaft and the casters on the collar were clamped tightly enough and set at a pitch to move the mechanism up or down at the desired rate based on motor speed.  There was a stop at full open and closed but no other safety procedures in place. According to his cousin Damian, if anything were accidentally left in-between the open and closed positions, the results were not pretty.

Most people would have simply driven to Sears but thats not how some of the truly great ones rolled.

New Math

 

THERE! I said it, and I have been trying to say it for years.  Now I am going to use my junkie pulpit to try to explain it in simple terms.

The basic rule of transformers is that the transform the load by the turns ratio squared.  This simple function allows an 8Ω speaker to present a 3200Ω load to a 300B by using a transformer with a 20:1 step-down ratio.  This makes the world an easy place to live in and keeps everyone sane UNTIL someone then asks a poor transformer winder for a 10K:600 linestage transformer and a hole is ripped into the space-time continuum.  The conversation typically goes like this:

Customer:  I need an 10K:600 lineout.

Dave:  What will this be driving?

Customer: Interconnects and the input of the amplifier.

Dave:  Do the interconnects have a 600Ω resistor soldered across them?

Customer: No.

Dave:  Does the amp have a 600Ω input impedance?

Customer:  Of course not.

Dave:  What is the amplifier input impedance?

Customer:  I dunno... 100KΩ... 10KΩ worst case.

Dave:  Then what is the purpose of the 600Ω secondary designation?

Customer:  A 5KΩ:10KΩ transformer would have a 1:1.4 step up ratio and I want a 4:1 step-down ratio to lower the output impedance.

Dave:  A 4:1 transformer loaded with 10K will load the tube with 160kΩ

Customer:  No I want 10K.

Dave:  Head hits table.... nappy time.

This is the thing that urban legends are made of.  Everyone treats transformers as if they all are used to deliver power to a load.  This is perfect for the vacuum tube output transformer since the entire purpose of the transformer is to take the high voltage high impedance anode of a tube and get it to a low voltage low impedance to drive a loudspeaker.  Universally applying this to every audio transformer simply leads to confusion and needless conversations like the one above.  I will categorically state that the worst thing you can do to a transformer sonically is to load it.  In the case of the tube-speaker interface this loading is a necessary evil. In just about every other case in audio, transformers are used to deliver voltage to a high impedance and not current to a low impedance.

I do not begrudge the really smart guys from Bell Labs who did the telephone grid at 600-900Ω.  I tolerate the audio engineers who borrowed the 600Ω impedance as a standard so everything played well together when any mismatch could prevent people from properly hearing Duane Allman at the Fillmore East.  Using those numbers today in audio where systems are meticulously curated is just begging for confusion and mediocrity.  

So back the the 10K:600 step down transformer.  The one place in audio where this transformer will really will be loaded with 600Ω is when used to drive the Pultec LCR Riaa module.  For everything else in audio, the 10K:600 has little if any relationship other than being a convoluted way to say the device has roughly a 4:1 turns ratio.  You will find many who insist that the transformer needs to be terminated with its characteristic impedance in order to work as designed.  With vintage stuff, that is often the case, but that is simply due to the fact that it was designed with the intent to be loaded with 600Ω.  

Lets assume a 4:1 ratio transformer is needed.  I can come up with two very different designs based on its intended use.  99 times out of 100 the actual secondary load will be the grid of a tube so the transformer will be operating essentially unloaded.  Rather than use an incorrect device designed for a 600Ω load, why not simply use a device designed to operate into the actual load? 

The proper (according to me) way to specify a transformer that operates in the voltage realm is to state the source impedance, turns ratio and expected load and then the proper device can be wound.  Using this approach takes what many call a black art back to the nicely ordered oblate spheroid we live on.

dave

Maggin'

I have been playing with cartridges lately and one of the central points to any cartridge is the magnet.  I built this charging coil to re-magnetize the alnico magnet in a denon 103.

For s sense of scale here it is in relation to a charge coil for the magnet in a Sequerra ribbon.

This is a piece of more contemporary audio history.  JC built the charger for Dick Sequerra to charge the magnets for his ribbon drivers.

 The charger uses an ignitron (yes I insist on mercury even in my cartridges) to dump up to 14,000µf @ 600V into the charge coil.

While running it through its paces I was able to reverse the field in a N52 Neo magnet and in my attempt to see if I was reaching maximum charge this happened when I set the voltage to 400V and got a larger "POP" then expected.

The coil was 10 turns of #16 wire encased in JB weld.  The wire broke into several parts and the JB weld was nowhere to be found.   I have always heard stories how they would often vaporize the charge coil in big magnets.... never thought I would experience it first hand.

From the Archives

The archives in this case being a dust covered cardboard box on a bottom shelf in the far corner of the 'Lab'.

The chassis work by Melissa & Doug represents the 'Early Davey Functionalist' era that predates the 'Drug thru the Hudson' look of the early 21st century.

It is a simple remote controlled 100K linear pot attached to some RCA plugs used explore loading options for MC cartridges.  At one point the concept piqued the interest of a well known Stereophile reviewer but upon borrowing the unit, he was terrified to plug it in to his system so into the archives it went.

The remote controlled pot was the handy work of of our good friend John Chapman and the concept evolved into the Opti-Load which replaces the pot with a relay controlled resistor matrix.

Marantz 7T

Alas the "T" stands for transistor and not triode but this one was personally modded by Sid Smith.

The insides...

and in case you didn't notice, it happened to be sitting on by far the most beautiful piece of gear ever.

Sid Smith's ESL speaker

I received a call from Ijaz to go pick up a piece of equipment from Sid Smith's son in law in New Haven, CT.  Many years ago Sid built an electrostatic speaker and I was to get the wire bending machine he built to make the stators.  Below are some pictures of the machine and what it was used for.

Apparently a successor to this speaker was shown by Joe Grado at the 1968 Philadelphia Audio Show and in today's dollar it would have been a $5700.  It is unclear whether that id for a single or a pair but even at double it is still a fraction of what the market commands today.

dave