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    Building, troubleshooting and testing of these amplifiers should only be
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Yaqin mc10L

Time for a little rewire of the signal cables. Straight forward enough, however the ones leaving the preamp board to power stages are 3 core. Can someone explain this and also identify the connector types please so I can get more of them :)

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hum on right channel speaker

Newbie in tubes here>>

This is great thread and forum for Yaqin MC10-L. I have a unit that is about 3 months old and IT DEVELOPED A HUM ON THE RIGHT CHANNEL. I can still hear the music but the hum is there..i checked the bias on V2 and it was 0.06v)

i contacted the seller for help and was told to do the ff:

Move V1 to V2 socket and if there is bias the problem was V2 (EL34).

my questions:

1.is this check enough to isolate that the issue was V2 (l34)? I ordered new ones and on the way..from CAnada..

2. When i put V1 to V2 how long do i have to wait to make a reading? seller says within 3 minutes? is this right?

thanks in advance!!!

Audio0412
 
SY said:
Unbalanced phase splitter? A quasi-SRPP (badly unbalanced) input stage?
I was going to say that the apparently "unbalanced" phase splitter was an attempt to correct for the lack of a CCS tail, but then I noticed that the anode resistors were the wrong way round so they increase imbalance rather than correcting it. Either a mistake or an attempt at 'euphonic' distortion.

The "quasi-SRPP" looks like the designer could not decide whether to do a proper SRPP or a proper mu follower, so just left it as an unbalanced SRPP - which will be worse than either of them! Given the relatively high impedance load a simple active load stage would be just as good, but Chinese designers do like the SRPP and audio buyers seem to like it too.

The output grid resistors are quite low in value so will load the LTP and increase distortion. Maybe low values are needed to cope with gassy Chinese valves?
 
Recently had a Krell amp here, the Krell won*, just, by its articulate upper bass. Then I upgraded the caps in the 10L, made a staggering difference. Now prefer the 10L any day.

*My speakers are an easy load to drive, so the Krell would have come into its own with different speakers