Unitra D-401

This "Recent Repair" was kindly contributed by Steve Pendlebury.


Introduction

Photo of SetI am probably going to cause a few ripples by saying this, but in my opinion, some of the Polish / Eastern European / Russian sets are a lot better than they are given credit for. I have found the Kaige set described on this site to be a reliable set with no problems, and being someone with a fondness for radio things of an unusual nature, I am somewhat drawn towards sets such as the Unitra range.

The D-401 is a Polish 3 valve superhet from about 1970-ish. Like many sets of this kind, it was imported with very little support (and hardly a chance of a service manual!) and sold cheaply through low end shops and catalogues.

The use of the High Slope Triode Pentode ECL86 is interesting, as this valve is seen mostly in Open Reel Tape Recorders. However, the use of such a valve reduces the standard valve count of a set and is one way of keeping the costs down.  A germanium diode is used in place of the usual Diode Triode (UABC80 or whatever) and the triode and pentode are in the same glass envelope. Despite the lack of service data, the circuit is still pretty easy to follow, given a good valve data book.


Electrical Repairs

So, standard approach, start at mains plug and go back to the antenna, taking in all the scenery on the way….!

This set is easy to work on. With the back off, the wavechange switch, a mechanical slide switch on the side of the set, can be released from the inside. There are four screws on the base of the set, and when these are removed, the top of the cabinet (complete with speaker) can be lifted clear.

When power was applied, we were rewarded after a minute with a few stations on all bands, more or less in the right place with quite bad distortion. A look at the voltages on the Control Grid of the Pentode section of the ECL86 showing a nice positive voltage, due to the usual capacitor problem. With this replaced, we had good clear audio and a good range of stations, but the set was prone to a little bit of whistling – I replaced the decoupling capacitors on the EF89 and this problem was cleared up.

The wavechange switch responded well to a good dose of switch cleaner. As the set is built on a PCB, I gave it a good going over to clear any dry joints.


Cabinet

The cabinet polished up surprisingly well and the set, when reassembled, looked and sounded good. I do feel that maybe the set does sound a little ‘cheap’, but I declined to do any modifications as these would have compromised its authenticity.

The set does give a good clear sound quality, however, and is sensitive and selective on its own antenna. This is with the original ‘Tesla’ branded valves. Eastern European radio valves from the late 60s / Early 70s do seem to be a lot better than their TV counterparts. If the original valves work OK, why waste time and money changing them?

Overall, when in restorable condition to start with and restored well, many of these cheaper imports from Poland, etc., can give good results. The Unitra sets are a good example of this.


Text Copyright © 2001 Steve Pendlebury




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Last updated 14th April 2006.