Rocket Issue

[strato17]

Hey all,

I've been using my rocket build for almost 3 years flawlessly. However, tonight on stage, the amp suddenly cut out. I through the rocket on standby, and switched heads.

I turned the rocket back on, and tested it. The amp worked again for 3 songs or so, then cut out again. There wasn't a pop or fadeout, just abrupt silence. Does anyone have an idea where to start?

chris

[strato17]

Also, it was pretty hot outside, however, far from the hottest show i have played in the past few weeks.

[Mark]

The 80uF capacitance after the rectifier bothers me. This is an obvious area where I'd be looking for issues. Where have you looked for issues so far?

I fixed a Princeton six months ago where the filter cap after the 5Y3 was 47uF. I seem to remember the issue was initially intermittent.

I'm in the process of building a Rocket. I'm thinking of splitting the two 40uF caps to reduce the current flow on turn on.

[martin manning]

You need to get it in its failed state so you can diagnose the problem. Maybe just leave it on for an hour or two and try playing through it every 20 minutes or so.

The 80uF reservoir cap is a shot in the dark at this point. The size of that cap is going to stress the rectifier tube some, but the problem could be anywhere.

Mark, if you split the reservoir into two smaller caps, you would have to put a resistor in between them to control the surge, and that will reduce all of the voltages. Was the problem in the Princeton the cap or the 5Y3?

[Mark]

Hi Martin

Thanks for your reply. Agreed the 80uF us a shot in the dark, but I think the 80uF is simply bad design, it relies on exceptional parts not the average.

The 47uF cap blew the brains out of the rectifier, I replaced the cap with a 33uF cap, I know 20uF would have been better but it is a Princeton.

I was thinking of having one 40uF cap wired to the rectifier then off to the standby switch and the other side of the switch off to the other 40uF cap.

I'm not visualizing the changes you propose, is it the Merlin Blencowe standby switch with a 47K to 100K across the standby switch?

[martin manning]

The way the Rocket is configured the rectifier will get a controlled start, charging the reservoir slowly as its filament heats up, so I don't think that is much of a concern unless the power is switched off and then on again while the cathode is hot (and the standby is left on). In "run" mode, the current spike on each charging cycle gets higher as the size of the reservoir increases, and that would not be reduced by moving half of the capacitance to the other side of the standby, unless there was some resistance added in between. Adding some resistance on the AC side would be an alternative way to help control the run current peaks, but that would also reduce the B+ voltage, and I'm not sure that the peak run current is an issue since the time-averaged current is essentially the same.

Chris, you could replace the rectifier tube and see if that cures the problem, but you can't be 100% sure even if it seems to.

[redshark]

Chris...are you using a 4 notch mullard GZ34?

that is the tube Ken chose to be in rockets.

It's the one that can be stressed out by the design and handle it with no problems.

Hope that helps!!

[strato17]

Last night, I opened up the amp and checked all the solder connections. Everything seemed fine, as did grounds. I took out all of the tubes, and cleaned the pins and sockets. I suspect that excessive heat may have been causing one of the pins to lose contact.

The amp worked flawlessly today for about three hours or so. No problems at all. I ordered some new JJ EL84's to be safe.

Chris...are you using a 4 notch mullard GZ34?

that is the tube Ken chose to be in rockets.

It's the one that can be stressed out by the design and handle it with no problems.

Hope that helps!!

I am honestly not sure with Mullard GZ34 this one is, but maybe you can tell me?

[Firestorm]

Looks later. Even Japanese despite the label. More pics I could guess better.

[redshark]

By the way, you don't need tube retainers or any metal around that GZ34!!

Any reasons for it?

[strato17]

By the way, you don't need tube retainers or any metal around that GZ34!!

Any reasons for it?

just wanting to make it more roadworthy. I assume its not a good idea? haha

[redshark]

No you don't need it. If any preamp tube is noisy just put a rubber o-ring to avoid mechanical vibration but if you don't have that problem don't use them. And once again since the wreck chassis is NOT upside down you don't need any metal tube shields or retainers. That is part of the design and you can find it documented in a couple of Ken's interviews that shields affected tone in an adverse way basically shaving a layer of harmonics. The science behind it? if you put a metal shield you are creating a capacitor in every preamp tube that will roll-off the highs.
Now if you have another problem with your amp it can be fixed.

[Blackburn]

By the way, you don't need tube retainers or any metal around that GZ34!!

Any reasons for it?

just wanting to make it more roadworthy. I assume its not a good idea? haha

You could easily install this one if you care about motion.

http://www.cedist.com/products/S-H142

[strato17]

Well today the amp is completely dead.... No sound or hiss. Wish I had an extra cab with me off stage so I could diagnose.

[martin manning]

Hey that's great news! Now you can find the problem and fix it.