I wanted to experiment with the so-called “Plumbers Delight” Yagi-Uda antennas – that is, directional antennae whose driven, active element is at the same potential as the boom so it’s welded together- which apparently delights plumbers, as they are so-named “plumbers delight”. These are both cut to resonate at 449 Mhz which is my repeater frequency.
This allows the element to be welded to the boom, making them very durable. The other advantages of neutral-potential Yagis are very low noise floor and relative lightning immunity as they can take a direct strike asthey are at ground potential.
The unusual element-to-boom potential required some nuanced feed impedances however. Originally I was going to implement a Gamma Match which basically adds capacitive reactance to the antenna.
This time I used a balanced Delta feed with integral 4:1 coax balun. Thus I can achieve a 52 ohm match with less than a 1.2:1 SWR at 449 Mhz. My next project is a an X-Y 144/444 Twist Yagi for AMSAT operation. They also make the perfect ant for terrestrial data capture systems with a UHF sattelite data uplink data-radio.
This is the first steel guitar amp chassis manufactured here on the island from my AutoCad drawings. It is the first custom amp being built completely from scratch including the chassis (click to enlarge). This new line of amps will probably be based on the Fender AA794 Vibroverb – Stevie Ray Vaughn’s amp of choice.
On the right is my ho-made (and I da ho) Fender Champ II clone. It’s currently getting a 5Y3 tube rectifier make-over as the current solid state rectification allows the B+ voltage to be too high which makes the 6V6s run way hot. The black box covers the high voltage electrolytic caps for safety, utility and aesthetics. (Update: ended up just swapping out the transformer for the correct one. The original transformer was actually for a Super Champ.
Here is the completely rebuilt circuit board assy (yes I built this twice!). All of the turrets (the little metal posts that the components mount on) were hand mounted. Click on images to supersize them. The new circuit will provide audio in/out looping for effects, noise gate and standby switch with delayed high voltage relay to save output tubes.
Update 4/26/2013 – Almost finished the electronics – come to find out the little OEM Fender input jack p/n 011028 has two separate outputs – those tricky bastards! so my stock Switchcraft input jack wasn’t working. I fooled it by connecting directly to the plate bypass capacitor of the first 7025 amplifier tube. Sounds reasonably good I think. See inset for schematic of the problem:
Here's the problem with the original circuit (click to enlarge)
The next project is aesthetics – I have 2 stainless steel plates that I had cut by On-line Metals.com that I will be punching out and silk-screening the labels on with epoxy based silk-screen paint. There will be both a front and back trim plate to fit within an original Fender Champ enclosure that I bought on eBay for $35.
Here’s a video snippet of the final product so far – juiced up a little bit to start with my GNX3 guitar processor but I play some dry ( no effects) at the end of the video. I do plan on adding some sort of pre-amp/processor internally as soon as I get the cabinet finished. So yeah, this was a three month pain in the ass, but learned a million things not to do when I build the next one. This particular amp if it were vintage would retail for around $1,000 at a guitar store. I built it for about $200 in parts and about $427,000 in time.
Build a $3000 computer for under $700 and win all of the computer pissing contests While my former computer was only a year old or so, it was in a big gamers case with room for 10 hard drives, (I only used 3), and took up an inordinate amount of space. Also it was [...]
This is the new Arcom repeater controller that’s going in to the repeater. It replaces the 7330 that was a bit complicated. The 210 provides speech synthesis and a host of analog to digital inputs that are fully mature and working for voltage, amps, temp etc. The sub-mini mono jacks on the right are for [...]
AKA the American Recovery And Reinvestment Act I get into this conversation a lot since I work in the healthcare technology business. The funny thing is that I get into this conversation with other people who work in the healthcare information technology business and slam “ObamaCare” mostly because as with most things in the United [...]
We finally got the top section of the tower mounted today with the help of Potelco lift trucks and crew. They were nice enough to come out in full force and had the top of the tower section mounted in under an hour. Now the process of putting the hard-line coax up to the antennas [...]
I found a Fender Champ Amp chassis on eBay for $20 plus shipping. So what was one to do but purchase said chassis and build an amp for it. I decided to do a Fender Champ II – a single ended 18 watt and with 2 – 6V6GT and 2 – 12AX7…something to “cut my [...]
Before you think that this is about a musical conflagration involving 70’s pop and classical compositions – stop right there… If you’re like me though, you would probably be intrigued as I was when I encountered a couple of really weird pieces of physical (as in physics) trivia and started thinking about what else do [...]
The saga of the never ending repeater project… This is the Voice-over IP UHF radio repeater system that Tim Hardy and I have been working on for over a year. It’s is a custom made radio repeater system that uses open source Asterisk voice-over-IP (VoIP) to allow the radio system to be remotely accessed via [...]
We all know that Google has had unfettered access to virtually all of our data. Google has long since had one of the most non-commercial search engines, allowing you to search for, say, “sodium” without being bombarded with ads for on-line merchants selling salt shakers. We’re all familiar with the Google “Street View” that allows us [...]