Masterpiece repair project

[Randy Rago]

I'm a member / restorer at the Asheville Radio Museum avlradiomusem.org and recently connected with a customer asking to restore a relative's Sott Masterpiece.

Been in the tube radio fixin' hobby since the early 70's and never came across one of these and saw a once-in- a -lifetime opportunity so of course I said YES!

From what i can tell, its mostly there but I have one question for the group. I have to re-cone the speaker but it has a 14 ohm VC, not the 38 ohm i've read about here. What are my issues if i run it with the14 ohm VC? THX

[Randy Rago]

To clarify, I was told the speaker was re-coned in the past

[George]

Ampifier will run with only half the output power due to the lower load impedance with possible audio distortion at higher levels. Since the human ear barely discerns a 3 dB change in volume and a halving of power represents a 3 dB change in power, I think nobody will notice it.

[Randy Rago]

Good news, thanks George!

[David C. Poland]

Unusual to replace the voice coil on a re-cone job. I have had several examples of this speaker, used on several late 1930's  Scott models using 6V6 output tubes. My experience is about half had a bad output transformer, half of primary open. Verify yours is ok. If not, with your replacement VC, the Hammond 15 watt universal be dandy (the 124 E, if I recall correctly) and you would be spared modifying the Hammond for the original 38 ohm  voice coil.

I am assuming you have the correct Scott badged Magnavox 12 inch special version with 2 field coils - one in B+ circuit and the other in the bias circuit of the output tubes. Output transformer mounted on the speaker. photo below:

IMG_0314.jpeg

[Randy Rago]

Yes David, thats the speaker. I isolated the VC and read the value directly. Its 14 ohms

[Scott Seickel]

If you read the resistance value of the VC directly with an ohm meter, it will be in the range of 30% or so less than the actual impedance. 

[Alex R. Whitaker]

Always remember that impedance is the resistance to AC (in this case, audio) at a certain frequency.  DC resistance is completely different.  

[David C. Poland]

A 38 ohm voice coil will read about 30 to 32 ohms on a VTVM - about what Scott said 

[Randy Rago]

Ok, so i dont have a 30 ohm VC, its been changed

[Randy Rago]

Last question is there a template here for the wood faceplate of the masterpiece? Mine is missing.

[Kent King]

Randy -

While we do have drilling templates for some models, I am not aware of one for the Masterpiece. I could probably create one, but I won't be able to work on it for a couple weeks.

Kent

[Randy Rago]

Thanks, Kent but ill work on it myself and ill post it when its done.