Understanding Tandberg TR-1000/1010/1020 Stereo Decoder Alignment Instructions

[vic_c]

Greetings!

TL/DR: Could someone please help explain what abbreviations and weird deviation figures mean in the instructions below. For more detail read on!

I've been working on one of my Tandbergs TR-1020 (pretty much the same as TR-1000 or TR-1010) for the last little while. It's not an easy receiver to align since it has a real IF transformer filter strip, ratio detector and discrete transistor based stereo decoder. No specialized ICs, no ceramic IF filters unlike the rest of TR-10XX and TR-20XX lineup. Just tons of transistors and coils

Front end, IF, and detector alignment is Ok simply following the manual. Only caveat is that the manual doesn't tell one to use a Pi- attenuator of about 20-40 dB when injecting signal into antenna input. And crank-up signal generator output accordingly. This is to avoid RF cable acting as a big FM antenna...

Stereo decoder alignment I'm still struggling with. I get the general idea, but the way desired generator signal instructions are written I just don't get it. See picture, for example:


Step 1 - 67 kHz dev. ca. 60 kHz
What does "dev. ca." mean? What am I supposed to do other than making sure the filter circuit output is the lowest at 67 kHz input?

Step 3 - 19 kHz dev 7.5 kHz
I can tune the circuit to peak at 19 Khz input, that easy. What I'm supposed to do with 7.5 kHz deviation? Sweep my signal 19 kHz +- 7.5 kHz and use XY inputs on my scope just like when sweeping IF filters with 10.7 Mhz? Or something else?

Step 5 - Right 1kHz dev.: 30-40 kHz and 19 kHz dev.: 7.5 kHz
This is the best one! It sounds like they want a pilot signal plus a test tone in the right channel, so basically an MPX encoded signal with dead left and a tone in the right. Great and I can sort of do it but what does 30-40 kHz and 7.5 kHz mean here?

Side note, if I get my right channel signal all the way to 30-40 kHz range (which should not be an actual stereo signal due to 15 kHz cutoff). Then I start observing some strong oscillations in 500 - 1500 Hz range in my output. I can tweak the same separation circuit to keep such oscillations low, but then my separation at 1 kHz test circuit is not it's best.

I recall there were a few AK members who are into Tandbergs and/or have good alignment expertise. Haven't had a chance to ask or comment before, but nice to meet you folks!

Stereo decoder circuit attached too.

Thanks in advance!

 

[vic_c]

Gosh, I just answered my own question. When they say deviation they are referring to the deviation of the carrier RF signal, and they imply that all of this is to be fed via antenna input and RF generator with stereo encoder. I can do that no problem as I'm using Leader 3216 which has a full MPX modulator.

Make total sense say if they say 7.5 kHz dev. it is 10% of 75 kHz, so it's simply the standard pilot signal amplitude they were referring to.

Now while I feel dumb I'm happy to keep an eye on this thread and support further Tandberg alignment conversation, if any.

 

[jdurbin1]

Excellent! Nice to have a fellow Tandberg receiver tech on the forum... and reads as though you already know the TR 10xx tuner better than me. I prefer working on (and owning) the Tr 20xx models and know those tuners (and the rest of the receiver) quite well - the TR 10xx, not so much!

I may tap you for info if I ever get around to restoring my TR200, and doing an alignment on the tuner in the process which I think is probably closer to the TR 10xx series in design.

John

 

[vic_c]

Hi John, yes good to connect with a Tandberg enthusiast like yourself!

Question - with TR 20XX have you found any need to replace uA703 op-amp in the IF section, and if so what did you replace it with? Or are they still reliable in your experience? I have a TR-2060 waiting to be restored, and I was wondering about this part ever needing attention.

Regarding TR-200, that's a lovely front panel design. I peeked in the schematics, in a way it's similar to the lower end TR-10XX range. Although front-end lacks dual gate MOSFET, and IF strip is simpler too. Ratio detector and stereo decoder are very similar.

I won't pretend to know a lot about, but I do enjoy the process and go on little research missions if there is something I don't understand.

What I found interesting with those IF tuned transformers is how the bell-curve of the signal vs frequency sweep reacts to changes in signal strength. I first adjusted them to center at 10.7Mhz using a fairly small input signal. Then I checked at a higher signal and the center had shifted from 10.7Mhz quiet noticeably. Furthermore, IF amplifiers have some sort of "max" level after which center frequency response gets flat. A little difference of the slope on either side of the center makes that plateau rather assymetric as the input signal is increased and it "clips".

So I did my second run of adjustments by varying signal strength repeatedly up and down (say from 20 % to 100% on the tuning meter). And making sure that my response curve remains centered at 10.7 across the range of input signal strength. And also making sure it remains symmetric when it hits that plateue at a high input signal. Two slugs of each IF can work very much together and affect both the left and the right side slope in a rather funny and non-linear way.

There could be debate whats the correct approach, but it made logical sense to me and also this is how ceramic filters behave. I'm looking to get a good THD analyzer next to have an objective spec to judge and compare.

Victor

 

[jdurbin1]

I have not had to replace that IC, but I also have a plethora of various models on hand, some too far gone cosmetically to bother restoring. So, original spare parts - so far, knock wood - haven't been an issue.

Good info on the TR200, thanks... I agree on the cosmetics, there's something I quite like about that one. I'd also be happy to have one of the TR220 models with cassette deck (and/or tt) on the top as well but they appear to have sold those primarily in Europe. I have a TA300 though, same form factor as the TR200 but no tuner. It also has a weak channel, go figure. At some point I'm probably going to have to get some coupling caps etc. on order for the two units.

John

 

[francisleo75]

Greetings!

TL/DR: Could someone please help explain what abbreviations and weird deviation figures mean in the instructions below. For more detail read on!

I've been working on one of my Tandbergs TR-1020 (pretty much the same as TR-1000 or TR-1010) for the last little while. It's not an easy receiver to align since it has a real IF transformer filter strip, ratio detector and discrete transistor based stereo decoder. No specialized ICs, no ceramic IF filters unlike the rest of TR-10XX and TR-20XX lineup. Just tons of transistors and coils

Front end, IF, and detector alignment is Ok simply following the manual. Only caveat is that the manual doesn't tell one to use a Pi- attenuator of about 20-40 dB when injecting signal into antenna input. And crank-up signal generator output accordingly. This is to avoid RF cable acting as a big FM antenna...

Stereo decoder alignment I'm still struggling with. I get the general idea, but the way desired generator signal instructions are written I just don't get it. See picture, for example:


Step 1 - 67 kHz dev. ca. 60 kHz
What does "dev. ca." mean? What am I supposed to do other than making sure the filter circuit output is the lowest at 67 kHz input?

Step 3 - 19 kHz dev 7.5 kHz
I can tune the circuit to peak at 19 Khz input, that easy. What I'm supposed to do with 7.5 kHz deviation? Sweep my signal 19 kHz +- 7.5 kHz and use XY inputs on my scope just like when sweeping IF filters with 10.7 Mhz? Or something else?

Step 5 - Right 1kHz dev.: 30-40 kHz and 19 kHz dev.: 7.5 kHz
This is the best one! It sounds like they want a pilot signal plus a test tone in the right channel, so basically an MPX encoded signal with dead left and a tone in the right. Great and I can sort of do it but what does 30-40 kHz and 7.5 kHz mean here?

Side note, if I get my right channel signal all the way to 30-40 kHz range (which should not be an actual stereo signal due to 15 kHz cutoff). Then I start observing some strong oscillations in 500 - 1500 Hz range in my output. I can tweak the same separation circuit to keep such oscillations low, but then my separation at 1 kHz test circuit is not it's best.

I recall there were a few AK members who are into Tandbergs and/or have good alignment expertise. Haven't had a chance to ask or comment before, but nice to meet you folks!

Stereo decoder circuit attached too.

Thanks in advance!

Hello, can you share with me the service manual? Tks ✌