Ugly distortion with tube amp when you play

[darkbluemurder]

I know this thread is over two years old but I have the exact same problem with my Hiwatt inspired build - an ugly ratty distortion on hard attacks, even with the normal/bright channel volumes only slightly open and the master at about half. Nothing in the Hiwatt schems indicate that the tone should be distorted at these settings so I doubt that this is normal.

I have had little time to troubleshoot so far but I can exclude tubes (changed the entire set bit by bit) and bias setting (does not affect it). It would have been interesting to know what caused the OP's issue but I doubt I have the same as my V1 wiring is quite different.

I will do some further troubleshooting and may come back with specific questions.

Cheers Stephan

[J M Fahey]

Hi Stephan, please start a new thread about *your* amplifier, post the schematic *you* used, "my V1 wiring is quite different" is absolutely insufficient, and if possible record and upload an MP3 or YT video showing "ugly ratty distortion on hard attacks" .
Thanks.

[Enzo]

Hi Stephan

I agree with Juan, provide us your schematic.

[1ampman]

Sounds like a ground is missing. Check the speaker jack for grd. Speaker wire. All grds.?... Center tap?

[J M Fahey]

Sounds like a ground is missing. Check the speaker jack for grd. Speaker wire. All grds.?... Center tap?

Please wait for the proper thread.
In any case symptoms mentioned do not match your suggestion pulled out of the blue.

[darkbluemurder]

I am not set up for recording but I will redraw my schematic and I will also post the voltages in a new thread. I can also include gut shots of the build when I performed further tests. These tests will include testing the preamp with a known good power amp and the power amp with a known good preamp to isolate the problem.

Thanks,
Stephan

[darkbluemurder]

Found it. It was a miswired output transformer, center tap was to one output tube and one side of the primary was to the center tap. Swapped the wires and all is fine. Problem solved.

Cheers Stephan

[Jazz P Bass]

Nice fix.

Where the OT wires 'standard' colors (Blue/Red/Brown)?

[darkbluemurder]

They are blue and brown for the plate connections and white for the center tap. I had the blue connected to the B+ (probably because this transformer was a 50W Marshall replacement, and they usually have brown and white wires for the plate connections and a red wire for the center tap so I must have thought the blue takes the place of the red).

I must say I am glad that my google search turned up this thread as I doubt I would have thought of a miswire of the OT's primaries otherwise. I even had measured the connections to what I thought was the center tap, got 87 and 43.5 ohms but I didn't get the clue. But after having checked the preamp through a different power amp and got fine tone, I knew the culprit had to be in the power amp section. Since I knew the PI was fine (tried 3 tubes there) and the power tubes were fine (tried two different sets), everything pointed to the OT. Checked the OT's data sheet and then it was clear. Took measurement between the right connections and got 43.5 and 43.2 ohms. Not only does the amp sound great now, it is also dead quiet.

This amp had me stumped for weeks. Now that it's finally working correctly I can move on to tweaking it.

Cheers Stephan