# Speaker rating and dating help needed etc.



## Electraglide (Jan 24, 2010)

Yesterday I bought a mid 50's Chisholm 960-MF radio/phonograph. I bought it for the parts, the Webster turntable looked like it would fit into my 1950 Electrohome radio/phonograph. The guy said that the lights came on and you could hear scratching when you stroked the stylus but that's about it so I asked him to plug it in. As I watched the tubes start to glow I noticed the power cord was breaking up as the wind moved it. So I told him to unplug it and offered him $15....he was asking $75. He took it. His wife flipped because he didn't ask enough and mine gave me "the look".
When we got home I unplugged the turntable from the chassis and plugged it in to an extension.....it works, need cleaning, but I can't swap it. Fair enough.
Then I noticed a couple of things. First, the speaker is a very early Electro Voice SP-12-B.
http://i1000.photobucket.com/albums/af129/Electraglide49/Photo_082612_002.jpg
No watt or ohm rating. Online info says they were 20 watt and either 8 or 16 ohm. Anyone have dealings with these speakers or could tell me how to accurately check with a multimeter. The speaker works but the cone needs a little repair.
Then I looked at the chassis. 
http://i1000.photobucket.com/albums/af129/Electraglide49/Photo_082612_003.jpg
Needs the power cord replaced. And it has two transformers, the small one is a Hammond 1616 and the larger one is a Hammond 276x60, so the possibility is there for rewiring with a grounded plug I think. There are no 50*** or 30*** tubes as I would expect on a radio chassis this age...the tubes are, 5Y3GT, 6SC7, 6SA7, 6V6, 6V6GT, 6SQ7, 6K7, 6KTGT and a 12AX7. With a power out and an RCA input. Possibilities for a low watt guitar amp with an AM radio are there. Maybe using the original speaker. Should be interesting.


----------



## Guitar101 (Jan 19, 2011)

Electraglide said:


> So I told him to unplug it and offered him $15....he was asking $75. He took it. His wife flipped because he didn't ask enough and mine gave me "the look".


Don't you just hate that? Another good reason to leave the wives at home when were out buying gear.

Speaker Codes, Amps, & More
This is the only thing I've got speaker code related. Maybe there's something you can use.


----------



## washburned (Oct 13, 2006)

For speaker impedance the resistance across the coil should read just under the rated impedance, for 8 ohm it should read 5 to 7, for 16 ohm 10 to 14 And you have a great start for an amp project. This might help: Converting Integrated/PA Tube Amps into Guitar Amps.


----------



## greco (Jul 15, 2007)

washburned said:


> For speaker impedance the resistance across the coil should read just under the rated impedance, for 8 ohm it should read 5 to 7, for 16 ohm 10 to 14


Just remember that you have to take the speaker wires off the speaker (unsolder or GENTLY pull off the spade terminals attaching the wires to the speaker) before taking the DC resistance measurements.

My apologies if you already know this.

Cheers

Dave


----------



## Electraglide (Jan 24, 2010)

Testing the speaker I get 10.8 ohms resistance across the terminals.....so, it's a 16 ohm speaker. I think after I change the power cord I'll plug it in and see what smokes. If nothing smokes I'll plug a guitar in on the phono circuit and see what happens. I normally keep things like this as original as possible. As far as "the look" goes, well after 7 years the wife is used to my purchases and I'm used to the look. I get it from her, the grand daughters and even her cat. The look was more for, "Where will that go?". That went away when I told her I was going to use it for parts and bought her lunch....I might have neglected to tell her I was probably going to put it back together.


----------



## loudtubeamps (Feb 2, 2012)

If the amp hasn't been fired up for an unknown period of time, the electrolytic caps will most likley be pooched,especially if they are the originals.To fire the amp up without doing any damge while still allowing you to test/hear the audio path.....build up a cheap and easy load tester.









It comes in handy when firing up questionable amps etc: If the amp (device) is in trouble it will draw excessive current which will be evident by the brightnees of the bulb.A dim bulb usually means the device is not going to blow fuses when plugged directly into the mains.
I use a 60 watt. Best to use a 3 condutor grounded circuit. The pic. above was the first one that came up in Google Images.
If the controls are original there may be a series of numbers with the date of manufacturer or date codes on the transformers or on the back side of the speaker cone(usually stamped ,white lettering) and /or a date code on the capacitor cans.
cheers, d


----------



## Electraglide (Jan 24, 2010)

http://i1000.photobucket.com/albums/af129/Electraglide49/Photo_082612_005.jpg
This is what the inside of the chassis looks like. Why it didn't smoke when it was plugged in is a wonder. And thanks for the basic load tester. I have one that used to be my dad's...in a box in the basement or the shop, somewhere. I'm just wondering if the amp circuit for the turntable would draw the same amount of power as the circuit for the radio. One way to find out I guess after I replace the power cord.


----------



## greco (Jul 15, 2007)

I'm impressed that this made sense to the builder !!

Cheers

Dave


----------



## loudtubeamps (Feb 2, 2012)

Know we know where the term "Rat's Nest" originated when talking about amp wiring.
I'm sure that pic. of your radio or this one will be beside the definition in the dictionary.












Wholy Shite!
Those original Aerovox caps will have a date code on them.
cheers, doug


----------



## washburned (Oct 13, 2006)

One lead at a time.


----------



## nonreverb (Sep 19, 2006)

This set up along with a variac is ESSENTIAL if you wish to work on any solid state amps. Failures are instant where transistors are concerned and the probability of multiple failures is real. This method allows for a period observation before things go *poof*. It's the only way to test to see if there are still problems after an initial repair.



loudtubeamps said:


> If the amp hasn't been fired up for an unknown period of time, the electrolytic caps will most likley be pooched,especially if they are the originals.To fire the amp up without doing any damge while still allowing you to test/hear the audio path.....build up a cheap and easy load tester.
> 
> 
> 
> ...


----------

