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| [#2362] Leak Club for Leakies or Leak users Check if the resistors have drifted in value after they were soldered onto the component broad? -------------- I have checked the values of all resistors before mounting in, they should be fine. For A&B resistors, I rechecked their values and they read: R2, 22k grid resistor: 24.2k for left and 24.3k for right R6, 3.3M: 3.42M for left and 3.47M for right R11, 3.3M: 3.51M for left and 3.50M for right R16, 10k output grid resistor: 9.67k for left and 9.68k for right R17, 10k output grid resistor: 9.62k for left and 9.67k for right R18, 12k negative feedback: I remember that are fine after soldering, but could check the value becos it is affected by the tranformer. |
Mercedes 正式會員218.xxx.xxx.104 |
2004-07-14 22:57 | |
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| [#2363] Leak Club for Leakies or Leak users typo: R18, 12k negative feedback: I remember that are fine after soldering, but could(n't) check the value becos it is affected by the tranformer. |
Mercedes 正式會員 219.xxx.xxx.5 |
2004-07-14 23:01 |
| [#2364] Leak Club for Leakies or Leak users 12AX7 tubes exhanged, but problem still exists.. ---------------------------------------------- Patrick, What do you mean by this? The set of voltages go with the tubes OR fixated at the particular positions in the circuit? ----------------- The voltage don't change much, it stays with the cap and here is the reading I just checked. Voltage inside a box is the second set of reading I measured when one pair of EL84 is exhanged.  |
Mercedes 正式會員 218.xxx.xxx.104 |
2004-07-14 23:04 |
| [#2365] Leak Club for Leakies or Leak users Something strange happens when I measure the low voltage side of C3, the reading first reads 17 or 18V and drops very slowly (about 30s to 60s) to 15.2V (left) and 13.7V (right). I don't recall such phenonmen when measuring before the modification. Anything bad about the cap? |
Mercedes 正式會員 218.xxx.xxx.104 |
2004-07-14 23:10 |
| [#2366] Leak Club for Leakies or Leak users And by the way, this is the final look of my main board, those 50uf are still untouched.  |
Mercedes 正式會員 218.xxx.xxx.104 |
2004-07-14 23:14 |
| [#2367] Leak Club for Leakies or Leak users Patrick, I assume that you have swopped V2(R) with V2(L) and vice versa but got simarilar voltage readings at V2 and V3 positions. There can be servals causations: a) Both V2(R) and V2(L) have non-matching halves. b) C3(R) and C3(L) are leaky that cause disparity in the current through the 12AX7 tube. c) R7(R) & (L) and R10(R) & (L) drift in value when current pass through them and when they run a temperature. d) R7(R) & (L) and R10(R) & (L) may have drifted in value due to excessive heat at soldering. (A mistake that I committed when I was new hand.) r |
rcwy 正式會員 221.xxx.xxx.250 |
2004-07-14 23:20 |
| [#2368] Leak Club for Leakies or Leak users Sorry, look into the schematic circuit, should be: " BLACK and RED poles of your multi-metre to GOUND and stage which 0.25 coupled respectively.." And the reading is better if less than 0.5V (my standard).." |
dd845 正式會員 203.xxx.xxx.63 |
2004-07-14 23:21 |
| [#2369] Leak Club for Leakies or Leak users .  |
Mercedes 正式會員 218.xxx.xxx.104 |
2004-07-14 23:28 |
| [#2370] Leak Club for Leakies or Leak users .  |
Mercedes 正式會員 219.xxx.xxx.1 |
2004-07-14 23:28 |
| [#2371] Leak Club for Leakies or Leak users a) Both V2(R) and V2(L) have non-matching halves. ------------- They were fine before I did the modification, they read 206V/195V and 207V/201V |
Mercedes 正式會員 218.xxx.xxx.104 |
2004-07-14 23:31 |
| [#2372] Leak Club for Leakies or Leak users Something strange happens when I measure the low voltage side of C3, the reading first reads 17 or 18V and drops very slowly (about 30s to 60s) to 15.2V (left) and 13.7V (right). ---------------------------------------------- This observation reflects what I raised about 'why 0.5V?'. The changing voltage measured reflects the changing loading of V2, the 12AX7 tube. Note there is a 22K and a 1K resistors in series between the cathode and ground! The changing loading of V2 causes drop drop between the two resistors in series and the ground. So, 13.7V(L) and 15.2V(R) reflect the voltage at the 22K resistors. Those these measured value is much higher than "0.5V", the rule of thumb, they MAY NOT mean any leakage of the 0.1uF C3 capacitors. ^__^ Checking leaking of C3 has to be done by other methods! r |
rcwy 正式會員 221.xxx.xxx.250 |
2004-07-14 23:31 |
| [#2373] Leak Club for Leakies or Leak users a) Both V2(R) and V2(L) have non-matching halves. ------------- They were fine before I did the modification, they read 206V/195V and 207V/201V ------------------------------------------ Patrick, Go on down the list for your experimentation/rationalization! ^__^ r |
rcwy 正式會員 221.xxx.xxx.250 |
2004-07-14 23:33 |
| [#2374] Leak Club for Leakies or Leak users b) C3(R) and C3(L) are leaky that cause disparity in the current through the 12AX7 tube. ----------- This has to be investigated, let me change back to old caps later to confirm this point. One more question, I notice that the polarity of the C3 is reversed, the red should face the centre, will that be the answer? |
Mercedes 正式會員 219.xxx.xxx.5 |
2004-07-14 23:35 |
| [#2375] Leak Club for Leakies or Leak users c) R7(R) & (L) and R10(R) & (L) drift in value when current pass through them and when they run a temperature. d) R7(R) & (L) and R10(R) & (L) may have drifted in value due to excessive heat at soldering. (A mistake that I committed when I was new hand.) ----------- This can be investigated if the left and right are exchanged. Let me do that tomolo. |
Mercedes 正式會員 218.xxx.xxx.104 |
2004-07-14 23:41 |
| [#2376] Leak Club for Leakies or Leak users DD, "Less than 0.5V" as a rule of thumb may work as far as power tubes are talked about (i.e. NOT talking about the driver tube) and the amp is self-biased. For example: The negative bias of EL34 is usually -30V to -36V to maintain the EL34 in a static condition (without glowing plates). The cathode resistor of EL34 is usually 235 ohm to 330 ohm. In self-biased amp, the voltage drop at the cathode resistor has to be 30V to 36V in order to maintain a negative potential at the grid equal to -30V to -36V. The measured voltage at the grid relative to the group is therefore has to be zero. Higher than zero means the coupling capacitor may conduct +ve voltage from the driver tube. ^__^ r |
rcwy 正式會員 221.xxx.xxx.250 |
2004-07-14 23:49 |
| [#2377] Leak Club for Leakies or Leak users I suspect that should be the problem of the two C3 more than the RMG resistors. Let me find out tomolo. Thanks Richard and David. |
Mercedes 正式會員 218.xxx.xxx.104 |
2004-07-14 23:49 |
| [#2378] Leak Club for Leakies or Leak users One more question, I notice that the polarity of the C3 is reversed, the red should face the centre, will that be the answer? ---------------------------------------------- TCC PIO caps are non-polorized. r |
rcwy 正式會員 221.xxx.xxx.250 |
2004-07-14 23:50 |
| [#2379] Leak Club for Leakies or Leak users If the C3 is leaking, will the amp still sing? |
Mercedes 正式會員 218.xxx.xxx.104 |
2004-07-15 00:02 |
| [#2380] Leak Club for Leakies or Leak users If the C3 is leaking, will the amp still sing? ---------------------------------------- Most probably that you can hear some music even C3 is leaky. But perhaps you can hear some distortion as well, particular at a higher output level. r |
rcwy 正式會員 221.xxx.xxx.250 |
2004-07-15 00:07 |
| [#2381] Leak Club for Leakies or Leak users "The measured voltage at the grid relative to the group is therefore has to be zero. Higher than zero means the coupling capacitor may conduct +ve voltage from the driver tube. ^__^" Sure! but some Sifu told me up to 10V is OK!Jesus!! |
dd845 正式會員 203.xxx.xxx.63 |
2004-07-15 00:15 |
