Electrical drafting is primarily done on a computer today, with software such as EAGLE or KiCAD. This wasn’t the case back when tube radios ruled the airwaves, though – schematics were drawn up by engineering draftsmen by hand. And as with any process with a human element, they didn’t always get it right.
I’m working on a 1934 Philco 66. It came to me in excellent original condition with little evidence of having been service, and throughout the process, I’d been relying on the schematics to guide me in the right direction. Unfortunately, along with a laundry list of other issues, my reliance on the schematic to be “the truth” led me around in circles longer than I needed to be to resolve a power supply problem.
Below is a schematic snippet of the power supply and audio sections of the 1934 Philco 66, with the RF chain to the left of the #75 Detector/1st Amplifier tube hidden for simplicity’s sake.
In green, I’ve highlighted the path B+ (high voltage) is supposed to flow from the rectifier cathode to the plate of the first audio amplifier. It’s a very straightforward path…if the draftsman had indicated that tube was supposed to be connected to the power supply. In red, I’ve indicated a missing connection symbol. Without it, there was no power being supplied to the first tube in the audio amplifier stage and the audio signal was being killed at that point before it could make it to the final output amplifier. Using an alligator clip, I restored that connection to test, and the radio sprang to life making noise on the next power-up.
The second filter capacitor should have been connected to both B+ and to the plate path for the #75 tube, rather than just the plate path. (Incidentally, the two capacitors are both at the same potential, so under the correct connection scheme could have been replaced with a single capacitor of a larger value.)
It’s not done yet, but I’m inclined to believe the final wiring issue has been corrected, and it’s on to performance.
I’d like to take some more detailed photos, and do some analysis, on a Bose 901 Series 1 and Series 2 equalizer. Since I don’t have any lying around my shop right now, I’m extending a special offer: $75 Full Reconditioning including free return – 40% Off regular service!
If you’re interested, visit the Bose 901 Active Equalizers page to see a description of the service and send me an e-mail! The offer is available until I note otherwise in this post.
I’d love to get to know my visitors a bit better so I can keep delivering interesting content and new material. Could you please take a minute and fill out the KF7LZE Visitor Survey? It’ll just take a couple of minutes. Thanks!
I’m moving towards hosting the majority of my content on an on-premises server, versus the mix of hosted services I’m using currently. I’ve been running into some issues, though, that maybe one of you who is reading could help with…
The issue appears to be: some users, for no particular reason I’m able to identify, are unable to access any of my web sites.
My web domains are pointed at my server’s public, static IP address. The DNS records are valid, and DNS resolution works as expected always returning the correct address. The server responds to ping, and can complete a trace route. But, for users who this problem effects, it’s as if the server doesn’t respond. From my mobile device, for instance, I receive an Error 504 Gateway Timeout, the cell phone network’s caching proxy can’t receive data from my server. Port scanning reveals the ports are open and accepting connections on the server, but bonnection requests time out with no received data from a system on a Time Warner connection, as well.
This is all occurring while other users are logged in and actively using some services, so it seems unlikely to be an issue with the server itself failing. Even more vexingly, it’s intermittent. My mobile web site was working yesterday. It is not working today, from my cell phone.
If anyone has troubleshooting suggestions, I’d love to hear them.
I’m looking at launching some easy to use kits of the most commonly needed parts, and maybe some helpful accessories and good instructions for the Bose 901 Series 1 and Series 2. No need to order the parts individually, just grab a kit and spend a few hours soldering and you’ll know you have exactly what you need.
Would anyone be interested in that? What other easy repair kits should I put together?
Let me know! Leave a comment or send me an e-mail.
I’m still around – there are actually 3 projects on my bench currently that are ongoing, and I’ll hopefully have a few posts in the next couple of weeks were I fix a Philco Model 66, a Silvertone 1708A, and a Westinghouse WR-8 Columnaire. Until then, I’m quite busy, so things are moving a bit more slowly than they otherwise might.
I bought an inexpensive aftermarket car stereo about six months ago, and it’s sat unopened in my closet until this past weekend when I was able to find 30 minutes and actually put it together. The process in my 2003 Honda Odyssey was incredibly simple – six screws was all it took. And now I have a great, brand new Blueetooth and Pandora-enabled car head unit!
The feature I already enjoy the most, though, is the HD Radio receiver. I’ve never owned anything with HD Radio before, nor can any of my SDRs decode HD Radio as it is heavily protected by iBiquity patents. Let me tell you – it’s like night and day. FM Radio around the Seattle area is always spotty for some reason which I’ve always attributed to the geography. Even a big station like KNDD (locally, 107.7 The End) pushing 18.2 KW of transmitter power has static intrusion, fade, and general sub-par audio quality beyond the normal loudness war audio degradation.
Every time I tune a station on this new head unit, it’s like an immediate A/B comparison between Analog and Digital radio. The tuner first locks onto the analog channel, and there’s some hiss and crackle and the sort of noise you expect from radio. Then the “ST” indicator disappears from the dial and “D” appears when the digital sideband locks in, and the audio quality jumps, the sound field expands, and the artifacts melt away entirely. I swear, it’s like I’m listening to a CD. Except for the commercials.
It’s just amazing. It’s by far the best feature on my head unit, because it makes the experience of being lazy and passive in my music selections better like night and day. Now the music I listen to when I’m bored of my CDs, sounds as good as the music I’ve put some planning into bringing with me. If you don’t have an HD Radio already, you should definitely get one.
French hobbyist Sylvain came up with a fascinating project using 8 Magic Eye tubes from old equipment to make an audio spectrum analyzer. I’ve worked with magic eye tubes quite a few times, they’re very fascinating. Originally precursors to CRTs, they’ve found a lot of use as level indicators in all kinds of equipment up through about the late 1960s.
He built a beautiful project case for them, too. Click through to his blog to see the build log and all photos!
I was very lucky to receive an awesome new oscilloscope as a Christmas gift this year, which will replace my aging EICO 460 vintage scope.
It’s a Rigol DS1102E digital storage oscolloscope with 100MHz bandwidth, built-in voltage and frequency measurements, waveform functions, and the ability to interface with a PC and export scope traces. This will make my life significantly easier when working with FM radios, and also make documenting the process on here easier as I can directly show the oscilloscope’s output as an image file.
I’ve been busy with a new day job, although my radio repair work has been continuing in the background. Look for several new updates in January. Merry Christmas, everyone!
I’m working on a couple of projects – another Bose equalizer, and a Grunow radio – but they’re not quite finished to post photos, so in the mean time I’d like to post some meta commentary for a moment.
WordPress provides great tracking statistics on visitors, including mapping them by country. In the last quarter, my site has been viewed by visitors from 122 unique countries – over half the world!
Most of my visitors are predictably from the United States, but I’m fairly surprised by the wide showing of the rest of the world. A total breakdown:
|Republic of Korea||74|
|United Arab Emirates||26|
|Trinidad and Tobago||8|
|Bosnia and Herzegovina||8|
|Macedonia, the Former Yugoslav Republic||6|
|Isle of Man||3|
|British Virgin Islands||2|
|Palestinian Territory, Occupied||2|
|Syrian Arab Republic||1|
Don’t forget to vote, everyone! If you live in Washington, today is the last day to return your ballot and have it postmarked or to return it to a ballot drop location. Otherwise, check with your local election supervisors or use Google Voter Information to look up your polling place. A list of King County WA ballot drop locations can be found on their official web site.
If you like watching results updated in real time, Politico has a web map of electoral votes by state with candidate breakdowns.