I previously have mentioned the Eico VFO that I picked up at the AWA Swap meet in May. It has ended up being a great bargain, as it has been working well. There was a knob missing, and it was very unique, so I doubt I will ever have the originals on it again, but it has been very functional.
Initially, I wanted to see if I could get it to work with my novice homebrew transmitter that I built in 1971. It has a built-in power supply (some VFOs from that era did not), so I saw that there were replacement caps, but wired underneath the chassis, and in parallel with the original can cap. That could double the capacitance, probably not a major issue, but if the old can caps were leaky or shorted, could be. So I disconnected the can cap. I thought about getting another can cap, or making one, but decided to wait. I also converted it to a 3-wire power cord.
My homebrew xmtr used an octal socket for the crystal, so I made up a cable using RG-174 with a male octal plug (luckily I had one) on one end, and a RCA phono plug on the VFO side. I had a Heathkit HG-10B VFO and a DX-60B back in 1972, but didn’t remember much about them, but they were obviously made for each other. All I had to do was hook them up like it says in the manual with the supplied cables. To learn more about this VFO, I downloaded a PDF of the Eico 722 manual, and they described 3 methods for keying the VFO. The VFO does have a key jack.
Long story short, but the quickest way to get it working, was to leave the VFO oscillator running by flipping the Mode switch to TRANS. Then key the XMTR with the key. I was using a couple different receivers, and hearing the oscillator all the time was not ideal. So without thinking it over much, I wired two cables to my key, and keyed the XMTR and VFO at the same time. This actually worked. I made QSOs and used it several times that way. But as I thought about it more, and looked at the schematics, I realized I was essentially connecting my VFO oscillator cathode and my single tube XMTR cathode together. Seemed like that might affect the biasing of one or both tubes, and decided maybe it was not such a good idea, and went back to not keying the VFO. I’m probably fortunate nothing blew up, though they were both cathode keyed, and probably similarly biased.
So I thought I would look into some better T/R switching methods at some point. Somehow, I came across a video of a Drake 2-C/2-NT station. That had been out of my reach in 1971, but I thought, why not? It might be fun to fiddle with. So you can look back at some of my previous posts about the Drake stuff. But now I needed to try and interface the Eico 722 with the 2-NT. VFOs are briefly mentioned in the 2-NT manual, but the Eico 722 was not specifically called out. An octal socket would not do for the 2-NT (unless I cut off 6 pins and center locator from the plug), so I needed to construct a cable. The 2-NT will take either FT-243 style, or HC-6/U. I had some old FT-243 style around, and they can be taken apart, somewhat, though some surgery is required. I removed the crystal, and cut the contacts that went to the pins. I drilled a hole in the end opposite the pins, for the RG-174 to pass thru. I solder each conductor of the RG-174 to the contacts that go to the pins, and buttoned the crystal back up. Here is a photo of the finished cable connected to the 2-NT.
One of the nice things about the Drake 2-C/2-NT combo, is it essentially has transceiver-like operation. T/R switching with a VOX like delay, a muting function, and a CW sidetone. Though Drake never offered a VFO with this pair, they did provide a keying output from the T/R switching relay, which works perfectly with the Eico VFO. To get full muting of the 2-C, the Function switch on the 2-C must be in the Ext Mute position. But this is essentially like a full transceiver mode. Just pressing the key is all one needs to do to go from RX to TX. With the Delay set to minimum, good semi-break in is possible.
As it is operating currently, the VFO is stable, and I hear no chirp when keying, even with the T/R delay at minimum. A few weeks ago, I was having some issues where the VFO would suddenly either start drifting, or jump about 8 kHz down in frequency. As I was troubleshooting this issue, I became aware that those power supply electrolytic capacitors were in the way. I don’t have a great photo, but this might give you an idea.
They were right above the buffer amplifier tube socket. So I decided to look for a can cap. Hayseed Hamfest is my usual go-to for this, but they didn’t not make one for the Eico 722 (not surprising). The original cap had three sections, all 20 mF at 500 VDC, though the schematic indicated 350 VDC. Those yellow caps were rated at 450 VDC. So I found Hayseed had a couple of 3 section can caps, all 20mF at 450 VDC. One was for a Hallicrafters radio, another was for the Hammarlund SP-600. I looked for physical sizes, but did not find any on their website. The Eico 722 had a relatively small opening for the capacitor terminals (triangular hole in photo above). I probably could have called them, but I took a chance and ordered one, knowing I probably would need to do some rework.
While waiting on the caps, I continued working on the drifting/unstable issue. I poked all over that vfo with a small wooden stick, and could not find anything. Finally, after taking the cover off the shielded section of the chassis, putting pressure on a wire that ran from the band switch to a coil, the frequency would jump 8 kHz. I resoldered those wires, plus a few others. I also changed a couple of resistors that were either out of spec, or looked somewhat used up. I have not had an issue with drifting or instability since then ( over a week, with several QSOs).
The new capacitor showed up, and physically it would fit in the general position, but the opening for the three terminals was marginal, and the four grounding/locating tabs would definitely not fit. So with a step drill, I opened up the hole for the main terminals, not worrying about the triangle shape, marked the location of the grounding lugs, and drilled some small holes on the chassis where the lugs needed to go. Then it was a process of getting those made into small slots with poking and filing. They didn’t need to be perfect, just big enough for the lugs to get through so the cap could sit flat against the chassis, and then bend the lugs over to keep it in place.
Soldering those lugs to the chassis is always a problem for me, I just don’t have a gun/iron that is hot enough. The chassis just sucks up all the heat. But I did get it good enough.
All is back together and working great with the Drake setup. I had 4 QSOs this evening on 40 meter cw. I will also be using it again with my homebrew XMTR. I don’t have enough room for all my radios on the operating table, so every once-and-a-while I will swap out different rigs.
Despite the issue I had with drifting, which I believe was an age related artifact, this VFO uses some temperature insensitive NP0 caps to keep it stable. And it works great with the 2-NT and my homebrew, keeping me from needing to locate a bunch of expensive and hard to find crystals.
