hi-mu triodes: 75, 7B4, 7B6 + 7F7

Alternative hi-mu triodes in place of my favorite octals

The type 75 is the grandaddy of all hi-mu audio triodes culminating with the ECC83/12AX7.

Grid-capped 75s in the JE Labs Simple 45/2A3 with Noguchi PMF10WS OPTs.

loctal base + socket

Loctal or Loktal (as trademarked by Sylvannia) tubes were developed concurrently with octal based tubes in the 1930s. But loctal tubes were aimed at the then emerging car and portable radio market - hence, the need for a locking-ability in the tube socket, which required a metal base that gave the additional benefit of better shielding.

The 7B6 is a loctal version of the 75

I originally built the je2A3 mono integrated amp with 7B6s in the phono stage. Right now I am running 7B4s.

The 7B4 has slightly lower Rp than the 7B6. NOS samples are still very affordable so try them both ;)

I built this stereo preamp for the November Hi-Fi Show 2016. It uses 2 x 7F7s for the phono section which are direct loctal equivalents of the 6SL7. The line stage sports 2 x grid-capped 6F8Gs.

7F7 vs 6SL7

JEL preamp at the November Hi-Fi Show 2016 dressed in Harana Audio woodwork.

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. ;(

Altec small format diaphragms: Aluminum vs. Symbiotik

I've been playing around with Altec drivers for almost 20 years and have only listened to aluminum diaphragms until now.

Vostok Bezel Mods

From NATO'ed to Bezel mods

Vostok Amphibia 110640 + Bandukh Bezel

Murphy 1050 bezel + Seiko 'Pepsi' insert
=

Vostok "mod" Amphibia 420432

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 many moons ago. Listening sessions were done through the same amp driving a single Altec 2-way speaker system. 

Noguchi Finemet

Just a preview ;)

Dr. Jose P. Rizal

Rizal portrait
by
Juan Luna

In commemoration of our national hero's martyrdom on December 30, 1896, let's reflect upon a few words of wisdom he left behind. They are very relevant today as they were over a hundred years ago.

On Education:

"My countrymen, I have given proofs that I am one most anxious for liberties for our country, and I am still desirous of them. But I place as a prior condition the education of the people, that by means of instruction and industry our country may have an individuality of its own and make itself worthy of these liberties."

What Rizal stood for:

"I do not write for this generation. I am writing for other ages. If this could read me, they would burn my books, the work of my whole life. On the other hand, the generation which interprets these writings will be an educated generation; they will understand me and say: 'Not all were asleep in the night time of our grandparents.'"

Dr. Rizal's Noli Me Tangere and El Filibusterismo have been required reading for high school students since the 1950s and the essence of these novels is still very pertinent in our present day society. But why have we allowed the oppressors to develop from within?

November 2016 Hifi Show Report

Sierra Audio

Back in the late 90s, I frequented a west coast based website, Sierra-Brooks, that featured beautiful hand crafted wooden horns. Half of that partnership was Victor Sierra, a Filipino from Cebu City. In the interim, Victor had been busy managing their family business. The local audio community warmly welcomed their premiere participation in this event!

Their demo featured 3-way horn loaded speakers.

Driven by a stereo SE45 designed and crafted by one of his collaborators (below, left) using locally wound transformers by Edrel Sison

Congratulations Victor (right). Good job!

Friends in Audio 

This group of audio enthusiasts featured a 2-way horn system + super tweeter using my favorite Altec 414 woofer and a handmade wooden horn driven by an Altec 806A + EV T-35 super tweeter. At the front end was a Garrard 301 with a locally crafted linear tracking tonearm. A custom tube preamp and amp completed the system. 

Harana/Setup/Tono

Garrard 401 with a Dynavector DV507 tonearm fitted with either a Denon DL103 or Ortofon SPU-GME and a laptop/DAC combo digital source fed through a pair of Western Electric WE111C repeat coils

JE Labs stereo preamp dressed in Harana Audio hand crafted wooden case, loktal 7F7 tubes for the phono stage + 6F8Gs for line level

Harana Audio dual mono SE300B amps - Jensen input transformer > WE417A > Tango NC20 > WE300B > Tango NY15-3.5S output transformer

Harana Audio 2-way horn speakers - 15" Beyma woofers in V-Vent II enclosures, JBL 375 compression drivers behind carved horns + JBL super tweeters

For more pictures and information, please visit the November Hifi Show FB page.