TR-2025

One of two Tandberg receivers I was entrusted with by Bromma Loppis (a big antique market/flea market in Stockholm). Let’s see if I can make it work..

Left channel speaker connectors had been taped over. But no channel did work, there was complete silence.

Opening it up. It looks ok, no blown components. Connecting it through my homemade current limiting lamp. Power on. All lamps are dark. One flickers. The current limiting lamp inside glows quite strongly, supposedly it is normal on the 2025.
Measuring the power supplies, the +25V pre amp rail and the power amp rails are ok.

Made my own schematics. Tracing the signals. Problems in both channels.

I took out every transistor in the Right channel power amp and measured it, all of them ok. I suspected one of the power transistors, because maybe the solder joints looked like they had been hot. This transistor measured perfectly however.

Not sure really if Q722 was the problem, or rather it’s solder joint. I resoldered everything in this channel. Then testing it and now this channel is ok. The sound however is generally weak. The other channel, Left, has intermittent problems.

I try to locate the problem with Left channel. Not easy. The volume potentiometer seems to be causing some problem, so I clean it thoroughly, this does not really remedy the problem. I had located the problem to the pre amp and started measuring voltages around the small signal transistors here.

Something is wrong with the transistors in R channel. Specially Q604/606, so I swapped them with the other channel and the problem also switched side. Faulty transistors. They measured ok on the transistor tester however. So I replaced these with equivalent BC149B I had in stock. Now both channels work, but R is a little weaker. There is a lot of problems with R channel, it works for a while and then dies.

I order a set of 50 BC549B transistors. These are of the type that schematics says should be in there, in this unit however they were of another type. These BC147A’s were definitely original. I replaced the suspected ones in the pre amp. Still R channel is weak.

At the same time I continue the recap. Now almost the whole unit has been recapped.

It suddenly become totally silent. The regulator protection lamp died. The regulator did become very hot. It is supposed to be running a bit hot, but this must be too much? The original heatsink is tiny, but I think the problem is that some part of the circuit is drawing too much current. Anyway, I was thinking of a mod which supposedly Tandberg did anyway on later models of the TR-2025, they moved the BD165 regulator transistor to the rear chassis instead of mounting it on the board (at least I have heard about it, never actually seen it). I decided to to the same.

I also replaced the regulator lamp, a Soffitte 6×36 mm 12V 3W. Actually I first bought 6x31mm and they were just a tiny bit too small. I wish there were somewhere in between in size. I bought them from Legantec in Germany and they were nice and let me exchange them, for the 6×36 mm. You can see the long Soffitte lamp to the left and in the middle in the photos below.

Next, I took out and measured the other transistors in the pre amp. Q607 and Q608 measured like diodes! The unit delivers but only amplifies with a factor of about 1:1,2.

After replacing all the transistors in the pre amp, the TR-2025 delivers a clean 32W into an 8 ohm load.

So it works, it seems. But there are other problems. First, the volume pot must be bad, because there is not equal volume on the channels, specially on lower volume. It cant be anything but the volume pot, signal tracing led me to assume this. So either I have to take it out and clean and inspect it, or try to find a replacement. I had a feeling this pot was worn out and a replacement is better. I had to study the Loudness circuit and try to find a pot with four legs, the normal pot in, out and GND, plus a center tap for Loudness.
Actually I found one on ebay, a NOS 25k Noble pot with center tap at 4k. It may work. I ordered it. Also ordered some backups from Audiophonics.fr. They are supposed to be Alps pots, but more likely are not really Alps. Looks like good quality anyway, maybe.

While waiting for the new old stock pot and the new pots I did some small fixes. A new Y-rated 0,01uF capacitor on the incoming power line. I had one of these old Rifa caps explode inside my bench power supply one day. It didnt destroy anything but it sounded like a gunshot and my ears were ringing and it blew a fuse. Better avoid this happening to a future owner of this magnificient TR-2025.
This is not my TR-2025, I am just restoring it for Bromma Loppis fleamarket/antique dealer. I had not expected it to be this much work. This is not a repair, this is a full restoration of a unit in bad shape. Very interesting and fulfilling job though.

Doing some work here and some there, maybe my method needs more of a strategy. Replacing some caps still, and finding another with an expired best before date.

So we have a working TR-2025, with a faulty volume pot, a faulty FM pointer light, a cable with a dirty switch on it, because the on/off switch was stuck so an earlier owner solved this by inserting a lamp switch on the cable.

The on/off switch that was stuck, I fixed that easily, with the absolutely fantastic, fabulous SGB Contact Grease Treatment! Thank the Hifi-Lord for this product!

On to the pointer lamp.

And the panel lamps. They were all burned out. Ordered new, from Elfa.se, if you live in Scandinavia you can buy them there.

The R channel intermittent, odd volume problem caused me lots of confusion. Everything in the pre amp was resoldered. I measured and cleaned, cleaned and cleaned.
But no, I took out the pot. Time to try out the replacements.

Well, the “Alps” pot fits in, barely, but it is 50k, not 25k like the original, and I will try out the NOS pot instead. It may be possible to fit in a new pot by using cables to the board and screwing it on to the panel, somehow. Not sure how to fix it to the panel, and I think the NOS Japanese Noble pot may work anyway, it is much smaller. Lets see.

The leg out configuration was wrong, so I had to reconfigure the legs by soldering on new legs and running them to the right position. I used old cut of capacitor legs.

The pot in place, and it works! But there is a problem, it is the wrong kind of axle, as you can see on the other pots. I found this really smart solution! A potentiometer extension kit from Audiophonics.fr !

However, with this axle extension, I still would have to adapt it to the Tandberg knobs. It solved only one end of the problem, so to say. I decided to try to “lathe” the other end. I have no such equipment and have never done anything like it, but I used a power drill with variable speed and a Dremel. Then another power drill. On the Dremel I used a cutter, to cut the axle in length, and then a grinder to sand down the 6 mm diameter axle to 3,9 mm. I also used a sanding lamella disc for the final polish, with a power drill on high speed.

But it was not good enough, the axle was not straight. I made two more attempts. The last one was ok, the axle is straight. It took me some time to make these.

The new pot in place. It has detents, clicking positions that is, which the original had not. But it is ok, it works fine. The problem with the weak channel was indeed the volume pot, the TR-2025 now works perfectly!

Cleaning, of course, this unit was grossly dirty. I did that before I put back the panel as above. Using just mild dish washing detergent, a brush for potatoes, a toothbrush and a microcloth.

In the front, between the aluminium panel and the board is a plastic sheet. I guess it stops light from the scale and indicators above to shine through where it should not? Anyway, I cleaned it and attached double tape to fixate it.

There was a bit of hum. Not good. But easy to fix, the new volume pot did not have the ground connection to the housing that the original pots have in their chassis “holder” that attaches to the board. This was remedied with a connection to ground.

Then adjusted bias. Checked the output. Everything is ok.
It seems this restoration was successful so far. Lots of work. The wood panels remain.

I was considering to sand them lightly. But hesitated, was it really necessary? Maybe not. Instead I cleaned them. On the top there was some ghastly grime, it washed off but left the wood dried and damaged looking. How would my own oil mix do on these? I mixed linseed oil and beeswax, just that. It was a mess, a hideous mess! I mixed in far too much beeswax. It left the surface covered in a matte white layer, looking stained. What to do. After trying several failed methods to gently strip off the wax I took to the heavy artillery, 80% vodka. It actually worked well, applied on a cotton pad, gently, wiping and polishing off the wax, it did not damage the wood and left some of the earlier applied oil but took of the surplus wax.
I then mixed lighter and lighter versions of the linseed/wax mix and came up with the right proportions. One more layer of that and the panels are alright. They now look great!

This completes the restauration.
First, before restoration.

Then after restoration.

Pretty not only on the outside, but the inside got a big overhaul. Rebuild of the pre amp, new electrolytic capacitors everywhere, new Y-rated cap over the trafo, new volume pot, new pre amp power supply regulator and moving it to chassis, new lamps everywhere, repaired power cord, cleaning, adjustments and wood treatment.

Last thing I did was to clean the internal cable shoes and pins. There are quite a few of them, as in many Tandberg receivers. Considering how dirty this was when I got it, it seemed like a good idea to carefully clean these internal connectors. I did it the usual way, using mini toothbrush, pipe cleaner and cotton ear cleaning “things”. Using deoxit type spray, washing with IPA and waiting 24 hours before reconnecting.
Then did a listening comparison with the Luxman L-210 which is just finished too. I expected the Luxman to be more open and transparent, but not so, the Tandberg has equal airiness and lightness, although they are different in this aspect. The Luxman is perhaps ‘colder’. My impression is that the Tandberg is livelier and has more meat to the sound. Again, the Tandberg has that “sparkle” that is so hard to describe. They are both direct coupled designs so I thought it would be interesting to compare them and expected them to be in the same family soundwise so to say, and maybe they are but probably 10 years or so separates them.

Have to return this to the owner, the antique shop. I will be sad to hand it over, will miss it.

It sold on a Swedish auction site. It went for about 270 euro. Too cheap, an absolute bargain considering it had new parts for 120 euro and I spent 56 hours on it.
Well, I liked it so much that I bought myself a TR-2025 and restored it. You can read about it here: https://tandbergista.home.blog/tr-2025-2/