Yaqin MC-100b schematic diagram

[bobrown14]

Originally Posted by Keepsake10

Hi everybody,
A full description of yaqin problems, how to solve them and how to improve the performance can be found on:

*** frihu.com *** Yaqin MC100B Verstärker-Tuning, Billiges Röhrenverstärker-Vergnügen(?) aus dem Land des Lächelns (1)

it is in german but can be translated, beside you will get all asistance you need at frihu...
Best regards to all,

I have one and suggest to have a friend build you one with the same tubes but different circuit.

Reading the German link tho I gotta say the one I have feeding it with 120V > stepdown104V> 72mA bias on the KT88s and I get decent sound from TT. KT88's (original)
1 /2 yrs and still test new, Silvania Chrome top=best, daily driver. Oh .. hey we are about to take a walk upstairs and take another listen.

Cheers,

Bob

[scutterflux]

Has anyone tried plugging in a 6sl7 as a 6sn7 replacement before modding. I'm thinking of trying this, the lower current requirements might make it a better match... maybe... I'm uncertain, can I have some free advice before I try?

Thanks

[costis_n]

Free advice from me: 6SN7 is different than 6SL7, you will need to change the bias point (both anode and cathode resistors) in order to have it operate it well.

For next advise, I will charge you.

[Keepsake10]

Originally Posted by scutterflux

Has anyone tried plugging in a 6sl7 as a 6sn7 replacement before modding. I'm thinking of trying this, the lower current requirements might make it a better match... maybe... I'm uncertain, can I have some free advice before I try?

Thanks

Different bias is not the only difference between 6SN7 and 6SL7. 6SN7 have a lower amplification factor but can manage higher current - it has as well a lower impedance which make's it better as driver. The 6SL7 need less current and have a higher amplification factor (higher impedance as well) - goes better to the first stages.

[Keepsake10]

Originally Posted by bobrown14

I have one and suggest to have a friend build you one with the same tubes but different circuit.

Reading the German link tho I gotta say the one I have feeding it with 120V > stepdown104V> 72mA bias on the KT88s and I get decent sound from TT. KT88's (original)
1 /2 yrs and still test new, Silvania Chrome top=best, daily driver. Oh .. hey we are about to take a walk upstairs and take another listen.

Cheers,

Bob

Hi Bob,
some years ago I built KT94 in PP ultralinear configuration and 6SN7 as drivers. First bias was as well at 72 mA - than I tried different values but I did not noticed any change in quality, therefore finally the bias was set at 58 mA. Since 4 years this amplifier is almost daily running without any issues.
Right now I am working on a KT120 PSE configuration and aikido as driver... many do not agree with this configuration but I think it deserve a try...

[scutterflux]

Originally Posted by Keepsake10

Different bias is not the only difference between 6SN7 and 6SL7. 6SN7 have a lower amplification factor but can manage higher current - it has as well a lower impedance which make's it better as driver. The 6SL7 need less current and have a higher amplification factor (higher impedance as well) - goes better to the first stages.

I was thinking for just the second stage after the 12ax7's, the "Schmit trigger" section where there appears to be less current than is optimal for a 6SN7 anyway, and was thinking/hoping the higher amplification factor of the 6sl7 would offer a cleaner sound (less THD... is this part of the circut kinda like a negative feedback?). You mentioned bias, but it seems to me it's not biased very well for 6SN7 and that's why the overly harmonic sound and maybe more geared for 6SL7 But Maybe I'm out to lunch, I do get funny ideas about things I'm not well educated in, I'm still learning.

[Keepsake10]

Originally Posted by scutterflux

I was thinking for just the second stage after the 12ax7's, the "Schmit trigger" section where there appears to be less current than is optimal for a 6SN7 anyway, and was thinking/hoping the higher amplification factor of the 6sl7 would offer a cleaner sound (less THD... is this part of the circut kinda like a negative feedback?). You mentioned bias, but it seems to me it's not biased very well for 6SN7 and that's why the overly harmonic sound and maybe more geared for 6SL7 But Maybe I'm out to lunch, I do get funny ideas about things I'm not well educated in, I'm still learning.

Everyone still learning - me too. Yaquin made some changes and improvements after March 2010 - nevertheless the OTP's have their limits. If your amplifier is made before that date, than you have to consider as necessary a "lift up" as described at: *** frihu.com *** Yaqin MC100B Verstärker-Tuning, Frischer Klang aus billiger Büchse - aber trotzdem kaum High-End (3)
It is not only the 6SN7. There are many components that request replacement in order to obtain a clear and detailed sound (I think this is the real problem and not the amplification factor). Beside, more amplification mean as well more THD. Only changing the SN and using instead SL would not solve much anyway.
Best regards,
Dan