Little Dot MK8SE / MK6 Super Mods (All verified mods are on first page)
Aug 9, 2018 at 6:52 AM Post #3,422 of 4,154
Yes, there is! The 5998!

Yes I know, I was keeping quiet about them, I know where I can get some. I dare say I will probably end up with those as a compromise..... with the bias mod suitably adjusted!

I think you said you liked them but they were not quite as dynamic as the 421A's.
 
Aug 9, 2018 at 7:04 AM Post #3,423 of 4,154
Yes I know, I was keeping quiet about them, I know where I can get some. I dare say I will probably end up with those as a compromise..... with the bias mod suitably adjusted!

I think you said you liked them but they were not quite as dynamic as the 421A's.
Right! I still have a NOS quad (+ 1 spare) WE421A.

If you're interested shoot me a pm.
 
Aug 9, 2018 at 12:16 PM Post #3,424 of 4,154
Right! I still have a NOS quad (+ 1 spare) WE421A.

If you're interested shoot me a pm.

Thanks Sonic, but it's not the right time. I intend to live with these 421A's for a while, then decide between these and some 5998's. I think I can get the 5998's for one third the price of 421A's,that will probably clinch it for me!

Another interesting tube is the TS 6080 and 6AS7 but they're impossible to get hold of.
 
Aug 12, 2018 at 10:42 AM Post #3,425 of 4,154
Still trying to find the problem and I have a couple of questions:

- The amp meters read 60mA, left meter, and 30mA, right meter with 6AS7G's in
- Power/driver anode/cathode readings all good
- Both terminals on the meters read 100v
- Both legs of the .68R in the middle of board going to left channel read 100v
- The sound appears to be all good
- the only discrepancies in voltage readings appear to be in the meter lighting circuit and so surely that is not important

Bearing that in mind where could the problem be and where on the board are the 2 circuits for the right channel connected?

Could the meter itself be a problem? This is not the meter that I changed.

I'm wondering if the output of only one circuit is getting through. I'm at a bit of a loss here.

Edit: I did notice that the resistance over the terminals of the right meter is twice that of the left meter, which could indicate a fault further down the line but I can't find any faults anywhere.
 
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Aug 15, 2018 at 4:55 AM Post #3,426 of 4,154
I've drawn a conclusion about this:

The voltages at the anodes/cathodes are good
The voltages at the meter terminals are both the same
The resistance across the meter terminals with the faulty reading is way higher than the other, new, meter
I can't find any fault with anything else.. so...

... the meter must be faulty, probaly gone open due to a voltage surge either when the capacitor broke off or due to the mistake with the resistors

I was probably right about a meter fault before but for the wrong reason - so the amp is off to the engineer again to get the other new meter soldered in place...... hope I'm right about this…..
 
Aug 15, 2018 at 5:10 AM Post #3,427 of 4,154
I've drawn a conclusion about this:

The voltages at the anodes/cathodes are good
The voltages at the meter terminals are both the same
The resistance across the meter terminals with the faulty reading is way higher than the other, new, meter
I can't find any fault with anything else.. so...

... the meter must be faulty, probaly gone open due to a voltage surge either when the capacitor broke off or due to the mistake with the resistors

I was probably right about a meter fault before but for the wrong reason - so the amp is off to the engineer again to get the other new meter soldered in place...... hope I'm right about this…..

Did you check if the new meter has a resistor soldered in line?
 
Aug 15, 2018 at 11:57 AM Post #3,428 of 4,154
Did you check if the new meter has a resistor soldered in line?

Do you mean the resistor on the end of the red lighting wire?

That one is still there, haven't checked the value though. But I measured across the terminals above that resistor, not from the other end of the 2 wires going into the terminals.
 
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Aug 15, 2018 at 12:54 PM Post #3,429 of 4,154
Do you mean the resistor on the end of the red lighting wire?

That one is still there, haven't checked the value though. But I measured across the terminals above that resistor, not from the other end of the 2 wires going into the terminals.

Nope there is a resistor in line with one of the terminals on the ammeter. If i remember correctly its a 68Ohm resistor in series on the positive terminal of the meter. Its pretty well heat shrunk, so hard to notice.
 
Aug 15, 2018 at 4:32 PM Post #3,430 of 4,154
Nope there is a resistor in line with one of the terminals on the ammeter. If i remember correctly its a 68Ohm resistor in series on the positive terminal of the meter. Its pretty well heat shrunk, so hard to notice.

upload_2018-8-15_21-29-41.png


You mean this one?
 

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Aug 15, 2018 at 4:44 PM Post #3,431 of 4,154
Aug 16, 2018 at 4:59 AM Post #3,432 of 4,154
Looks like it yeap.

upload_2018-8-16_9-48-46.png


Yes, that's the low voltage backlight circuit, with the resistor to lower the voltage, which you found when you were working on your amp. The other circuit is the power circuit coming off those 2 x 0.68R resistors, which I mistakenly thought were 0.68k, which could have blown open the meters. The fact that the resistance across those terminals is different must result in the different current at the meter.... I hope!

Edit: you were right the resistor under the heatshrink is 68R.
 

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Aug 19, 2018 at 8:32 AM Post #3,434 of 4,154
Well.... it was the meter, 2 new meters installed and everything's fine now thankfully!
 

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