Wednesday, March 15, 2017

Radio Shack


In February of 2015, Radio Shack filed for Chapter 11.


 So I was delighted to see this Radio Shack store announcing a comeback in midtown Manhattan during a visit in the summer of 2016.

When I was a student in NYC in the 80s, a neighborhood Radio Shack store was just around the block if I needed a resistor or capacitor for a project on a Sunday afternoon. By 2008, I was in the suburbs and Radio Shack was in a strip mall just a mile and a half away. Now I have to drive 35 miles to the next town ;(


In the early 90s, many SE amp DIYers started their foray into efficient speakers inspired by this book by David B. Weems. The speaker projects used various raw drivers from the Radio Shack catalog.

40-1354A



Radio Shack no longer had 2A3 triode tubes on their shelves when Sound Practices started publishing in 1992,  but one could still buy this 5 1/4" full range driver listing for less than $10, IIRC. This speaker was efficient enough to be driven by an SE2A3 amp to satisfying levels.


I used this driver in a compact bass reflex box...

from David B. Weems book

...as well as in a Tapered Quarter Wave Tube (TQWT)



Not quite in the same league of sophistication and refinement as the Altec 2-way, but lots of fun since they can boogie on a couple of triode watts ;)

Time Warp



During a recent "let's see where the wheel takes us" expedition, my wife and I spotted this in Pennsylvania. 

40-1310



As I browsed around the store, a pair of 40-1310 super tweeters bearing their original sticker price immediately caught my eye. I told my wife about them and she insisted that I get this pair of NOS Chinese-made plastic version for $60 + tax, so I can time travel.


These drivers developed quite a following in the 90s because the original all-aluminum units embossed Realistic were allegedly OEM'd in Japan by Fostex. The graphs above and below should corroborate this speculation. Later versions with a plastic pod and horn were subcontracted in South Korea and then China.

Fostex FT17H

I didn't join that 90s bandwagon. Instead, I bought a pair of the equivalent Fostex FT17Hs sans pod from Madisound for $70. I used them as super tweeters for Altec 755Cs and 755Es until they were superseded by a pair of superior Altec 3000Hs.

 Brand new Fostex FT17Hs are now made in China and can be had for a little less than $100/pair. I still believe they are excellent value for the money. Perhaps the early Japanese all-aluminum 40-1310s can command a slight premium, but beware of unscrupulous eBay flippers asking ridiculous amounts for the plastic version.

Subtlety



Before inserting the 40-1310 into the Altec 2-way, I bypassed the built-in electrolytic cap/choke crossover components. For the past 20 years, I've been using smooth and natural sounding paper in oil caps in the signal path of my preamp, amp and crossover, nothing else.

Altec 2-way + 40-1310

Altec 2-way sans 40-1310

In this application, the 40-1310's positive terminal is protected by a 1uf PIO cap and then connected to the high-pass section of the crossover. The effect of the super tweeter is subtle...just a touch more air.


As I was about to sit back to reminisce the 90s with the 40-1310, an internet friend informed me that Radio Shack just filed for another bankruptcy claim ;(

This prompted me to visit my favorite branch...




...fingers crossed. ;(

Wednesday, March 1, 2017

Altec small format diaphragms: Aluminum vs. Symbiotik



I've been playing around with Altec drivers for almost 20 years and have never questioned the dictum of using only aluminum diaphragms for high-fidelity applications until now.



Altec Aluminum Diaphragms


Altec 20275
Aluminum voice coil
DCR = 9 ohms

The 16 ohm Altec 20275 is the original diaphragm fitted to my cherished green hammertone 802D. This is the Altec diaphragm I am most familiar with and to my ears its tonal balance favors the midrange more than the later 34852, which is known for better high frequency extension.

I speculate that late 40s to 50s wrinkle charcoal gray/brown and late 50s to 60s hammertone green 802s, 804As and 806As command premium prices IF they are fitted with original and intact 20275s, which are now unobtainium. By early to late 70s, black 802s and 806s were fitted with either the 16 ohm 34852 or the 8 ohm 34647.

Altec 34852
Copper voice coil
DCR = 12.5 ohms

My Altec 605B Duplex should have been originally equipped with a 20275 but by the time I acquired it, this 34852 was already fitted. Maybe that's why I still got it cheap ;)

As previously noted in my 605B experiments, I hear a significant sonic difference between a 34852 and a 20275, so much so that I cannot recommend their use as a stereo pair. Jeff Markwart has more 20275 vs. 34852 info if you scroll down to the bottom of this page

GPA 34852
Copper voice coil
DCR = 11.5 ohms

AFAIK, Great Plains Audio is the only source for Altec diaphragms made to original Altec specifications. Even if they have a website, they prefer to do business the old fashioned way. I always call Bill Hanuschak to place an order and never had problems.

I haven't had a chance to compare this GPA 34852 to the Altec 34852 because the 605B Duplex was left behind in the attic;( But there's no doubt that this GPA is the real thing - very dynamic, with clean and clear harmonic overtones up the wazoo!

Altec Clone


Chinese Aluminum Diaphragm Clone
Copper voice coil
DCR = 11.9 ohms

For kicks, I made an offer to one of the Chinese vendors on eBay and got this pair of 16 ohm diaphragms for about $24/pair, shipped. These clones will tide you over in a pinch. However, even a casual comparison to an Altec original or GPA diaphragm revealed smeared harmonic overtones and compressed dynamics.

Spot the fake



Left picture (clockwise from left) - older version Altec diaphragms used screw terminals on a raised platform, later Altecs and GPAs have tabs, Chinese clones do not have a raised platform for the screw terminals. 

Right picture - The raised platform in the Altec uses tapped machine screws whereas in the Chinese copy the screws are self-tapping.


Altec Symbiotik


I recently acquired a couple of unloved 70s era 802 and 808 drivers, some fitted with Symbiotiks. 

Two abused Altec diaphragms:
Symbiotik on the left and aluminum on the right

The Symbiotik was Altec's initial response to the 60s demand for a higher power handling diaphragm. As pictured above, due to the rigidity of the aluminum suspension, it can shatter when overdriven. I can only surmise that the Symbiotik  diaphragm, which uses a polyimide/mylar type suspension, evolved from a research and development project at LTV by John Hilliard and Jonas Renkus.


Early + Later Symbiotik diaphragms

In early Symbiotiks, the abrupt 90 degree angle voice coil termination (left) also caused failures in the field due to metal fatigue. I repaired this early Symbiotik by carefully flowing solder between the broken ends with a low temperature soldering iron. This issue was rectified in later production Symbiotiks (right). 

Uncovered: Altec > Emilar


Top = early Emilar with brown mylar suspension
Bottom left = later Emilar with gray mylar suspension
Bottom right = Altec Symbiotik

I have written favorably about Emilar and Renkus-Heinz compression drivers, and noted that their extreme top end was a bit reticent compared to Altec drivers with aluminum diaphragms. Let's see how the earlier Symbiotik technology stacks up.

Top = later Altec Symbiotik with tabs and
improved termination
DCR = 6.7 ohms
Bottom = early Altec Symbiotik with
screw terminals
DCR = 7.5 ohms

In retrospect, Altec aficionados may have been hasty and/or unkind in their initial reception of the Symbiotik. Even if the Symbiotik rolls off earlier than its aluminum brethren, it still reproduces proper harmonic overtones. It sounds very sweet, airy and open, with none of the smearing and compression I hear from the Asian clones. A Symbiotik equipped 802/808 sounds more organic than its descendants from Emilar and Renkus-Heinz. To my ears, the Symbiotic diaphragm has a niche in Hi-Fi and may well be the antidote to those who find the aluminum diaphragm a bit aggressive. 

Unfortunately, there are no modern replacements for Symbiotik diaphragms. You'll have to find original units that did not suffer catastrophic meltdowns. Although it's just a hunch, the Radian replacement diaphragm for Altecs should have Symbiotik DNA because of the Emilar/Plus One connection.

Octave RTA by Onyx


Since affordable audio measurement apps have become available, I got this $5 app for my iPhone as suggested by my buddy Joe Roberts.

Test set-up

The Altec 414A housed in a 3.5 cu. ft. repurposed Madrid (861) bass-reflex cabinet is driven full-range, J-Rob style, while the Altec 32A metal horn + driver combo is protected by the crossover + EQ below.

Crossover + EQ

I was quite surprised to see pretty decent RTA results since I've been building/tweaking crossovers for over 20 years without a computer simulation program or an RTA.

Altec 802-8D + GPA 34852

Altec 808-8A + Chinese 16 ohm diaphragm

Altec 808-8A + Symbiotic

Emilar EA175-16 (alnico)

Emilar EC175-8 (ferrite)

These graphs pretty much represent how these driver/diaphragm combinations perform except the Chinese clone which looked good but sounded rolled off, compressed and smeared as mentioned above. Unlike human ears, an RTA will measure sound waves but will not discern unmusical harmonic overtones. Even my wife thought the Chinese diaphragm sounded muffled. Although she argues that if I can afford only a $12 diaphragm, I better be happy with it ;(

It goes to show that it is much easier to satisfy audio measuring equipment than human ears. And I'm lucky to be blessed with a tolerant wife ;)


Tuesday, February 21, 2017

Vostok Bezel Mods

From NATO'ed to Bezel mods



Vostok Amphibia 110640 + Bandukh Bezel


Murphy 1050 bezel + Seiko 'Pepsi' insert
=


Vostok "mod" Amphibia 420432

Wednesday, February 1, 2017

Budget SE OPTs - Edcor and Noguchi



All output transformers were tested in the je2a3 amp using the same procedure as I did in the Hammond 125ESE. Listening sessions were done through the same amp driving a single Altec 2-way speaker system



Tango (Hirata) U808
Square Waves @ 100hz, 1khz and 10khz

The long discontinued Tango U808 last sold for around JPY12,100. It has been my benchmark budget OPT due to its multi-tap configuration and impressive performance until it was trounced by the Hashimoto HC-203U. Nevertheless, it still is a classic OPT in my book. 

Primary Z = adjustable from 2K, 2.5K, 3.5K, 5K
Power = 20W (3.5K/40hz)
Frequency Response = 35hz-60Khz, pri. Z = 3.5K/-2dB
Inductance = 11H - 21H
Max. DC current = 130 ma.

Edcor GXSE15-16-3.5K
Weight = 2.75 lbs


Primary Z = 3.5K
Secondary = fixed @ 16 ohm
Frequency Response = 40hz - 18khz, <1dBu 
Maximum DC current = 190 ma.
Core Material = M6, 29 ga. grain oriented steel

I ordered this Edcor OPT to get a feel on what's available to a cash-strapped US-based DIYer. It took over 3 weeks to be delivered to my doorstep at a total cost of $58.67. The nice square waves indicate quality manufacturing. Bass performance was at par with the Noguchis. But from the midrange to higher frequencies it was not quite as open and transparent. Maybe the Japanese manufacturers use higher quality laminations than the M6 steel used in this Edcor? Since the Hammond 125ESE now sells for about $60 before shipping, the GXSE15-16-3.5K would have been much better value for the money if it were offered with at least two secondary taps.  

Noguchi PMF10WS
Weight = 3.2 lbs

Price = JPY 9,070
Approx. US$80


These two pairs of Noguchi transformers were Akihabara souvenirs from our 2015 Tokyo trip. In spite of the significant difference in price, the PMF10WS and PMF15WS are physically the same in size and weight. Based on specs, the PMF15WS has greater bandwidth and more flexibility for use with various output tubes.

Both OPTs tested well on the bench. Even if the 10khz square wave test does confirm better top end response from the PMF15WS, I could not detect its sonic superiority over the other.  Sonically, the PMF10WS is just as good if you don't need the extensive multi-tap flexibility from its more expensive sibling. In terms of tonal balance, I prefer the warmer presentation of either of the Noguchis over the leaner and more analytical Tango U808.

Noguchi PMF15WS
Weight = 3.2 lbs

Price = JPY12,560
Approx. US$112

I'm not sure if Noguchi accepts international orders. But if you're visiting Tokyo, their basement shop (closed Mondays) at Tokyo Radio Department Store is a must see!