RA117 serial number N0489

In the PSU area, the RA117 differs from the RA17 and 17L in that the ubiquitous GZ34 rectifier has been replaced with a semiconductor bridge, the mains cord is hard-wired in and there is no mains voltage selector.

The two EF91 audio pentodes have been replaced with a 12AT7 double-triode and a 6AQ5 pentode. The latter provides a more comfortable 1W output compared to the feeble 50mW of the UK version of the RA17/17L. It can be argued that the RA117 is a derivitive of the RA17C12 which was manufactured for the North American market and sported a genuine S-meter and ‘beefier’ audio stage.

It should also be noted that the RA117 (followed by the 117A and 117E) was NOT a replacement to the RA17L. It came about in response to a specific requirement and was manufactured alongside the RA17L.

As can be seen, some of the PSU/Audio components had been previously replaced. However the only one which I retained  was the 0.47uF capacitor across the negative bias line. In the RA117, the 165R resistor is replaced with a 120R one.

PSU/Audio compartment before and after

September 2012 … I finally have an RA117 !

This had sat in my radio room awaiting refurbishment for several months … other more pressing projects having precedence. When I picked it up I was forewarned that it was faulty. Fortunately it was complete, so getting it working was as far as I was concerned, just a matter of carrying out a full refurbishment. The main tuning bezel is attached by way of three screws and there is a small scuff in the bottom left corner of the front panel where the primer coat is visible. Behind the front panel, the chassis bore the usual signs of ageing and the warning label shielding the RX-mute terminals was missing … but apart from that, the set was in good condition. … So, on with the job!

Curious as to exactly what the fault was, I ‘fired’ it up as soon as I got it home. Just to be safe, I ran the volts up slowly via a variac. I didn’t want any ‘loud’ surprises! It actually worked! Granted, it was very deaf though. But it was indeed a good start. When it came time to start the ‘refurb’ proper, I removed all the under-chassis covers and looked over each compartment with a ‘close eye’. The first thing that caught my eye was the tiny EA76 wire-ended AVC Clamp Diode where two of the wires had snapped off right at the glass envelope. Normally this would automatically be replaced with a silicon diode such as an 1N916. However, since I had a spare unused EA76, I decided to fit that instead. It didn’t fix the fault. I didn’t expect it to either, but it just seemed right to fit an original thermionic diode. … Time to focus on the job and that meant turning my attention to the PSU and audio amplifier compartment …