Stromberg Carlson ASR-120
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century tek
Addicted Member
Should be no problem. Just listen for distortion. Not sure of the efficiency of your Ohm speakers but the higher efficiency rating the louder volume with lower wattage. I believe the output transformers are 4Ω so that wouldn't be a problem either!
FlaCharlie
Super Member
Has anyone tested the frequency response or square wave response of these transformers as they're used in the original amplifier? I have a pair that I removed from an ASR-120 (the power transformer was used in another project), and trying to decide if they're worth repurposing for hi-fi. They look a little small, but performance might be OK if materials and winding techniques are good. Anyone have any data?
Jack
Jack
Thanks, that's very helpful. I'll save them for guitar amp projects or sell them off.
ASR -120 output transformers are ultra linear the circuit is a cathode follower. output transformers primary side is 6500 secondary are 4-6 ohm output Ive been using them for yrs pushing 8 ohm speakers 3 way. added a schematic so you can see the power circuit with all voltages plus,
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That's correct, the ASR-120 is straight pentode. SAMS Photofact shows replacement transformers at 6K P-P, but I don't know how much I trust that.
SAMS Stromberg ASR-120
Jack
SAMS Stromberg ASR-120
Jack
I revised this entire post because A) it seemed confusing (too much information) and B) I wanted to correlate the measurements better to be sure the numbers are accurate. The problem with these tests is that only a small error in the secondary voltage reading results in a fairly large error in calculating the impedance transformation. After multiple attempts, it has become clear that the method I usually use, which requires interpreting an analog oscilloscope trace, simply isn't sufficiently accurate. The most accurate and repeatable appears to be the use of a DMM for measuring both the primary and secondary voltage. In addition, I used a known-accurate X10 AC test amplifier ahead of the DMM when measuring the much smaller secondary voltage to eliminate any errors that might occur from changing the scale.
To sum it all up, my ASR-120 transformers have the same part number stamped on top as yours. At 1kHz, driving the full primary with 20V pk_pk (7.07V RMS), they measure about 12.1K with an 8Ω load, and 10.5KΩ unloaded. Not sure why this is so different from your measurements, but even driving the transformer at 60 Hz doesn't explain it. Considering all the past controversy regarding measurements of output transformers , I would certainly be interested in nailing this down.
Jack
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I used a Wayne-Kerr impedance analyzer, also at 1 KHz, no longer have access to that or the transformer that I measured.
[Note that I revised my earlier post #11]
I'm sorry to hear the transformer is NLA. I was hoping you could perhaps duplicate my effort in measuring the voltage ratio, just for a sanity check. To be sure I understand, you used the impedance analyzer to look into the primary when the secondary was loaded with 8Ω, and a different method to determine the voltage ratio with no load, correct? Did you happen to measure the voltage ratio with the secondary loaded?
One other question - Does that particular impedance analyzer provide a phase angle readout? I wonder if that might explain the discrepancy between the analyzer and a simple voltage measurement. Of course, my numbers are different from yours even when measuring the voltage across the unloaded transformer, and I wouldn't expect to see so much vector displacement in that case. How did you make those voltage measurements?
Jack
In that case, I don't know how to explain this. The 8Ω load should be transformed up in accordance with the turns ratio (plus losses). It's possible the transformers are different, but that seems unlikely.
I would expect that to be less accurate than simply measuring voltage with the transformer secondary unloaded. I say this because subtracting DCR from the loaded value won't account for all the coupling losses that contribute to the measurement when it's loaded.
I'm thinking it might be worthwhile to put one of these back on the bench and drive it from the secondary. I suppose the primary load should be about 10K, being as that's the reflected load expected for the tubes.
Jack
your wrong sir. the ASR-120 is in fact cathode follower the output transformers are ultra linear. ive had mine worked on by a factory McIntosh 30 yr tech who agreed that it is ultraliner....and cathode follower circuit.
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Not to be a know it all, but its neither. ALso it can't be both at the same time. Ultralinear transformers have a connection to the plate and the screen. This does not have that. The screens are powered from a fixed DC supply, which is pentode mode.
Cathode followers apply fixed DC to the plate, and when dealing with a pentode there is also a DC supply to the screen. Output is from the cathode.
This is cathode biased, but it is not a cathode follower.
If you had a Mac guy work on it and tell you this, either he doesn't know what those things are, or has spent too much time around their completely different unity coupled circuit to be aware of what other output stages look like.
for reference, this is what an ultralinear push-pull output stage looks like
and this is what a triode-wired pentode cathode follower output would look like.
if you ran the screen to some DC supply that is not B+ it would be pentode mode but it wouldn't really change how it acts. It would simply flow less current.
Cathode followers apply fixed DC to the plate, and when dealing with a pentode there is also a DC supply to the screen. Output is from the cathode.
This is cathode biased, but it is not a cathode follower.
If you had a Mac guy work on it and tell you this, either he doesn't know what those things are, or has spent too much time around their completely different unity coupled circuit to be aware of what other output stages look like.
for reference, this is what an ultralinear push-pull output stage looks like
and this is what a triode-wired pentode cathode follower output would look like.
if you ran the screen to some DC supply that is not B+ it would be pentode mode but it wouldn't really change how it acts. It would simply flow less current.
Sorry, but this is totally nonsensical. It's clearly not what you think, and no McIntosh tech ever told you that. The schematic speaks for itself.
Jack
i see the difference in your draft of the circuit. yet i see a similar circuit design on the ASR-120 when it is feeding the 20v to r61/r62 which is not heaters for the 7408 or any family of 6v6gt tube.. I took mikes explanation of it being ultra linear output. i took the cathode follower from the owners manual. this new computer is not set up to send photos due to it being a non windows, Linux pureOS system that i only had for a few weeks now. have a VPN and firewall that so far i cant figure all the setting out how to allow to post photos to a allowed address. im not going to argue about my friend who had 40 + years working on McIntosh amps for his life until Clark music closed and he does his work at his home lab. he had many years there with many framed service diplomas from McIntosh....
That circuit is to elevate the 6.3 vac heater supply. Bias is developed from current flow across R63. There isn't any current at R61/R62, its just giving that +20v to the heater line equally. R63 also serves as the ground reference for the heater supply.
That heater supply is indeed feeding the 7408 tubes and the 7199 tubes. Note the W and V markings, and what the heaters on the tubes in the amplifier are connected to. They just didn't draw the lines in so the schematic isn't so messy to look at.
That heater supply is indeed feeding the 7408 tubes and the 7199 tubes. Note the W and V markings, and what the heaters on the tubes in the amplifier are connected to. They just didn't draw the lines in so the schematic isn't so messy to look at.
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