the resistor of 1meg is often used in the chinese amplifiers, if you remove it from the grid ground path then I know it will all go inside the volume pot.
If the pot is well grounded and don't act up there will not be issues but ! when you turn the volume it will scratch super loud. I know some volume pots are rate 0.01 watts or something similar, so even small grid currents could deteriorate the pot. Leave it as it was built by the Chinese, you have only a little more insertion loss with the 100k and 1meg parallel than just 100k.
If the pot is well grounded and don't act up there will not be issues but ! when you turn the volume it will scratch super loud. I know some volume pots are rate 0.01 watts or something similar, so even small grid currents could deteriorate the pot. Leave it as it was built by the Chinese, you have only a little more insertion loss with the 100k and 1meg parallel than just 100k.
As I said, even a small DC current can make a pot noisy. 12AX7 could certainly have enough grid current to do it. Simply placing a fixed resistor from grid to ground is not sufficient, as some current will still go through the pot. The correct solution, as I said, is to add a coupling capacitor (as well as the resistor).
Why some 'audio designers' seem unaware of this is beyond me. Don't leave it as it is if the Chinese (or anyone else) got it wrong.
Why some 'audio designers' seem unaware of this is beyond me. Don't leave it as it is if the Chinese (or anyone else) got it wrong.
I'm not sure what you mean by 0V bias, but if you mean 0V from grid to cathode then that will guarantee some grid current and so create some distortion unless the source impedance is low. If fed from a volume pot then the source impedance will not be low at moderately high volumes. So 0V bias can raise distortion.
For a 12AX7/ECC83 you need the grid at least -1V from the cathode to get little or no grid current.
For a 12AX7/ECC83 you need the grid at least -1V from the cathode to get little or no grid current.
This is very linear tube with high gain needed for tube power amp. It is almost always used with NFB - either local or global. So this is not a real issue.
Fine with heavy feedback. With no cathode resistor (which is what we were talking about) there is no point to insert feedback. Grid leak bias is usually used in low level inputs without feedback. The aim is to reduce hum from heater-cathode leakage by allowing the cathode to be grounded directly.
usually there is a black line, stripe or dent in the metal for the AC/DC input on caps. I think it doesn't matter much as I have installed randomly 'boutique' caps in some equipment and I don't care to change them. If you can't sleep well you could check out for the AC to be at where the text starts , at left of text, the far right of capacitor text should be the 'exit' point. iow the signal follows the writings on the caps, input left, output right
No.gabdx said:
If caps are marked then the outer foil should go to the lowest impedance point, which will often (but not always) be the source. This reduces the risk of hum/interference pickup, although it has no effect whatsoever on the music signal itself. Caps don't know about AC 'input' or 'exit'.
12ax7 question
Shortly after getting my MC100B I changed the tubes to Genelex 12ax7, EH 6SN7, and Genelex KT88. That greatly improved the sound from the original tubes. Recently I got to thinking about tubes and I recall that many posts said to focus on the 12ax7 for the greatest improvement. I did a search of "best 12ax7" and my research led me to believe that one of the best 12ax7s of all time was the Mullard NOS. I found a pair online and decided to order them. I haven't received them yet, but was wondering if any of you have tried Mullard NOS and what your feedback is.
Shortly after getting my MC100B I changed the tubes to Genelex 12ax7, EH 6SN7, and Genelex KT88. That greatly improved the sound from the original tubes. Recently I got to thinking about tubes and I recall that many posts said to focus on the 12ax7 for the greatest improvement. I did a search of "best 12ax7" and my research led me to believe that one of the best 12ax7s of all time was the Mullard NOS. I found a pair online and decided to order them. I haven't received them yet, but was wondering if any of you have tried Mullard NOS and what your feedback is.
This forum has been quite for a while? Is anyone still listening?
As a follow up to my previous post I did upgrade my 12ax7 to NOS mullards. the improvement in sound was incredible - well worth the high price i paid.
I did some research on 6sn7s and what i found was the best 6sn7 is a Shuguang Treasure CV181Z. So I bought a quad. They sounded great when I plugged them in, but there are two problems. (1) they barely fit and you can't put the cover on with them in. (2), I use a voltage regulator to drop my voltage to 110V and it made a periodic clicking sound with those tubes in, so I took them out.
The bottom line is doesn anyone know if it is ok to use these CV181Zs. As I said earlier, they were a great improvement over my EH 6sn7.
As a follow up to my previous post I did upgrade my 12ax7 to NOS mullards. the improvement in sound was incredible - well worth the high price i paid.
I did some research on 6sn7s and what i found was the best 6sn7 is a Shuguang Treasure CV181Z. So I bought a quad. They sounded great when I plugged them in, but there are two problems. (1) they barely fit and you can't put the cover on with them in. (2), I use a voltage regulator to drop my voltage to 110V and it made a periodic clicking sound with those tubes in, so I took them out.
The bottom line is doesn anyone know if it is ok to use these CV181Zs. As I said earlier, they were a great improvement over my EH 6sn7.
so do i understand that correctly , you had gold lion 12ax7 from genalex and changed it to 12ax7 NOS Mullard? I thought gold lion reissue were based on those mullard. Is it really such a difference in sound , can you try to describe differences?
I started using 6f8g instead of 6sn7 and only can say
you have to find a really good and I mean really good 6sn7 to play same good as any 6f8g. they are much better in all terms in my yaqin 100b and a lot cheaper, but hard to find those days.
I started using 6f8g instead of 6sn7 and only can say
you have to find a really good and I mean really good 6sn7 to play same good as any 6f8g. they are much better in all terms in my yaqin 100b and a lot cheaper, but hard to find those days.
Yes, the NOS Mullards are a major improvement over the new Gold Lions. I would not have believed it until I tried it. Everything I have read told me that the 12ax7s are the most important tubes in this amplifier, in terms of what to replace to get a major improvement, and those articles were correct, in my opinion.
Back to the 6SN7s - I read in more than one place that the CV181z is the best 6SN7. It is supposedly equivalent except it requires more filament current. When I tried them, they did make a major improvement to my amp, however - my voltage regulator started making a clicking noise periodically, telling me that there is an issue, and second, the tubes are bigger than 6sn7 and so the grill cover for the amp will not fit. I was hoping someone could tell me it if is safe (electrically) to use these tubes.
Back to the 6SN7s - I read in more than one place that the CV181z is the best 6SN7. It is supposedly equivalent except it requires more filament current. When I tried them, they did make a major improvement to my amp, however - my voltage regulator started making a clicking noise periodically, telling me that there is an issue, and second, the tubes are bigger than 6sn7 and so the grill cover for the amp will not fit. I was hoping someone could tell me it if is safe (electrically) to use these tubes.
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