Dr. Z help needed. Tube going out?

[reverbbb]

My Dr. Z Maz 18 Jr. has been misbehaving lately. Sometimes the amp will not make any sound, even though the pilot light is on, and the pre-amp tubes are all glowing. I noticed that when this happens that the Sovtek 5AR4 tube is not glowing. So, I turn off the amp and wiggle that tube and several others. Then I turn the amp back on and it may or may not come on. The few times that it did come on, I could hear the amp fade out to no sound, and I watched the tube glow go out.

So, I have almost concluded, that the tube is either making bad contact in the socket, or the tube is bad. But, the tube does not looked wrecked in any way - not discolored, nothing loose, nothing at all.

I noticed that the label stapled inside the amp, calls for a GZ-34 in that location.

1) Is the 5AR4 and the GZ-34 the same tube?

2) Do I need to re-bias the amp if I put a new tube in?

3) Any other suggestions of what might be causing this loss of sound?

4) Any suggestions of an inexpensive, but good replacement tube?

I just had the two EL-84 tubes replaced and re-biased by my amp tech. That was to get rid of some annoying hiss in the amp. For some reason, this loss of sound would never show itself to my amp tech. You know the saying, "If it ain't broke, I can't fix it". But, just as soon as I got it home, it started doing it again and with a lot of regularity. It is a lot of hassle to tote my amp back again (I have to take off work and drive to the other side of Dallas).

Somebody help!!!!!!

[zook]

reverbbb,

The 5AR4 and GZ34 are one-in-the-same tube.

Try cleaning the pins on the tube, then retensioning the socket. When you retension the socket, unplug the amp and turn both switches on for about 5 minutes. This will assure that any residual voltage has been drained.

If push comes to shove, get a new tube.

Winnie

[reverbbb]

If I replace the tube, will it need to have the bias readjusted (assuming that I might get another brand)?

I will try the cleaning and retention things first. I'm hoping that is all it is.

[zook]

Originally Posted by reverbbb

If I replace the tube, will it need to have the bias readjusted (assuming that I might get another brand)?

I will try the cleaning and retention things first. I'm hoping that is all it is.

reverbbb,

You won't need to rebias since it's a rectifier tube, not a power tube.

Winnie

[tomtheguitarguy]

I hope this problem didn't originate from you using both of the speaker jacks like you had discussed earlier. If so, it could be more than just a tube. But I would suggest just changing out the rectifier for now and seeing how it acts after that.

Did you ask Dr. Z about it?

Hope this helps.

tomtheguitarguy

[reverbbb]

Originally Posted by tomtheguitarguy

I hope this problem didn't originate from you using both of the speaker jacks like you had discussed earlier. If so, it could be more than just a tube. But I would suggest just changing out the rectifier for now and seeing how it acts after that.

Did you ask Dr. Z about it?

Hope this helps.

tomtheguitarguy

I also hope that this is not a problem that I caused. However, the information that I was getting from the other thread, is that the most danger of damage would be at the PT. This problem does not appear to have the symptoms of a bad PT. I would agree that the rectifier tube should be replaced, after I check for the continuity of the tube to the socket. It is possible that I stressed some tubes, though I don't know which ones.

I have not addressed this issue directly with Dr. Z (Mike). He did however, provide me with a solution to wiring two 8 ohm cabinets. He said that I could use a "Y" cord and wire them in parallel. This will give me a 4 ohm load that I could plug into the 4 ohm jack. The danger is, that I could insert the "Y" cord into the 8 ohm jack and overload the PT.

So, I opted for Winnie's suggestion and disconneted and capped the positive wire to the 8 ohm jack and hardwired a jumper from the 4 ohm positive to the 8 ohm labeld jack. That makes both jack capable of handling a 4 ohm load, and an 8 ohm load will not harm anything (at least as far as I know). So, if both cabinets are 8 ohms, then I can use a single cabinet or a dual cabinets, any time I feel like it. The major difference is, the single 8 ohm cabinet is louder than the two cabinets. But that is a good thing to my ears. I still have plenty of volume headroom when using two cabinets.

[reverbbb]

Thanks Winnie. Retensioning the socket did the trick as far as I can tell. I have added about an hour of usage singe this adjustment, and the problem appears to have gone away.


You're the DUDE!

[zook]

Aw shucks.

Glad to have helped.

Winnie