10/12/2026
I try to switch each of my tube radios on at least once a month and run it for 30 mins or so. However, there are four radios in our lounge (three floor-standing and one table top) that I tend to forget about as they have been relegated to a small 'backwater' that is rarely trafficked due to surrounding furniture, and, admittedly, some clutter (plants, etc).
I remembered about these sets this morning, and thought I would switch one of them on - a Canadian Westinghouse Model 534 table top set dating from the 1934-35 model year. I had bought this radio in June 2006 (yikes! - over 20 years ago!) in an antique mall in Cloverdale, BC (the mall has long since been closed down), and was attracted to it because of its rather fancy cabinet and a low price - I think they were only asking $40 for it, which seemed like a bargain to me in my first flush of 'vintage radio enlightenment'...
The circuit of this model is a little unusual - its a 5-tube superhet circuit with an IF of 175KHz, sporting an RF amplifier stage ( #78), converter (6A7), IF amplifier/detector/AGC/1st audio amplifier (6B7), audio output ( #41) and full wave rectifier ( #84). The 'unusual' part is that the 6B7 tube does a lot of work in this circuit(!) - it amplifies the IF, detects the signal/produces the AGC, and then amplifies the audio (I recall building a solid-state radio in my youth that made a transistor do 'double duty' by amplifying both the RF and AF signals).
Anyway, the set did start to work (with only a 1' length of wire as an antenna!), though I noticed that the tuning control stopped tuning below around 800KHz on the Broadcast band, ie. it would not turn the dial, and the 'Police Band' did not always switch on reliably.
It is many years since I refurbished this radio, so, as my bench was clear after packing the tellurometer away, I thought I may as well take a look to see what the problem was.
I soon identified that the issue was mainly due to thickening of the grease in the slow-motion tuning drive and the front (ball race) bearing on the tuning gang. I cleaned this out with Q-Tips soaked in naphtha, and then re-lubricated the ball race bearing with lithium grease. While I was at it, I cleaned the ground contacts with Deoxit D5 and added a small drop of light machine oil to the rear bearing and to the slow-motion drive.
I than took a look at the band switch. This is unusual in that it comprises five leaf switches that are operated by cams on the switch shaft. Two of the contacts switch taps on the antenna and RF stage coils, two more contacts switch in trimmer capacitors on these tuned circuits, and the fifth contact switches in a trimmer on the local oscillator tuned circuit. These contacts were tarnished, so I used a glass-fibre pen to clean them where I could access them easily, followed by a wipe over with Deoxit D5-soaked microfibre pad on all contacts. That fixed the switch issue, and I was now able to tune across both bands reliably
I then connected my small active magloop antenna. Tuning through the Broadcast band, a very strong local station tripped the set into oscillation, causing an audible heterodyne tone when any station was tuned in after that (even weak ones). I found that I could then only stop the oscillation by turning the volume right down, the up again (did not always work), or removing the magloop antenna, and cycling the power to the set off/on again. This issue did not occur with a short wire antenna.
I suspect that the problem is happening in the IF/1st audio amplifier stage (6B7 tube), but I did not have time today to investigate it... a job for later this week!
