Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: 6v6Pin1 on July 09, 2015, 09:39:02 pm

Title: Stout kit cuts out at high volume
Post by: 6v6Pin1 on July 09, 2015, 09:39:02 pm

I just finished a stout amp and when I turn it up all the way it starts cutting out. From reading, I gather this is parasitic oscillation.
I was hoping someone could give me some things to check.

I checked my voltages against the schematic (I disconnected the feedback resistor):

v1
1: 191.0
3:     1.8
6: 198.0
8:     1.8

v2
1: 275.0
2:     0.0
3:     8.2
6: 289.0
7:     0.0
8:     8.2

v3
3:   10.8
7: 297.0
9: 304.0

v4
3:   10.8
7: 297.0
9: 304.0

Caps
A: 310
B: 308
C: 285
D: 278

Title: Re: Stout kit cuts out at high volume
Post by: markmalin on July 10, 2015, 03:43:21 pm

Can you post some pictures of the inside?


Mark.

Title: Re: Stout kit cuts out at high volume
Post by: EL34 on July 10, 2015, 05:41:55 pm

Hard to say
Your voltages are different from mine here
http://el34world.com/Hoffman/files/Hoffman_Stout.pdf (http://el34world.com/Hoffman/files/Hoffman_Stout.pdf)


What power transformer are you using?

Title: Re: Stout kit cuts out at high volume
Post by: 6v6Pin1 on July 16, 2015, 12:30:38 pm

I finally figured out that I made a mistake wiring the lugs together. The v2 voltages were way out of line and that was the clue. I fixed that and the amp sounds great now.

The transformers are by Hammond for an 18w Marshall.

Title: Re: Stout kit cuts out at high volume
Post by: Willabe on July 16, 2015, 01:49:06 pm

Quote from: 6v6Pin1 on July 16, 2015, 12:30:38 pm

I finally figured out that I made a mistake wiring the lugs together. The v2 voltages were way out of line and that was the clue.

Good reasoning! 

Quote from: 6v6Pin1 on July 16, 2015, 12:30:38 pm

I fixed that and the amp sounds great now.

              :bravo1: