Author Topic: New Project  (Read 927 times)

1988bluebird

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Re: New Project
« Reply #30 on: January 28, 2020, 03:36:01 PM »
That cabinet is looking very nice now, good work!  This radio reminds me somewhat of the GE model J-62 "treasure chest" radio https://commons.wikimedia.org/wiki/File:Vintage_General_Electric_Wood_Table_Radio,_Model_J-62,_Broadcast_%26_Short_Wave_Bands,_6_Tubes,_Circa_1940_-_1941_(14683411058).jpg
My consoles:
1939 Zenith AM console 8S359
1949 RCA Victor AM/FM "dual phonograph" console 9W105
1958 RCA Victor New Orthophonic HI-FI phonograph console SHF-6
1950 Magnavox Wedgewood AM/FM phonograph console CR-216

TC Chris

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Re: New Project
« Reply #31 on: January 28, 2020, 06:44:54 PM »
Same era, the '40s, and the same reliance on English neoclassical style, Hepplewhite or Sheraton.  They both have a band of fretwork on the cabinet.  The GE has SW but no transformer and only 6 tubes.  No RF amp.  The speaker is 5" on the GE, 8" on the Emerson. The GE is single-ended with claimed 3 watts output, while the Emerson's ad claimed 20 watts with the P-P 6L6s.  I'm surprised the Emerson didn't have at least one SW band; they did have a tuned RF amp.

Chris Campbell

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Re: New Project
« Reply #32 on: January 28, 2020, 09:00:29 PM »
I'm just in from the shop where I was checking resistors.  They tend to come last because they usually drift high and cause less unhappiness than capacitors, which can short out and burn things up.  Six were high (and since I was checking them in-circuit, where they may have had some parallel resistance that would tend to make them read low, that means HIGH).  One little one was cracked, always a bad sign. I  had replacements for two 1/4 watt ones, but nothing for the 1 and 2 watt bad ones, and nothing for one value not included in my Radio Shack vast assortment sets (best buy ever).  I could have put two in series but the location doesn't have much lead length so I'll see how close I can come by buying a single.

It's hard figuring out which resistor I'm looking at in the circuit.  As we know, parts can be electrically correct even when they're in the wrong part of the chassis.  My old Riders schematic has blurry numbers so I'd have to trace the ends of the test resistor to see where they landed in the circuit.  The Riders doesn't have tube pin numbers, either, making it harder to analyze.  Sure makes me appreciate the clarity of Sams.

Now dinner is cooking.

Chris Campbell

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Re: New Project
« Reply #33 on: February 02, 2020, 10:02:25 PM »
My project is slightly stalled while waiting for caps and resistors from Sal Brisindi.  I wonder if he's been ill... he's usually fast but was slow replying and shipping this time.  I'm getting all impatient, of course, so tonight I wandered out to the shop while listening to the blues show on WCMU.  The goal was to drill some holes in the bottom cover, a solid wood thing that basically cut off all under-chassis ventilation.

Question for tube guys: HOW IMPORTANT IS VENTILATION??

Yeah, so I used hole saws in the drill press to make quite a few 5/8" holes--4 under the power transformer and about 6 of them marching across the chassis  width from there.  When I re-install it, there will be some shims to create a gap all around the edge.  Convection ought to draw the air in through the holes and maybe exhaust some of it around the edge or through the tuning-cap cutout in the chassis. The holes got some stain so the fresh cuts don't stand out but match the brown-ness of the board.

Chris Campbell

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Re: New Project
« Reply #34 on: February 13, 2020, 11:17:33 PM »
The problem with Sal was solved--some sort of PayPal snafu and he got behind but now is caught up.  I got my capacitors and resistors in the mail today and headed out to the shop to install them tonight.  On this project I assumed that the old paper caps were bad because I don't have a tester.  I checked resistors and replaced only those that had gone high.   Tomorrow I may test the tubes (or maybe not; sometimes ignorance is bliss with regard to tube quality) and then partly reassemble the radio so I can fire it up with the dim-bulb tester. I've done some videos along the way and will post them on YouTube once the radio is working.

Chris Campbell

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Re: New Project
« Reply #35 on: February 14, 2020, 11:39:54 PM »
Success!  I switched out one capacitor, exact value for almost-right, tucked the chassis back into its cabinet, connected up the speaker and the phono-input switch, found a light bulb for the dim-bulb tester, and plugged it in.  Bright-dim-bright, AOK, and even some audio.  So I removed the tester and went with full line voltage.  It works!

It oscillated at a few points on the dial and the volume control was noisy so I pulled it out again.  Applied DeOxit to the tuning cap bearing points.  Used their control lube on the volume pot.  Cleaned the dial pointer's track, straightened the pointer, and used a tiny bit of paraffin wax on the track.  I broke down and tested the tubes.  All OK. Then I made some shims for the wooden bottom cover to allow extra ventilation in addition to the holes I had drilled, and put it all back together.  No more oscillation, no more control noise, stations all up and down the dial on this cold winter night at midnight.  There's a bit less sensitivity at the low end of the dial.  It probably could use an alignment.  And the bass is still flabby when cranked up a bit--not the amount of clean sound I would expect from P-P 6L6 outputs.  I remember it used to be that way and I was hoping the new caps would make it better.

Chris Campbell

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Re: New Project
« Reply #36 on: February 15, 2020, 12:03:06 PM »
See it on YouTube:
https://www.youtube.com/watch?v=Sw4YIXCK0U0

Chris Campbell