[HarleyMYK]

I turned on my MiniWatt S1 today and the on/off switch lit up, but the tubes did not.  I am guessing the fuse is blown, but I do not see how to access it.  I took off the top with the transformers and still did not see the fuse.  I am guessing I am overlooking something easy and will be embarrassed when told how easy it is. 

[yo2tup]

It should be right next to the IEC inlet on the outside of the case.

[HarleyMYK]

THANK YOU!    What I thought was just an icon of the fuse area was actually a tiny drawer with the fuse in it.  I finally figured out how to pull it out with some extra effort after your reply got me to focus on it some more.

[HarleyMYK]

False celebration.   
The fuse conducted electricity, no problem.  Anyone else ever have an S1 go dead except for the light in the power switch?

[JakeJ]

Got a digital camera?  Can you post a couple of fairly high resolution photos of the innards?  Failing that look for a burned out resistor or other components.  It stands to reason that if the pilot light (led?) comes on then the power fuse is OK.  There may be another fuse you don't know about inside.

I tried to search for a schematic but came up empty.  Anyone got one?

[HarleyMYK]

Thanks! I will take a picture these evening of what is exposed when the top comes off. I also plan to try replacing each of the tubes in the unlikely instance that blowing one tube shuts the unit down (could that even be possible?).

[JakeJ]

I found a picture of the S1 online, tiny lil' thing ain't it?  If there isn't a separate fuse for the heater circuit (the part of the tube that glows) then I suspect a resistor has given up the ghost.

That picture you take needs to be the highest resolution jpeg format you can produce.  Next you may not be able to upload the photo to AudioCircle due to the large file size so upload it to a photo sharing website like Photobucket or Flickr.  We need to be able to zoom in on the picture to be able to see the components close up.  If you don't have an account with one of those websites I can PM my email address to you and you can send it to me directly.  I'm off work today but start my work week tomorrow.

Jake

[HarleyMYK]

Jake, I sent a link to some high res photos in a PM.  Unfortunately, there is a plate blocking much of the insides that I cannot figure out how to pull out.  I still have not yet tried replacing each of the tubes, but that is my next step.  Thanks again for any thoughts.

[JakeJ]

OK, nothing obvious on the one side of the tube board visible in your photos(and what I am looking for will be obvious).  That plate is probably for shielding purposes and you will need to get it out of the way to see the components under it.  If you remove the four screws holding the tube board in place you may be able to access the screws holding the plate.

How many amps are wired is with the tube heaters in series, one tube heater in line after another.  So trying one tube at a time may show that the first tube has a bad heater and the others will glow when inserted in a socket.  It should not hurt the amp to try this.  However, I think the heater circuit is the problem and getting at the components under the plate is likely where the problem lies.

WARNING: DO NOT POKE AROUND IN THE BOTTOM OF THE AMP WITH THE POWER CORD CONNECTED OR THE AMP POWERED ON!!  THERE ARE HIGH VOLTAGES PRESENT AND CAPABLE OF CAUSING DEATH!!  If you are not familiar with tube amps and do not know what you are dealing with then you will need to get experienced help.

Here is my "edjumacated" guess from what I see on that first photo of the tube board.  In the upper right corner are four connections labeled "G, In, In, G", those are most likely the input connections from the RCA jacks on the back.  In the upper left corner are four connections labeled "G, B, V+, G", I think these are "G" ground",  "B" positive voltage, "V+" is another voltage from the power supply.  And "G" ground  The "B" is likely the B+ which is somewhere around 200 volts and the "V+" may be the heater voltage.  Next are the wires coming off the bottom of the board labeled "B, P, OUT, G", again the "B" is like the B+ to the center tap of the output trannies, "P" I'm not sure without a schematic but maybe another connection to the output trannies, the "OUT" is the signal from the output tubes to the trannies, and "G" is another ground.  From what I see all the amplification is contained in this board and (without seeing the other side) it appears there are no coupling capacitors in the amplification circuit.  Nice little amp from a design standpoint.

I'm hoping you can get that plate out of the way so I can see the power supply.

[HarleyMYK]

Thanks!  I took a couple minutes at lunch and popped in the original tubes with no success.  There are about twenty screws on the bottom that I guess I will remove tonight.  My fear is that there are some nuts on the other side that I will never be able to get in, but hopefully they are all sheet metal screws that just friction fit to the boards and sheet metal.

[JakeJ]

Sorry I couldn't respond earlier in the day but I had a really bad night at work.  Punched in @ 3 PM and punched out @ 3:30 AM (shoulda been 11:30 PM).  NOT happy since it was caused by someone who was sleeping peacefully while we tried to figure out what they did wrong.

Sorry about the twenty something screws but hopefully they have no nuts and are drilled and tapped into their little holes of receptacle-ness.  It was assembled so its gotta be able to be disassembled.  Go slow, post pictures and ask questions when things get confusing.  BTW, how are your soldering skills?  I am thinking that once we get into that power supply you are going to need to replace a component or two.

[Ericus Rex]

And do you know how to discharge caps?

[HarleyMYK]

Swamped with work and have not had a chance to open it up.  I am not great at soldering, but I do have a couple of soldering irons and solder.  I have never discharged a cap, but I am guessing there is some safe way to short it out with something that has some resistance.

[JakeJ]

Yup, a big sandblock resistor, say 1K ohm & at 10-20 Watts, will do.  Oh, and hold it with a pair of insulated pliers in case it carries a bunch of current as it might heat up and burn your fingers.    I usually just use a leather work glove.  If you don't have a resistor they are pretty cheap @ Radio Shack.

Just touch the resistor leads across the positive and negative connections on the big power supply caps.  Make sure the filled area on the resistor is pointed away from you, just in case.  All the little caps will have drained off through the rest of the circuit.  Wish I could find a schematic then I could give better instructions.