Stromberg Carlson ASR-444 - Studio 60 series. WOW

[gadget73]

Outside the feedback loop, I'm pretty convinced component selection has a big impact. Within the power amp, not so much. Either way, off-value parts are not going to perform the same as on-value parts for what seems like obvious reasons.

 

[Treyphan]

Outside the feedback loop, I'm pretty convinced component selection has a big impact. Within the power amp, not so much. Either way, off-value parts are not going to perform the same as on-value parts for what seems like obvious reasons.

Agreed @gadget73 ! With the huge selection of components we have today. I just love trying them all! Even if some people don’t hear a difference. It’s worth it to me for the quality alone. I really kinda went bonkers on this 444.

I’d really like to replace the internal wiring, but as I’m sure you know all too well. Man, these SC amps really didn’t make that very easy. I’d have to disassemble the entire front Face Plate. Which would just be to big of a chore right now for me anyway. It’s pretty dang quiet. While better routing would most likely yield less noise. I don’t really hear much at all. Even with 106db K-Horns it’s virtually silent. While the signal runs look like spaghetti, somehow it’s good enough. Too many projects to devote that much more time to this. One of those, “time vs results” deals. So I think I’m good to go on this finally.


Can’t thank @gadget73 and @Tom Bavis enough for their help when I started this. What a great community we all have here!

Another big thanks to Tom for putting together such an awesome SC website. It was certainly helpful. I’m sure I’ll use it much more as I’ve got the SC bug now.

If anyone ever needs help with one of these 444’s PM me. I’d be glad to help if one of the other “Resident SC guru’s” isn’t available.

 

[gadget73]

The stock wiring does look messy, but its electrically very sound. Very few were doing star or star of stars ground systems like S-C did, and not much used shielded wires for signal leads inside the chassis. It makes for a very quiet amplifier, but messy internal wiring. Myself, I can't see the wiring from my chair with the covers on.

 

[Treyphan]

@gadget73 Touché!

Yeah, didn’t mean to make it sound like S-C’s wiring approach wasn’t very solid. The fact they used Star Grounding and Shielded Signal Wire really surprised me when I first saw it.
I get a little carried away sometimes. Like ya said, not like I would see it while listening. Nor do I think any increases that may be had, would be worth it.
Overall, I’m really impressed with the design/build quality. Now if I could just find a set of those co-ax or tri-ax S-C speakers!!

 

[Treyphan]

Well, this will probably be my last post for this thread, unless people have further comments/questions.

I’ve got about 100 hours on the newest parts I installed. I finished all the parts under the ‘tone control cover’, up top. Which made a really nice difference. I used a mix of orange drop, Mallory ‘mustard’ film caps, AudioCap Thetas and nice Metal Film vishay resistors. All the tone controls were also given another thorough cleaning with D5 and a nice follow up with FaderLube to seal/lube them.
I’d still had some issues with a few of the pots. But that solved almost everything. The Volume pot kept giving me just a bit of a problem, with a small amount of scratchiness and cutout. Even after many detailed cleanings.
So I ordered an Alps Replacement Pot(100KAX2) which is a HIFi staple and a killer volume pot, with like 2% tolerance.
While it was a pain to get at, I was able to get the Alps in there, and still save the original pot. Just Incase.
However, the Alps Pot, put it over the edge. The channels being so closely matched allowed the soundstage/image to just “fall into place”. Couldn’t be happier.
Of course I forgot to take pics of the Alps Pot Mod. I’ll take some and edit this post to add, probably tmrw.

This ASR-444 is just a wonderful amp. I’m really happy I stumbled across it. It was quite fun to restore/supe up.

I tried some Telefunken E 80 CF’s in the 6U8 spot and those are the best yet. For me anyway. The E 80 CF was a special 10000 hour, gold pin, low noise tube, a Euro Version of a 6BL8. Which is a sub for 6U8’s. These are stellar, and relatively cheap for NOS/NIB still.

Well, enjoy your Stromberg’s everyone! I know I do

 

[Coryo]

I realize this thread is a bit dated but maybe someone could help out.

So I picked up this one a few weeks ago. No tubes, no info other than it had caps replaced and said it worked 25 years ago. Didn't pay that much just had to drive from Cleveburg to Pittsburg.

Put it on the variac and brought up voltage slowly and notice I wasn't getting any voltage at test points. I start bumming thinking power transformer is cooked. It does smell and had some tar leakage in the past.

I reach out to Tom B and he suggest a couple things to check. Sure enough it was just the breaker that failed.

I'm doing some voltage checks with KLH 17,s hooked up. Absolutely a beautiful sounding amp. If the 17,s sound this good I'm sure it will make my larger systems dance. I put in a quad of some 6L6GB,s I have. Not sure of the year but if someone knows if these are considered black plates please let me know. Keeping the voltage at 110 volts while on test and listen. A recap is in order.

After listening for a while this may be one the nicest sounding amps I have at a lower level of volume. Can't imagine it not sounding as good turned up. Amazing detail, each insturment and vocal just hanging there. The 17,s are sounding more like my old pair of Maggie's MG IIB,s. Thats how good this amp is. Would like to see how it sounds after recap and a quad of 7027,s are put in?

Another question is that I found a broken lead. Black wire with blue marker tape on broken side. This shielded wire carries a ground wire also. It goes back to the balance control switch I believe. I'm pretty sure the broken end goes to the 6AV6 tube, not sure what pin.

Any help on that would be appreciated along with any other info.
Thank you in advance.

 

[psychmonster]

So I’ve read a bit about Stromberg Carlson in the past. Apparently they were a formidable force in the early HiFi days.(1930’s-early 60’s). Though I’d never stumbled across one of their units before.

Well I recently was GIVEN an ASR-444, along with a few other tube amps and about 1000 tubes. The tubes were quite a surprise. Lots of good audio stuff. Most still in boxes. The amps, besides the 444 were a Harmon Kardon HK-20 EL84 mono, which is gorgeous in its copper chassis and tube cage and also a SC Studio 6 7189 pre/amp combo that can be separated at the chassis.

The ASR-444 immediately caught my attention as it was running 4 7025a RCA output tubes. A “suped up” version of the 6L6GC. Which coincedently are the tubes my Mac MC240’s run. I’d hoped the quad was good and I’d be happy with that alone.

I must also mention none of the amps worked. Which is why they were free. So I went at the 444 first. Tested the 7027a’s which all tested great. Then the 12AX7’s and the 6AV6’s, the 6U8’s tested meh, as usual. Replaced those with some RCA blackplates I had on hand. I’ve got a TON of 6U8’s for my MX-110. Nice! I opened her up and inspected resistors, caps etc. nothing looked burned. So I gave all the controls, including the odd circuit breaker, a good Deoxit and cleaning as well as tube sockets and pins. Plugged her into my Variac, and brought her up slow. All the tubes glowed that glow we all love. Could it be? This thing works after sitting idle in a Midwest attic sense the “late 60’s”? Yup, it sure does. Hooked up some period correct Bozak B302a’s(restored Tobin mods) and my Tube DAC and a TD-121. Wow, this thing sounds delightful with all types of music.
I now plan to go through it and keep it. One of the BEST amps I have ever heard. EVER! A full restore will happen soon. As well as a custom cabinet.

For reference I run 2 MC240’s(completely restored with all NOS tele’s And RCA Blackplates) with a restored MX-110z, Thorens TD-124 MKII with SME and a Tube DAC. The Stromberg Carlson hangs with that system. No it doesn’t have quite the power of strapped 240’s, but it’s just wonderfully full, detailed, big soundstage and revealing. With all the tube yumminess too. The high end is glorious. Not etched or fatiguing at all, but cymbals sound so real. I can’t imagine how good this will sound once gone through.

Also got the HK20 to fire up after a quick cleaning. It sounds great too, would love another for a stereo setup if anyone has one? I may use with a third speaker from the center output of the MX-110. Just for kicks sometimes.

The other SC runs a quad of 7189’s, which I only have 2 of right now, someone poached the originals. I think I have a couple hid away somewhere. Won’t take 6BQ5/EL84, which I have a bunch of. So once I find a few more of those. I’ll get into it. It did have two perfect RCA 7199’s and 3 1960 Mullard mC6 Blackburn AX7’s and a 1960 Amperex Bugle Boy AU7. Which all measured super strong and I believe are original with the matching codes applicable to production time. Why someone left those babies is beyond me. The mC6 AX7 May be my favorite AX7, even over Tele’s!

Man, even in 2019 there are valve treasures to be found. Love being “that stereo guy”, people give stuff too! Usually lame 80s/90’s gear these days. But this I why I ALWAYS at least go look. Got my Sansui 1000a the same way, and a TD-124. I’ve told the owner I’ll throw them a bone if I make any $. Wouldn’t feel right otherwise. They didn’t realize what they gave away. Nor did they really care even once I told em. “NBd, you’re doing all the work, thanks”


I can now say, that imo, SC is a force. Get one if you see it! Anyone else currently running Stromberg Carlson tube gear and love it as much as me?My Fisher 500c May be on its way out, with what they get nowadays. This SC isn’t going anywhere.

I just pretty much did a ground up restoration on two SC 220s and with upgrades are pushing a legitimate 20 wpc and I couldn't be more thrilled....also found a sleeper Knight KN 735 that screams in stock form...why fix it if it ain't broken

 

[psychmonster]

I just pretty much did a ground up restoration on two SC 220s and with upgrades are pushing a legitimate 20 wpc and I couldn't be more thrilled....also found a sleeper Knight KN 735 that screams in stock form...why fix it if it ain't broken

 

[gadget73]

I realize this thread is a bit dated but maybe someone could help out.

So I picked up this one a few weeks ago. No tubes, no info other than it had caps replaced and said it worked 25 years ago. Didn't pay that much just had to drive from Cleveburg to Pittsburg.

Put it on the variac and brought up voltage slowly and notice I wasn't getting any voltage at test points. I start bumming thinking power transformer is cooked. It does smell and had some tar leakage in the past.

I reach out to Tom B and he suggest a couple things to check. Sure enough it was just the breaker that failed.

I'm doing some voltage checks with KLH 17,s hooked up. Absolutely a beautiful sounding amp. If the 17,s sound this good I'm sure it will make my larger systems dance. I put in a quad of some 6L6GB,s I have. Not sure of the year but if someone knows if these are considered black plates please let me know. Keeping the voltage at 110 volts while on test and listen. A recap is in order.

After listening for a while this may be one the nicest sounding amps I have at a lower level of volume. Can't imagine it not sounding as good turned up. Amazing detail, each insturment and vocal just hanging there. The 17,s are sounding more like my old pair of Maggie's MG IIB,s. Thats how good this amp is. Would like to see how it sounds after recap and a quad of 7027,s are put in?

Another question is that I found a broken lead. Black wire with blue marker tape on broken side. This shielded wire carries a ground wire also. It goes back to the balance control switch I believe. I'm pretty sure the broken end goes to the 6AV6 tube, not sure what pin.

Any help on that would be appreciated along with any other info.
Thank you in advance.

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6av6 is the tone control amp. A wire disconnected there, either input or output, would kill that channel. If you have sound from both channels either thats not where it goes, or someone has done something odd and jumped something around. Offhand not sure which side the blue cable goes to but it will likely go to one of the two spots I have marked in highlighter here. The 0.01 cap will run from the tube to a terminal strip next to the tube, and the cable would connect there.


You really want to recap this thing. Those paper caps are very prone to failure that causes tube death.

 

[gadget73]

oops, that was the 333 schematic. This is the 444, essentially identical though