Sonzera 20 - Is this normal?

[IndyPilot80]

Hey everyone. I finally was able to pickup my first tube amp at a good price. I got a Sonzera 20 used. Everything seemed fine for the first day I had it and then it start developing a couple weird sounds.

First, it has a low-level hiss at any setting. Almost sounds like a fan, even though I know it doesnt have one. Second, it has a metallic rattle sound.

Being new to tube amps, I've tried everything I could think of. Tried all settings, channels, reverb on/off, etc... I reseating the tubes, I checked the bias (left was 30, right was 32). Tried a different guitar cable, tried different guitars.

Here is an audio file: https://voca.ro/1nUugMJYuvMK.
You can hear the hiss at the beginning but you may need to turn the volume up a bit. I then play a couple notes and you can hear the rattle trailing at the end of each note.

Any ideas?

EDIT: Well, the only thing I didn't try was a different speaker. I disconnected the internal and plugged in an extension and the rattle went away. Ugh....

 

[alantig]

Sounds like you have something a little loose in the cabinet or on the chassis. I'd bet if you poke around (not necessarily literally - lots of high current flowing in the chassis), you can localize it. It may be as simple as tightening some nuts and bolts and screws.

 

[IndyPilot80]

Sounds like you have something a little loose in the cabinet or on the chassis. I'd bet if you poke around (not necessarily literally - lots of high current flowing in the chassis), you can localize it. It may be as simple as tightening some nuts and bolts and screws.

Thanks for the suggestion! Actually, I went ahead and took the head and the speaker out, tightened all cabinet screwed, and put everything back in snug and it seems like the rattle has gone away!

Now, when I did this, I pulled all of the tubes out to just be safe and I think I found something interesting. V1 should have been the JJ tube but, if I'm remembering correctly, when I pulled them out I think the JJ tube was in V4. Either I'm imagining things or whoever had it last installed them incorrectly. If the JJ was was V4 instead of V1, would the amp still have worked? I mean, it sounds MUCH better now but, again, I may just be imaging things.

 

[Alnus Rubra]

Great result. Make beautiful music.

 

[shinksma]

Now, when I did this, I pulled all of the tubes out to just be safe and I think I found something interesting. V1 should have been the JJ tube but, if I'm remembering correctly, when I pulled them out I think the JJ tube was in V4. Either I'm imagining things or whoever had it last installed them incorrectly. If the JJ was was V4 instead of V1, would the amp still have worked? I mean, it sounds MUCH better now but, again, I may just be imaging things.

JJ is just a manufacturer. What matters, according to the PRS website, is that the Tubes should be as follows:

V1 12AX7, Common Input Gain Stage
V2 12AX7AC5, Gain Channel
V3 12AX7AC5, Reverb
V4 12AX7AC5, Phase Inverter

I have no idea what would happen if you swapped V1 and V4 - I am not knowledgeable enough about the various tube types to know what a "regular" 12AX7 does vs the 12AX7AC5.

EDIT: I found a website that seems to show that the regular 12AX7 has full gain in low, mids, highs, but is a bit noisy, while the 12AX7AC5 is lower gain overall and less noisy. But I have no idea if that is true in general, and is what makes them useful for particular roles.

https://www.amplifiedparts.com/tech-articles/12ax7-comparison-current-made-tubes