[baronbeehive]

Just found one caps problem and replaced, then try to on again, however bad luck still, this time another resistor smoke (Red arrow from picture below), so have to turn off immediately.

Just a shot in the dark but it could be wiring. You could approach the problem from that end and check the XLR output jacks on the rear panel, check each pin to ground to see if there is a grounding problem. This can happen and be difficult to see. Only pin 1 of each output, left and right, should be connected to ground.

 

[klnglim]

Thanks!

Its kinda baffling how some of the wiring is just routed so poorly.

On another note, one of my 100Ohm 5W resistors went up in smoke... any idea what could cause this ? I turned off the amp instantly and have ordered 10W Mills resistors instead. But im rather curious what could be the reason, everything else looks perfectly normal.

EDIT - Well found my idiotic mistake that cause one of the filter caps to go bye bye -

In case anyone new is wondering, that circled wire need to goto the ground pad to the left.

Sad i have to wait 2 more days now, everything was looking so pretty -

I have same mistake as u mention picture above , can u tell me what went wrong?

 

[bloodhawk]

I have same mistake as u mention picture above , can u tell me what went wrong?

I wired the one on the right incorrectly -

 

[klnglim]

I wired the one on the right incorrectly -

ok, now I got it. Will go back and check my amp later. Hopefully will work this time, thanks a lot anyway!

 

[baronbeehive]

Yes, that occurred to me so I measured resistance. I made another mistake when I thought that there was a dead terminal on the ammeter. I just remembered what bloodhawk said about there being a resistor in the backlight wire, so that's obviously why I couldn't measure continuity through that wire, probably nothing wrong with the blasted meter after all.

But as a warning to anyone buying new ammeters the new ones I got which displayed continuity across the terminals must be a different batch. Both the new ones showed continuity across the terminals, whereas both old ones didn't. The old meters measured 200 on the board and 300 ohms out of the board, which disagreed with the new ones, therefore I would conclude that the new meters may have different ratings which may vary according to which ones you buy.

Just quoting myself because I wanted to correct something I said: there was nothing wrong with the ammeters, it was the wrong value resistor that Sonic pointed out that was causing the problem. Both meters do display continuity over their terminals which reads as a low resistance on the ohmmeter as Maxx said, that's OK now that I've changed the resistor…... BUT.... I've switched on after upgrading the PSU resistors and others totalling 10 in all, plus a new Jupiter cap, diodes and transistors. Now there is no smoke like kinglim but one meter reads 60mA correctly and the other reads 30mA so something needs looking at again. At least the meters aren't behaving erratically like before!

Anyway next step take some voltages etc etc…..

Bit of a bummer that, I tried to be so careful, checked everything in triplicate but this amp just likes to bite back.

 

[klnglim]

I wired the one on the right incorrectly -

Well, I have checked all connection, nothing's wrong. When turning on, the left side meter light up follow by right side meter warm up slowly, unfortunately reading '0' and totally silence.
From what I have seen, the meter lights are too bright so I turn off the amp immediately to avoid component smoke again, I guess need to add small resistor to dim the meter light, by now
still searching for the cause of silence

 

[baronbeehive]

That's pretty weird, I've just taken voltages and they're all good:

power cathodes all read -80v/-104v give or take on respective sides of the cathode cap
power anodes all read 76v/101v give or take on respective sides of the 330R
driver cathodes all read 0.1mv/1v give or take on respective sides of the 377R
driver anodes all read 140v/186v give or take on respective sides of the 33K

...… yet the right hand meter reads 30mA only. This meter was not the one that was changed.

Only thing I've done on this circuit was to desolder the gain switch but the resistors all read good, and a desoldered switch is the same as a switch in place in the "off", (high gain), position, so it can't be that.

My reasoning now is that if the driver and power stages are OK I need to look elsewhere, after the power stage in the circuitry, or check out the connections from the meter back, any bright ideas anyone?

 

[baronbeehive]

I don't know if these voltages mean anything to anyone If so say now before I take the PCB out again!

1 & 2 are the red and white wires going to the left meter on the .68R
3 & 4 are the red and white wires going to the right meter lighting circuit, marked "right meter" on board
5 & 6 are the white and red wires going to the left meter lighting circuit
7 & 8 is the resistor marked "left meter" on board

I also measured 100v on each of the meter terminals.

Both channels sound fine and equal volume so without taking the board out, I'm not sure of the problem. I'm speculating that a meter resistor could have fried when a leg broke on one of the Jupiter caps, or maybe something on the back of the board.

Edit: Thanks Sonic for the pic, better quality than mine..... also his amp LOL.

The lighting circuit terminals were difficult to get at but measure 3.0mV each in the meter with the correct reading of 60mV, whereas the other 2 terminals read 0.26v (white wire), 11.7v (red wire), so something not right here.

I've made some corrections to this since first posting.

 

[baronbeehive]

OMG...…. just been listening to one of my fav tracks with the complete set of 421A's...… all I can say is simply stunning.... I'm speechless.... I'm going to have to have some time getting used to this!

On a side note there doesn't seem to be anything wrong with the amp, must be just a meter issue.

 

[SonicTrance]

OMG...…. just been listening to one of my fav tracks with the complete set of 421A's...… all I can say is simply stunning.... I'm speechless.... I'm going to have to have some time getting used to this!

On a side note there doesn't seem to be anything wrong with the amp, must be just a meter issue.

Do you have the 5998/421a bias mod in place? I can't remember. That also makes a huge difference in the LD! Great sounding tubes .

 

[SonicTrance]

Sad day, but it's time....
https://www.head-fi.org/threads/little-dot-mk-vi-super-modified-we421a.885848/

 

[baronbeehive]

Do you have the 5998/421a bias mod in place? I can't remember. That also makes a huge difference in the LD! Great sounding tubes .

Yes I have the bias mod in place..... but haven't used it yet as I'm concerned about the amp atm, it seems ok but until I sort the issue with the meter I won't use it, or the 421A's, the next step is to try the various cathode-anode settings on SQ.... and finishing with the CCS some way down the line!

Sad day, but it's time....
https://www.head-fi.org/threads/little-dot-mk-vi-super-modified-we421a.885848/

Sad indeed... I have considered this also, it makes sense for you though now that you have your other main amp.

Stay on the thread though Sonic!
.

 

[Maxx134]

Sad day, but it's time....
https://www.head-fi.org/threads/little-dot-mk-vi-super-modified-we421a.885848/

Wow, Dumbfounded...
Sale of the century(!)..

Will never see such a moded beauty for sale like this again...

Not sellin mine, but I like to follow SonicTrance footsteps into making one more amp in the fall...

Damm that amp is sweet.

 

[SonicTrance]

Thanks guys!
I really love this amp but I'm having too much fun with my DIY amps. Can't keep everything sadly, too little time.

 

[baronbeehive]

I just wanted to mention a few observations about the amp with the 421A's in, I know one or two of you will be interested. I've tried it twice briefly now and so I'm able to say one or two things:

I had two slight reservations about the amp before which were:

- bass lacking slightly in articulation - the bass is now very lively, good definition and balance, just the right amount

- some treble frequencies missing - these frequencies are back and the amp now performs at a very high level indeed. I had suspected all along that this was down to the RCA's which are a bit lacking in extension, I still like them however.

Also I noticed straight away the resolution and transparency has gone up massively and contributes to the soundstage accuracy and intimacy which was good before and is now top notch. I can't say about the size of the soundstage because my HE500's don't do massive soundstage unfortunately.

Everything else is spine tingling to the extent now that I can't imagine anything better. The only slight thing is that with a top level system the bass would be slightly tighter and snappier sounding, Maxx will know what I mean because I feel it's still better on the other amp. If the problem is down to the PSU and balance then the CCS mod could sort this, when I get round to it, but I suspect this is down to the amp design and probably the NFB. Possibly those massive film caps of coinmaster might do the trick - but I haven't got room in the house for them.

These are brief impressions but I would say now I'm pretty well totally satisfied with the amp, it has certainly come alive for me!!

Just a pity these WE's are so damn expensive and there's nothing really in between the RCA's and them sadly.