Late 1960's watts = how many RMS watts?

Discussion in 'Audio Hardware' started by 62vauxhall, Oct 21, 2017.

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  1. 62vauxhall

    62vauxhall Forum Resident Thread Starter

    Regarding a circa 1968 receiver I picked up the other day.

    Never having encountered before the brand Rolecor, I did some Google searching and found next to nothing information wise. Except some year's old forum posts by others stating the same conclusion.

    And a 1970 newspaper ad from the US East Coast.

    The ad was for two models of Rolecor receivers, an RTA-630 and the one I have - RTA-650 for which the ad indicated an output of 165 watts. Presumably that was total power and obviously not stated as RMS.

    My guess is it's actual power is in the 25 or perhaps 30 WPC range. Assuming 165 watts refers to "music power" what fraction would that figure translate to in RMS?

    FWIW, power consumption is 160VA . Synonymous I believe with watts.

    EDIT: measured rail voltage is 52.
     
    Last edited: Oct 21, 2017
  2. Thouston

    Thouston Forum Resident

    Location:
    Mattoon, IL
    .707xPeak=RMS
     
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  3. 62vauxhall

    62vauxhall Forum Resident Thread Starter

    So 58 watts per channel then. More than I guessed.

    Thanks!
     
  4. action pact

    action pact Music Omnivore

    Good knowledge! Using that formula I can confirm that my '59 Fisher X-100 tube amp is 14wpc RMS, which is what I thought.

    "40 watts both channels" per the owner's manual = 20w per channel (peak)
    20 x .707 = 14.14.
     
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  5. Higlander

    Higlander Well-Known Member

    Location:
    Florida, Central
    Not doubting the guesses, but any chance you could put up a pic of it?

    Just from memory, from 60's recievers, that sounds a bit optimistic.
    Most normal ones were often in the 25-50 range at best.
     
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  6. GuildX700

    GuildX700 Forum Resident

    Location:
    USA
    It would be fairly rare for a 1968 receiver to have 58 true WPC RMS.

    What bandwidth and distortion is this measured at?

    An average modestly priced receiver from 1968 would have around 12 to 30 true RMS per channel, and most off name brands were seriously fudging their watts back then. So considering they advertised 165 watts, they sound like they were the type of company that would fudge any and all specifications.
     
  7. McLover

    McLover Senior Member

    The 165 watts quoted in the ad was likely PMPO watts. PMPO is Peak Music Power Output. 25-30 watts RMS at less than 1% THD is I think accurate at 20-20,000 Hertz. This practice was cracked down on by the FTC a bit later on, and the Institute of High Fidelity and the Federal Trade Commission adopted the methodology for amplifier power ratings used for many years (and still used by honest companies in audio today).

    In 1968, receivers with more than 40 true RMS watts/channel were very rare. And usually priced in the neighborhood of $400-$500 new in that era list price. Sony, Sansui, McIntosh, and a very few others were the main known manufacturers this early. My 1969 Sansui 4000 (40 watts/channel RMS into 8 ohms, less than 1% THD, cost over $400 list price in 1969 new)
     
    Last edited: Oct 22, 2017
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  8. Higlander

    Higlander Well-Known Member

    Location:
    Florida, Central

    I did not want to rain on the party, but most decent receivers rated them True watts per channel back then.
    Anything using Peak power or Combined watts was out of the ordinary.

    But from my experiences, with older audio, it was not uncommon for average receivers to be quite low powered.
    Normal ones were as you say 12-30 watts. 50 or 60 was considered fairly pricey and out of the ordinary.
     
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  9. Metralla

    Metralla Joined Jan 13, 2002

    Location:
    San Jose, CA
    A fair assessment.
     
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  10. tumbleweed

    tumbleweed Innocent Bystander

    That "165 watts" is what we in the biz referred to as ILS power - "If Lightning Strikes".:D

    Or, "downhill, with the wind behind it."

    Cheers,
    Larry B.
     
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  11. 62vauxhall

    62vauxhall Forum Resident Thread Starter

    Since this forum does not permit attaching photos directly from a PC due to space restriction of the server....no. I attempted storing pics externally once in order to do so but was unsuccessful.

    It's not crucial that I know this receiver's output power as I acquired it just out of curiosity.

    It may not even see the light of day due to high DC offset. Last night I found and replaced what I believe were the differential transistors pairs which dropped and equalized it at 0.52 volts. But there's no service manual/schematic that I can find online anywhere so anything else I do (blind component replacement) is a shot in the dark.

    I don't have the resources to acquire test equipment so can't track down faults. All I'm armed with is a DMM.

    In the late 1960's I owned a couple of receivers, both supposedly around the 30 watt range. A used Chrysler branded tube model that weighed a ton and a solid state HH Scott bought brand new.

    Judging from remembered weight and feel, this Rolecor is reminiscent if the Scott so 30 watts is what I thought it might do on a good day. Would not surprise me though if it was less.
     
  12. head_unit

    head_unit Senior Member

    Location:
    Los Angeles CA USA
    ±52 volts? If so 0.707*52=36.74V, square that and divide by 8 to get 169 watts. Per channel. So I am skeptical that is the actual rail voltage. (If that is zero to +52 and then divided up you'd get 42 watts). IF the power consumption was 160 watts max, (IF!), and a class AB amp like what let's say 33% efficient is it? Then you get like 50ish watts of actual amp power, divided by two channels.
     
  13. 389 Tripower

    389 Tripower Just a little south of Moline

    Location:
    Moline, IL USA
    Maybe the 165 is the power consumption spec from the line cord??
     
  14. JohnO

    JohnO Senior Member

    Location:
    Washington, DC
    Rolecor was exclusively sold by the E.J. Korvette discount department store chain, it was essentially a private label brand, their store brand of good receivers, amps, and tuners at the time about 1969-1972. Does it say E.J. Korvette on the back label? It was made by Rotel aka Roland (good stuff). The newspaper ads were from Korvettes, so the ad might claim anything. The Korvettes record and audio departments were legendary and solidly good.
     
    Last edited: Oct 22, 2017
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  15. deadcoldfish

    deadcoldfish Senior Member

    Location:
    Santa Rosa, CA
  16. Mike from NYC

    Mike from NYC Senior Member

    Location:
    Surprise, AZ
    It really depends on when in the 1960s the equipment was offered for sale. In the mid 60s it was an anything goes when it came to power claims and then the government clamped down and required all audio equipment to be rated in 'RMS' and not claims of 'IPP' which was Instantaneous Peak Power. The industry was also behind the push of more uniform power ratings.

    The power rating claims were as laughable as the power ratings for cars back in the day and the government cracked down on that also.

    The public was being sold a bunch of crap about power and lawsuits would have been rampant if it was done today
     
  17. 62vauxhall

    62vauxhall Forum Resident Thread Starter

    Thanks for the pics dcf.

    What's on the back of this RTA-650 is a not exactly the same as it does not state "Exclusively for E.J. Korvette". And instead of "Manufactured by Roland Electronics Co. LTD, Tokyo, Japan" it says "A Quality Product of Roland Electronics C0. LTD Tokyo, Japan".

    From my limited experience inside such things, this brand is very intelligently laid out by which I mean simple and lots of room to work. Plus the PC traces are more substantial than other pieces I've seen that would have been more expensive when new.

    I'm going to put up Info Wanted posts on DIY Audio and AK on the off chance someone has a service manual or first hand knowledge of where to measure for bias voltage and what that voltage is supposed to be.

    I've been advised to check the pre-amp board as being the possible reason for high DC offset. A few electrolytics there and another differential pair of the the same transistors as were on the driver boards but if after replacing those there is no improvement, I do not know where else to look.
     
  18. JohnO

    JohnO Senior Member

    Location:
    Washington, DC
    Here's the Rolecor RTA-630 with two XAM speakers, which is what I see blurrily now in a couple newspaper ads and probably was usually advertised that way. The XAM speakers are Korvette's house brand, possibly made by Coral.
    [​IMG]
    [​IMG]
    [​IMG]
    [​IMG]
     
    Last edited: Oct 22, 2017
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  19. JohnO

    JohnO Senior Member

    Location:
    Washington, DC
    From all that I've seen before, I knew of the RTA-650 and the RTA-630, and later the 600 - but I thought they all said Korvette on the back. There were two tuner models and two amp models, or more, too. Could you possibly upload a pic of the label on your 650 without Korvette? Just upload to imgur.com and copy the link. I don't need the serial number but I would like to see that label.
     
    Last edited: Oct 22, 2017
  20. Higlander

    Higlander Well-Known Member

    Location:
    Florida, Central
    Not to go too off track here, but I googled Rotel Vintage Receivers and found pics of several receivers that looks VERY similar to some older Radio Shack units from the 70's!
     
  21. JohnO

    JohnO Senior Member

    Location:
    Washington, DC
    One key to these Rolecors as a private brand is that the name is only on the glass - easy to change in production for whatever retailer they were sold to or made for. They could even, on finished assemblies, change the glass, and the name, and repaint the back if they needed to, to sell it to another retailer. The same models might show up for even smaller other retailers or "brands" too. I like these mysteries.
     
    Last edited: Oct 22, 2017
  22. 62vauxhall

    62vauxhall Forum Resident Thread Starter

    [​IMG]
     
  23. JohnO

    JohnO Senior Member

    Location:
    Washington, DC
    It is done today, maybe not by major brands, but by many smaller brands. But the FTC does not care any more. The FTC rule came in 1974. At that time many FTC employees were probably audio enthusiasts. Not so much now.
     
  24. 62vauxhall

    62vauxhall Forum Resident Thread Starter

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  25. GuildX700

    GuildX700 Forum Resident

    Location:
    USA
    Judging from the small size of the case I'd say it's about 15 RMS per channel max. There just is not enough room to heat sink much more power than that in a chassis that small with that old of technology.
     
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