Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: anteriorl5 on May 12, 2020, 08:29:46 pm

Title: '54 Super high frequency noise at volume: parasitic oscillation?
Post by: anteriorl5 on May 12, 2020, 08:29:46 pm
With no grid stoppers on the 6L6 power tube sockets I'm going to solder them in and see if that takes care of the problem. Wanted to make sure they go on same as on a Twin Reverb with same R values. Do I need both the 470K and 1500 ohm?
Title: Re: '54 Super high frequency noise at volume: parasitic oscillation?
Post by: sluckey on May 12, 2020, 08:46:43 pm
The TR uses 1.5K for stoppers and mounts them between pins 1 and 5 on the socket. It also uses 470Ω (not 470K) for screens and mounts those between pins 4 and 6.  Look at this layout for an example...

     http://sluckeyamps.com/misc/AB_Lite_II.pdf
Title: Re: '54 Super high frequency noise at volume: parasitic oscillation?
Post by: anteriorl5 on May 12, 2020, 09:20:28 pm
Just looking at the layouts for the supers; the 5E4 has 1500 ohm grid resistors across pins 5 and 6 and the grid input is soldered to pin 6. They are absent on the earlier models. So should I switch the grid input to pin 6, put the 1.5K resistors across 5 and 6 like the 5E4?
Title: Re: '54 Super high frequency noise at volume: parasitic oscillation?
Post by: sluckey on May 12, 2020, 09:27:42 pm
You said "Wanted to make sure they go on same as on a Twin Reverb with same R values." That's what I showed you.

But you can put them on any way you like.
Title: Re: '54 Super high frequency noise at volume: parasitic oscillation?
Post by: anteriorl5 on May 12, 2020, 09:42:26 pm
Perfect. I understand now, just wasn't sure if it mattered what pins to use. Thanks much!
Title: Re: '54 Super high frequency noise at volume: parasitic oscillation?
Post by: Willabe on May 13, 2020, 09:15:16 pm
Do I need both the 470K and 1500 ohm?

I always use both grid and screen stoppers on power tubes.

And they work best mounted as close to the grid socket lug as possible.