New member - Scott 16

[Robert Feenstra]

 I just got into this fascinating hobby.  Just redid a couple of radios I grew up with - a Majestic 1941, and Philco Model14 - 1933, chassis only. Now working on a Philco 96, 1930.  I decided I needed a real radio and found a Scott 16 in an Acousticraft cabinet.  It's not in the greatest shape as there is a fair amount of chrome damage and it is missing a few parts.  The receiver, power supply and speaker are intact and fairly unmolested, but I need knobs, the large dial pointer and a replacement plastic dial cover.  Are there reproductions of these parts?  Or, in particular, does anyone have a pointer they might want to sell?  I guess I can live with non original knobs and I think I could vacuum form a new dial cover.  I couldn't find anything at Radio Daze.

This project will be on the back burner for awhile, especially as I research dealing with the rust areas in the chrome.  Not sure I want to completely strip the chassis and have it re-plated.  I guess it depends on what it's value might be completely restored.

I've done a little research on the 16 in the forum's archives.  I'm not really sure of what I've got. I don't know how popular the 16 was or how it performed compared to the other Scott models.  Any input would be appreciated.

Thanks!

[mike hadley]

It's not very clear in the photo but there are three ball bearings in the brass shaft, the old grease had set hard and made  the whole assembly really difficult to get apart,

the center shaft has a conical end that the three balls run on, this stops the shaft coming out, that is where the small ball and spring come in, they push the this cone against the larger balls and the outer shell,

do you have the rest of the mechanism, 

[Robert Feenstra]

Ta da... it works.  I just need to find a ball bearing for the spring.  In the mean time,  it is assembled and working almost as good as new.  This was kind of fine work for my lathe and my bits left things a little rough (I know nothing about running a lathe so it is, no doubt, operator ignorance as to getting a very fine finish.)  Here's a couple of pics.  Seems to be about a 3 to 1 ratio

[mike hadley]

Robert;

if that's your first attempt, wow congratulatios.

Try looking in an old lever switch or similar, the ball and spring may be the right size.

did you make the end of the shaft hollow to take the ball and spring.?

Mike

[Robert Feenstra]

No, the spring goes down into the brass portion and pushes on the end of the steel part.  Right now the spring is pushing directly on the shaft, so it's not a good bearing.  Putting a ball in between will complete the assembly and reduce the friction.  I hope I made the shaft long enough. I didn't have an example.  It should be ok for a knob with set screws.  if I have to make another, I will.  Practice makes perfect!

[Robert Feenstra]

Output transformer question for those of you more technically inclined.  David kindly provided an original output transformer with an open primary for my Scott 16.  I've rewound several transformers and am in the middle of this one.  This one is unusual in my experience as the  secondary is wound between the 2 halves of the primary.  Both the inside half of the primary and the outside half have the same number of layers and turns.  Given that the outside half of the primary has a considerably higher diameter because of the thickness of the secondary windings, the length of the wire will be considerable longer, producing a substantially higher resistance than the inside half, much more so than a typically wound primary.  Does anyone know why this was done and what effect it has on the performance of the amplifier?

[David C. Poland]

That would also explain why the DC resistance of the the two halves of the primary differ a bit on resistance.

Curious the nature of the failure of the primary. Bad solder joint? corrosion? broken wire?

[mike hadley]

It's all about compromise, there is a trade off between wire gauge length etc, but the turns ratio wins out,

I think that if you measure the inductance you will find that they are similar, within a few percent, there is that trade off again,

also the inter winding gives better coupling across the transformer, helping to balance the anode to anode load,

this is typical of a tube output transformer.

[Robert Feenstra]

David, as I unwound the primary, several times the wire either broke or was broken. I assume that it was corrosion (though I could not see it) or the wire had just deteriorated.  Most of the breaks were on the outside 2 layers.  Perhaps heating and cooling stressed the wire?

Mike, I have rewound several transformers from Philco radios and the primary sections were continuous with a center tap.  This is the first one I've seen that was divided.  I've never worked on one from a higher quality amp so maybe Philco just chose the cheaper route in winding their transformers!  Thanks guys.

[mike hadley]

splitting the winding's in the output transformer has a lot to do with residual inductance, a bit like a lossy capacitor, not doing this will play havoc with the frequency response,

transformers being made from iron will change their inductance with frequency with all sorts of kinks and bumps as you go, you can at a push use a power transformer in an output stage but don't expect hifi, remember Scott was aiming for 16khz frequency response,

try looking up ultra linear output transformer construction, you will find that this type of construction used, with even more split windings.

[David C. Poland]

Mike - thanks for additional insight. Explains the good solid sound of my other "lesser" Scott models using 6V6's, this speaker and output transformer - my Super 12 and my 14 tube Scott Masterpiece  sound really good with an FM tuner or CD player despite lack of a separate tweeter.

[Robert Feenstra]

Thanks Mike!  Excellent info.  I'll rewind the TR exactly as it was.  Waiting for some new 24 awg for the secondary.  If I'm putting new wire in for the primary, I might as well for he secondary as well.

[Robert Feenstra]

Transformer re-wound.  Thanks David and Mike for your help. Can't really test it till the radio is finished, but all dc resistances are good.