Drake TR-4Cw
I've always been fascinated by electronics, building kits, understanding the principles of basic circuit analysis and design. I've pretty good with a digital volt meter but its been a while since I've had a project that could benefit from a good oscilloscope.
With the Drake I will bring on these skills together. Also known as a "boat anchor" these tube type radios require a lot of knowledge and maintenance if you want to be a fine business operator.
This lesson was reinforced when I first opened the box. I fired up the rig but couldn't even get the bias voltage set (per the manual). Having never worked on tube operated electronics I was hesitant to do any troubleshooting. I ordered a hardcopy Drake TR-4Cw manual and waited for its arrival.
First came the friendly advice from Joe KI5O (a ham buddy and fellow member of RWK) to join the DRAKE-RADIO groups.io which is full of drake experts who are willing to give advice.
Lucky for me thru the list I met Bob WB9RHW is a local ham here in Dallas and offered to spend an hour with me to test it out. Turns out both the rig and the refurbished AC-4 power supply were fine. But some of the tubes were loose and needed to be re-seated after shipping. Bob showed me a few things to get me started and tuned up rig on the main ham bands- generating 100W or more on all but 10M, but with some fiddling we got it close to 80W if I recall. Bob said that was typical.
As soon as I got home, I took the rig apart and inspected it. Bulbs for the meter and VFO were weak, so I bought replacements - Blue Shaded LEDs that are very close to the Drake Blue hue we all love.
I tried to make a CW QSO but the key was a mess and I could hear the T/R rely sticking (K1). I cleaned it up with some Deoxit DS and reseated the relay, being careful not to hit any of the pots or plastics with the DS. Problem solved. I tested K2 while i was in the rig (seems to operate normally) and cleaned up the other switches with a few shots of Deoxit while working the switches back and forth.
Drake TR-4CW Carrier Osc Adjust C130
The next problem to solve was poor SSB audio when the SIDEBAND switch is in the X position and no CW was getting thru the 500Hz filter. Stations on LSB were very bassy, while stations on USB were attenuated and very tinny. I assumed the aging USB/LSB crystal filters were the issue, but after spending a day on the groups.io page came across a process to balance the 9MHz carrier oscillator by adjusting C130 and switching the sideband mode till the audio output was equivalent.
Yes, this procedure to do this is one of many alignment procedures described in the maintenance section of the service manual.
As I learned from this video by Bill Ncham the audio problem is exactly what happens when the carrier oscillator is not balanced across the two filters. You want the audio response pretty even across both USB and LSB modes. You can listen to the audio by toggling USB/LSB and balancing C130 capacitor by ear, which is what I did. Close enough for . I want to find a used Palomar Engineers Noise Bridge and the PC application Spectrogram to recreate Bills test on my own.
Since then I've made a dozen or so QSOs on 40 and 20M. I've called CQ and gotten good spots on RBN. I've listened to my CW on other SDRs and thru the RX only antenna of my Flex. The transmitted CW sounds FB - much better than what emanates from the Side Tone generator! The 500 Hz CW filter works perfectly, had great audio, and is an absolute must for picking up individual stations when the bands are crowded.
Remaining issues to solve:
1) The 10M crystal in the rig is for 10M-B - 28.5 MHz. I've ordered the 10M-A (42.5MHz) and 10M-C (43.6 MHz) from Kevin K8KVN so I can work 28.0 - my favorite CW portion of the 10M band. Doubt I'll ever work 29.1 but it will be handy to have for completeness.
2) The VFO display is off by about 30KHz on 40, 20 and 15M. Workaround for now is to mentally add or subtract 30 from the VFO dial, depending on the band. I will also get a frequency counter so I can monitor the exact frequency of my transmitted signal.
3) The side tone POT doesn't seem to control the side tone volume. Side tone is basically either on or off. Could be something else in the alignment (still yet to complete) or could be a bad pot. I cleaned up the pot with F5 but improvement was minimal. Work around is to reduce the RCVR GAIN (aka Volume) during transmit.
4) The rig as a switch for the Noise Blanker, but a dummy plug is where the 34-PNB Noise Blanker plugs into the rig. I'll be on the lookout for one of these.
5) I haven't tested any SSB phone mode capabilities. Need a high impedance mic like the Shure 444 Desk Mic or the Astatic D104. Many of these mics have crystal elements that no longer work. There are some nice D104 Silver Eagle Microphones on eBay that would work well.
A Note on the Drake's SSB filtering scheme
During the process I stumbled across a great article that "unravels the mystery of the Drake TR-4 SSB" scheme written by Jeff Covelli WA8SAJ. Good understanding of why 20M works "backward" on the VFO, and how the frequency crystals mix with the 9MHz carrier and the 5.5MHz VFO so that the desired HAM band is produced! Mixing frequencies produces the sum and the differences of the products as we learned when studying for our FCC license exam
40M RBN Spots
20M RBN Spots
15M RBN Spots
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