Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: TubeGeek on December 11, 2019, 11:54:13 pm

Title: Silvertone Model 1300 (1947) field coil replacement
Post by: TubeGeek on December 11, 2019, 11:54:13 pm

Hey guys,


I have a cool amp on the bench right now from 1947. It's a Silvertone Model 1300. 


So far I have got it working and now I am asking for advice on whether you think I should have the torn speaker re-coned or replace the speaker with a modern permanent magnet type.  The original speaker has a field coil. 


Am I correct in thinking that I can replace the field coil with a 1k 10W resistor?  If a resistor isn't proper, a choke?


I measure 600 ohms across the field coil.

Title: Re: Silvertone Model 1300 (1947) field coil replacement
Post by: TubeGeek on December 11, 2019, 11:55:59 pm

guts

Title: Re: Silvertone Model 1300 (1947) field coil replacement
Post by: DummyLoad on December 12, 2019, 04:29:42 am

you could replace the FC with one of these (https://www.tedss.com/2021009944) - it should work fine. 45V across FC with about 100mA (75mA output stage at idle) at full blast. so FC drops 45V with 100mA, that's about 5W dissipation - 25W R should not get too warm. use a 4ohm speaker. idle current = V of FC / R of FC = 45V/600 = 75mA

if it were mine, i'd try to find a decent speaker shop and have the speaker re-coned.

--pete

Title: Re: Silvertone Model 1300 (1947) field coil replacement
Post by: shaun on December 12, 2019, 10:53:04 am

Nice amp!
Fwiw, I'd want to keep it original, plus I've heard that when done right, field coil speakers can be very smooth sounding, so I'm hoping to keep one in a rebuild I'm doing.
Also, almost all the fc speakers I've seen were very nicely constructed - ie quality. Of course, there's the hassle of re-coning - if you can find a re-cone kit to suit. Maybe someone here can point you to a good re-cone supplier.
Also, Uncle Doug has a nice video on how to re-cone on youtube. Good luck with it.

Title: Re: Silvertone Model 1300 (1947) field coil replacement
Post by: whoops on December 12, 2019, 03:10:13 pm

Quote from: TubeGeek on December 11, 2019, 11:54:13 pm

So far I have got it working and now I am asking for advice on whether you think I should have the torn speaker re-coned or replace the speaker with a modern permanent magnet type.  The original speaker has a field coil. 

Very nice looking amplifier,
I would recone the speaker with the closest material and corrugation possible and then have a listen, maybe you like it a lot.

How much damage does the speaker have? can you post photos of the speaker damage?

Title: Re: Silvertone Model 1300 (1947) field coil replacement
Post by: TubeGeek on December 22, 2019, 11:32:43 pm

I decided to ship the speaker to Weber for re-coning.  It seemed like the right thing to do.


I tried to repair it with paper towel with no success.


here is a pic of the tear: