PT-6A Horn Tweeter

It's been many years since I listened to 2 cubic foot slanted front boxes loaded with 755s. The 755E was chosen because I have had the least flying hours with them. In the past I used either Altec 3000H or Fostex FT17H to fill in the extreme top end on the 755C and 755E. But the FT17H has been gone in a trade for quite some time. 

While browsing my favorite local electronic parts supply store, I found this pair of plastic horns for a little less than $20/pair. With specs and a price like that it would be worth the fun playing with them had they turned out to be duds.

The model number and trademark printed on the box don't exactly match what are stamped on the unit itself. Back in the 70s-80s, Micro was a 100% Philippine manufacturer of speakers and drivers. It doesn't seem to be that way anymore ;( I am guessing the "K" = Konzert, and "PT-6"A is an allusion to the vintage Pioneer PT-6 from the 60s from which, I speculate, this unit was inspired (or cloned). 

Mylar, phenolic or?

I was tempted to open a unit just to see what was inside and in particular, what material was used for the diaphragm. Unlike compression drivers which have field replaceable diaphragms, vintage horn tweeters can be very tricky, if not impossible, to reassemble without the proper jig and tools. I returned to the store a few weeks later and found out that there were no more PT-6As in stock. So I decided not proceed with exploring the innards of this horn tweeter.

Even if there were no reference points for the claimed 94dB sensitivity, to my ears it was pretty much within ballpark of 1 meter/1W because it did not require much attenuation used above the 755E. A 1 uf paper in oil cap  in series gave the most subtle blend between the PT-6A and the 755E.  

Comparing the PT-6A head to head with the Altec 3000H is pretty much an exercise in futility. The 3000H is a very tough act to follow. Instead I will report more on the fun factor I derive from the PT-6A coupled with my distant memory of the FT17H as super tweeter for the 755C and E. 

The PT-6A performed well beyond my expectations. Just like the Fostex FT17H, it aided the drooping  high frequency response of the 755E without deleterious effects on the midrange performance for which the 755 series is known for. Perhaps it is a tad less extended in the extreme top end than the Fostex but there were no nasty spikes to be heard.  I doubt if I can find a better performing super tweeter for the 755E at this price range ;)

Fuji X-E1

I have been a happy user since October 2013 ;)

Altec 2-way XO update

The Altec N1600C series crossover has been a significant constituent in the evolution of my Altec 2-way horn speaker system. C. G. McProud's 1947 article on page 101 of Audio Anthology, Volume 1, was my first encounter with series crossovers although Western Electric was already using the topology in the 1930s. As an aside, my knowledge of electronics is basic. I don't even own a circuit simulation program and rely on my collection of audio electronic textbooks, old magazines plus what my ears tell me as reliable internet sources for "techie stuff."

JEL/N1600C 2-way Crossover

Based on Earl K's simulations and analysis at the Lansing Heritage forum, Altec configured the N1600C 2-way crossover with staggered filters. In this application, a 2nd order/12dB/octave high pass filter @ ~ 1600 hz is provided by the 4 uf capacitor + 1mH inductor, while the 1mH inductor series connected to a 16 uf capacitor functions as a 1st order/6dB/octave low pass filter @ ~ 1100 hz. The 30 ohm potentiometer is part of an upper midrange frequency attenuator/high frequency EQ boost circuit I derived from reading through Altec 30923 discussions at Audio Karma and at Lansing Heritage. Altec incorporated this circuit in their Model 19 crossover and Jeff Markwart used it in his phase corrected Altec 605 crossover. 

In subjective terms, the combination of staggering the crossover point + upper midrange attenuator creates a "dip" in the crossover region where harshness and congestion can easily be detected by critical listeners, while my Altec 3000H tweeters were made redundant by the high frequency EQ boost.

Outboard crossover built using
paper in oil caps, low DCR air core chokes and
non-inductive resistors

Altec 2-way horn system redux

Truth be told, I was never fully satisfied with the performance of the Altec 2-way which is why I never uploaded the old article in the Arkiv.

Let's recap how the 2-way horn system evolved...

The project was conceived in mid 1998 because I needed a monitor system that was more efficient than the OB/755 so I could listen to SE amps with 2 watts output and below.

I commissioned my cabinet maker neighbor to build 614 bass reflex cabinets and loaded them with Altec 419A 12" drivers + 811 horns (early version/heavy sand cast) and 804A compression drivers gathered from hamfests and radio shows. Crossover was a textbook 1st order/6dB/octave hinged at 900 hz and the horn padded down to match the sensitivity of the low frequency driver.

Altec 614 cabinet plan

Eventually I acquired proper 12" woofers - Altec 414As, which lack the upper midrange nasties of the 419As. The 414As have great midrange quality even if they lack the bass end of their larger 416/515 brethren.

Note damping is applied only
on two sides and the back.

802D compression drivers replaced the smaller magnet 804As

Altec 802D

+ super tweets...

Altec 3000H 

Series crossover

While exploring proper monophonic playback, I discovered the N1600C crossover which came with a single 605B Duplex I acquired. When I inserted it into my Altec 2-way, it sounded significantly better than the textbook parallel 1st order/6dB per octave crossover I had been using.

N1600C clone

Using paper in oil caps and low DCR air core chokes, I cloned the N1600C and thought it was as good as it gets with my Altec components...

ca. 2006

Lessons learned over the past 15 years

1. Choose a woofer with excellent midrange characteristics.
2. In hindsight, the 804A/811 was a much easier combination to tame than the 802D/811. Perhaps this is due to the smaller magnet on the 804A which makes it 3dB less efficient. Note: the 806A is similar in specs to the 804A but some sources say they are built differently.
3. Horns sound better crossed over at least one octave above its rated cut off.  I'd go as high as possible if my woofer can play well into the upper midrange.
4. Don't be afraid to pad down the compression driver which is at least 10dB more efficient than the woofer.
5. Try series type crossovers like the Altec N1600C above or N1500A which have lower insertion loss due to the 1st order/6dB/octave low pass filter. Note: the high pass section =  2nd order 12dB/octave 
6. I only use paper in oil caps in my crossover. 

811>32C

Through the years that I had been attending radio shows and hamfests, I got to know people who opened rare opportunities for me to hear the Western Electric 753C, Western Electric 757A and Altec 1505 horns with Western Electric 555 field coil drivers on top of 825 cabinets loaded with 515s. Most memorable was a single Western Electric 15A horn  + WE555 field coil compression driver driven by a pocket FM radio my buddy Ding and I heard at Scott Stilwell's shop in Philadelphia. The huge horn produced mid bass and rolled off like a 755C or 755E. Thus, "shouty," honky or harsh is not something I associate with good horn speakers.

Altec 32C/802D + Altec 3000
trial ca. 2009

A pair of Altec 32C horns I got in trade back in 2009 had been languishing in my storage bin despite realizing its potential after an initial test run. Given the 32C's pedigree - a direct descendant of the metal Western Electric 32A horn found inside a Western Electric 753C monitor speaker - I had an inkling that it would be better than the 811. But a busy schedule and other life matters got in the way. ;)

Replacing the 811 horns with the 32Cs transformed the 2-way horn system. The 32C/802D blended with the 414A/614 without any crossover alteration. If the 811 projects an in your face/front row seat perspective, the 32C is more like sitting at the middle to back row seat wherein instruments and/or vocals have been given enough time to reverberate in the concert hall. Exactly the kind of sound perspective I prefer!

Despite its polite and refined presentation, the 32C retains the transient speed, dynamic ability and top end extension expected from a horn such that I found the use of 3000H horn super tweeters redundant. In fact extreme high frequencies from 32C/802D sounded airier than the 811/802D + 3000H combo. I have a feeling that most detractors of the 90° bent horn design never heard an original Western Electric 753C, Western Electric 757A or even the more recent Altec 9849 monitor speaker.

Although there's another tweak I am experimenting with at the moment, this horn is here to stay. As Johnny Hartmann sings, "...it's wonderful..."

HAPPY NEW YEAR!

Water Pump

I visited a friend the day after Christmas. On the way home the water pump started squealing badly ;(

The radiator and fan had to be removed.

Old pump off - I hosed the water jackets in the engine block and cylinder head until the water became clear. Lots of rust.

New water pump to the left ready for installation.

Done - elapsed time ~ 2.5 hours

Vault Special Issue 2013

Check out JE Labs in the latest issue of Vault Magazine.