Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: ernie_jr on February 24, 2019, 05:07:28 pm

Title: 5f6a help
Post by: ernie_jr on February 24, 2019, 05:07:28 pm

Afternoon to all,I built a 5f6a with a hoffman board for a friend of mine. At first, the amp worked great. Friend calls me and says he moved the amp set it down (amp not in a cabinet yet) and recto arced. He shut it off right away. So, I bring it home andinstall a new rectifier (5ar4) and channel 2 (bright) works great, but channel one is full of distortion, mainly on the attack of the note. I have swapped out the 12ay7 without and change in sound. What do I need to look for?Thanks to all,Ernie

Title: Re: 5f6a help
Post by: sluckey on February 24, 2019, 07:14:12 pm

Check voltages on V1.

Replace the cathode r/c with a 1.5K/22µF. Any better?

Title: Re: 5f6a help
Post by: ernie_jr on February 27, 2019, 01:11:46 pm

My set up was a 1.5K on each cath. Bright has 22mfd cap across, normal has 220mfd. changed the normal to an 820 ohm and left the 220 cap on. No change. swapped in a 12ax7, no change. checked voltages, both side of tube are about the same. I am stumped. The bright channel plays great, but the normal still has bad distortion, especially on the attack of the note.Any other ideas?Thanks,Ernie

Title: Re: 5f6a help
Post by: sluckey on February 27, 2019, 01:25:23 pm

Replace the 220 with a 22.

Title: Re: 5f6a help
Post by: ernie_jr on February 27, 2019, 02:03:14 pm

Thanks, that pretty much cured it. Question? If it played fine before the recto flashed and fuse blew, what would cause it to sound so bad now with the 220mfd cap in there?Thanks,Ernie

Title: Re: 5f6a help
Post by: sluckey on February 27, 2019, 04:23:01 pm

Don't know. Maybe you don't have the full story? Maybe the cap just failed. Put another fresh 220 in it and see if it still sounds good.

Title: Re: 5f6a help
Post by: ernie_jr on February 27, 2019, 06:45:02 pm

Thanks for all your help Sluckey. I think I will leave the 22 in as I can not tell much difference between the 2. The person I built the amp for isa guitar player and uses the bright channel the most. I am sure there is still something missing since I dont know what cause the recto to flash
and blow the fuse, but at least I have a good amp to give back to him.Thanks again.Any new SUNN stories?Starting my build (finally) of a 200s with KT 120s and a second pre-amp based off the Ampeg B25 and Sand recto. Should be good for about 80 to 90 watts.Take care,Ernie

Title: Re: 5f6a help
Post by: sluckey on February 27, 2019, 06:48:19 pm

Quote

Starting my build (finally) of a 200s with KT 120s and a second pre-amp based off the Ampeg B25 and Sand recto. Should be good for about 80 to 90 watts.

Sounds like fun. Hope you will share that project with us.

Title: Re: 5f6a help
Post by: ernie_jr on February 27, 2019, 06:52:18 pm

Yep, Sure will