The Canadians Invade: Highway Advisory Radio Interference in Seattle from Saskatchewan (CBK)
Flammable cargo was prohibited under the Washington State Convention Center on I-5 last weekend according to the large Smarter Highways signs along SR-520 in Washington, as there’s some sort of maintenance happening. There’s a highway advisory radio station on 530 AM and I tried to tune in to see what it had to say about it.
.jpg/200px-Thruway_Info_(1).jpg "Highway Advisory Radio")
As it turns out, the station was completely unintelligible due to bad interference. I could just barely make out the fact it was a highway message, but not the contents, in my car radio. With my GE F-135 radio, I couldn’t pick up either so it was time to break out the big guns, my Hallicrafters 8R40 attached to an 85′ helical antenna and managed to bring it in quite clearly.
The station beat very closely with 530AM in my receiver making a very obvious beat note, but they identified themselves as a CBC station a couple of times and were playing PRI’s The World. Some digging about where CBC stations are located, and I was able to identify the interfering station as CBK AM 540, a 50 kW clear channel station broadcasting out of Watrous, Saskatchewan - about 1100 miles away!
Clear channel stations running that high power at night can definitely propagate that far – or further, an experimental station in the 1930 was able to cover the entire western hemisphere and was known to take requests from as far away as Buckingham Palace. There’s nothing that can be done in this case as the interference is coming from a licensed user in another country and happened due to natural atmospheric conditions. I guess the right thing to do is just hope there’s no important traffic information being broadcast during the nighttime DX window.
CBK-AM is the furthest distance AM broadcast station I’ve yet received. I should probably keep a map of some kind.
Buy the Album, Guys. [EVE 6 - Speak in Code: Audio Quality]
One of my favorite bands, EVE 6, recently got back together after a multi-year hiatus and put out a new album. “Speak in Code” came out a few weeks ago. I caught the band on their tour through Seattle just before the CD release, so ended up having to order mine from the Internet instead.
I bought the vinyl of the album because it seems like a more interesting collectible than a CD, and while waiting for it to arrive downloaded the MP3s of the album from a non-BitTorrent download site. Just yesterday, my copy of the album arrived and inside was an unexpected code for a Dropcards.com Free Digital Download of the album! I went to check it out and download the files and got a great surprise – the free digital downloads were uncompressed WAV files. That’s about as close to the master as you can get without knowing the sound engineer who mixed it.
I wanted to see the difference between the purchased uncompressed files, and the less-than-legitimate free alternative so I generated two spectrum analysis plots (FFT) and placed them on a common axis. I used the second track on the album, “Victoria” which rated decently on the top Alternative charts.
On the left of the frequency plot, the “Inner Sanctum” release MP3s – the only MP3 downloads of this album I was able to find. On the right, the free digital download from Dropcards.com. As you can see there are some differences – both large and small. Click the chart for the full sized version. If you’re not familiar with an audio spectrograph, the vertical axis of the chart plots frequency with bass notes towards the bottom and treble towards the top. The horizontal axis represents the amplitude, or volume, of that frequency in the song. The further away from the center you go the louder the sound.
The MP3 track starts dropping off more sharply than the uncompressed track at around 12 kHz and completely starting at 19 kHz while the uncompressed track carries more detail in those higher frequencies and extends all the way up to 22 kHz. You’ll have to listen for yourself to hear the difference, though, so go and buy their album!
I might post a more detailed comparison later, with some more analysis points, if I can come up with an iTunes version of this track for comparison…if you have one and don’t mind sharing it for this experiment, get in touch!
Welcome Back!
I’ve been offline for a bit as I’ve been too busy at my career to do much on the side. My workload has died down a bit and I’m back at it. Currently on my bench is a Philco 38-C-12 “Coronation” model. It’s a Canadian model, with a 25-60Hz power transformer, but other than that it’s identical to the US model 38-12 code 121.
The tube line-up is 6A7 78 75 41 84. This was on the more economical side of price, and only one of the two IF transformers is located above the chassis and properly shielded. The other IF transformer is unshielded below the chassis and has some very specific lead dress instructions for professional service.
Again hinting at the economy nature of this radio, there are only a handful of capacitors that are immediately suspect. The unshielded IF transformer is visible at the bottom center of the radio, mounted perpendicular to the tube sockets.
The tuner on this model is nearly seized. It’s uncommon for them to be this badly stopped up, but not unheard of. I’ll be replacing this radio’s bad paper and electrolytic capacitors and cleaning and re-string the dial and tuner. Stay tuned, I’ll also have some more about exactly which coronation they’re talking about.
Slow Postings – Vacation
Its been a slow week as I’ve been traveling away from my projects for the week, to Makati (Metro Manila) in the Philippines on business.
Postings to resume next week!
Build Log and Review: Mable Audio VT-86PP Kit Hi-Fi Amp Project [Chinese Gear]
About a year ago, someone left a comment that really looked like spam on one of my pages advertising a web store selling tube audio gear and parts for guitar and audio amplifiers. Against everything I’ve ever learned about behaving on the Internet, and my better judgement, I ended up actually buying a kit from that vendor Mable Audio located in Shenzhen China. They have several kits available with a few options: 6V6 or EL84 for output, 6SL7 or 12AX7 for the input stage and also a beefier EL34/12AX7 amplifier for about double the price. They have a ton of components and guitar amplifier parts and kits as well.
I selected the 6V6/6SL7 kit because I like the larger tubes, and had a set of 1937-issue 6V6G tubes that look more interesting than the small GT-style tubes it came with.
The kit arrived as a box of miscellaneous parts and the chassis. There was no particular documentation included, but the schematic was sent to me via e-mail. Also, the silver decorative plate (in the center of the photo) is no longer included in these kits despite being pictured, as I was told after I purchased. Not the end of the world, though. The kit included a large power transformer, two output transformers (23% Ultralinear), two huge 470uF 450V filter capacitors, all the needed tubes, signal capacitors, connectors, controls, high quality ceramic sockets and lengths of 600V-rated wire to assemble it all with.
The amplifier itself has decent schematics, on paper anyway, although the output impedance is inaccurate on the datasheet: the datasheet, schematic, and transformer color code documents all specify multiple taps but the provided hardware only supports an 8-ohm speaker. This is acceptable, though, as most home theatre speakers are 8 ohm anyway.
INPUT IMPEDANCE : 100K ohm(RCA)
OUTPUT IMPEDANCE:4ohm – 16 ohm8 Ohm
OUTPUT POWER: 12w x2/(ultralinear)class AB P-P
DAMPING FACTOR : >3
FREQUENCY RESPONCE: 20Hz-20KHz(REF.OUPUT)
TOTAL GAIN: 28dB
INPUT SENSITIVITY: 300mV-600mV
S/N: >89dB (HUM NOISE <3mV
CHANNEL BALANCE: <1dB 20Hz-20KHz (MAX.VOLUME)
CHANNEL SERPRATION:>65dB 20Hz-20KHz
TUBE COMPLEMENT: 6P6P(6V6) X4
6N9P(6SL7)X2
POWER REQUIREMENT: AC220V OR 110V OR 240V + -5% 50~60Hz
Assembly wasn’t terrible, but the build quality of the chassis was marginal at best. The top surface of the chassis bolts to the chassis pan itself to hide mounting rails and dividers, and the holes on the top panel didn’t perfectly line up with the socket locations on the bottom panel. This meant that after mounting the sockets to the bottom where they belong the top cover wouldn’t slide over them because it was interfering by about 1mm on one of the sockets. It took significant pressure to force it on and made a very loud snapping noise when it did so, but the socket and cover were all intact. It’s definitely not coming off again, though. Additionally, the cover over the transformers is supposed to mount using several screws at the corners, but only two screw holes lined up.
The sockets are ceramic and the sockets gold-plated, and the transformers look appropriately sized, though, so it’s on to building past mounting up the parts. This project was a long time in the making, as I mounted the sockets and chassis up on July 12th 2011 and then did no further work until March 2012. I worked my way through the schematic, roughly right to left. This amplifier is a power supply, and two identical amplifier channels. I’d highlight on the schematic as I completed both mirror halves, and this made it easy to keep track of where I was going.
Some photos showing filling in the components:
After assembly, I had a few left-over parts:
A really weird assortment of leftover parts at that. I declined to connect the headphone output (on advice that it was probably not safe for any headphones that I might actually like due to the connection – not unique to this amp, many other circuits have similar issues) which accounts for 2 of those resistors, but there’s still 13 more + a small capacitor that weren’t called for anywhere. And there are two extra panel-mount RCA input jacks. And a ton of extra wire. But for all the extra they did include, there were 4 resistor types (8 resistors total) that were not included, so it was a trip down to Vetco Electronics in Bellevue to pick up replacements. The replacements are the Red- and Tan- bodied resistors. Not quite sure what to make of that.
I elected to replace the LED power indicator with an NE-2A neon bulb instead, so it would be the same color as the glow of the tube heaters.
There is a minor issue with this one, though. There is an anti-arcing capacitor across the switch. I placed the NE-2A between the switched side of the switch and the AC neutral (it runs directly from AC mains through a 150K 1/4W resistor). With the switch turned off, the capacitor allows AC leakage of a few mA to pass to the cold side of the switch. The current leakage is less than the excitation current of the transformer, so the transformer appears “open” to the low signal as it’s entirely eaten because it’s not strong enough to set up a magnetic field. This causes the current through the 150K resistor and neon….so the bulb lights up when the power is off, now. With the power on, the capacitor is out of the circuit and the transformer is an extremely low impedance, so all the current goes through the transformer primary and none into the 150K resistor and the NE-2A bulb. The result? The power switch indicator is backwards. The light comes on when the device is turned off, and goes out when you turn it on. I intend to fix this at some point, but am not entirely sure what the best approach might be. The volume control itself is abysmally low quality, probably the only part in the kit I actually think is just plain “bad”. The return spring is weak and the switch touchy and it binds up easily.
There was also another issue: I wired the volume control backwards. “Right” is lower, now, instead of “Left” as is the convention. I evaluated fixing this problem, but while poking around one of the volume control’s pins started coming out of its molding and I didn’t want to risk destroying the control, so that’s a problem that won’t be fixed in this iteration.
I did a quick visual for obvious shorts and powered it up the first time with the 6P6P (Chinese 6V6GT) tubes which were included, as I didn’t want to risk my classic tubes. If there’s going to be a problem it’d be on first power up, for any amplifier from anywhere. The transformers all made a great *THUNK * noise when they energized for the first time, but quickly de-energized again. I poked around some more and found I’d missed a solder connection on the bridge rectifier. I soldered it back on and tried again and everything was fine! First power-up successful, with no re-work needed.
Then again on the test bench with the 6V6G tubes:
Still good! And for some post-production glamour shots:
Now, I’ve moved the amplifier onto my desk and will use it for personal stereo when not using the Surround Sound receiver.
In conclusion: Mable Audio is a reputable supplier. Their product sounds great, and was of acceptable build quality for an entry-level amplifier. The chassis and platform itself will be a great starting point for more modification projects in the future. I rate this kit as a 3.5/5 due to the mechanical issues with the chassis fit and the power switch, but the electronics quality and circuit design seem to be solid. I would recommend this kit to anyone who wants to build an inexpensive tube amp from parts – but, given the complete lack of instructions or documentation beyond a schematic and some color code diagrams, make sure you go slowly and check your work and are somewhat familiar with how to read electrical schematics.
- Pro: Inexpensive for what it is.
- Pro: Good quality components, for the most part.
- Pro: Attractive styling.
- Pro: Fairly straightforward build.
- Con: Terrible quality power switch. Just terrible.
- Con: Mechanical fit on mine wasn’t the best.
- Con: Only 99% of the parts in my kit were the right ones.
For $175 + shipping from China, it’s not a bad deal. Similar kits from more well-known sources, or U.S./European makers, run at least double the price. Once assembled, it’s very attractive and has a lot of potential for future upgrades. This was a fun and rewarding project and a nice change of pace from vintage gear while still keeping the tube connection.
QFC Value Club Card
The Advantage Card is practically mandatory at my local QFC grocery store if their steak prices are any indication:
How Television Benefits Your Children [Vintage Ad]
Motorola, leader in television, shows how TV can mean better behavior at home and better marks in school!
Own a Motorola and you know you own the best.
Does that clown look terrifying to anyone else?