Ceriatone Forum

I just clipped one of my KT77's and broke the damned thing, so now i'm hanging out while i wait for a replacement.
Mean time, and while i wait, i'm hoping someone might be able to give me a pointer.

Before the tube broke i had biased the amp up and was ready to plug in my guitar.
I plugged in and turned up the volume and, nothing.
No sound.

All of the tubes were lit up and getting power.

I checked my guitar cable and changed to four others, same result.
I swapped guitar, same result.
I even swapped speaker cable and cab.. same result.

I've drained the caps and taken out the preamp board and the power amp board and checked the wiring and it all looks good.

I've checked the wiring against the layout diagram and it looks good, but i'll check again when i have a clearer head. I'm a little pissed at my self for being dumb and breaking the KT77.

I've traced the wiring from the boards to the chassis mounted components and it all looks good.

I realize this is a bit abstract, but where would you be looking?

There have been no pops or bangs.
No burning smell.
The tubes biased up fine and the amp seemed happy sitting with current running through it.
Every thing seems all good, except no sound.

Any tips?

Cheers.

Did you build this amp yourself?

What I do for troubleshooting, which almost always finds the problems, is first - take some time off. Get some rest. Attack the problem with a clear head, well rested. Then, take your DMM and put it in continuity testing mode, and just start going over every single connection that you soldered. Test from component to component, not just solder to solder - if there's problems outside of the solders you want to find them. Also check that connections aren't being made to nearby things that aren't supposed to be connected! Use the layout while doing this, perhaps a new printout of it, checking off connections after you've cleared them. Hopefully you'll turn up a cold solder or a solder that you forgot to make - this is the kind of thing that plagues even experienced builders. Be patient doing this - and allow hours to go over everything.

Oh, and if you built this yourself, double (triple!) check the input jack wiring - the way it's shown on the layout can be a bit confusing. Likewise for the output jacks.

Yeah..

Built my self.
I'm taking your advice about the time off.
I'm a tad annoyed at my self for busting the tube the way i did :-[

When you say check the input/out put and then you mention the layout can be confusing, what do you mean exactly?
I'm thinking this is going to be a problem related to either of these simply because i get no sound.
I'm wondering if i might have them wired backwards.

In the diagram the jacks have four pins each.
The jacks are shown on a slope.
I assumed that the jack was sloping away from the chassis.
So, the pin at the top of the slope was the pin closest to the chassis wall.

Does that make sense? 

Oh, and one other question..

Do i need the amp to be tubed up and powered on to do the continuity test?

NO! Not only is it not needed, but would be somewhat dangerous for just a general continuity test.

It sounds like you have the right idea about the input jacks. Maybe that's not the problem.

Here's how i did mine - I flipped them to the outside of the chassis to have better access but still have the spacing correct - mine's a bluesmaster, but it's probably close enough -
(http://home.comcast.net/~sduck409/ampkit%20011.jpg)

Speaker jacks are wired mirror back wards.
So the bridging wires that are nearest the chassis should be on the out side of the jacks and visa-versa.

Just out of interest, and at the risk of sounding dumb, how would i go about testing the whole amp with my DMM set up in continuity test mode?
I figured it was a case of putting one probe at one end of a chain and the other probe at the other and waiting to get a beep.
But that doesn't seem to work..

Cheers for all the help so far.

Yes, that's one of the things that can be confusing about the layouts - the stuff on the back panel is kind of backwards in relation to how it's depicted on the front panel. I found it easiest to use common sense as a guide - know which connections are supposed to go to ground and work from there.

About continuity checking - set your dmm for that - so that when you touch the 2 probes, they beep (or give some kind of indication on screen, depending on how yours works). Then you just start checking connections - like in the input section, you might want to plug a cord in the high input jack, and put one probe on the unplugged tip end of the cord, and then poke the 2 resistors on the terminal block near v1 with the other probe - you should get beeps on both resistor leads (on the sides closer to the terminal block). Switch the cord into the lo input, you should only get a beep on one resistor - A2. Basically, you want to check the integrity of all your solders; so anything you soldered should get checked. There are a lot of them, so take your time; be thorough. From what I've heard, problem areas to start with are all the ground connections - it can be hard to get a good solder on these, especially if you've bolted down the connections before soldering - the bolt acts as a heat sink, so it takes longer for the solder to really heat up enough to make a good connection. Likewise with the bus bar over the knobs. If you have a way to attach an alligator clip to one probe of your dmm it'll make testing all the ground connections a bit faster. I'd also recommend triple checking everything around the main controls - there's a lot of detail stuff there, and just one wrong connection and it won't work. And don't forget to test stuff that looks obviously connected - like in the picture I posted, that green wire that connects the 2 jacks - put your probes on the lugs of the jacks and check that both those solders actually work - cold solders can fool you - they can look fine but won't be making a good connection. (btw there are a few less than good solders in that picture - I think I went back and redid some of them after taking that)

Oh, and make sure you've drained all the caps before doing any of this! And obviously disconnected the power.

It Lives!!

It was the speaker outs after all.
10 minutes to fix and now i'm rocking.
My wife is very pleased, it means she can get that corner of our bedroom back that has been turned into my building station.

Thanks for all your help.
 ;D ;D 8) 8) 8)

Yay! And good work. Now play that thing til it's gold...