[Kenneth F. Besso Jr.]

How is your Wrist,,,must have did it at different times,,,,over a week,,,I say,,,Fantastic job,,,God bless you with Patiences,,CHEERS

[rfeenstra]

First I cranked it 16500 times to unwind the TR, then 16500 times to wind it!  it was a 3 day project with frequent breaks.  My wrist and eyes demanded the breaks.  Being round, it actually wound easier than the square bobbins I did previously.  I'm glad it's finished!

[Eliot Ness]

16500 hand cranks x 2    

Very nice work, that old Grebe is looking good

[Phlogiston]

That is some serious dedication.

What was your DC resistance compared to the original?

I usually bulk-wind these - when I have to. The smallest wire I use is 39 but it is easier to break when the winder is motor driven.

[rfeenstra]

Not sure of the resistance since the secondary was open.  If the other TR is the same, the secondary resistance is 8K ohms.  My rewound secondary measures 8.8K ohms.  Micrometer measurements of the wire led me to 40 guage, though it was not exact by the charts.  Actual measurement was considerably less than 39 guage, but a few .0001's more than 40 guage.  Not at all sure of the thickness of the insulation layer.  I assume manufacturing tolerances, especially in 1927, would account for the difference in resistance.

The question I pose to you is (cuz I don't know the answer!) does bulk winding produce the same results as the layer method?  I would assume it does.  However, your bobbin diameter would be less.  Again, I doubt that makes a difference, but I don't know.  But then, given the age and lack of precision in designs of these early radios, I doubt it would be audible.

One more question, a repeat question, what effect does several shorted windings have on the performance of the TR?  it seems that it would affect the impedance dramatically.  How much more effect would shorted windings have over the effect of the copper strap around the circumfrance of the finished coil (as shown in the pics)?   Questions that are beyond my knowledge base!  I haven't googled it yet but maybe there are answers aout there.

Rob

[EdHolland]

When I rewound my interstage and O/P transformers for the 16X, the resistance was quite close to the values provided on the schematic. Original values, I can't say because they were open circuit. I did notice that the finished numbers were low, and this was measuring in a cold garage where I did the work. The value changed noticably when it was warmer, certainly a several ohms or more increase on ~370 Ohms. There was also a slight difference between the inner and outer portions of the center tapped winds, as the outside section is a little longer. More modern transformers use bifilar winds to maintain a better balance (and for other reasons).

The effect on sound of layer vs. bulk wind? That would depend on the frequency response of the rest of the system, and the effect the added capacitance would have in combination with other circuit values. Also, bulk winds, unless kept really neat (which is hard to do with fine wire) tend to build up more than expected. I could speculate that the layer method was used as much to aid manufacture as it was for performance.

Hope I'm not explaining the obvious to you good people

Ed

[Phlogiston]

It is hard to get that much wire on there. The insulation between the layers takes up space too. I just stock a few lbs of 39, 38, 36 and 34.

I bulk wind mine because my coil winder does not have the precision to layer wind, but I don't have 3 days to put into it either. The way you did it is better, if you have the patience.

One suggestion would be to cut off the wire and weigh it. Then calculate the length needed to rewind. You need a good scale.

I don't know, but I would say that the shorted windings would matter more depending on how many are shorted out of the circuit - not many, little change - a lot would mean poor results, BUT any shorts will mean that the transformer is unreliable.

[rfeenstra]

Little doubt that bulk winding would save an incredible   amount of time. Just laying the paper and shellacking it in place takes almost as much time as the actual winding.  I'm also fairly careful not to cross windings as I wonder if the pressure from subsequent layers would eventually short out a winding.

Given that the radio must have passed quality tests for sound originally, even with a section of a layer about 1/4" wide shorted,  a single shorted winding is, perhaps, no problem.  But with a band 1/4" wide shorted, one would think that those shorted windings would change impedance matching severely,  probably reducing the audio signal level significantly.  Perhaps the volume control easily compensated.  While I fully understand winding ratios, I confess ignorance on the subject of TR impedance issues!

Russ, if bulk winding has worked satisfactorily for you, next time, I'm gonna do it that way too!  I'll motorize my winder.

Thanks guys!

[rfeenstra]

There is no doubt in my mind that this radio would far exceed all UL requirements for safety.  The top terminals are straight off from the rectifier,  The bottom 2 terminals go to the AC switch in the tuner section.  The speaker + terminal goes to the 180 volt power supply feeding the output TR, and the speaker - goes to the plate of the 71A from the output TR.  All are readily touchable in the back, especially the speaker terminals.  Looks good to me!

       





No tubes yet, but there is a glimmer of hope!

[Electrothaumaturgist]

BEAUTIFUL!!!  What a very interesting thread... Keep it coming!!!  

[rfeenstra]

It lives again!  Got all globe tubes from FindATube - my tube tester rates them a bit below replacement levels, but they work.  Bob is great to work with.  One Cunningham CX326 drew enough grid current in the rf amps to pull the negative 4 v bias up to nearly 0 volts.  It must be a bit gassy.  It worked in the af driver position, but Bob is sending me another, no questions asked.

It certainly needs a bit of work yet as the hum level is a bit unacceptable.  I suspect the filament resistors to ground are unbalanced.  Only one is adjustable.  This radio certainly needs a long wire antenna as sensitivity is otherwise poor.  It's interesting that this radio has both a local/distant switch and an antenna adjustment.  It also seems to be more sensitive to noise from the line than the other radios I have.  Lack of AGC is annoying!  Getting all of the tuning caps to line up precisely is fun, and the very tiny bit of hysteresis in the linkage is noticeable when tuning.  I need to work on getting all 4 of the caps in the right position so that the hysteresis is not as noticeable.  Could be tricky.  While I'll probably rarely listen to this radio, it's kind of satisfying to take a fairly unique piece of history and make it work again.

Russ, if you read this, how was the performance of your AC 7?  Did you have any problems getting the tuning caps lined up?  I believe you have an extra tuned stage over the AC 6.  This is a 1926-27 radio, one of the early AC radios.  I know progress was being made at an incredible  rate in those days.  This radio does not stack up - so far- to the performance of my Philco 96 (with AGC, 1930), or even my Atwater Kent 55 (w/o AGC, 1930).  From what I've read, the Grebe was a good performer in its day.  I think I have a bit of work to do yet.

More comments later.

[Phlogiston]

I think that a lot of manufactures added an extra RF tube/stage to decouple the antenna and/or increase gain for the radios that were sold with one-knob tuning. They all have some issues with lash in the tuning mechanism. This will compensate for stages that are not-quite tuned but does nothing for selectivity.

As I recall the Sync. 7 performed well considering the tuning issues. In other words, it was nothing to brag about.

[rfeenstra]

Thanks Russ.  I suspected as much.

[EdHolland]

Great to hear that this is running again - A superb job

[rfeenstra]

Wow! I just found a picture of this cabinet on line and I now know what the doors should look like.  I don't think I'll be duplicating them.  Turns out this cabinet is a Berkey and Gay made in Grand Rapids, MI. 20 miles from where I live.  I've been in the building!.  Berkey and Gay was one of the larger furniture manufacturers in GR back when GR was known as the Furniture City of the country.  They made various custom radio cabinets for various radio manufacturers.  This was not a typical cabinet for the Grebe but was a custom installation.  No wonder I couldn't find any pictures in any of the Grebe literature. Now I need to find another cabinet so I can get the doors.  This one sold w/o a radio a few years ago for $35.00.