My first tubes! C-J ASR-433 and SR-455A

[Metalsmith]

My first tubes! S-C ASR-433 and SR-445A



So, my usual Craigs hunts have paid off with my first tube integrated and tuner for a paltry sum! While I have most of the parts I need to put together a Sansui 1000 based amp, I have had to turn to my dads custom KT-88 monster and DQ-10s to get a tube fix up till now. Hopefully after a small amount of work and a hunt for output tubes in my dads stockpile that will soon change!

I present to you, my new friends the Stromberg-Carlson ASR-433 Integrated and SR-445A Tuner.







The shop needs a good cleanup, then they shall get put on the bench and see how they perform as is as they have supposedly been used and recently, if I am impressed the Integrated may live in my system until I have one of my receivers that are in que buttoned up.

Both face plates are immaculate as well as all but one knob, the tuner has one lense out of place but that should be simple enough to put right, it wont see much use until I manage to find a multiplex adapter anyway. I plan to do a full recap in the near future either way, and will even consider a few mod's as I will most likely never have use for the Ceramic and Tape Head inputs. I will keep you guys updated!

 

[gadget73]

The ASR-433 is a surprisingly good sounding amp for not looking all that impressive. I will warn you that almost all of the resistors in mine were way off tolerance, so be prepared for some overhaul work.

The tape head input you should be able to make full-time phono without much trouble. That one is different than mine, but I believe the EQ switching is a 100k resistor switched in or out of the circuit, or something as similarly basic. Mine has a phono/tape eq switch where yours has a channel reverse.

 

[elliott66]

Nice find! Let us know how it goes.

 

[Metalsmith]

Thanks for the input and experience guys! I'm very excited.

I have been going through every ones impressions and the schematics I have found and think I have made some decisions as far as what direction I will take it. i will probably just go for a stock rebuild with a few slight modifications to improve performance. I've been planning on building a decent quality external input selector, and experimenting with a few stand alone phono preamps so this will likely be an excuse to get to that.

I have a list started of what caps I will be needing at least, probably have most parts I will need on the shelf. I'm not looking to spend a fortune but as simple as this circuit is I'm sure component selection can have some impact. As far as power supply caps go, I'm thinking of picking up a JJ 40/20/20/20 multi for up top and maybe a pair of 220uf ~400v caps for the doublers, any favorite choices for these positions?

 

[elliott66]

For the doubler caps I usually use 330uf Cornell Dublier 'snap-in' low ESR high ripple. You could use 220 and it would be fine.

Mouser 5985-380-450V331

 

[jaymanaa]

Hard to find them that clean.

 

[Jcricket]

so you are the dog that beat me to that unit and tuner.
Good grab for sure!!!!!!!

The ASR433 is one of my favorite amps of all the vintage tube units I have heard. When properly restored, these amps kick butt.
Good luck with it.
mark

 

[Jcricket]

So, my usual Craigs hunts have paid off with my first tube integrated and tuner for a paltry sum! While I have most of the parts I need to put together a Sansui 1000 based amp, I have had to turn to my dads custom KT-88 monster and DQ-10s to get a tube fix up till now. Hopefully after a small amount of work and a hunt for output tubes in my dads stockpile that will soon change!

I present to you, my new friends the Stromberg-Carlson ASR-433 Integrated and SR-445A Tuner.







The shop needs a good cleanup, then they shall get put on the bench and see how they perform as is as they have supposedly been used and recently, if I am impressed the Integrated may live in my system until I have one of my receivers that are in que buttoned up.

Both face plates are immaculate as well as all but one knob, the tuner has one lense out of place but that should be simple enough to put right, it wont see much use until I manage to find a multiplex adapter anyway. I plan to do a full recap in the near future either way, and will even consider a few mod's as I will most likely never have use for the Ceramic and Tape Head inputs. I will keep you guys updated!

good luck finding an SC multiplex adapter. I have only heard of one and Tom has it.

 

[Metalsmith]

For the doubler caps I usually use 330uf Cornell Dublier 'snap-in' low ESR high ripple. You could use 220 and it would be fine.

Mouser 5985-380-450V331

Good to know, I may spring for some nicer coupling caps but was hoping electrolytic would be just fine for this use.

Hard to find them that clean.

Both pieces are in wonderful shape, the first pre 1980 pieces I've managed to find without some major scuff or scratch on the face.

so you are the dog that beat me to that unit and tuner.
Good grab for sure!!!!!!!

The ASR433 is one of my favorite amps of all the vintage tube units I have heard. When properly restored, these amps kick butt.
Good luck with it.
mark

I was afraid I'd hear that I beat another member to these! The guy said he had other interested parties so I rushed over as soon as I could get cash in hand. If ever I decide to part with them I will make sure you are the first to know. And you're completely correct about the multiplex adapter, nearly unobtainium. I may try a Fisher if I manage to get ahold of one once the tuner is cleaned up and in rotation, if not I don't listen to much FM so a little mono wont kill me.

 

[analog addict]

Make sure you have the right schematic. There are several versions floating around, but most amps have an actual paper copy glued to the inside of the bottom plate

 

[Metalsmith]

Make sure you have the right schematic. There are several versions floating around, but most amps have an actual paper copy glued to the inside of the bottom plate

Good advice, and I made sure to take a nice high res photo of my amp's schematic today. Opened up the integrated for the first time today to assess the situation inside now that I have flat spots in my shop again. One coupling cap has self immolated at some point, and there are quite a few leakers, so definitely time for a refresh. One output tranny has leaked some wax, not a good sign I fear. I have a quad of Tung Sol EL84s on the way, once they get here I may bring it up on the variac to see how bad off it is, then I will start ordering parts.



And a high res photo of the schematic:

 

[gadget73]

just looking at the pic, I can tell you yours is a little different than mine was. I had PECs in the phono stage, which had failed. Yours looks like discreet components. Someone has also added a fuse in place of the original circuit breaker it looks like. Probably not a bad thing. I always thought just having the circuit breaker was smart. Lots of gear from that time period had no fuses, breakers, or anything else to offer any sort of protection in the event something went wrong. You just had to hope the breaker or the part would burn out before the whole thing went up in flames.

 

[nerdorama]

In mine the large brown power caps were mostly shot based on my ESR meter. I would think carefully about bring it up in any manner until the power supply is rebuilt.

Great looking units. It's funny about different visual tastes. I think they are really cool looking. A friend of mine can't stand them.

John

 

[Metalsmith]

Well, after waiting for parts to come in and the usual interruptions from life a good bit of progress! Went ahead and replaced all of the electrolytics before bringing it up on the variac, go figure one of the 10Ks and the 220K in the power supply were lisdexified from the factory! So far its working without any fire works, red plates, or horrid smells. Didn't look too bad on the o-scope and HP Audio Analyzer, a bit more distortion at 40 Hz than I would like to see. Then I hooked up my bias meter and clearly the 150 Ohm's in the output section were way off each other so they were replaced yesterday as I've gone through and replaced all of the PIO and ceramic caps underneath. Other than those two resistors I haven't found any far out of spec, new power supply resistors went in with the can cap as a matter of habit.

I've tried to stay frugal in the parts category and use a bit of what I have around and attempt to buy the best budget parts I can find otherwise, no virgins blood dielectric and platinum foil caps here. Finding doubler caps that will fit in this chassis is quite a challenge if you want to go away from stock sizes, nothing over an inch in diameter will fly. Went with Nichicon 100uF 450V for now, may go to a 220uF 250V pair at some point. For the can cap I went with a CE 40/40/20/20uF 525V, had to mount it from below as its a good 1/4" taller than advertised. All the other electrolytics are Spragues. I plan to replace every ceramic and PIO capacitor in the signal path with silver mica or film and foil. Sprague 716P's in the phono section as it probably won't see much use for now, Obligato Premium Golds in the output section, a pair of Mundorf Evo Aluminum Oils between the voltage amplifier and phase splitter sections of the 6U8 as they were tiny and easy to sneak in, as well as a pair of Russian K40Ps in the preamp section.

As I said, everything underneath is pretty well done minus any issues, so after bringing it back up on the variac again my next step will be my first listening test I think, very excited after all this work. Then I will go on to replace all the PIO and ceramics in the chain hidden behind the face plate, most of these will be AMTRANS film and foil and Vishay MKP-1837s. Once thats done it will go into my system for a while, but I have some ideas for modifications brewing. First and foremost, a tone control defeat, second, removing the tape head inputs from the phono pre and make them a standard line level in, third, play with the phono section and see if it can be made a bit more refined.

 

[gadget73]

Cool. Since you have the test gear, what sort of frequency response and power output are you getting? I'm just curious since I own one of these amps, but not the gear to really get test data from it.

 

[Metalsmith]

Cool. Since you have the test gear, what sort of frequency response and power output are you getting? I'm just curious since I own one of these amps, but not the gear to really get test data from it.

Our Audio Analyzer is one of my dads babies so he took the reigns for that portion, next time he gets a chance to give me a hand I will see about jotting down a proper response curve, distortion wise going full bore it was at about 1% from 10 kHz down to about 50 Hz then it started rising so my guess is its not going to dig the whole way down to 20 Hz very well with its cute little output iron.

Power wise with the out of spec cathode bias resistors at ~190 Ohms and ~220 Ohms I was seeing about 9 and 10 watts, this should be up to about 12 watts with fresh 150 Ohms in there now. :yes:

 

[Patrice B]

The tuner is an obscure gem BTW. Excellent sounding mono tuner...

 

[gadget73]

Our Audio Analyzer is one of my dads babies so he took the reigns for that portion, next time he gets a chance to give me a hand I will see about jotting down a proper response curve, distortion wise going full bore it was at about 1% from 10 kHz down to about 50 Hz then it started rising so my guess is its not going to dig the whole way down to 20 Hz very well with its cute little output iron.

Power wise with the out of spec cathode bias resistors at ~190 Ohms and ~220 Ohms I was seeing about 9 and 10 watts, this should be up to about 12 watts with fresh 150 Ohms in there now. :yes:

Cool. I actually replaced all of the resistors in mine since they were pretty grossly off-value. Interesting how one example is terrible, and yours check out mostly OK. Must be a storage condition thing, or maybe yours used better parts initially than mine did.

One thing that *may* help a little with LF response is bigger cathode bypass caps. I think I may have used 100uf in mine.

Interesting thing with the S-C design is they actually ran the tubes pretty damn close to book values. Not many did that. Maybe thats why the S-C doesn't chew tubes up and has a nice clean sound to it.

 

[wa2ise]

good luck finding an SC multiplex adapter. I have only heard of one and Tom has it.

Other brands of tube based adapters will work electronically. They all connect to the unequalized FM detector output (the jack usually marked "MPX"), which most tuners looks the same in terms of impedance. You shouldn't need to adjust anything in the adapter, as the stereo signal looks the same in every tuner. I assume your tuner has a MPX jack, and a pair of jacks to accept the left and right audios from the adapter. If the SC adapter was a module that was to be installed inside the tuner, you'll have to do some mods.

 

[Metalsmith]

So, my amp and I spent a few hours getting to know each other last night, I guess I did something right as it is dead quiet. Sound wise its a peach, now to go through the tone controls over the weekend and get it into my system so I can hear it with some more proper sources than a phone playing FLAC files through the headphone jack.

Cool. I actually replaced all of the resistors in mine since they were pretty grossly off-value. Interesting how one example is terrible, and yours check out mostly OK. Must be a storage condition thing, or maybe yours used better parts initially than mine did.

One thing that *may* help a little with LF response is bigger cathode bypass caps. I think I may have used 100uf in mine.

Interesting thing with the S-C design is they actually ran the tubes pretty damn close to book values. Not many did that. Maybe thats why the S-C doesn't chew tubes up and has a nice clean sound to it.

After doing a bit of reading around this forum one reason for carbon resistor drift may very well be moisture absorption. In which case here in the high plains desert you'd have to bury it or stick it in the rain for them see any moisture as humidity is not an issue here.

And to bass response, listening wise its very decent even through a pair of Klipsch Heresies. But supplementing the output cathode bypass caps with a few uF of poly bypass is something I have been pondering, as well as replacing the 4uF electrolytics in the Voltage Amplifier stage with some poly's. Definitely not an amp to bother with low efficiency speakers though, has me lusting after A/D/S, bigger Klipsch, and Altecs already.

Other brands of tube based adapters will work electronically. They all connect to the unequalized FM detector output (the jack usually marked "MPX"), which most tuners looks the same in terms of impedance. You shouldn't need to adjust anything in the adapter, as the stereo signal looks the same in every tuner. I assume your tuner has a MPX jack, and a pair of jacks to accept the left and right audios from the adapter. If the SC adapter was a module that was to be installed inside the tuner, you'll have to do some mods.

Funny you mention this, the Sansui 1000 chassis I have laying around that I plan to build a power amp from just happens to have its MPX module still. I have a plan to pull it, put it in its own enclosure, build a power supply and see how it works. The tuner has a power out for an MPX I could maybe work with but I'd rather it be usable with other tuners if need be. Not likely to happen very soon but I have a plan.