Monday 31 July 2023

Tau DHT Amplifier - first build.

After completion of the breadboard stage the questions were laid to rest. After more than a year exploring the circuit variations which tugged on the curiosity the circuit wound up back at the original design with parts section as anticipated. I should add here that the "natural motion" of an interstage or output transformers spoken of in vintage tube building lexicons that does indeed sound more natural than any of the other topologies such as, Ultra Path, Parafeed, plate chokes, plate resistors, plate CCS etc... The AC activity moving in both directions simultaneously within the transformer might have something to do with it. This speaks directly to the hierarchy of circuit over layout, layout over parts.

It was time to build up the first basic unit using mostly off the shelf parts and M6 cores. 

Initial layout and parts mounting.

Wiring begins with earth rails and cathode supplies... 

Rear panel goes on to allow signal input wiring and power entry.

Basic model uses Chimera Labs interstage and LL2766AM Opts.

Wiring complete. 10% silver clad copper in PTFE tubing is used through out. Air is the primary dialectric inside the PTFE as it is not snug. Silver oxide will develop but the copper is hermetically isolated from the atmosphere.

Completed unit in provisional livery to get it going - final design to be published soon.

Power Supply
Since this is the heart of an amplifier it should probably be explained a little. The centre piece is the AC transformer designed for this amplifier. It has low DCR is internal shielded and drained with grain oriented electrical steel. No resistors are used to adjust voltage as they dissipate musical dynamics into heat. Four heater supplies are provided - one for each tube section. These utilise Schottky rectifiers and CMC choke loaded supplies on both positive and negative rails. B+ supplies share the AC transformer, rectifier and ground leg damper diode. The mercury vapour rectification provides not only regulation with very low resistance but also does not sag under load. The current creates a plasma bridge which increases or decreases with load maintaining the same voltage drop. The plasma's response to load also provides a very natural sounding regulation. The low DCR of the AC transformer is not compromised thus. 200H of low DCR inductance does the filtering with low ESR capacitors of high quality in an LCLC configuration for the power section. Inductance dominates the supply. This is furthered by a current source, nickel chokes and VR tube regulation to provide the driver section with clean dynamics. As good as the new Vishay DC Link caps are the long standing favourite of GE 97 and 27 series oil caps still win the day and are used at the final stage of the power section. No other oiler sounds like them.

Wiring in place

Mercury Vapour Rectifier and damper diode.

Cover in place and a little long exposure.


Later versions with 226 first section

 Final Version of the Chassis coming soon... as well as impressions of Finemet, Nickel and silver wound interstage, volume and output transformers...

Friday 26 May 2023

Life before Audio ...

People often ask me what I did before audio so I put this little vignette together. Interest in audio began in high school when I took courses in acoustics and sound reproduction. By the time classical studies at St. John's College rolled around I was already smitten. This can be seen by a drawing done in math tutorial at seventeen years of age where I was probably better off paying attention to the demonstrations of the assigned Euclidian propositions... That little system was an AR turntable, an Advent receiver, and a pair of ESS/Heil AMT 1A.  I was seventeen then.

A shared ride in a small airplane as a cheap and interesting way to travel during college opened a new perception. The rest of my adult life was spent either with music, literature or in the sky. 

I transferred from St John's College to Embry-Riddle Aeronautical University - from Liberal Arts and classical literature to Aeronautical Science.

Posing for a photo on the Riddle ramp Prescott Arizona. 1984

Corporate Lear 31 Dallas Love Field

After instructing in airplanes and helicopters I was invited to fly corporate as well as my first overseas contract with GTZ in Somalia flying geo-biologic survey.
GTZ us the international aid agency of Germany. Since 2011 it has been known as GIZ.

In north Somalia I first witnessed mass grave sites which collided with the news at the time as Siad Barre, supported by the US government, tried to exterminate the Somaliland population in several genocidal campaigns such as the Isaaq genocide.

Mogadishu beach, 1988

Rolph and Frederich my boys, where have you gotten to?

This, combined with the fermentations of classical literature, began to separate me from the collective perceptions of the west. In Sudan a video of 8,000 freshly killed SPLA, including women and children, were documented in a 360° pan with a newspaper to date them, received zero attention from any news agency despite the footage being in their possession. Why would massacres of the present day not get air time?  I stopped then observing the news or listening to anyone who talked about it. As they spoke I saw them only as marionettes. The question was: "who was pulling their strings to make them dance?"

As an alternative to the nonsense I hung out at Peter Beard's Hog Ranch, played guitar and let Peter persuade me that the whole thing was a corrupted mess - which it certainly appeared to be. The Easter Island narrative repeating itself endlessly - Francis Bacon was not wrong.

Back in Somalia 1991 providing support for refugees, NGOs and Rimfire - de-mining operation. I also supported the SPLA flying ICRC (Red Cross) and Catholic Missionaries in relief to the SPLA, Dinka and other tribes, who were being systematically wiped out by the government there as well. Since they were then "rebels" this support was illegal and flight plans were filed only as far as Lokichogio Kenya. After that we were on our own. North Sudanese Mig 21 Fishbed pilots spoke Farsi. Iran, as well as other middle east governments, were staying close to the oil grab. I could tell when they spotted me by the excitement on their radio coms. They could not slow down so I would get low on or between tree tops, pop flaps, and get real slow. They'd fly by before they could descend, loose visual contact and "Bobs your Uncle", their air to air radar was useless. The first time I operated on this intelligence was a bit concerning though…

 South Sudan is recognised today as a sovereign state while the atrocities of the north were never recognised by the west. Somaliland (North Somalia) has still not achieved sovereign recognition thar and of course the genocides have been ignored. Perhaps because the USA supported the genocide in the attempt to obtain a naval port on the horn overseeing the Suez canal shipping lane. Since Said Barre's regime failed it never happened. Somaliland piracy on the same shipping lane is a finger to the USA who supported the genocides and continues to obstruct their recognition. In South Sudan Iran and other Muslim states did not have the international clout to obstruct recognition.. World events vary from reality to the screen's shadows. Just like Plato's allegory of the cave... grow a pair or stay in the dark.

The inevitable expressions of aviation exuberance.

Working for Dornier in Kaduna Nigeria an agricultural endorsement was obtained where my instructor also taught me to water ski the canals... just for fun... and it was.

Qualification day...
After this indoctrination - airline bus driving was not going to be for me.

I flew many types of aircraft from the beginning of my career. Here in Kaduna Nigeria working for Dornier I flew the Super AG Cat, Dornier 228 and Hughes 300C helicopter.

Moi escarpment Kenya.

Bosaso Somalia

Grumetti River Camp Serengetti plain

Fuel stop Tabora Tanzania, only fuel available in the vast expanse of southwest Tanzania at the time.

Kagera, very northwest corner of Tanzania. They are hurrying because they had been told that once the sun comes up and warms the air there won't be the performance required to get off the short strip and either we stayed another day or someone was staying behind. That got them moving.

Break time, Ngorogoro crater, Tanzania and yes, I often flew in shorts (and sometimes flip flops...)

Flying over the shira or the saddle between the peaks of Mt. Kilimanjaro with my buddy from the Belgian Congo enroute Nairobi - Zanzibar. Oxygen masks were removed for the photo op, the Shira is over 14,000ft so we must have been 16,000 to 18,000ft on this one - unpressurised.

Cooling off after a hard day above the Sudan drinking Bols with the boys... 

Based in Zanzibar for a while, here heading out to Bawe island for a break.

A little downtime, Kichwa Tembo Camp - Masai Mara Kenya...

Somehow, after five years in Africa, Bell Helicopter scouted me into their instructor program.

After a few thousand full touchdown autorotations under the tutelage of the these experts I got pretty good at them... and at teaching from the most concentrated pool of aviation knowledge and experience I ever encountered. An autorotation is landing without engine power.

The mission called however and I moved on: Fire Fighting, EMS, VIP, Law enforcement and Search and Rescue operations. 
North California fires.

with "the beast" - civil version of the CH-47 Chinook - Boeing 234. This had a 250ft longline swinging 3,000 gallons  (25,000lbs) of water with 10,000 HP on tap to move it around. Notice our little white helmets inside the bubbles as DVOC is employed. (Direct Visual Operating Contact)

Posing yet again - landing site in the burn zone.

Some views from the office... dipping and deploying behind a Skycrane.


Riyadh, Saudi Arabia Civil Defense, pose. 50°C with no aircon... KV-107

Perennial work bench...
here a Naim CDS being raped, pillaged and grossly improved. 1995

CH-46 civil variant BV-107 a solid workhorse after the CH-47/234 which broke big all the time. Here in the centre of the South Saudi Desert

Kuwait Emir Dewan
Flying solar panels for the radio shack in the mountains South Oman coast.

UAE: SOC, Police and Civil Defence.
HEMS, Law enforcement, VIP and Sea SAR with NVG and full SEASAR automation.

NVG briefing before goggle up.

HEMS scene response Doha between maritime patrols.

Qatar Airforce

HEMS patient off loading Doha Hospital

Offshore Black Sea, Constanta Romania

Known icing conditions and rubber suits...

Over 10,000 hours and 50 aircraft types logged...

... rescue missions were always the drug of choice.