Stromberg and Carlson ASR-120 - Replacement transformers?

[txtune]

I have a ASR-120 model tube amp that I am considering restoring. I have found schematics and rebuild kits online, with the exceptions of the transformers. Maybe the transformers are still good, but they look kind of rough.

[sluckey]

Post schematic

[txtune]

Post schematic

See attached.

[sluckey]

Maybe the transformers are still good, but they look kind of rough.

Those transformers look fine to me. They could use a little polishing up, but I bet they are all fine.

The output tubes are very similar to 6V6s so output transformers would be the same. You have voltages given for the power transformer, so if you need a replacement, just get one that will fit the footprint and provide the same voltages.

I would not even consider new transformers before doing a power on evaluation. Once more, I bet they are all fine.

[txtune]

The output tubes are very similar to 6V6s so output transformers would be the same. You have voltages given for the power transformer, so if you need a replacement, just get one that will fit the footprint and provide the same voltages.

I would not even consider new transformers before doing a power on evaluation. Once more, I bet they are all fine.

Would you kindly point me in the right direction on how to evaluate these transformers? Thank you. 

[shooter]

I'd pull the PA tubes, OHM from tube socket pin 3 to "other" tube socket pin 3, should be ~~220ohms  (no speakers)

[sluckey]

I'd pull the PA tubes, OHM from tube socket pin 3 to "other" tube socket pin 3, should be ~~220ohms  (no speakers)

And then pull the rectifier tube and measure the AC voltage on all secondary windings.

[PRR]

> schematic

Cropped:

[shooter]

Thank, thank you


 

[PRR]

Agree there is no reason to fret about the OTs. Yet.

It is not mil-spec, sure to last 50 years in a sandstorm in the arctic. Early 1950s S-Cs used enclosed OTs but clearly the Stereo Craze forced them down-market to "kitchen radio transformers" (larger, but still semi-open construction). I have cheap iron that old and older in my Kent and Philco, and they play fine today.

*ME*, I would take it out on the driveway with a long cord, hide my eyes, plug it right in. People will say "that's dangerous and bad for the gear!!" Well, gee, buy new gear if you don't like blowing-up and fixing stuff.

[txtune]

I'd pull the PA tubes, OHM from tube socket pin 3 to "other" tube socket pin 3, should be ~~220ohms  (no speakers)

Just to clarify, you would pull the 7408 tubes and OHM between pin 3 on two of the 7408 tube sockets at a time? This is done with no power to the unit right? I feel like I am about to get tomatoes thrown at me. 

[txtune]

*ME*, I would take it out on the driveway with a long cord, hide my eyes, plug it right in. People will say "that's dangerous and bad for the gear!!" Well, gee, buy new gear if you don't like blowing-up and fixing stuff.

That is kind of my style, what would you do next... if nothing catches fire? What about if something does catch fire? Would you then replace only the burnt portion and start from the top?

[shooter]

YES, No power, and yes, do it twice.  Then as Sluckey said, pull Rec tube, THEN power up n check Power supply secondary voltage AC

[txtune]

YES, No power, and yes, do it twice.  Then as Sluckey said, pull Rec tube, THEN power up n check Power supply secondary voltage AC

Ok. Should the two 7408 on the L side and R side should have ~220ohms between them on pin 3?

Is there any reason I could not pull all tubes first? Check the L and R 7408 sockets, between pins 3 on each socket, then power up and check the supply secondary voltage AC?

I am going to do this at my shop on Monday where, at the very least, somebody can call 911 if I get lit up... though I will use appropriate PPE.

[shooter]

not sure the confusion, there are 4 tubes and 2 OT, left side has 2 tube 1 OT, same for Right.  so pull ALL 4 PLUS rectifier tube, make 2 measurements 1 for L side, pin 3 to pin 3. 1 for R side, pin3 to pin3. NO power just ohms
THEN apply power and measure Volts AC on the secondary side of Power transformer

[txtune]

not sure the confusion, there are 4 tubes and 2 OT, left side has 2 tube 1 OT, same for Right.  so pull ALL 4 PLUS rectifier tube, make 2 measurements 1 for L side, pin 3 to pin 3. 1 for R side, pin3 to pin3. NO power just ohms
THEN apply power and measure Volts AC on the secondary side of Power transformer

That is what I was proposing in my last thread. Of the total 7 tubes on the unit I do not know which one is the rectifier tube though. Is it the tube next to the power transformer?

[shooter]

look at the documentation you provided, it spells out all the tubes, V13 is the rectifier

[txtune]

Thanks shooter you have been super helpful!

[txtune]

I'd pull the PA tubes, OHM from tube socket pin 3 to "other" tube socket pin 3, should be ~~220ohms  (no speakers)

And then pull the rectifier tube and measure the AC voltage on all secondary windings.

I just got around to this today, work has been busy. When I OHM from pin 3 to 3 I am getting 237 on one side and 240 on the other. I checked with two different multimeters, both of them gave the same reading. Would that be considered ok? Is the secondary side of the power transformer the black and red wires, in the schematic, that are shown connecting to the rectifier tube socket, labeled 320VAC?

Thanks

[AmberB]

237 on 1 side and 240 on the other side sounds pretty good to me.  They're not always that close.
You will have 4 wires connected to the rectifier socket from the power transformer.  2 of them should be yellow for the 5 volt heater, although they're not always yellow.  The other 2 are the secondary high voltage winding.  There should be a ground wire from the power transformer to the chassis for the high voltage winding.  If you check with the multimeter between the high voltage windings, you should get some amount of resistance.  If you check from each of the high voltage wires to the chassis, you should get approximately half the resistance from each wire on the high voltage side to ground.

[txtune]

237 on 1 side and 240 on the other side sounds pretty good to me.  They're not always that close.
You will have 4 wires connected to the rectifier socket from the power transformer.  2 of them should be yellow for the 5 volt heater, although they're not always yellow.  The other 2 are the secondary high voltage winding.  There should be a ground wire from the power transformer to the chassis for the high voltage winding.  If you check with the multimeter between the high voltage windings, you should get some amount of resistance.  If you check from each of the high voltage wires to the chassis, you should get approximately half the resistance from each wire on the high voltage side to ground.

I get 130 between the two secondary side wires, and 67 and 62 between ground and each of the secondary wires. Should I now plug in and check for AC voltage? On those wires? If so, what should I expect to see? thx

[shooter]

1st, what is the MAX AC volts your meter can read?


I would measure each leg to ground 1st
so gator clip the black lead to chassis
gator clip red lead to either red wire
power up, get reading
power down, discharge caps
repeat for 2nd red wire
post volts

[DummyLoad]

EIA 352 is Magnetic Windings Co., Easton, PA

maybe a stereo low-power (30W) SUNN type amp with a split chassis for preamp? you could rewire for use with 6AN8 or 6U8, as as those are lower cost and easier to source than 7199.

for monurol use, strap OT's in series and you should be able to drive a 4Ω to 8Ω load, or strap a 8Ω speaker and a 16Ω speaker in parallel for 5.33Ω


--pete

[txtune]

1st, what is the MAX AC volts your meter can read?


I would measure each leg to ground 1st
so gator clip the black lead to chassis
gator clip red lead to either red wire
power up, get reading
power down, discharge caps
repeat for 2nd red wire
post volts

Max voltage on the meter is 1000

It did not show any voltage on either of the red leads going to the rectifier tube socket.

[shooter]

my bad, missed this, that DL alluded to


either cut the 2 wires that go to 6 and 9 EDIT: and twist n solder, or solder a jumper across 6-9
then measure volts AC red to red since your meter can handle it
If it seems good ( maybe 400-600vac)
being careful measure green to green (filament)
and Yellow to yellow

[txtune]

Nothing on red to red after I soldered 6 and 9 together.

EDIT: You are talking about the red wires I have circled AND the 6 & 9 pins from the modular plug that I have circled, correct?

[shooter]

yep;
verify the fuse is good
what's the black chunky thing on right - accessory plug?
i'm sketching up an eliminate rat's version

[shooter]

here's a hot wire "fix" IF... the fuse is blown


IF the fuse is not blown;


measure VAC from each brown wire to chassis ground to verify there's stuff coming in

[txtune]

yep;
verify the fuse is good
what's the black chunky thing on right - accessory plug?
i'm sketching up an eliminate rat's version

Glad to hear this, I really thought I had to be doing something wrong.

Black chunky thing is indeed an accessory plug for the radio or the turntable, cannot remember which.

[txtune]

here's a hot wire "fix" IF... the fuse is blown


IF the fuse is not blown;


measure VAC from each brown wire to chassis ground to verify there's stuff coming in

Continuity was intermittent on the fuse, not sure I have seen that before. I plan to make some modifications to this device anyways, so I will go ahead and install the hotwire 'fix'.  I cut the two wires you circled, then reconnect them based on your diagram, correct? Just checking that the brown and black in your diagram are the two that you circled. Thank you.

[shooter]

yes the ones you cut, power wire (brown) feeds fuse, tranny wire (black) feeds the tranny


decide where you want your power switch, drill n mount it.  decide where you want a fuse, drill and mount it.
hook up like diagram, use a 3 prong power cord, connect the green wire somewhere close to where it comes in.  I typically drill a hole and bolt it down near the power in

[txtune]

Could I use a pop out breaker like this in place of the slow blow fuse?

Also, if I am replacing the power cord... where should I connect the incoming white/neutral wire? Should I cut the wires (circled in green) loose and tie the incoming white to the black?

[shooter]

yes and yes
fuse/breaker the black, the white goes like you indicated


you "might" get nuisance trips from the breaker vs a slo-blo, so if you're planning on maskin up hitting the gig trail, fuse might be better, at home in boxers the breaker should be fine

[txtune]

yes and yes
fuse/breaker the black, the white goes like you indicated


you "might" get nuisance trips from the breaker vs a slo-blo, so if you're planning on maskin up hitting the gig trail, fuse might be better, at home in boxers the breaker should be fine

The 'other' white wire, right above the green circle in my markup, can I cut that out completely?  I may use that cutout in the frame for a power entry module. 

Boxers and breakers it is. 

I went ahead and bought this restoration kit on fleabay... perhaps from someone on this forum. 

My overall plan is to be able to input a radio or TT (via RCA) and output to some bookshelf speakers. I have zero idea how to get there, but I am going to give it my best.   

[shooter]

I colored out all the wires you can delete. 
strip down the terminal strip AFTER you have enough original pic's to be happy
NOTE ANY wire that comes from the tube OR the PT (power transformer)
once it's all shiney clean, draw up "your vision" for best use of the nice clean ready to use terminal strip
draw it schematically 1st, then layout 2nd, you'll be listenin to bookshelf music soon


I'll do some sketchin, but I didn't retain any early stuff so I gotta go back for 2nd's


edit: attachment 

[txtune]

Wow, thanks shooter! 

I will take many photos before, during, and after. Would you recommend I first install the 'hotwire' and get a reading from the secondary side of the PT? Or should I just start removing wires and get it down to bare bones, then start building back from there?   

[shooter]

depends;
if it smokes are you gonna stay with it and throw parts at it til music comes out?
If so, i'd get the 1st load of junk out, "start the process"


If NOT, hot-wire with duck-tape n gatorclips, make sparks 

[txtune]

depends;
if it smokes are you gonna stay with it and throw parts at it til music comes out?
If so, i'd get the 1st load of junk out, "start the process"


If NOT, hot-wire with duck-tape n gatorclips, make sparks 

Ok, so I wanted to try it out first to make sure I got voltage off the secondary side of the PT. It occured to me that the old style power cord on this unit could be plugged in either way... meaning I could remove the plug from the wall and turn it 180 degrees and plug it back in. The way I was plugging it in caused the brown wire, circled in red, to be the incoming 120VAC. So I put the hotwire, breaker, and switch, in right there. Then I tied the other brown and black together and turned it on, which resulted in 716VAC on the two red wires connected to the RT socket. Now then, when I go to hook it up in the permanent configuration... does it matter which of those black wires I use for the neutral and which I use for the incoming hot wire from the wall?   

[shooter]

Nope, but I believe there is a CT red/yel, where THAT wire goes is important, should be connected to ground.


so do you get ~ 6.3vac across the filaments (green-green)?  does the lamp light?
are the tubes still in?  IF so do the filaments glow in all 5(?) tubes?

[txtune]

Nope, but I believe there is a CT red/yel, where THAT wire goes is important, should be connected to ground.


so do you get ~ 6.3vac across the filaments (green-green)?  does the lamp light?
are the tubes still in?  IF so do the filaments glow in all 5(?) tubes?

CT = Center tap? I see the red/yellow wire you talking about. It goes to the bottom of the round metal housing near the RT. Orange arrow pointing to it.

I will go test the across the green wires.

I have the tubes, I will try them and see what happens.

[txtune]

so do you get ~ 6.3vac across the filaments (green-green)? 

I was getting right around 7vac

does the lamp light?

The small lamp does not light.

are the tubes still in?  IF so do the filaments glow in all 5(?) tubes?

I put the RT and the four large tubes back in and all of them lit up!


What's next? The smaller transformers and tube sockets?

[shooter]

nope
staying with power
take all tubes out except the rectifier, put that in
look at the schematic, to the right of the rec tube "looks" like C52?
put the red lead on the + side of cap, the black lead on chassis ground
power up and measure Volts DC!  leave it on maybe 3-5 minutes watching the meter like a mother hen, keep your nose n eyes working for ANY sign of "she's gonna blow"
If you make it that far, we might have music soon, so hunt down your favorite junk speakers

[txtune]

Would you be so kind as to point out the + side of the cap in one of these pictures?

[PRR]

> does it matter which of those black wires I use for the neutral and which I use for the incoming hot wire from the wall?

No. Not a bit. If it does, you have a bad connection "sometimes".

Since you have seen 700VAC come out, I strongly suggest you find a FRESH gig-worthy power cord with a ground pin/wire and do-up the 120VAC wiring properly.

> point out the + side of the cap

99.44% of the time, the "can" of a can-cap is negative, the lugs in the middle are positives.

[shooter]

Use your schematic to "follow" along;
start at the rec tube, find the pin that "feeds" the DC "power rail" (the "line" with voltages going "up")
you can measure (ohm NO power)the resistors as you go and verify with schematic, anything within 25% is good for now :)
once you're happy you have the correct point, THEN you can switch to VDC connect meter and watch, closely 

[txtune]

Since you have seen 700VAC come out, I strongly suggest you find a FRESH gig-worthy power cord with a ground pin/wire and do-up the 120VAC wiring properly.

Yes, I agree.

[txtune]

Use your schematic to "follow" along;
start at the rec tube, find the pin that "feeds" the DC "power rail" (the "line" with voltages going "up")
you can measure (ohm NO power)the resistors as you go and verify with schematic, anything within 25% is good for now :)
once you're happy you have the correct point, THEN you can switch to VDC connect meter and watch, closely

I took these photos yesterday before I read your latest post, which I am quoting here. The vdc leveled out at 450 on the pin, pictured below, that I chose at random.

[shooter]

monitor it for the 3-5 minutes, look for sudden drops or surges, slow bleeds.  If it stays basically "centered" then you're good for now.


look at the schematic, upper right in blue
NO POWER, ohm that resistor to make sure it's close to stated value.
IF close, black lead to chassis, red lead probes each of the 4  socket's (tube side), each tube should ohm ~ the same as the resistor. look at the schematic, trace that circuit so you get the correct tube pin to ohm.

[txtune]

monitor it for the 3-5 minutes, look for sudden drops or surges, slow bleeds.  If it stays basically "centered" then you're good for now.


look at the schematic, upper right in blue
NO POWER, ohm that resistor to make sure it's close to stated value.
IF close, black lead to chassis, red lead probes each of the 4  socket's (tube side), each tube should ohm ~ the same as the resistor. look at the schematic, trace that circuit so you get the correct tube pin to ohm.

The one I circled in orange? I got 150 on it.

[shooter]

assuming that's the correct 150ohm;
look at the schematic;
one side of the 150 should go to ground
the other side should go to all 4 PA tube's cathodes
Verify by following wires, use meter to ohm ALL 4 PA tube cathode pins to ground (ohm at tube side of socket)




once that's done find yourself a stereo jack 3mm 1/8", 1/4",RCA, whatever you want to use to plug your music source into.  also scrounge up 2 caps, .1 - .01uf.


did your voltage stay about constant during the 5 minute test?