[Deleeh]

Hello,
My Little Dot 1+ broke last week.
I was able to find the fault and it seems to be the capacitor.
I will replace it and make a few improvements that are not pretty from a manufacturing point of view, but nothing more.
My first question is the film capacitor from Mex.
This one
https://www.conrad.de/de/p/tru-comp...f-275-v-ac-10-15-mm-l-x-b-x-h-18-1564957.html

Can I also install this one from Wima?
https://www.conrad.de/de/p/wima-mkx...2-f-275-v-ac-10-15-mm-l-x-b-x-h-1-451671.html

It should be the same in terms of the values.

The second question is when the whole conversion is finished.
Do I have to readjust the bias control by changing the condenser and film capacitor or can I leave it as it is?

Would be very nice if someone could help.

 

[TrollDragon]

As long as you are using the same value caps there shouldn't be a problem.
There are no bias adjustments on the Little Dot.

 

[Deleeh]

As long as you are using the same value caps there shouldn't be a problem.
There are no bias adjustments on the Little Dot.

Hello,
Thank you again for your answer and help.
I was able to clarify the issue with the film capacitors.

But I think it has a bias control, I saw on the picture the two small blue boxes could be adjusted.
I'm just not sure if you have to realign them even if you used the same capacitors after the repair.
I measured it once and it was 30 on the right side and the left side was below 30 and fluctuated all the time.
And the tube failed after 1 minute.
When I held it in my hand to check something, the led indicator started to light up briefly even though there was no current.

 

[TrollDragon]

Hello,
Thank you again for your answer and help.
I was able to clarify the issue with the film capacitors.

But I think it has a bias control, I saw on the picture the two small blue boxes could be adjusted.
I'm just not sure if you have to realign them even if you used the same capacitors after the repair.
I measured it once and it was 30 on the right side and the left side was below 30 and fluctuated all the time.
And the tube failed after 1 minute.
When I held it in my hand to check something, the led indicator started to light up briefly even though there was no current.

The two blue 10K trim pots are for adjusting the Vbe multiplier of the output transistors, they have nothing to do with the tubes.

The tubes in the LD I+ run in a cathode follower configuration.
http://www.valvewizard.co.uk/accf.html

 

[Deleeh]

The two blue 10K trim pots are for adjusting the Vbe multiplier of the output transistors, they have nothing to do with the tubes.

The tubes in the LD I+ run in a cathode follower configuration.
http://www.valvewizard.co.uk/accf.html

All right, thank you again. I haven't changed anything on this control, fortunately.
I got the parts today and installed them.
The base is new and also fixed now.
The Fine Gold capacitors from Nichichon are also installed.
I bought the wrong capacitors from Audionote, I was a fool.
I didn't even look at the dimensions.
That's why they were so expensive.
Now I have found some from Audionote again, these are here, but they are normal improved "standard" caps.
https://www.hificollective.co.uk/catalog/1000uf-25v-audio-note-standard-electrolytic-capacitor.html

Only with the right value 2200 to 25V.

The others are beautiful but unfortunately they don't fit, there isn't enough space and I didn't want to make a big change just because of the caps.
It annoys me but that's the way it is now.

I made a temporary solution to see if it works again.
If I pull the headphone plug out very slowly, the right one goes out and the left one comes on.
I think the contact in the Rca socket is not right or the cable itself.
I'll have a closer look next week when I get the right caps.

By the way, the Wima film capacitors did not fit.
Because the wires were too short or separated from the factory and you can't bend them as you need.
I installed new Mex and was able to bend everything the way I needed it.
The new Mex I ordered from Conrad are much thicker than the ones I had.

 

[TrollDragon]

If I pull the headphone plug out very slowly, the right one goes out and the left one comes on.
I think the contact in the Rca socket is not right or the cable itself.

Pulling out the headphone plug very slowly will cause the sound to go from one channel to the other as you are making/bridging connections while the plug is moving across the contacts. I always have the volume set to zero when plugging in or removing headphones and I only turn the amp on or off with no headphones attached.

 

[Deleeh]

Pulling out the headphone plug very slowly will cause the sound to go from one channel to the other as you are making/bridging connections while the plug is moving across the contacts. I always have the volume set to zero when plugging in or removing headphones and I only turn the amp on or off with no headphones attached.

Yes, I'll do that too.
Okay, yes, that makes sense.
I checked again today.
I bought a new cable and will lay it as originally.
Because the cable I ordered was too thick, I took a headphone cable, but that was also a waste of time.
I also saw that a bit of solder had come loose from the tube socket, so maybe that was an additional cause.

I'll have to wait until the right capacitors arrive anyway, until then I can't do anything to check it again.

Thanks again for your help.

 

[Deleeh]

Hello,

it seems that the Little dot has completely given up the ghost.

The new capacitors are in and I have a hissing sound when I switch it on.
And only the right channel runs relatively quietly.

The left one definitely doesn't get any power because the tube doesn't even start to heat up.
I almost suspect that the transformer got one too.

In general, the device I got at that time must have already been in use.
So I probably got a replacement unit that was defective.
It's not normal for it to give up the ghost after 300 hours.

What a pity. So the attempted repair was unfortunately a failure in that respect.

 

[TrollDragon]

If you just changed out caps by installing new ones using the same polarity as the old ones there shouldn't be a problem with no sound or a tube not heating up. There has to be a wire disconnected from the board, a component unsoldered/bridged etc. You will need to go through with a meter and check the heater voltage, DC power levels, making sure that power is getting where it is supposed to be etc.

I can't see the transformer going bad unless it was hard shorted and you would have smelled it getting hot. I would check to see if there is AC voltage on the secondary windings going to the board. There should be a pair going to the tube heaters and a pair going to the DC rectifiers. Checking the voltage on both sides (AC in / DC out) of those rectifiers is a start.

 

[Deleeh]

Hmm okay.
If something was conspicuous, then it was the cables that came loose from the transformer to the circuit board, but these were all isolated ones that could not be mixed up.
I took photos beforehand and compared them.

And I also looked at everything again to see if anything had no contact - visually there was nothing to see.
But I'll probably have to measure it, I'm a bit of a sucker at that.
Where I measured was on the picture with the yellow marked arrow on the back of the plus to the minus lines or where the cables from the transformer are soldered on. I think this must be the power supply. The middle one shows values, which is also the right channel, and the lower left one (left channel) shows zero.
The light emitting diode also no longer works.
Either only part of the voltage is there and there must be an interruption somewhere.
Which is more likely.

Nothing smelled and the fuse remained intact and can be switched on and off normally.

 

[tomchr]

First fix. Then modify.

As long as you haven't touched the bias pots you should be able to get it working by swapping the dead capacitors. Just pick some decent ones from Nichicon, Panasonic, KEMET, or other good manufacturer. As you've discovered, get some that are of the same dimensions (diameter, pin pitch) and fit within the chassis (so the height can be different as long as it fits in the chassis).

Film caps only rarely go bad. You can kill them with over-voltage, but that's about it.

If you're now getting hiss, you probably have a bad solder joint.

It's normal with some scratchy noises when you unplug the phones. The 1/4" connector will briefly connect left and right channels together. You can also get the right channel shorted to ground. Some MILSPEC connectors have a little hump between the ring and the sleeve and tip, respectively, to prevent this. If the amp does not have a built-in current limiter it's best to turn it off when you plug/unplug the phones.

Tom

 

[tomchr]

If something was conspicuous, then it was the cables that came loose from the transformer to the circuit board, but these were all isolated ones that could not be mixed up.
I took photos beforehand and compared them.

Excellent!!

Where I measured was on the picture with the yellow marked arrow on the back of the plus to the minus lines or where the cables from the transformer are soldered on. I think this must be the power supply. The middle one shows values, which is also the right channel, and the lower left one (left channel) shows zero.

A dead power supply cap can take out a bridge rectifier (the round, black thing with the + on it).

There are two terminals on the rectifier marked with a ~ symbol. Connect an AC voltmeter to those two terminals. Do you get voltage there?

If you do get AC voltage into the bridge and no DC out, the bridge rectifier is dead. That style is called WOG. 2W10G from Vishay (Mouser P/N: 625-2W10G-E4) would be a suitable replacement. It's worth checking the supply caps before you swap the bridge, though. If the supply is discharged (i.e., you measure < 1 V on it) you should see a fairly low resistance when you measure across the supply. This resistance will rise towards infinity as the supply caps are being charged by the ohmmeter. If the resistance remains low, the caps are dead. But given your explanations so far, I'd look for bad solder joints and disconnected wires first.

Tom

 

[Deleeh]

Hello,
Thanks for your help.

yes, the lower one shows nothing when I measure from plus to one of the signs.
The upper one does, however, where it also shows me measured values.

Is that perhaps the reason?
If so, I'll have to see where I can get it.

 

[tomchr]

You should measure with the voltmeter on the AC setting. Stab one probe of the meter on one ~ pin and the other probe of the meter on the other ~ pin. That should show an AC voltage. If you get that but no DC on the output (measure from + to - with the voltmeter on the DC setting) the bridge is likely dead.

The WOG style rectifiers are very common. You should have no trouble finding a replacement. Get one rated for 800-1000 V. It's the same price as those rated for lower voltages.

Tom

 

[Deleeh]

You should measure with the voltmeter on the AC setting. Stab one probe of the meter on one ~ pin and the other probe of the meter on the other ~ pin. That should show an AC voltage. If you get that but no DC on the output (measure from + to - with the voltmeter on the DC setting) the bridge is likely dead.

The WOG style rectifiers are very common. You should have no trouble finding a replacement. Get one rated for 800-1000 V. It's the same price as those rated for lower voltages.

Tom

If I measure between the characters I get no values only if I connect Plus to one of the characters I get some.
As you have just written.

One of them is probably broken if it doesn't show anything.

Can I find some at Conrad?
It says 2W10 on these parts.

Thanks again for the information.