TR-1040

TR-1040 was Tandberg’s first direct coupled receiver. It means, in short, a new amplifier topology without capacitors after the power amp. The earlier models TR-1000, Huldra 10 e t c were capacitor coupled.
It delivers 40 watts per channel into 8Ω, 60 watts into 4Ω.
Tandbergista thinks this is one of the finest receivers Tandberg made and one of the finest vintage receivers ever!

I bought a whole set consisting of TR-1040 receiver, TCD-310 cassette deck, TD166 Thorens/Tandberg turntable and TL-3050 speakers.
All needed serious care. First, the restoration of the TR-1040. The other units in the set are posted on their own pages.

This was after the Huldra 10 nr 2 project, in 2019. It was my first restoration of a faulty receiver in otherwise unknown condition. It went well and it now sounds absolutely fantastic and delivers true audiophile performance.

This is how I found it in an ad. Very thankful to the girl who sold it to me, it had belonged to her uncle who treasured it very much. All the pieces, which she had inherited, had been in storage for some time.
The buttons were more or less stuck on the 1040. It had been powered up, the seller said, so I dared to do the same. At the time I had no variac. I built a simple current limiting lamp, to protect it if there was a short.
One channel was dead, the other weak. Pots had massive oxidation. But in pristine cosmetic condition.

The recap (replacing capacitors). Starting with the power supply.

Holes for the new filter caps were too small and a Dremel was used to slightly enlarge them.

All the electrolytics were replaced. In signal path mostly Elna Silmic II’s.

The surface paint on the boards does not go well with IPA or any solvent based defluxer. This disturbed me greatly, but there was nothing to do. I specially ordered several kinds of ‘gentle’ defluxer and cleaning agents but none of them left the paint intact. Perhaps on this very machine the paint that had been used was extremely sensitive. I just had to take care not to spill and be careful when cleaning. For residues of old, hard flux, I bought a defluxer pen which made it more easy to be precise.

Ready for a test. I had bought my first oscilloscope, a cheap DSO from China on ebay. It worked and was a great introduction to learning how to use one. Later I bought a real bench oscilloscope.

Measurements were checked. All ok.

On the first test run I noticed two problems – Left channel gets weaker at times and there is a hum (more on one channel). The volume pot was taken out and cleaned. This was not the problem, or maybe there was a little bit of oxide and dirt in it.

I located the source of hum to the AC cable leading to the power supply board. It runs straight over the power amp boards, maybe interference? An alternative route was deviced for this cable in front of the power amp boards inside the “ditch” of the chassis. A new cable was bought, a shielded Faber 2x1mm cable.

With an audiophile ambition I wanted to see how good a TR-1040 can be if restored to top condition and with top components. Playing with my new, cheap oscilloscope I saw that the ripple was relatively high and going even deeper under load. So I build a primitive test bench to be able to try out different combinations of filter caps and measure the result.

Instead of the two large cans of 4700uF each, 4 Wurth 3300uF were put in, increasing total capacity from 9400uF to 12600uF.

Lets try two more Wurth 3300uF capacitors.. They are supposed to be low ESR type. Where to put them? A capacitor holder was constructed and made to fit on top of the radio board, one of the few places where there is some space left. I took care to make sure this mod can be reversed without any trace.

The new bank in place. Now 6x3300uF Wurth caps, for a total capacity of 19800uF, compared to original 9400uF, an increase of more than double. Rectifier and transformer seems ok. My ‘test bench’ measurement hinted that this capacity kept ripple very low and kept ample of power in buffer, but increasing more than this would be meaningless.

AHP fuses. Three of them actually, 1,25A and 2×6,3A (one 5A fuse is for lamps, no need for a fancy fuse). 5x20mm. 20 euro/piece. “Icing on the cake”.. Medical equipment and sensitive electronics use special fuses. Why shouldn’t your hifi too? Now, don’t go replace and throw away your original fuses. Unless its blown.

Modifying the power cable. Not necessary in hindsight. A shield was put over the original cable, which was attached to the wall plug’s ground connection. The shield was terminated only on that end. Outside the shield a ‘sock’, or what you call it. Plug is from Supra.
I now avoid touching the Tandberg power cords, unless it is broken, like on the later TR-1000 project.

Tech facts: Why is there a relay that clicks on power up? This relay sits just before the speaker outputs on the back. It protects your speakers if something goes wrong inside the amp. If for example a transistor in the power amp should short, you may find DC on the output and your speaker would be fried, because speakers don’t like DC. There is a protection circuit that constantly monitor the output and shuts it of if there is any Direct Current on it.
Some amps don’t need a relay, in case they have a DC blocking capacitor after the power amp. This is another type of design, like in TR-1000 and Huldra 10, Tandberg receivers before the TR-1040. So the TR-1040 was Tandbergs first Direct Coupled design.

There was another problem – left channel disappeared sometimes. It took me a while to find out why. The protection relay had oxide on the contact plates. I took out the power board and cleaned with deoxit type cleaner. It got better, but not perfect. I did it again, now using just melamin sponge (slightly soaked) – just a tiny cut of if, being very very careful not to damage the relay. Then washing with IPA and letting dry. General consensus among old Tandberg hands is that you should not use sandpaper, not even superfine grit.

I spent more than 200 hours on this project (no doubt it can be done faster, because I am a novice and had to learn along the way). It was really worth it – what a performer!

One proof of how good this receiver really is, is when I lent it to my brother who is a discerning, modern audiophile. We connected it to a pair of Sonus Faber speakers (costing 15.000 euro, not that price matters..). The result was stunning. Dynamic, superb imaging, a clear top end which do not cause listening fatigue, and perhaps most of all – musicality. It makes music sound emotional, organic and human. It has some of the character of a good tube amp. There is something very special with the TR-1040. My brother said it is one of the top three setups he has had in his home ever (without ranking these three), and he has had gear costing 30.000 euro at times.
So considering this, a TR-1040 is a bargain today. It outperforms modern gear costing tens of thousands of Euro.

Intermittent channel problems – a common vintage amp malady

Much later. Right channel went silent sometimes. I suspected the relay again. Traced the signal and it was ok until the relay. The replacement is Omron G2R-2A-DC24. 6,5 euro at Mouser. 24VDC, 5A relay.
The old relay was maybe shorted in the coil, or partly shorted. It measured 156 ohm over the coil, the new relay 1,1k. The original is marked only Dfg 0008. Not sure what it is. The relay should most likely be 1,1k, 24VDC. This type is used on the TR-20xx series as well.

Space is tight under the power supply board and the new relay is actually a little bigger than the original.
One method is to use an IC base like this.

I decided instead to solder wires (Neotech solid core 0,52mm) to the relay legs and carefully bend and adjust them.

Vintage receivers are like vintage cars – they need some care now and then.
Well, new audio gear will too, eventually, just that modern gear will largely be unserviceable, like modern cars.

The TR-1040 still lost right channel intermittently, but less so than before relay replacement, now it just weakened a little. Possibly we had two problems to begin with. Now we have to trace the signal to where it weakens, when it happens. This is the problem with intermittent faults, you have to wait for it to appear. I connected the oscilloscope first to an 8 ohm dummy load, with the signal generator running a 500 Hz tone, then moved the probes carefully to pre amp out (on the pre amp PCB) when imbalance appeared. We had a weak Right channel here – so the problem is in the pre amp. This way I located the problem to the area below.

Interestingly this is the area around Lo-Filter and Hi-Filter 1. The signal actually pass through these two switches in both on or off position. Note that Hi-Filter 2 is located elsewhere and does not pass signal directly. Dirty filter switches can cause problems like this. If you have a TR-10xx receiver with a channel that intermittenly weakens or behaves oddly, this could be the problem and it is easy to fix. I sprayed these two switches with PRF 6-68 (sort of like DeOxit from Finland) and IPA. I also resoldered everything in Right channel in this area (except those components in the on position), including spraying the switches and resoldering them directly after. You won’t need to resolder, just check solder joints. Probably a light spray will suffice (don’t shower the board in electronics cleaner please, a little goes a long way!).

“If you don’t run you rust”, as car people say. Receivers need to be used too.
Since we don’t use the Filter switches often, or ever, try motioning them if you have such a problem.
Tandberg receivers are built to last. Everything can be fixed!

Enjoy your TR-1040 and enjoy the music!