Retro Tech & Electronics | Mike & Toby snack time @retrotechandelectronics | Uploaded April 2023 | Updated October 2024, 7 hours ago.
General Mike and Toby evening snack video... Their attempt at a youtube short. Reposting this for them because they have no thumbs.
General Mike and Toby evening snack video... Their attempt at a youtube short. Reposting this for them because they have no thumbs.
![Sears Silvertone Twin Twelve 1484 Major Restoration Project [3/6]](https://i.ytimg.com/vi/SAU2KmtoJUQ/hqdefault.jpg "Sears Silvertone Twin Twelve 1484 Major Restoration Project [3/6]
Here in part 3 we continue with preparation with turn-up by installing the pot needed for the hum balance which replaces the filament center tap. After this a dry run without tubes is conducted just to be sure everything is ok. If the tap cant meet 6.3 without tubes it cant be the right tap and i have to switch to the next one. Given the one at around 7 volts its time to add the tubes to the amp.
With all of the tubes in the amp we come to find that the final filament voltage is 5.9. It looks like another turn or two will be needed out of that transformer. A retest with 2.5 wraps shows 6.2 volts at 120vac.
Following this The temperature gun will be used to measure the heat off of the transformer after 30 minutes or so. No heat issues were found. To celebrate, the transformer covers were stripped and painted, as well as the rewiring of the reverb tank.
I break out the impedance bridge to test the cabinet and confirm the impedance at 8 ohms.
I found an extra speaker jack that was inappropriately added to this cabinet that I could remove to place the hum pot into. After that, its time for the first full smoke test.
I wish this amp had an adjustable bias..... also I discover at this time that the standby circuit is garbage. I end up having to use several tubes from Cornerstone music to find something that operates within safe parameters.
This brings the project into the noise isolation phase. and there is no shortage of noise in this amp; all sorts of different types of noise from different stages.
This starts from the finals backwards to the phase inverters. Where things are already looking strange.
#retrotechandelectronics #vintagetubeamprepairs")
