Tandberg 3006A

[feds27]

My latest project is a filthy 3006A. My current setup is a Tandberg TR-2080 driving a pair of Tandberg Studio Monitors. I’m debating recapping the Studio Monitors as some of the caps aren’t measuring to spec and the crossover has a Frako cap on each channel. Anyway, I’ll open a separate thread for that.

As for the 3006A, it was listed locally and I got it cheap. I figured as a long as I can get it tuned up I could use it with the DIY Pass/First Watt B1 buffer I built a few years ago. I had tried the B1 with the amp section of my TR-2080 and really liked the way they sounded together.

I’m afraid to fire it up. I’ll probably remove the FETs and regrease and replace mica before trying to fire her up. I’ll have to remember to use a dim bulb tester too.

Out of curiosity, can the FETs be tested in place? Would like to get a feel if they are working before digging in.

Here are some pics.

 

[jdurbin1]

You should certainly be able to tell if any of them are shorted, but given your correct thought about removing/regreasing I'd just test them off the board.

With that serial, make sure you reference the later zero feedback version schematics: http://sportsbil.com/tandberg/tpa-3006a-circ-align.PDF

That's a pretty typical-looking 3006A IME, don't see any obvious signs of someone working on it before and they are notorious at hoovering up dust like that.

I have a cap list that includes a specific cap recommendation from an audio designer for upgrading those input coupling caps (the big red blocks), if you're interested. I don't normally go the full recap route myself but a guy had me go through a pair of these a few years ago based on this designer's suggestions to him, thought they sounded good afterwards.

John

 

[feds27]

Hi John,

Thanks for replying to the thread. I’ll follow your advice and will pull the FETs to measure and regrease before firing it up.

Are there any parameter values that are important when measuring the FETs? Do they need to measure a certain Idss? What sort of procedure should I follow? And we’re these matched at factory?

I noticed the brochure says metal film resistors and polypropylene caps were used in the signal path so that’s great. If you don’t mind sharing your upgrade list I’d be interested in seeing what others do. Also, the TR2075II and TR2080 I have use awesome Siemens power supply caps. Are the large Elna cans in the 3006A special? Do they tend to go bad? Thanks.

 

[jdurbin1]

They were matched, and you want to put them back in the same locations they came out of just as a precaution. It doesn't look like they've been removed to me, so other than the cleanup and reinstall, I would just check each one with an appropriate tester to make sure there aren't any obvious issues.

I only replaced the electrolytics, and that pair of big film caps on the inputs of either front end board. The owner said he was told the originals had a bit of a dark tonal quality, ymmv as would mine. The ones I did had blue parts there, so possibly a different maker than in yours. This pair were around serial 2000 and 2800 roughly so a bit later. Yours is pretty early on, with the transition from global negative feedback to feed-forward happening after 0970 serial per the manual cover.

The big Elna PS filter caps are very good on these, never seen bad ones so far. In fact, an acquaintance of mine overseas recently bought the four leftover caps I had saved from this project and put them to good used. I did replace them in the pair I overhauled purely because the owner wanted that and for that I used matching dimension Nichicon KG series parts from Michael Percy Audio. Worked out well but it was a bit of armwrestling to get them to install with the OEM screws and brackets etc. where the harnesses connect to the caps. The rest of the replacement caps were either Nichicon audio series parts or Panasonic FC. I have the file in Excel format with embedded links and can email it, AK doesn't support an upload in that format and my pdf-creating SW is currently not working.

The input coupling caps were replaced with ASC 5uF/100V metallized polyester (the originals are 4.7uF as I recall) and I want to say I found those at Allied Electronics, but again those were this other guy's choice and you could certainly sub a number of different highly regarded types in that application if you wanted to.

John