Finished repairing Tango 211 amp

For the past two years, I've been slowly working on refurbishing a Tango 211 amp that my wife inherited. Yesterday, I completed the work, turned it on, and (to my surprise) it worked! The moment music came out was exhilarating. Here are pictures of the amp before the work:





The amp was in pretty bad shape both externally and internally. All the caps were leaking, the diodes no longer worked, some resistors were blown, and some were out of spec (I attached a close-up of one of the sections). The worst and most complicated was the B+ section in the upper right corner. This is the area that sites beneath the can caps pictured above.

Fortunately, I found the schematic. I broke the amp up into 4 quadrants and started working on one at a time. The top left section (the 'small signal' section) was not in that bad of a shape. I replaced all the caps there (in fact, I replaced every cap in the amp) and some of the resistors. The lower-right section (where the power transformer sits) was also OK except for the diode and some bad wires due to deteriorated solder joints. The other two section (lower left and upper right) I replaced completely essentially ripping everything out including the terminals and starting over. Planning the upper-right section was most complicated and had to be done in 'layers'. First the can caps, then all the wiring, then the resistors, then the diodes for the doubler and capacitors. The new can caps are TMC Audio 100uF 600V caps that my wife got me from Akihabara on a trip to Tokyo. Here are photos of the amp after the repair:






The last four joints were the diodes and white caps above. Then it was time to test it. I was quite anxious and got with a friend on the phone who is much more knowledgeable than I am (which is not saying much ) I connected the amp to a Variac and slowly lifter the voltage. I tested the bias on the 211 grid but I was getting 0V the whole time. Then I realized I was testing VAC (duh). Once I switched to the correct setting on the multimeter, I started seeing negative bias voltage as expected. Variac is now at 100V and I tweaked the bias to -56V as required by the schematic. Plate voltage was at ~950V. OK, next is connecting a source. No music. Since voltages were correct and there was no smoke, my friend asked me about the small signal tubes I'm using. I admitted to using old tubes just in case, and he asked me to replace the 12AX7 tube. Sure enough, that tube was dead. I replaced it and ... music! Here's a picture of the test setup:



I forgot to mention. This amp was first built in 1977, and it may not have been used for ~20 years. It was the amp my wife remembers listening to as a kid all the time. I had also found some of the replacements parts in my father-in-law's components box. We also suspect that he designed or participated in the design of the circuit since the schematic has his name on it with the year 1977. In refurbishing, I tried to keep as much of the original work as possible just in case my father-in-law was the one who built it. I feel that worked out well in making the project feasible and keeping with the original spirit of the amp (see the second photo after the refurbish). You can imagine the elation when it worked.

Not all is done though. The pots are waaay too scratchy, so I should replace them or eliminate them. There is hum, but I haven't tweaked the 3 hum pots yet (there's one for the 12AX7 tube).

Cheers

 

Congrats. What an epic and awesome project.

 

A really great rebuild on a classic amp.

Looks like it could be an original DIY effort by your father in law, using top of the line TANGO iron. Not aware TANGO made complete amps. His layout and point to point soldering is textbook perfect. It should sound exceptional.

Thanks for sharing!

 

After the initial test, I only listened for a short while. Even with the crappy speakers, treble and mids sounded clear, natural and focused. The amp drove the speakers with authority. These speakers lack resolution and bass though. I'm in the process of replacing the FE103En in my OBs with the FE108Sigma and I'll test again. In the mean time, I want to re-adjust the bias for the pictured VT4C tubes (I was testing with Chinese tubes), and I want to tweak the hum pots. I'll post back when all that's done.

 

I made a few more changes to the amp. First I re-did all voltage measurements with the VT4C tubes instead of the Chinese 211 tubes. The amp measured very close to the notes on the schematic. Now the plate of the 211 tubes was receiving 985V. One problem I found is that a 350V rated cap had 335V across it. That makes me uncomfortable so I replaced it with a 400V rated cap. The slight problem is that the new cap is radial whereas the original caps and all the ones I recapped with are axial ... it doesn't look as pretty but at least I have some priorities straight:



Next I got rid of the volume pots and replaced them with 100K resistors to ground, and I re-routed some wires (the new white ones in the pic below) away from filament supply wires. The small signal wires are taken from CAT5 cable:



Taking out the volume pots resulted in more resolution. The pots in there were cheap and so old they made horrendous sounds when being moved at low volume. Here's the amp from the outside without the volume pots (plugged with some rubber grommets), new 12BH7 tubes, and an IERC shield covering the 12AX7. I'm not sure the shield does anything, but it looks pretty



As for the sound, one has to keep in mind the whole chain, but the amp drives speakers with so much authority (I'm not sure how else to put it). It is powerful and engaging (of course I love it because I am extremely biased here).

The one thing that's slightly bothering me is a buzz that I can hear from the speakers when music is not playing (not hum ... tweaking the hum pots got rid of the hum, but the buzz was not affected). I thought initially it had to do with the (positive?) feedback loop from the cathode follower to the 12AX7, but removing that loop resulted in a ton of noise (I tried it when I was re-routing the wires). It could be the power, or the step down autoformer. While it's not audible when playing music, I'd really like the amp to be ~dead quiet when no music is playing. I've reached the limit of my debugging so if anyone has any ideas, please let me know.

 

Thanks for posting this epic rebuild, thoroughly enjoyed reading and re-imagining the journey. Well done..dB