Retro Tech & Electronics | Sears Silvertone Twin Twelve 1484 Major Restoration - Demo Day @retrotechandelectronics | Uploaded January 2019 | Updated October 2024, 15 hours ago.
I was able to get some time with Pete at Cornerstone music to test and critique the Silvertone 1484. Not only do my restorations generally get critiques here, but it was from this very place that I picked up the amp when it was first dropped off.
I was able to get some time with Pete at Cornerstone music to test and critique the Silvertone 1484. Not only do my restorations generally get critiques here, but it was from this very place that I picked up the amp when it was first dropped off.
![Sears Silvertone Twin Twelve 1484 Major Restoration Project [4/6]](https://i.ytimg.com/vi/gMNh0eFGOnI/hqdefault.jpg "Sears Silvertone Twin Twelve 1484 Major Restoration Project [4/6]
With this the fourth part in the series , we continue the troubleshooting with the 6FQ7 phase inverter section. A method employed was simply disconnecting the phase inverter section from the finals physically and ruling out that section. With this the final section was quickly ruled out as the culprit. Interesting point, given the different output and no tube in the socket, a passible component must be producing the issue!!!!
I quickly learn that we have some considerably STRANGE resistor issues throughout!. Resistors out of spec are simply replaced, thats a no brainer. and i got lucky too because that fixed one of the first issues in the amp. Though its improving, there are so many artifacts, thee are other things too.
At this point I bust out the T4 Heathkit signal tracer. With this I can hear the clicking, and the hum and the his and everything, But its noise mode that really finds things like this. Turns out its a noisy resistor causing this one. Even removed we can hear the resistor cracking in the T4 in noise more. One less noise in the amp. but still work to do, but the phase inverter is finally cleared.
Working back to the pre-amp section, there is no shortage of problems either. Though, voltage measurements show that there is more resistor changes to be done, identifying complete failures in circuit.
Even with the voltages finally within reason, I continue to find noisy resistors, so I continue swaps just for that reason alone.
An added bonus is a tube socket pin repair I did, as I managed to break one off. Luckily I keep spare parts for this occasion.
A function test is done to include reverb, tremolo and also.... AM radio.... Yes.... AM radio
Another round of voltage re-measurements are conducted and shown to be good, except for a few minor changes to do.
We get the amp sitting straight on the bench and begin some signal testing one issue I found was an oscillation in the reverb section i could not initially identify that was tied into the treble somehow. I get it back in test position to validate the feedback. Turns out, I needed a smaller test speaker when the amp is out of cabinet. No trouble found. The Crapola mini test speaker validated this. Including my no frills Peter Framption impression.
A last walkthrough is done with the T4, and the output coupled to a dummyload.
A last artifact lead to an interesting event, finding a bad connection during more resistor testing, turns out it wasnt the resistor, but its solder to the phase inverter. Test with the T4 shows no hum at the 6AU7, and a test on the speaker sounds good.
Not a single artifact is heard through the speaker on a shorted input with the volume turned up. That completes this portion of the project. Tune in for the next video in the series.
#retrotechandelectronics #vintagetubeamprepairs")
