Stromberg and Carlson ASR-120 - Replacement transformers?

[txtune]

Much neater IMO.

Will do, what about the yel/blk coming from the PT? Put a lug on it and bolt it down too?

Glad I invested in the solder sucker gun!

[sluckey]

Ain't no yel/blk coming from the PT.

[txtune]

Ain't no yel/blk coming from the PT.

Red/yellow is what I meant to say. Put a lug on it and place it under the keps nut with the green wire and brown resistor lead?

[sluckey]

Many ways to skin a cat.

[txtune]

Many ways to skin a cat.

Got it, I will go ahead and land the red/yel at the chassis ground with the others. Try to keep them as consolidated as possible.

[sluckey]

Crimp ring lugs are fine but I prefer these solder lugs...

     https://www.tubesandmore.com/products/solder-lug-6-or-8-hole-locking

     http://sluckeyamps.com/hammond/closeup.jpg

[txtune]

Crimp ring lugs are fine but I prefer these solder lugs...

     https://www.tubesandmore.com/products/solder-lug-6-or-8-hole-locking

     http://sluckeyamps.com/hammond/closeup.jpg

I have some of those, that would look much better. I will redo this in the morning.

[sluckey]

Looks good as is.

[shaun]

I'm obviously a bit late to the party, but as I just redesigned a Stromberg Carlson, I thought I'd throw in my 2cents worth.

Using the original transformers and chassis, I redesigned the unit as a simple stereo SE amp, almost like a pair of Champs, with a 12AX7 in the preamp stage followed by a TB Princeton style tone stack, followed by a 12AT7 PI. Then, with the JJ6V6S power tube for each amp, I had 7 tubes total, including the 5U4 rectifier. I also added a simple balance control just before the power tubes. Then I added a bluetooth input for stereo audio.

I found it worked quite nicely, but I couldn't get rid of distortion in the speakers. After much head-scratching, I changed the old alnico speakers for some old Eminence ceramics, and the distortion disappeared - almost. (I like alnico, but the older magnets apparently loose their zip, and the result was distorted sound.)

Trouble-shooting the distortion: The OTs measured different passive impedances, and each side sounded different, so I knew they were no longer a balanced pair (if they ever were:). So I screwed around with replacing them, first one side, then the other. I used Hammond 125CSE trannies from Tubes and More. They were much less expensive than Ultralinear audio trannies, and while they may be designed for an instrument amp, the specs are good. When I replaced the weaker of the original OTs, the sound improved on that side, so much so that I then realized that the side using the remaining original tranny still had distortion. So in went a second 125CSE, and the thing is now really singing. And very loud for a small amp. JJ6V6S has a max dissipation of 14w, and I have it biased down a little to around ten watts per side. It's really thumping.

I love re-using old gear, but I must have rebuilt that amp a dozen times, trying to clean up the sound. Lesson learned.

I have found something interesting about SE stereo amps, which also has me guessing. It is easy to exchange the OT leads on a mono SE amp when we get NFB howl. But I have found - having rebuilt this amp so often - that one side is usually okay, but the other side howls. The problem that arises is that I cannot change the howling tranny's leads without incurring stereo phase cancelling. I have been unable to find anything online that deals with this issue. I guess it doesn't pop up too often, but if anyone can help me out, I'd be one happy camper.

Best to all, and Happy Thanksgiving.

[sluckey]

The problem that arises is that I cannot change the howling tranny's leads without incurring stereo phase cancelling. I have been unable to find anything online that deals with this issue. I guess it doesn't pop up too often, but if anyone can help me out, I'd be one happy camper.

Flip the two wires at one speaker cab.

[txtune]

Looks good as is.

Thanks Sluckey, I may redo the green wire... I don't like how it's pulling away from ring lug. So long as the attachments look good, I will clean it up and solder it in place and see what happens when I turn it on.

[shaun]

Flip the two wires at one speaker cab.
[/quote]

OMG. As simple as that. Thank you Sluckey!

[txtune]

...I just redesigned a Stromberg Carlson...

Do you have any photos you can share? I am interested to see other ASR-120s.

Have you seen this blog?

https://origaminightlamp.blogspot.com/2020/04/stromberg-carlson-asr-120-stereo-tube.html

https://origaminightlamp.blogspot.com/2020/05/stromberg-carlson-asr-120-stereo-tube.html

[txtune]

Looks good as is.

See attached. Last look before I fire it up. Does everything look correct? I know it's not neat...

[shaun]

Thanks for the blog link, txtune. Very interesting.

I will put some photos together at some point; documenting my builds is probably my least fav part of the process, but it has to be done for learning purposes. And so I don't forget what I did:). But what I ended up with looks nothing like that clean machine in the blog. Your work looks fairly neat, as far as I can tell.

I usually fire up an amp for the first time using a variac style transformer, bringing it up to about 70vac for a few minutes. Then, if nothing smokes or crackles and pops, or hums too loudly, I'll bring it up to 120vac before checking voltages.

Good luck with it!

[txtune]

Your work looks fairly neat, as far as I can tell.

Are you sure you are looking at my work. 

Thanks! I look forward to comparing notes and photos.

[shooter]

now the hard part, which song to play 1st 

[txtune]

now the hard part, which song to play 1st 

[txtune]

No more humming noise! Also, no fire or smoke!! 

The sound is extremely flat. This time around I had it connected to some larger speakers, Klipsch Heresy model to be exact... not sure if that could be an issue.

[shooter]

all the EQ has to be done "up front", i would start there.


does it get loud?  left and right side ~~~ =?  one side "flatter" than the other?

[txtune]

all the EQ has to be done "up front", i would start there.

Up front??

does it get loud?  left and right side ~~~ =?  one side "flatter" than the other?

It will get loud. Both sides are equally flat.

[sluckey]

No more humming noise! Also, no fire or smoke!! 

The sound is extremely flat. This time around I had it connected to some larger speakers, Klipsch Heresy model to be exact... not sure if that could be an issue.

I'd say you're done. It's supposed to sound flat. It's only a power amp. You need a stereo preamp to add the good stuff.

[shooter]

3/4 my music is digital, computer stored n played.  took me some time tweaking the music player to get the EQ the way I liked.  Even after that I wasn't happy with bass, so I split the signal and fed mono to a SS bass amp driving my Altaic Lansing 15".  my Klipsch bookshelf's run the stereo n we're all happy   

[txtune]

Does this tuner from the ASR120 have the preamp built into it?

[sluckey]

Does this tuner from the ASR120 have the preamp built into it?

most likely

EDIT... Let me clarify. There is no preamp on that SR-130 tuner chassis. The tuner has a high enough output to go through a passive tone control to drive the ASR-120 power amp. And the phono input to the tuner is also high output/poor quality ceramic pickup that's also able to go through the passive tone controls to drive the power amp.

Do you have the tuner chassis? If so and you want to use it you will have to rewind back to the point where you removed that multi-pin plug and wires. The tuner was powered by the power amp. IMO, you are way past the point of no return. I sure ain't up to any rewind. I would forget about that tuner and look for another tuner/preamp that can plug into the RCA jacks you installed.

[sluckey]

Reviewing all your pics and I just spotted an error you made long time ago when you were installing the RCA jacks and input caps. You put 470Ω (yel-vio-brn) resistors on the original input jack. Those resistors should be 470K (yel-vio-yel)

[shooter]

look at page 1 reply #41, the "extra credit section"
you'll see 2 black arrows for IN, the plug on right is the OUT to the PA section you have.
you'll have to "untangle" the rotary switches, i did my time with them while you were eating Cap'n crunch n watching sesame street 

[txtune]

i did my time with them while you were eating Cap'n crunch n watching sesame street 

 

[txtune]

Reviewing all your pics and I just spotted an error you made long time ago when you were installing the RCA jacks and input caps. You put 470Ω (yel-vio-brn) resistors on the original input jack. Those resistors should be 470K (yel-vio-yel)

The two in these pictures?

[txtune]

I would forget about that tuner and look for another tuner/preamp that can plug into the RCA jacks you installed.

I thought about it some more and came to the same conclusion. This project is enough for me as is.

After connecting a very basic pre-amp to the RCA jacks, the treble must be turned to 25% and bass to 100% for the music to sound 'normal'.

[shooter]

then you're there, the dial goes to 10, it sounds normal, what more do you want 
i'm using the non-tone control version of your pre to drive my 20yr old powered computer speakers.


do an experiment;
connect your meter, set to VAC, across one speaker
find an annoyingly long "held note" and loop it, or just hit play over n over
try and "ballpark" an average reading while that's playing max volume use just your amp, no pre

[sluckey]

Put the correct resistors on the input jack and you may like it better. Most likely be louder too.

[txtune]

Put the correct resistors on the input jack and you may like it better. Most likely be louder too.

Will do. Thanks for pointing this out!

I am not sure what that connection point was for, where the resistors and caps connect... it's not being used on the top of the chassis any longer. I was thinking a small terminal strip, would be a cleaner place to land those wires, caps, resistors... it would also free up that opening in the chassis for something else down the road.

[txtune]

then you're there, the dial goes to 10, it sounds normal, what more do you want 

heh ... I will put the meter on it and let you know what I find. What am I looking for?

I still have the caps left from the 'kit' I purchased early on. They replace the six 400v film caps on the board toward the front. Is that an 'eyelet' board? What would be a suitable replacement material to rebuild that board completely? Could I use a turret board??

[sluckey]

I am not sure what that connection point was for, where the resistors and caps connect... it's not being used on the top of the chassis any longer.

The audio output from the SR-130 tuner connected to that 3 pin socket.

[shooter]

since you don't have a scope or sig-gen, we're cheating.
if you take the Vac value, square it, then divide by 8 = very approximated power out measurement

[txtune]

The audio output from the SR-130 tuner connected to that 3 pin socket.

If I moved everything to a small terminal strip, per the attached drawing, could I do away with that 3 pin socket?

[PRR]

Can be simpler?

[txtune]

Can be simpler?

Nice! I left out one wire though, the white wire coming from the 'board' ... it is tied together with the chassis ground and the ends of the resistors. See attached.

[sluckey]

Don't forget the cap and resistor must connect to pin 7. Solder the white wire directly to that bent up chassis tang.

EDIT... THE RESISTOR VALUE IS 470k.

[txtune]

EDIT... THE RESISTOR VALUE IS 470k.

Updated drawing.

[txtune]

Don't forget the cap and resistor must connect to pin 7. Solder the white wire directly to that bent up chassis tang.

EDIT... THE RESISTOR VALUE IS 470k.

It sounds a LOT better with the correct resistor. Thanks!

I really want to redo the circuit board. Would you use a turret board and start over?

[sluckey]

I'd get some mineral spirits, denatured alcohol, and a variety of small brushes, ie, tooth brush, acid brush, 1" paint brush, etc. and clean it. That's all.

[txtune]

I'd get some mineral spirits, denatured alcohol, and a variety of small brushes, ie, tooth brush, acid brush, 1" paint brush, etc. and clean it. That's all.

Would you not replace the caps?

[sluckey]

I would not.

[PRR]

....Would you use a turret board and start over?

No.

[txtune]

I'd get some mineral spirits, denatured alcohol, and a variety of small brushes, ie, tooth brush, acid brush, 1" paint brush, etc. and clean it. That's all.

What is the best description of the board on this amp? Is it simply referred to as the 'circuit board'? What material would you guess it is made of?

The amp ran all day today, connected only to the FM tuner and a pair of Heresey speakers.  All of the Stromberg Carlson tubes are still working, as best I can tell. The tubes may not be 'original' from when my grandfather purchased the stereo in the 1950s, but they are all SC brand. 

I get where you are coming from - 'don't fix something that ain't broke'. So I won't... I would like to clean up the wiring a bit and will try to gently clean that board off without removing it.

What is the goo that has run across the circuit board and, also, what is the wax looking substance that appears to be 'growing' on some of the wires like mold?

[PRR]

...All of the Stromberg Carlson tubes are still working, as best I can tell. The tubes may not be 'original' from when my grandfather purchased the stereo in the 1950s, but they are all SC brand.  ....

Stromberg Carlson never sold tubes over the counter, certainly in the period this amp was made. Those were installed at the factory. They were not made by S-C: every hi-fi maker contracted with the big 5 tube makers for own-logo tubes.

[txtune]

That's all the more impressive if these tubes are original.

[shooter]

Glad you're clicking along, I landed in your state, it's FRIGGIN colder than MI!!!  the upside I landed in a place time forgot, no cell/WIFI for 30miles in ANY direction!!