Siera Aristona SA2211A (late 1960s)

The Model

The SA2211A is branded Siera Aristona, but it was designed and manufactured by Philips in the late 1960s. The Siera brand targeted the Belgian market, while the Aristona brand indicated the company's low-price lineup. It is a small "kitchen radio", more affordable than a big living room tabletop.

I could not determine the exact year that this model was manufactured, but it is almost the same radio as the Philips BX42A produced in 1964/1965 by Philips in Austria; the only difference I could notice is that the BX42A has banana plugs for the antenna connections while the SA2211A has IEC 3-pin FM (DIN 45316) and AM (DIN 45315) plugs. Since these plugs were introduced in mid-1966 I guess the SA2211A is somewhere between 1967 and 1970. If you know more, please drop me an e-mail.

The SA2211A has a hybrid design using transistors for FM reception and vacuum tubes for AM reception and amplification. Rudolf Drabek, designer of the BX42A, explains that tubes were cheaper at the time, but dissipated too much heat, which was a problem for the plastic enclosure. In the end, they settled for a hybrid design balancing cost and thermal budgets.

Schema

IMG_5256.MOV

The Object

By December 2020 I had finished working on two big tabletop radios from the late 1950s, and was looking forward for a different project in a smaller form factor. I found this radio on Marktplaats (the Dutch equivalent of eBay) offered by Rene, a gentleman from Hoorn, a town north of Amsterdam. The radio had been purchased new by his parents but stopped working in the 1970s and had been since lying around. My intention was to pay for the radio, but when Rene found out that I drove from Eindhoven to Hoorn to pick it up, he gifted me the radio. Thanks again, Rene!

This radio came housed in a yellow plastic cabinet, and in very good cosmetic condition. The metal strip with the Aristona logo is slightly bent and the black paint faded at some points, but nothing dramatic. I plugged it in carefully with my dim-bulb tester and confirmed what Rene said: the radio was completely dead. It made no sound or light.

I started the restoration right away in December 2020, but after ordering some parts I got distracted by other projects and only returned to it almost an year later, in September 2021.

The Restoration (still ongoing)

After printing a copy of the schematics, I opened the cabinet and removed the chassis. It was a fiddly process, removing multiple screws from the bottom and front of the radio, but eventually everything came out, including transformer and speaker (this radio has a single one).

A visual inspection revealed a (surprisingly low) number of electrolytic capacitors, which I always replace. The selenium rectifier had a bad look, cracked and stuffed up. I confirmed with a multimeter that the transformer windings were intact. However, the rectifier was indeed dead: no continuity at all, in any polarity. Next step: replace the old defective selenium rectifier by a modern silicon bridge with a 100 ohm 5W resistor in series (following this excellent article).

The next step was replacing all electrolytic caps. There were about five of them. It was an easy job, with the chassis out of the enclosure all soldering points were accessible. The exception was the filter caps can, which was hard to get loose off the chassis.

After the recapping, the heaters of the tubes started glowing. I replaced the dial lamp, which was broken. The radio was now making sounds!

IMG_7012.MOV

Unfortunately the sound also included a lot of buzz, especially on the AM frequencies.

My first suspicion was leaky filter caps, but it turned out they were good. I even tried hooking up a couple of filter caps that I knew to be good, to no avail. The oscilloscope showed a steady DC voltage, with normal levels of ripple.

My next suspect were the tubes. I don't have a tube tester, so I had to resort to tapping them with a pencil during radio operation. I noticed that the EBF89 (IF stage) caused sudden volume changes when I tapped it. I replaced the EBF89 and it seemed to help out a bit, but I'm still not convinced that is the root cause.

IMG_7044.MOV

Before EBF89 replacement

IMG_7045.MOV

After EBF89 replacement

The radio is now working, but I have already burned out two new dial lamps. I suspect that the 7V AC line that supplies the heaters and the dial lamp have a slightly high voltage that may be overheating the tubes, causing the buzz. I need to check that immediately, as high heater voltage will reduce tube lifespan.

Cabinet Restoration

There wasn't much to do here, mostly cleaning all plastic parts with a toothbrush in soapy warm water. Inside the cabinet there is a foil sheet to protect the plastic by dissipating heat, which was originally stapled to a sponge-like material that disintegrated with age. I have reattached it to the cabinet top using double-sided tape.

The dial marker was kept in place by a tight nylon string, which I wasn't able to attach back without breaking the plastic pin it attached to. I ended up replacing it by a bit of common sewing thread. One of the small red plastic station markers broke when I removed it, but the other two are still good.

The yellow plastic got darker with age (the inside of the cabinet, which doesn't get sunlight exposure, has a noticeable lighter shade), but other than that the radio looks pretty good and original.

Sound of the restored radio

IMG_7062.MOV

The radio is now working again, but I'm afraid it's not yet out of the woods. I will do further testing to ensure that all voltages are nominal before considering this project ready.