3 for 3

My parents were in town this past weekend for another visit. This time my father and I had more time to spend working with three amp projects. First we looked at the Champ 5E1 project that started all of this. We confirmed that I do not have a center tap on my RCA power transformer so my options are to either create an artificial tap and use the 5Y3 for rectification, or create a bridge rectifier using 4 diodes, donated by my neighbor (thanks Bryan!). Next we spent time slowly powering up the Western Electric 124c Dad pulled out of the town dump! This thing was THE workhorse of the early '50s. As you can see in the photo above, this amp has 19" rack mount ears on either end of ths chassis and a full-size face plate that mounts on the bottom which is actually the front. Click on the photos to see larger versions.

The third amp was the Hammond AO-35 which was donated by Ron Ashcroft last year. I installed new tubes which I bought at the Dayton Hamfest in June 2008. These were two Sovtek EL-84, two Svetlana 12AX7, and a NOS Sylvania 5Y3 made in 1975. We slowly powered this up as well, using the variac I bought at the '08 Hamfest. This amp has no gain control pot, so after a little squealling with a microphone, we plugged my Samick Telecaster in using the Switchcraft adapter I bought from Antique Electronic Supply (visible on the right of the chassis). The amp sounds good, but a thorough test of all the parts will likely turn up some leaky caps. A gain pot would also be helpful.

Pulling Parts from the RCA HG-765L

My folks were in for a visit, and after my dad looked at the layout of the TV chassis, he wondered if their wasn't a rectifier tube somewhere in the circuit. If so, this may indicated the needed 5 volts to operate the 5Y3 rectifier tube in the Champ plan. We'll look closer at the tube layout for this console to learn more.

Tektronix Oscilloscope for Parts & Variac Made Functional

Another Craigslist freebie! The Tektronix Oscilloscope seen here is a vacum-powered tube unit from probably the mid-60s. (click the photo to enlarge) I hope to pull various components off of this. I had the opportunity to spend a couple of hours rewiring the Variac I bought at the Dayton Hamvention last year. My Dad told me I may be able to rewire the coaxially mounted M5 variable transformers, from 3-phase 240vac to 120vac. I did this and the test I performed afterwards is in the video below.

Console #4: RCA HG-765L

This unit was likely made in the mid to late '60s. Paula is overjoyed that yet another old console will sit in the garage while I strip it. This is another Craigslist freebie. What I am likely to do with this is pull the TV chassis out, along with some other very small pieces, and dump the rest. Though the TV chassis is tube, the audio component is solid state. This is the same configuration that I found in the Magnavox that I got at the very beginning of this project. Yes the Pavarotti LPs came with it. THANK YOU BRIAN FOR YOUR HELP GETTING HOME!

Inside the Variac

I haven't touched the amp project in nearly a year. I have acquired additional test equipment though, to include a an a capacitance decade box, capacitance analyzer, a bridging transformer for impedence mathing in audio inputs, an RF Signal Generator, a DC ampmeter, and an older multimeter. But of course the hard part has been finding time to put this stuff to good use. I did pull out the Variac that I bought last year, with the goal of getting it into action. I will need it to safely test amps and individual components like transformers. For starters I cut the wires off, and removed the cover. I have obtained enough technical information about this that I hope to get it wired for 120vac-to-120vac use soon. But not without a call my pop first. Please click on the photos here to see enlarged versions.

Oscilloscope arrives!

I haven't touched the amp project since getting parts at the Hamvention early last summer. I hope to spend some time on it over the next few months though. Today I finally got my hands on an oscilloscope. Thank you Mike! It is a B&K Precision Model 1461. I am not sure how old it is but I would bet 15-20 years. It appears to be in nice shape. I don't know much about these so I will have to do some reading before I even turn it on. One sour note, B&K Precision doesn't provide support directly for their older equipment. They transferred the rights to the technical documents, to a subsidiary. This company wants $25, plus shipping, for the 35 page owner's manual! I may end up spending the money though.

Hamvention 2008 - Dayton, Ohio

The only other time I've been to the Hamvention (or Hamfest) was about 30 years ago. It is still big. Way too big to be taken in thoroughly in one day. Tickets at the door were a steep $25 but that is good for all three days, inside and out. It really is targeted at amateur radio folks, but all kinds of electronics are available in the flea market. Of course my interest was in parts for the Fender Champ 5E1 I am building, as well as tubes for the Hammond AO-35 that I just acquired. In that department I got the following: EL84(2), 12AX7(2), 5Y3(2), 12AT7(1), 6V6GT(1). Two are used, the rest are new. I paid an average of $7 per. New tubes like this would run me $12 and up not including shipping. I also got I handfull of high-voltage caps, four tube sockets, and some IEC 320 sockets (for AC power cables). I found a turret board with capacitors and large pilot lights attaced for $2, and a pile of selenium rectifiers for $5. The best, and least expected, deal of the day was the 3-phase VARIAC I found on the way out of the show which I paid $20 for. I hope to use this to slowly power up amps when testing. Since the flea market is so large, some folks use wagons or backpacks to tote stuff around. I met a guy who had the gest solution I've seen. He built a cart from angle iron, which holds milk crates and coolers, with two PVC tubes in the back for antennas. He actually mounted a spare wheel and tire underneath in wagon, just like a truck. You can see this in the photo at the bottom of this post. Remember to go to my actual blog and click on the photo thumbnails to open larger photos.