Losing power

[shujinko]

Hi all,

Looks like I'm having a power issue with my Crack.  The unit is about 13 months old.  I've tried several different tube combinations and different volume levels and it happens regardless.  The power switch seems to be working because when it's on I can feel a faint buzzing from the 6080 tube and I can hear the "click" interference with my desktop speakers.  Recently, on occasion, I have had to turn the switch off then on again to get power, but this morning it just doesn't want to come on.  On a few attempts I have gotten sound for around 90 seconds, but then it quickly drains and I can see the tube glow disappear.  The capacitors seem fine and all my solder connections look okay (besides some mild discoloration on certain contacts).  I am very much a novice when it comes to this, so don't take my word for it.  I'd be glad to provide pictures if necessary.

I keep my Crack at the office and I don't have a multimeter on me right now, however if there are connections I should be checking can you please let me know which ones?  I still have the original documentation at home (somewhere) so I can check voltages against that when I get home.

This may also be worth mentioning:  I've gotten a bit of static in the last few months.  I can usually make it go away by jostling the tubes in their sockets slightly so I am guessing they are just getting a little dirty.  Any recommended cleaners for the tubes and the sockets would be appreciated.

Thanks.  This is going to be a long day of crack withdrawal...

[Laudanum]

For the static, just insert and remove the tubes from the sockets several times for starters.  The friction will clean the tube pins and socket contacts.   

Smarter folks will be better at giving you advice for starting points for the power issue.  Sounds like it could be (and probably is) very simple and may be the switch eventhough you say you dont think it is.  You could start with resistance checks and for or starters,  I would probably jumper the switch contacts  (alligator clips on the ends of a short piece of wire)  bypassing the switch internals just to rule out the switch.  Simple and quick.  Just make sure it's unplugged before doing so.   But again,  more thorough advice will be forthcoming.  Hang in there.

[Doc B.]

First and foremost, redo all of the voltage measurements. That will give us something to work with.

[Laudanum]

First and foremost, redo all of the voltage measurements. That will give us something to work with.

Im not the sharpest pencil in the drawer but I would have suggested the same.  But the OP cant get the amp to turn on.

[Doc B.]

I guess I was reading that he hears a buzz from the 6080 and gets sound for 90 seconds. The condition described sounds like a connection that has come loose or a tube going south.

[shujinko]

I hear the buzz from the 6080 when the switch is on no matter what.  The tubes just never get juice.  Once in a while (if I switch on and off many times) they get juice for a little bit and then die.  I'll see what the deal is when I get home to the multimeter.

EDIT:  For what it's worth, the buzz may or may not be coming directly from the 6080, however when my hand is resting on it feeling for heat that is where I feel the buzz.

[Laudanum]

Sorry, I misunderstood.  I thought that as of this morning you got nothing at all. 

[Doc B.]

Sounds like maybe a bad power switch

[shujinko]

Finally got around to testing this.  I think the transformer might be bad.

Power is on.  Multimeter set on AC shows 117 volts coming in from the socket, into the switch, out of the switch, and still 117 at terminal 1 of the transformer.  When I switch to DC and check terminal 1, the reading flops back and forth between 2.5 and 2.7 volts.  Does this mean the transformer is bad?  Should I continue testing anything?

[Doc B.]

Measure the voltage with the meter set on AC, as DC is irrelevant on the transformer primary. Check it by putting the black test lead on power trans T2 and the red test lead on power trans T1. Should be 0VAC with the power switch off, 117VAC or so with the power switch on. If it is intermittent, the switch has probably worn out and needs to be replaced. This can happen because the plastic bodied switch sometimes gets a bit soft from overheating when soldering, and sometimes it doesn't show up until the switch has been through a lot of power on-power off cycles.

If that voltage is OK, measure AC volts across T4 and T6. This should be about 6.3VAC. Then measure AC volts across T9 and T10. This should be in the 150VAC ballpark. If all those readings check out the transformer is fine.

[shujinko]

It's powering on and off now.  No idea why.  It has not powered off yet, either.

I tested several times and T1 and T2 behave the way you describe above (normally).  However, T4 and T6 show 82.5 VAC.  T9 and T10 show 162 VAC.

[Doc B.]

Oops, my mistake. I meant to type

measure AC volts across T4 and T5. This should be about 6.3VAC.

[shujinko]

No worries.  5.73 between T4 and T5.

It seems okay now.  The next time it starts acting up I will check the switch.  Think I should order one anyway to have on hand?

[Grainger49]

The problem is the switch and trying to measure AC when your meter is set to DC.  (insert smiley face here)

You don't get DC till you go through the rectifier diodes.  On the downstream side of the diodes you have very, very lumpy DC which gets filtered through the caps and resistor.  Then you have smooth DC.

[Doc B.]

No worries.  5.73 between T4 and T5.

It seems okay now.  The next time it starts acting up I will check the switch.  Think I should order one anyway to have on hand?

Based upon the behavior my educated guess would be yes, get another one and go ahead and install it. You might try wiggling the existing switch a bit while it is in the on position to see if you can get it to cut out.