Author Topic: Tubes, an Amp and More  (Read 1352 times)

ed from Baltimore

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Re: Tubes, an Amp and More
« Reply #15 on: March 11, 2018, 11:14:55 PM »
Sorry to do another double reply---I should look more carefully. I didn't optice the gold front panel at first and I couold just ake out the RCA round symbol and the High Fidelity logo. The knobs are identical to the mystery chassis I saw although I remember a more medium blue shade, but the chassis blue looks identical.  I now now notice your extended shafts for custom mounting---a shame to hide that pretty blue chassis in a cabinet.
       A lot of the RCA hifi lined seemed to make it schematically into the RCA tube manual of "suggested circuits", although they didn't always mention that they were in production.  One amplifier I remember had 4 6V6s, 2 6AU6s separate plate and screen supplies and a multiple feedback circuit. They even gave all the requency and distortion specs. It might have been the companion unit for the tuner-preamp I saw, and I wonder if it also had the blue chassis color. 

TC Chris

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Re: Tubes, an Amp and More
« Reply #16 on: March 13, 2018, 12:17:54 AM »
Since we're talking about RCA....  In high school I knew the guy who cleaned my Dad's office.  His "day job" was as projectionist at the biggest movie theater in town.  I loved all the technical/mechanical stuff so Dad got us an invitation ito the projection booth one night.  The theater had a multi-channel stereo system then (probably about 1964 or '65).  Off on one side there was this rack of about 8 big RCA commercial amps.  I always wonder what happened to them.  It would be cool to see if they are still there.  The theater closed and as converted into a party space.  Could be that they were simply ignored as old fashioned and left there in their rack.

Chris Campbell

TC Chris

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Re: Tubes, an Amp and More
« Reply #17 on: March 13, 2018, 12:26:27 AM »
Continuing the double-post tradition here, I'll add that the blue paint plain gloss, no hammertone effect, and the knobs are brown. 

I've got a little Grommes 50PG amp that's very similar, a 6V6 P-P device.  That one evades my diagnosis efforts.  Too many projects, not enough time. 

Chris Campbell

ed from Baltimore

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Re: Tubes, an Amp and More
« Reply #18 on: March 13, 2018, 04:53:49 AM »
     You would be surprised, you never know.

       If they're good and heavy, they probably haven't be moved very far, just out of sight beind something.

         BTW I have been calling RCAs fancy hi-fi model the Berkshire and now realize that Berkshire is a Magnavox console name. The RCA model I'm thinking of was named after some famous New England music festival, Ravenswood or Ravensbrook ?

        And I keep wanting to post somewhere in the RCA website to see if anyone knows the origins of the unique RCA phase splitter circuit. The circuit looks normal but the resistor values are all different and I don't see how it is balanced. It's in all their 6CG7 -6V6 or 6BQ5 stereo power amp circuits from about 1959 on, even in the three channel amps.

       It might not have been successfully posted because my early posts I was  going beyond the 60 minute default log-in time, and losing all my long-winded typing when I tried to post cuz I was logged out. Frustrating !!  I didn't have the heart to retype all  that hunt-and-peck typing. So a lot of my non-replies were actually never posted. It's easy to miss the small type no-post message.

      I lost a really long post about reforming original electrolytics with a variable DC power supply and a current meter. If you can get to them before someone plugs in a long-unused console there's a good chance of doing a high-reliability reforming of the cap's original voltage rating. 

ed from Baltimore

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Re: Tubes, an Amp and More
« Reply #19 on: March 13, 2018, 05:12:48 AM »
    Another double-post !   Sometimes I run across a second example of the exact same model but maybe made in a different "run".  No idea if the different run was a month later or several years later, but the differences when the two examples when side-by-side are sometimes hard to believe, and often both examples are different from the picture in the catalog or advetisement. The brown knob-blue knob is a good example. The chassis paint may vary from smooth to hammertone to wrinkle finish. Printing on the glass dials can be intense or faint. A tube socket might say 12AX7A or ECC83 or 12AX7A/ECC83/7025  !    Maybe the drawings weren't specific, or there's an employee turnover. Then there's the fact that I saw the last one 30 years earlier !!

Harbourmaster

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Re: Tubes, an Amp and More
« Reply #20 on: March 13, 2018, 02:46:49 PM »
Chris why don't you just change your settings to keep me logged on always, or whatever the exact wording is.
-- Aloha, Ken

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ed from Baltimore

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Re: Tubes, an Amp and More
« Reply #21 on: March 14, 2018, 11:15:24 PM »
   

         That's the first thing I do when logging in now "logged in always".  60 minutes goes by pretty fast when you read slowly and type even slower. Plus now I look at a lot more sites and looking at a lot of the previous pages.
         A lot of times I've chimed in on a "current" discussion only to realize later that it was all in Jan. 2017 and we are in Jan 2018.       
         I do a lot of the browsing just before bedtime , which might explain a lot of long-windedness.
         Some of my phrases seem to have triggered emoticons. Little round yellow face with uneven eyebrows.
           Old geezes like myself learn slowly.

 Ed from Baltimore

Bill

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Re: Tubes, an Amp and More
« Reply #22 on: March 17, 2018, 10:26:58 AM »
You are not the only old geezer that learns slowly.  ;)

Bill

firedome

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Re: Tubes, an Amp and More
« Reply #23 on: March 22, 2018, 01:52:18 PM »
The RCA MI stuff was their commercial industrial line but there was overlap, they did make a high-end home HiFi line for awhile in the '50s, even speakers like the famous LC-1. Their amps for comm/indust use usually had oil caps and other requirements for near continuous use. I had an MI amp (forget the #) that had oil caps and round transformers as well, I think it was a BA-14, but it also had an MI-xxxx number. Sold it to a guy that has a commercial recording studio, as they were used as studio and radio station monitor amps originally.

They also made a ultra hi-end MI home hi-fi line in Gr Britain that made McIntosh stuff look crappy... see pic. They employed lower noise tubes like EF86 instead of the usual 12ax7s &c, as well as KT-66 outputs vs the usual 6L6 family. Would kill for a pair of those!

There was indeed an RCA Berkshire, probably one of the most expensive mono sets ever made, in the late 40s, it would cost in the $20K+ range today. Norm Braithwaite wrote an article about it in the mag I used to write for, Vacuum Tube Valley, and also this piece for Antique Wireless:
http://www.antiqueradio.com/Dec07_Braithwaite_RCABerkshire.html

Harbourmaster

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Re: Tubes, an Amp and More
« Reply #24 on: March 22, 2018, 06:18:20 PM »
Those are sure pretty, but would be pretty much useless here with the 50c/s transformers... yes?
-- Aloha, Ken

No Console Left Behind!

SeniorSteve

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Re: Tubes, an Amp and More
« Reply #25 on: March 22, 2018, 08:46:19 PM »
Actually if those are 50 c/s transformers, they would have more iron in them and run cooler than the 60c/s transformers that we would have here in the US.  Those amplifiers sure look nice to me.  Like the copper color.

Steve

ed from Baltimore

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Re: Tubes, an Amp and More
« Reply #26 on: March 26, 2018, 01:12:28 AM »


     Beautiful. That chassis has plenty of vertical room. Maybe for some vertical mounted  terminal boards large enough to fit  .25 uF 600 V coupling capacitors between the solder lugs. And maybe to fit some 8 uF 600 V non-electrolytic oil filled filter capacitors. A filter choke that huge doesn't seem to be needed with a 40 uF 450 VDC electrolytic. Must be an elegant circuit with only 2 EF86 pentodes. Have you ever seen the underneath of a Leak power amp ?  The components must have been clamped in a test fixture while being soldered to the terminal board. The lacing of the wire harness looks like a sewing machine stitched it. These units probably looks the same.BTW I didn't see impedance selector even though there were damping factor controls. Maybe for BBC ?

    Saw an RCA M series unit on E-Bay. It looks like a stereo tape deck electronic chassis with 2 magic eye tubes,  and 2 identical layout 3 tube channels but only one mike and headphone jack and  a switch to select "student 1" or "student 2". maybe for speech  training classrooms ?

    Also an E Bay ad for Magnavox-Electroacoustic "PlayFellow"  3 tubes and replaceable steel needles single play 78 RPM portable phono.

firedome

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Re: Tubes, an Amp and More
« Reply #27 on: March 26, 2018, 03:42:09 PM »
Most TOL Brit amps were made on turret boards with neatly bundled wiring and everything mounted in parallel rows, Leak, Quad, and the UK-made MI RCAs were typical. Marantz tube stuff that I had built in the '50s was similarly designed, and IIRC H-K Citations were also constructed that way, had the amp and preamp but forget now, it's been 20 some years.

Here's the RCA BA-14 I had, it was a tube studio monitor amp, look at all the plug in caps! The red German one was repainted non-original, the one in the link is original looking. These babies were designed to run 24/7/365 for years! Sold that one about 2 years ago.

https://reverb.com/item/6927702-rca-ba-14a-monitoring-and-recording-amplifier

ed from Baltimore

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Re: Tubes, an Amp and More
« Reply #28 on: March 28, 2018, 08:15:54 PM »
    Neat info. I've always had a soft spot for vintage British audio  and their design features. Really classy A to Z.
       That LC-1A looked neat. I've only ever seen a cutaway drawing of it but never a picture of one in the flesh. I think several other speakers had concentric coaxial design but only the Olsen design had woofer and tweeter both concentric and coplaner whereas all the others had the tweeter diaphram  several inches behind the woofer cone so the frequency response still had dips and peaks in it compared to the LC-1A. I wonder what types of music showed its superiority the most--maybe rapid piano runs or percussion ?  A shame it didn't catch on.

firedome

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Re: Tubes, an Amp and More
« Reply #29 on: March 29, 2018, 02:29:20 PM »
Dunno but good ones bring crazy prices these days, as do the TOL vintage concentrics from Jensen, Altec, Stephens and others.  I wonder if some of the new AlNiCo repros from Jensen sold at www.tubesandmore Antique Electronic Supply are any good?

Picking up an Ethan Allen custom stereo console cabinet this w/e, minus receiver but w/ TT and speakers, both unknowns, it's always interesting to see what is actually in there, will report in.