Z28- Sound out of speaker when inserting tubes, powered up, then died. Help please!

[bgio]

Hello all,

Recently moved states and had to move my gear in the process. All the amp works fine, except the Z.

I removed the power tubes for the drive. When I put the power tube in I heard a sound in the speaker (power cord wasn't even plugged into the amp). Then fired the amp up. Light turned on fine, turned standby off and there was no sound. So I powered down and removed all the tubes and reseated them. Again, same thing happened when putting in the first power tube. Fired the amp up, turned standby off, some muffled sounds and then the light went out.

I removed the power tubes and shook them lightly and can hear some rattling in one. Also pulled the fuse and it was blown. Any ideas/help?

Thanks all.

 

[Jeff Gehring]

Did the keyway happen to break off one of the 6V6s? If so, it is easy to insert the tube wrong in the socket, which may or may not cause problems. Sounds like (at minimum) you'll need a new pair of 6V6s for it (and a re-bias and replacement fuse).

 

[Vanyu]

The sound you heard when putting the tubes in isn't out of the ordinary for amps that still have a little bit of power stored up in them from when you last played them.

With that being said, it sounds like you've probably developed a short in one of your power tubes, probably from a substantial jolt they may have had in the process of the move. Another possibility is that the tube could be shorted out by that piece of debris in the tube itself. See if you can shake that loose piece of debris to either the bottom of the glass, or to the bottom of the mica if it's blocking access to the bottom of the glass. Also make sure you're putting both tubes in the correct way, the plates should be facing the exact same way. Either way, you'll probably be needing some new 6V6's. To diagnose if it is 100% the power tubes, remove them from the amp, and power the amp up and take it out of standby. If your fuse still blows, something else is at fault. Make sure there isn't a signal going into the amp while you do this.

 

[bgio]

Thanks for your help everyone. I tried Dr Z's troubleshooting guidelines. Nothing blew the new fuse. I'll keep on eye on it, but everything seemed fine. Maybe something got jostled during the drive?

 

[Vanyu]

That's probably what happened. Have you tried powering the amp on out of standby with no power tubes installed?

 

[pdf64]

Note that the DrZ standby arrangement hot switches the reservoir cap onto the rectifier.
In the case of a tube rectifier, that pulls excessive surge current through the rectifier as the cap charges up, and will tend to reduce the operational life of the rectifier.
Standby has no technical merit, it seems to be included as a user convenience / because customers expect a high quality tube amp to have that feature.
It's not beneficial to tube life, and in this case, as described, is likely to be detrimental.
I suggest that you don't use standby; just switch the amp on / off as required, mute it by turning the volume down or pulling the input lead out a bit.