Saturday, June 28, 2014
Monday, June 16, 2014
Foldr Project
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| Spalding 3 speed |
A Japanese folding bike that resembles a Raleigh 20.
The Shimano 3 speed internal gear hub that came with it has some issues engaging the top gear.
But this laced and trued set of Araya rims with a Shimano Nexus 3 hub for the rear should fit.
Friday, June 6, 2014
Sunday, May 25, 2014
Radiotron Designer's Handbook
Most of my knowledge in Audio DIY have been gleaned from the Radiotron 3rd Edition. The 4th Edition is just over the top of my head, but looks better sitting on my bookshelf ;)
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| Page 53, Chapter 8 |
Tuesday, April 15, 2014
Monday, March 17, 2014
Sunday, March 2, 2014
RC-12 Tube Manual
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| © 1934 |
All the tubes I am using in my Hi-Fi System were being manufactured by the time the RC-12 was published.
But I also keep an RC30 copy!
Thursday, February 27, 2014
Jensen Ultraflex redux
A few updates to the Jensen Ultraflex
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| Revised crossover + EQ/HF boost |
The fixed resistor attenuator was inspired by the Jensen Duette crossover + recent knowledge gained in boosting frequencies above 7khz using an EQ network in my Altec 2-way XO experiments. Try it on your Heathkit SS1 or Eico HFS1 which AFAIK, used only a 2uf beeswax paper cap + L-pad.
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| Damping removed paper in oil caps for crossover and EQ |
Happy Listening!
Saturday, February 15, 2014
de Forest 410 Mesh Plate
I've been feeling nostalgic lately especially after unearthing a box of prints and negatives which I've been scanning and uploading in the Arkiv.
Monday, February 10, 2014
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 ;)
Sunday, February 9, 2014
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