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Messages - TC Chris

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Chat / Re: The old GE radio
« on: January 19, 2019, 07:15:19 PM »
While Greg has his TV on the card table, I have my GE E-86 on top of the table saw.

This evening I walked down to Ace Hardware to buy an extension cord to make a cord for the GE.  It's cheaper than buying raw zipcord and a plug, plus I still have the short end I cut off to make a short extension cord out of.

After that was attached I pulled the rectifier out, poked the VOM leads in the socket's plate holes.  Whee, lots of volts (>500 VAC, 'cause that's where my VOM tops out unless I move it to the 5 KV input).  It bounced the needle a little bit.  That means I have a power transformer and can proceed.

So then I turned to the rubber-coated wires, the ones that lie against things and create a danger of shorts.  Geez, GE really packed the parts in tight.  I'm used to old Zeniths with lots of real estate.  GE probably worried more about RF performance and such.  The rubber-coated ones often bear against the chassis or other terminals. In any event, I worked until I had used up my red wire.  Now I need black, which will mean a trip to the hardware store tomorrow unless I find some suitable gauge in my wire stash.  Where the wires run to tube sockets or the IF cans, I've mostly been cutting off the old one, leaving a short length that I can curl up to make a solder terminal.  Un-soldering is not feasible because of the tight quarters.

Chris Campbell

Tube Consoles / Re: V-M 557 Plate/Screen Grid Voltage Questions
« on: January 18, 2019, 10:24:04 PM »
Clutter is my problem.  I simply can't keep my bench neat and organized.

Sounds like my garage shop.  Every horizontal surface has filled up with future projects, things I'll surely need some day, containers that I'll need as soon as I recycle them, and other important stuff.  The GE radio cabinet stands on the Workmate bench so my service on the chassis is being done on the table saw.  If and when it's working and reassembled there will be a crisis about where to put it, because my house is stuffed already.  Don't get me started on the Victor radio highboy cabinet that I took to make sure it didn't get trashed/surely somebody would want it, or the Silvertone console radio that looked lonely in the roadside trash pile, or the outboard  motor stand for the sailboat motor, or the sturdy (heavy) footlocker/trunk that my Dad shipped his stuff back from Europe in after WW II.  A POW painted his name and address on it in very nice letters.  Geez, you can't just toss something like that out. But where am I going to work?

Chris Campbell

Chat / Re: The old GE radio
« on: January 18, 2019, 07:21:02 PM »
Well, the output tube coupling cap can make me nervous.  Once I found a nice old Silvertone guitar amp in the trash.  It was a smaller one with P-P 6V6 output.  I took it home and plugged it in and it worked!  But then I noticed a dull cherry-reddish glow on the 6V6 plates.  Guessing that the bias was off, I replaced the coupling caps and all was well.  Now that's one I attend to for fear of burning up expensive stuff. 

My plan for this weekend is to pull the rectifier out and power up the power transformer to make sure it hasn't died.  That burned-up/replaced Candohm makes me a little nervous.

Chris Campbell

Chat / Re: The old GE radio
« on: January 17, 2019, 10:58:47 PM »
I like the idea of just doing the filter caps first.  That one on the 6L6 plate was cooked-looking so I'll either do the series thing or buy another for it. But the others, well, some of them are nicely buried, so maybe I'll wait on those and leave them in if the radio works.  I'll focus on the crumbling rubber wire where it's close to the chassis or other metal.

I just walked out to the shop and retrieved my schematic.  What had looked like more electrolytics than I expected turned out to be dual-section electrolytics paralleled in a previous repair.  Then I looked closer at the big wirewound resistors, which turn out to be a replacement for most of the big chassis mount "Candohm" voltage divider.  So I'm guessing that at some past time, the filter caps shorted and took out the original resistor. 

The schematic also shows me that while GE went with a single-ended output amp, that big 6L6, they used two IF amps instead of the more common one.  And since this has tuned RF, the extra IF amp may make it a good performer.  The radio also has a tone capacitor that is switched in when the SW bands are selected.  So they designed for lower noise in SW and higher fidelity in MW.  Interesting. 

Chris Campbell

Electronics / Re: capacitor working voltage
« on: January 17, 2019, 07:56:38 PM »
Is this a place where a ceramic cap would be superior?  It's not in the signal path so wouldn't be objectionable from that standpoint.

Chris Campbell

Electronics / capacitor working voltage
« on: January 16, 2019, 10:45:56 PM »
I started to recap the GE radio tonight.  I picked one that looked toasted--a big paper cap from the plate of the 6L6 output to ground.  .01 mfd, and then "1600."  ????  So I found the schematic and it didn't give a voltage value.  The parts list did--1000 VDC.  Again, ???  Seems like a high rating, especially for an old paper and wax cap. The plate voltage is shown as 290 V.  I was wondering if I could get away with a modern film cap of 600 or 630 WVDC.  I've got those on hand.

My only guess about the voltage is that it has something to do with the output transformer primary, maybe acting like a choke or something.

Any advice?

Chris Campbell

Tube Consoles / Re: V-M 557 Plate/Screen Grid Voltage Questions
« on: January 16, 2019, 07:58:36 PM »
Well, no, or sort of. There are different types of designs in ultralinear, but as they apply to these basic designs where the pentode is used.....You start out wrong and then do delve into the basic concept.If the Plate and Screen are at the same voltages, or close, you have not achieved what is called "ultra-linear".

I had posted this link:

Scroll down to "Table 1" and note the plate and screen grid voltages shown for EL84/6BQ5.  It's a Mullard table.  They're equal. 

Chris Campbell

Tube Consoles / Re: V-M 557 Plate/Screen Grid Voltage Questions
« on: January 16, 2019, 07:52:44 PM »
                   If it's the last thing I do, (which scares me to use the phrase as I get older  !! ), I am going to set up a comfortable table/bench with a chassis holder, good lighting, now with magnifiers as I age,  radios nearby tuned to good stations, soldering irons on variacs, nice old boat anchor test equipment,  push carts on  wheels, a coffee percolator and fridge close by and a good digital camera that will let me share current activities and projects with the "gang".
         How's that for a dream ?  The projects are all here and waiting and so is most of the boat anchor test equipment, thanks to some recent ebay buying binges.  oops, post time again !!

Chris grins.  Occasionally now I calculate what age I will be in 20 years, a period of forward looking that never seemed especially daunting before.  Geez, that's scary!  I am closer to 100 than I am to 40 (scarier still...).  And I have the same "some day" plan to have an ideal bench with good lighting, convenient access, lots of time.  But in the real world, I was out in the shop last night working on the 1935 GE, which is sitting on top of the table saw, propped up with a bock of wood, and illuminated (sort of) with a clip-on reflector lamp hanging from a rope.  The little soldering iron is clipped to the saw's table with a spring clamp so the cord doesn't pull it skittering off onto the floor.

It's important not to let the perfect be the enemy of the good enough, or even the barely acceptable, of you want to get things done. 

Chris Campbell

Butyl rubber surrounds may be a better option when they are available.  Foam has a limited life, especially when exposed to light  and airborne contaminants.  When my living room speakers had the foam expire--all at once--I had them reconed with rubber.  I didn't do it myself because I had just had hand surgery and was very fumble-fingered at the time.  I did my shop speakers, curbside trash-pile finds, with foam surrounds about 20 years ago.  It was a fairly easy process and worked well.  They are mostly in the dark so haven't failed again so far.  Rubber wasn't an option then. 

Chris Campbell

Chat / The old GE radio
« on: January 15, 2019, 11:38:14 PM »
The GE E-86 console radio project ground to a halt last spring after the cabinet repair and refinishing was done.  Now I've finished one project, fixing up an old steel "ice cream chair" with a new wooden seat and some linseed oil on the steel frame.  That made room to start on the GE's electronic renovation.  Tonight was the first part--replacing all 5 grid cap wires, which were all rubber-insulated and crumbling.  Two were from IF transformer cans, so the cans had to come off.  On the first one, true to form, I got the sequence wrong--soldered the cap connector to the wire instead of soldering the wire to the IF, then poking the wire through the can, then soldering the cap connector on.

Next I'll make some sort of chassis holder so I can work on the underside, replacing capacitors and the rubber insulated wires that are placed so as to create hazards.

Chris Campbell

Introductions / Re: New guy in Georgia USA
« on: January 15, 2019, 07:39:41 PM »
Part of the fun here is the "identify this console" game.  More photos!

Chris Campbell

Chat / Re: Buck/boost transformers
« on: January 15, 2019, 07:31:49 PM »
As to the 5U4s... they do put out heat, and their filament current adds to it also in the transformer. You could use solid state diodes and leave the 5U4s in place with filaments disconnected, for show. 

And yeah, those old transformers do seem to go on forever, as long as we don't murder them with failed, shorted filter caps.

Chris Campbell

Sightings / Re: GE white FP console - MD
« on: January 14, 2019, 07:51:09 PM »
I like that light under the lid!  I've got a ca. 1925 Sonora acoustic phono console with an under-hood light.  The Sonora is quite the machine.  The mechanics of it, never visible to users unless you disassemble the device, is lacquered brass, a lovely European mechanism.  But the light, that's a good addition.

Chris Campbell

Tube Consoles / Re: V-M 557 Plate/Screen Grid Voltage Questions
« on: January 13, 2019, 09:35:23 PM »
Me too.

Here's what Wikipedia has to say about it, which seems to apply to the V-M circuit.

Here's a 1953 article describing it.

And here's an extended discussion.  Toward the bottom there's a "Table 1" showing EL84 and EL34  characteristics.  It shows equal plate and screen grid voltages for the EL84/6BQ5.

Chris Campbell

Other Tube Console Brands / Re: 1962 VOM model 868
« on: January 13, 2019, 04:09:30 PM »
Looks like a substantial unit.  I'm glad you rescued it!

Chris Campbell

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