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Thread: Another magic JBL speaker/tube amp combo...

  1. #1
    Senior Member GordonW's Avatar
    Join Date
    May 2003
    Marietta/Moultrie GA USA

    Talking Another magic JBL speaker/tube amp combo...

    Ahh, yet another great week, for 40 year old hifi gear!!

    At work late last week, a guy stopped by, and asked us if we wanted this old tube amp, that he was simply throwing it away. Of course, we said "sure!"...

    Got to tinkering with it... an old Stromberg-Carlson ("a division of General Dynamics Corporation" :shock: Nuclear missles and hifi out of the same plant! ) ASR-333, with EL84 outputs, from about 1961-1967 or so. I can't find much reference on it, but from the EL84s and the voltages involved, I'm guesstimating about 20w/ch rated power...

    I cleaned up all the connections, and fired it up... and it actually played. Garbled, but actual music coming out. Pulled the bottom, and happily noted the schematic inside! Started probing test points for voltage... and quickly found that one tube on each channel had NO POWER (in effect) due to bad resistors!

    Well, after quickly changing out the bum resistors, I fired it up again... and WOO HOO... CLEAN MUSIC out of both channels!!

    I let it warm up and "burn in" for a couple hours, and after it started sounding better and better (slightly mellow sound, but GOOD low bass!), I thought to myself: "Huh, I wonder... how would THIS sound hooked up to the Lancer 77s?"...

    The answer? WOW. Holy cow.

    If I want to maintain my resolve to sell this old gear and get it out of my way, I seriously need to NOT listen to this combo much, because the inclination is to scarf it all up, and take it home with me. Man, this combo sounds GOOD. The mellow midrange of the S-C amp is JUST the ticket, to smooth out the upper mids of the L77, which can get a bit abrasive sometimes. With this amp, no such problem. Dang near INSTANTANEOUS transient response in the midbass and midrange (man, is the EL84 a "FAST" tube, or what???), with some SERIOUS bottom end extension. Possibly the only real noticable fault was a lack of treble "air"... but after changing out the (original from the factory!) EL84s with some new Sovteks, I don't even think anyone could make that complaint anymore. Amazing as it would seem to some, there's also PLENTY of power, at least for those who aren't insisting on Ted Nugent Live levels of SPL in their living rooms- it has plenty of oomph for big sounds Uncannily good!

    Amazing how well this stuff works, when it's teamed up with stuff that would have been available in the same era, isn't it?? Time-co-incident design ethos, anyone??


  2. #2
    Senior Member
    Join Date
    Apr 2003
    GTA, Ont.

    Cats' Out of the Bag

    Hi GordonW

    Thanks for that review of the SC amp. The little bit that I can add about the company is that for at least a short while they aspired to compete head to head with Western Electric/RCA in a few areas - HiFi audio & Telco products being two such areas . Nice to actually know that they did a fair job at it .

    regards <> Earl K

  3. #3

    SC audio equipment

    I have 2 Stromberg Carlson voice and carrier amplifiers that are 1 unit rack mount with the mini pin inpit and output with an umbilical on one side with a hinge that allows them to be swung out while still in rack. A very nice design. Theay are a 12ax7 in a two stage resistance coupled amplifier with a pot for attenuation and a 6aq5 cathode coupled output via a 10uf 250 volt cap. It contains a 5 henry choke and a dual section 15uf at 450volt cap for a supply but needs an external transformer and rectifier. Theay are nice and liniear up to 500K where the coupling caps make the waveform squirly. Quite a deal at 5 bucks a piece and a pair of 5881's

  4. #4
    Senior Member GordonW's Avatar
    Join Date
    May 2003
    Marietta/Moultrie GA USA
    They seemed to like those 6AQ5 and 6BQ5 (ie, EL84 by another name) outputs at SC...

    Just in case others happen across one of these amps without the bottom plate (where the ID was), this amp had a 6AV6 input amp stage, followed by a 6U8/6GH8 pentode/triode (both, in one bulb) for voltage gain and phase splitter, respectively. EL84/6BQ5s are in push-pull for outputs (total of 2 per channel). AFAIK, most of these ASR-333 amps were installed in consoles... the one we have, was in one, originally. Heh, I wonder if this is the first time it was ever hooked up to a TRULY GOOD speaker??


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