Mixmz, you asked me to describe the improvements of the NOS 12ax7. I am afraid that I am not articulate enough to put into words, exactly what sounded better. My definition of the perfect amp is that it makes my cds sound like I am actually at the live recording of the cd. To that end the 12ax7s helped achieve that goal, as did the cv181-z
This is the link to where I got my NOS 12ax7
Mullard CV4004 / 12AX7 British New Old Stock - Upscale Audio
Mullard CV4004 / 12AX7 British New Old Stock - Upscale Audio
I’ve read all 24 pages of posts about this amp and most modifications and recommendations are way beyond my comprehension and ability to implement them,
but the one post that I could fathom was that the output transformer is too small for the KT-88 tubes and that the voltages driving the KT-88 plates is too low.
Costis_n stated that KT-77’s should be installed instead and biased to 40mA.
I’m currently using the Eh KT-88s and Psvane KT-88 tubes in the Yaquin with a Transcendent Grounded Grid pre-amp and using the Yaquin as a power amp only . Other tubes in the Yaquin are RCA Grey Glass 6SN7s and 5751s.
The 88s sounded very full and powerful but I prefer the KT-77 because the bass is tighter and the sound is less muddy, more detailed and refined than the 88 tubes. Imaging, detail and soundstage was also markedly improved in comparison to the 88 tubes. The 88s sound like someone turned on the loudness switch on an old Sansui integrated. The 88 tubes give the impression of deeper bass but it is really only louder and fuller but the ultimate bass frequency is not deeper. High frequencies were very smooth and I could listen for hours without listener fatigue. In that respect I found that the high frequency output with Psvane tubes was less sibilant than the EH tubes, but the JJ Kt-77s were smoother than the Psvane’s, the EH tubes were harsh and unlistenable. My vented towers with an upper MTM array and 2 woofers below are 92 db efficient so the lower power output of the 77 tubes is not an issue. At high volumes the bass via the 77 tubes was very tight and accurate like a high current SS amp with a high dampening factor and doubled headroom. A quad of JJ KT-77s from the Tube Store cost 85.00 with delivery and is an inexpensive upgrade. Lastly, I would like to thank Costis_n for the suggestion of trying the KT-77 tubes
but the one post that I could fathom was that the output transformer is too small for the KT-88 tubes and that the voltages driving the KT-88 plates is too low.
Costis_n stated that KT-77’s should be installed instead and biased to 40mA.
I’m currently using the Eh KT-88s and Psvane KT-88 tubes in the Yaquin with a Transcendent Grounded Grid pre-amp and using the Yaquin as a power amp only . Other tubes in the Yaquin are RCA Grey Glass 6SN7s and 5751s.
The 88s sounded very full and powerful but I prefer the KT-77 because the bass is tighter and the sound is less muddy, more detailed and refined than the 88 tubes. Imaging, detail and soundstage was also markedly improved in comparison to the 88 tubes. The 88s sound like someone turned on the loudness switch on an old Sansui integrated. The 88 tubes give the impression of deeper bass but it is really only louder and fuller but the ultimate bass frequency is not deeper. High frequencies were very smooth and I could listen for hours without listener fatigue. In that respect I found that the high frequency output with Psvane tubes was less sibilant than the EH tubes, but the JJ Kt-77s were smoother than the Psvane’s, the EH tubes were harsh and unlistenable. My vented towers with an upper MTM array and 2 woofers below are 92 db efficient so the lower power output of the 77 tubes is not an issue. At high volumes the bass via the 77 tubes was very tight and accurate like a high current SS amp with a high dampening factor and doubled headroom. A quad of JJ KT-77s from the Tube Store cost 85.00 with delivery and is an inexpensive upgrade. Lastly, I would like to thank Costis_n for the suggestion of trying the KT-77 tubes
HI, I would like to buy Yaqin mc100b, but I am not shore about input voltage. My home voltage is about 235v and less, so I can choose between 230v and 240v input voltage. Is this related to 6.3v for heating valve or something else what is important to know? Maybe is better to choose transformer with 240v primary? Help, can somebody explain, thanks
I've re-read all 29 pages of this, and I'm still not sure what the recommended changes are for the MC-100B. I have an early version of the amp, purchased in 2008. I've been running it pretty much non stop every day. I had a set of JJ Tesla KT88s last almost five years before one of them started running hot (discolored the label paint). Switched to KT120s and biased at 1.0 volts, and have been running that way for over a year. So, that's speaking something to reliability with this combo.
My memory of the JJ Teslas is a little fuzzy right now, but I remember nice tight bass and warm overall sound. The Tung Sol KT120s I have now sound great with some sources, and like total crap with others. If the bass has a nice hit to it, like a kick drum or something, it's a nice controlled wonderfully deep sound. If it's electronic music, like daft punk, it sounds boomy and downright terrible.
My amp is currently un-modified, and I'm looking to improve its performance. I've heard a lot of talk about EL34, 6550, KT77, and KT90 tubes to deal with the lower than optimal plate voltage. I've seen talk about jumpering a resistor to increase plate voltage. What actually works, sounds good, and increases power capacity?
Also, I run almost exclusively in UL mode. I can't really tell any difference between triode and UL, so I went for the mode with more power available and have just kept it there. Will any of these modifications work better in one mode or the other?
Thanks!
Charles.
My memory of the JJ Teslas is a little fuzzy right now, but I remember nice tight bass and warm overall sound. The Tung Sol KT120s I have now sound great with some sources, and like total crap with others. If the bass has a nice hit to it, like a kick drum or something, it's a nice controlled wonderfully deep sound. If it's electronic music, like daft punk, it sounds boomy and downright terrible.
My amp is currently un-modified, and I'm looking to improve its performance. I've heard a lot of talk about EL34, 6550, KT77, and KT90 tubes to deal with the lower than optimal plate voltage. I've seen talk about jumpering a resistor to increase plate voltage. What actually works, sounds good, and increases power capacity?
Also, I run almost exclusively in UL mode. I can't really tell any difference between triode and UL, so I went for the mode with more power available and have just kept it there. Will any of these modifications work better in one mode or the other?
Thanks!
Charles.
Hello charles,
with tube rolling you can change the sound signature of the amp.
This is a nice but costly hobby. The biggest influence on the soundsignature has changing the feedback. Just ad a 100k potmeter in the feedback and adjust it until you have your favourit sound.
Nobody can tell you what you like best, you must try and listen for yourself.
Ronny
with tube rolling you can change the sound signature of the amp.
This is a nice but costly hobby. The biggest influence on the soundsignature has changing the feedback. Just ad a 100k potmeter in the feedback and adjust it until you have your favourit sound.
Nobody can tell you what you like best, you must try and listen for yourself.
Ronny
Right, right. I've tried tube rolling. I want to upgrade the amp beyond just tube rolling. What I'm getting from this is I need to remove R15 and jumper it with a wire to get a little more power, and replace R6 with 43k? Then install a resistor and cap in series across each octal socket in order to get the ringing under control? Does that sum it up?
Charles.
Charles.
In the end I tested myself in my Yaqin mc-100b a KT77 JJ Platinum Matched Quartet and a KT120 Tung-Sol Platinum Matched Quartet. I ordered online and received them recently. I made hearing comparisons, reference being the sound produced by my following basic configuration:
- 2 x 12AX7 Tungsol
- 2 x 6SN7GTB Tungsol (V1&V4), 2 x 6SN7JJ (V2&V3)
- 4 X KT88 JJ
- diy speakers TQWT (Ciare HW204 + HT264) + 2 subwoofers (2 x Jamo Sub 660)
First the KT120 Tungsol Platinum Matched Quartet:
I started with all Bias Potentiometers clockwise rotated to minimum bias current position. After 5 minutes I read different values for the four tubes, much different. I kept the higher value unchanged and approachead the other (670 mV). After 30 minutes I readjusted to approximative 700 mV ( 70 mA bias current). Background noise relatively high. The sound was banal, lacked the deep bass, high mids pronounced, missing the warmth. The output transformers heat up more, long therme I think is a dangerous operating regime.
The second test, KT77 JJ Platinum Matched Quartet:
I biased the tubes to 30 mA (300mV), one of them is unstable bias and slightly noisy, the plate voltage in my amplifier is 465V. Background noise very low. The amp sounds fuller, warmth, the bass very deep, devastating. Operating conditions of the transformers is easy, less heat up.
Going to do tests with other lamps upstream change.
- 2 x 12AX7 Tungsol
- 2 x 6SN7GTB Tungsol (V1&V4), 2 x 6SN7JJ (V2&V3)
- 4 X KT88 JJ
- diy speakers TQWT (Ciare HW204 + HT264) + 2 subwoofers (2 x Jamo Sub 660)
First the KT120 Tungsol Platinum Matched Quartet:
I started with all Bias Potentiometers clockwise rotated to minimum bias current position. After 5 minutes I read different values for the four tubes, much different. I kept the higher value unchanged and approachead the other (670 mV). After 30 minutes I readjusted to approximative 700 mV ( 70 mA bias current). Background noise relatively high. The sound was banal, lacked the deep bass, high mids pronounced, missing the warmth. The output transformers heat up more, long therme I think is a dangerous operating regime.
The second test, KT77 JJ Platinum Matched Quartet:
I biased the tubes to 30 mA (300mV), one of them is unstable bias and slightly noisy, the plate voltage in my amplifier is 465V. Background noise very low. The amp sounds fuller, warmth, the bass very deep, devastating. Operating conditions of the transformers is easy, less heat up.
Going to do tests with other lamps upstream change.
hold on a second, are you saying you running kt77 just instead of Kt88 along with 2 x 12AX7 Tungsol, 2 x 6SN7GTB Tungsol and 2 x 6SN7JJ on stock amp without any modification?
Kt120 takes a lot of time to "burn in" , I also tried many different combination in this amp and for me after about 100hrs on kt120 bass become stronger but to boomy I was running them at 0.9v, at first 30 hours remember that I didnt like them as there was not enough bass but it changed over the time at the end preferred tungsol 6550 as they were most detailed with most precise bass, quality over quantity and also top end was slightly exposed, but never tried kt77.
Kt120 takes a lot of time to "burn in" , I also tried many different combination in this amp and for me after about 100hrs on kt120 bass become stronger but to boomy I was running them at 0.9v, at first 30 hours remember that I didnt like them as there was not enough bass but it changed over the time at the end preferred tungsol 6550 as they were most detailed with most precise bass, quality over quantity and also top end was slightly exposed, but never tried kt77.
I received permission from the store to send back the KT120 set . Tomorrow I'll send the parcel. They will be replaced by KT88, one quartet and KT77, one quartet and i'll pay the price difference. IMO the KT120s require too much the output transformer and shortens their life. I don't like their sound, lack of deep bass, very noise, very microphone.
For KT77JJ I just tuned the bias to 30mA, nothing else. The bass is deeper than KT88, probably the output transformers works more relaxed.
For KT77JJ I just tuned the bias to 30mA, nothing else. The bass is deeper than KT88, probably the output transformers works more relaxed.
I made a new experiment, I replaced the two 12AX7 with ECC803S(JJ) gold pins.
My conclusions: lower the background noise, gain a little smaller, mid-high a little more pronounced, sound timbre of voices changed little. I returned to 12AX7 Tungsol, currently I like more.
I made a soft-start circuit that works well for several months, attach wiring diagram and the way in which I placed in my Yaqin amplifier.
Sorry, the relay driver transistor is BD139 ,I misspelled.
My conclusions: lower the background noise, gain a little smaller, mid-high a little more pronounced, sound timbre of voices changed little. I returned to 12AX7 Tungsol, currently I like more.
I made a soft-start circuit that works well for several months, attach wiring diagram and the way in which I placed in my Yaqin amplifier.
Sorry, the relay driver transistor is BD139 ,I misspelled.
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