Silvertone 1484 repair *help*

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Silvertone 1484 repair *help*

Postby Jacobgaughf96 » Thu Oct 06, 2016 9:26 pm

Hi guy! Ok here is the shakedown...I just acquired a "sears" silvertone model 1484 head from a friend at work who just recently had a family member pass away. Upon inspection of the amp it would not emit any sound, All the valves would warmup nice and bright so I proceeded so flipped it over to get a look at the inside of the chassis.... a couple of wires were unsoldered from the output transformer and soldered in places that I just dont even understand the reasoning behind lol mainly being the ohm taps and the speaker jack(resolved except two ot wires). As of the moment I have gone through and measured most the carbon comp resistors and will be replacing the electrolytic caps very soon and honestly everything else is checking out except for 3 wires that I honestly have no idea were they go or what they do. I am still very new to tube amp circuits and schematics still look like gibberish to me so I wanted to ask if anyone is up to the task wouldn't mind helping me find where these mystery wires might be placed??? and see if I can perhaps get something from the amp before I start spending money on tubes and checking the output transformer and such. Thanks guys! and I most defiantly would appreciate it!

The first pic is of the two wires from the output transformer that I do not know of, the second being a red wire that was snipped for some reason and the third the schematic and fourth just for reference.

I know they're are so many factors that can go into this stuff like tubes considering they are all the original RCA tubes and the ot might be blown being I also heard they like to kill them but I know without a doubt before those are suspect incorrect wiring needs to be fixed first, Thank you so much guys!!-Jacob
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The wire to the right is a black/grayish color and the blue to the left
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Sears_Silvertone_1484_Twin_Twelve_REPRODUCTION_Manual-page-004.jpg
Sears_Silvertone_1484_Twin_Twelve_REPRODUCTION_Manual-page-004.jpg (224.73 KiB) Viewed 1214 times
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Jacobgaughf96
 
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Re: Silvertone 1484 repair *help*

Postby EWBrown » Fri Oct 07, 2016 5:20 pm

It looks like the primary of the output transformer may be disconnected (wires cut or unsoldered) from the 6L6GC plates. Typically, the primary winding's plate wires are blue and brown, and the center tap (which connects to the 480V B+) is red. The previous owner may have been trying to effect repairs on it.

When troubleshooting this amp, it would be a good practice to work "backwards" from the output stages, after checking that the power supply is functional.

A quick check is to 1: make absolutely sure that ALL power supply electrolytic caps are FULLY discharged, and that the power cord is unplugged. (Safety First)!

2: Measure the resistance between the two 6L6C plates (pin 3 on each one). It should read approximately 170 ohms (85 + 85). If it reads as "open" or as a very high resistance, then this shows that the OT primary is either disconnected, or open (burned out).

A typical 6L6GC OT has a 6600 ohm primary, and 4 ohm or 8 ohm secondary - in this case, 4 ohms, to accommodate the two paralleled 8 ohm speakers.

A replacement OT is readily available, if needed.

Try these, and let us know what you've found.

HTH

/ed B
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