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‘79 DR103 mod question!
Posted: Mon Feb 06, 2023 5:49 pm
by Paul Sherman
Just picked up a beautiful 100 watt Hylight era head; can someone identify this mod with the pot on it?
Thanks!
Paul
- B181F1CD-28B7-4A8C-AFDC-A2E3876C6B94.jpeg (315.72 KiB) Viewed 979 times
Re: ‘79 DR103 mod question!
Posted: Tue Feb 07, 2023 6:44 pm
by mhuss
Looks like a voltage doubler for the bias - a common and useful mod for older DR103s, which in stock form don't supply enough bias voltage for modern EL34s. The pot is there to adjust the bias to the correct level.
When these amps were made, the original Mullard EL34s Hylight used were very consistent and robust, so they "hard coded" the bias voltage, providing no adjustment.
Re: ‘79 DR103 mod question!
Posted: Thu Feb 09, 2023 4:38 pm
by Paul Sherman
Excellent, thank you!