Sansui TU-70 Tuner

[comanche]

I just picked up a NOS   TU-70  ; untouched, still in box, mint, unopened, and unused.
It's been in that box since 1964. The build quality seems pretty amazing. It's a tight little tank.
Not much info on the net.
Anyone familiar with this unit ? Doc ?
It's on the variac, right now.
Besides the obvious way to treat a 50+ year old piece of tube equipment...are there...
Any mods that I should know about ?
Pit falls to avoid ?  etc. 
Design issues ?   
I love the fact that a schematic is included in the manual.
This should keep me out of trouble for at least a week.
Thank you for responses.
Billy

[Natural Sound]

I have one in similar condition. Its a decent tuner but I use a lightly upgraded Dynaco FM3 instead. I think it sounds better in my system. Sadly there isn't much on the FM band worth listening to around here. I mainly listen to a college station on the low end of the band. But that's usually just one day a week for a blues show. Occasionally I'll tune in the local classical station. But that's about it really. The rock stations are heavily processed, are loaded with annoying commercials and generally un-listenable. I wish we had a Jazz station but we don't.

Let us know how you like it. I might break mine out again and play around with it.

Oh yeah, I just remembered. There are a couple of the Japanese tubes that should be changed for better sound. I'll see if I can find my notes.

[comanche]

Thanks Natural,
 That would be great.
 No surprise;   it's loaded with Japanese tubes.  NEC, Hitachi, and Matsushita.

Sadly, Clear Channel and their likes have ruined FM.
However, we do have a few local outlaw stations here in and around  Austin; also a couple of decent public/ college stations.
I will appreciate any help with this tuner. However, I don't know if it can replace the Scott 350. But, it sure is pretty.
Also, I have a FM-3 that I plan to hot rod. Still doing the research. Always looking for good ideas with that project, too.
Thanks for your time.
Billy
 

[Paul Joppa]

Back issue of VALVE has John "Buddha" Camille's FM3 article.

[Doc B.]

And I have Buddha's FM-3.

[Natural Sound]

There really isn't much information on the TU-70 online. My notes don't reveal that many revelations either. The extent of my experimentation was mainly in the audio stage. After doing a bit of tube rolling I found the best bang for the buck was experimenting with different 12AU7's. I tried everything from inexpensive Chinese tubes to high end Telefunkens and Mullards. Ironically the one that wound up staying in the tuner was a black plate Sylvania 12AU7 re-labeled for CONN organ. These seem pretty plentiful and are inexpensive too. My notes also show that I was planing some capacitor upgrades in the audio signal path although I never pursued it all that much. My notes show the values .02uf (off the plate of the 12AU7 (X2)) and .05uf (connected to the RCA jacks (X2)) were the caps I was targeting. I believe polypropylene film types were in mind. I also planned on bypassing the output level pot although in the end I just left it turned all the way up. There are also some caps in the MPX section that might benefit from an upgrade. The tuner section itself is pretty robust. It uses a High-Mu 6CW4 "Nuvistor" tube in the front end that makes it very sensitive and selective. The tuner has potential to be a great performer. I'm surprised there isn't (wasn't) any interest in it on the internet. If you experiment, please share your results here.

As for the Dynaco FM3 there is a bit more discussion. Some of the links I had bookmarked are now broken but I'll include the ones that are still good below. I also have an excellent document in rich text format that I can send you if you are interested. Just send me your e-mail in a PM.

The Dynaco is less sensitive than the Sansui. One of the first things I did was mount a dedicated FM antenna up on the roof. It is one of those 6 element Yagi styles that Radio Shack sold for years before it was discontinued. A friend of mine uses a current model Winegard HD6010 with good results. Unlike the Yagi, the Winegard is omni-directional. So if you have signals coming in from different directions this may help. I found that the outdoor antenna produced much better results than any of the twin lead dipole or rabbit ear solutions. http://www.fmfool.com/ can help you to determine what specific signal conditions exist for your area.

https://sites.google.com/site/mpbarney/dynacofm3
http://www.quadesl.com/refurb/refurb_dynaFM3.html
http://www.audiocircle.com/index.php?topic=62800.0
http://home.indy.net/~gregdunn/dynaco/schneider.html
http://db.audioasylum.com/cgi/m.mpl?forum=tuner&n=4186&highlight=stellavox&r=&session=
http://home.indy.net/~gregdunn/dynaco/components/FM3/index.html

[Natural Sound]

And I have Buddha's FM-3.

You lucky dog. Do you use it?

[comanche]

Thanks
I'm always interested in learning all that I can. I'll PM you.
I listened to the TU-70 tonight. It picks up stations well. It is sensitive and selective.
The sound,however, is .....a little thin. It doesn't have near the depth or bass of my Scott.
It definitely needs something. I have a lot of different 12AU7's. I'll start there and keep you posted.
You are right, of course, no real info on the net. But, I'll contact the FM tuners group and see what they have to say.
(great group of folks)

[Natural Sound]

You have mail.

I forgot about the FM Tuners group. That is an excellent resource. I may go over there and look around too. Haven't been there is a long time.

[comanche]

Ya, those guys are good.
They helped me figure out what my HH Scott Type 315 is.
Hint: There is no spoon.
I'll post about that later..right now ;I need to flip my remastered version of "Amused to Death".
Loving my Reduction...
Billy