Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Sonny ReVerb on March 29, 2022, 05:15:46 pm

Title: Trem Injection
Post by: Sonny ReVerb on March 29, 2022, 05:15:46 pm

I want to add tremolo to a cathode biased amp I'm planning. I found a similar circuit in the Gibson GA-17RVT Scout. The PI is on the left, with the trem signal coming up from the bottom, and the cathode bias cap and resistor are on the right. I'm just wondering about the 220k grid leak resistors and the 330k resistor from their connection point to ground. What impedance would the power tube grid see? 550k? 880k?

The amp I have in mind has the same PI coupling caps (0.01uF), but 470k grid leaks and 6V6s. Thanks for any illumination...

Title: Re: Trem Injection
Post by: PRR on March 30, 2022, 11:09:02 am

With two worst-case tubes, 880k. One weepy tube, 550k. Two good tubes, it does not matter.

It worked for Gibson. Why second-guess?

Title: Re: Trem Injection
Post by: sluckey on March 30, 2022, 11:27:32 am

And if you want an intensity control for that tremolo look at this...

     http://sluckeyamps.com/RCA/Ampeg_J12B.pdf

Title: Re: Trem Injection
Post by: Sonny ReVerb on March 31, 2022, 09:16:09 am

Thank you, Gents. I was just concerned with the rated max grid resistance of 0.5 Meg. I will give this a try and report back.