I've been doing alot of reading, oscillation can start in the 12ax7 and work itself up to the 12au7. Go figure. so I guess I would have to put grid stoppers on both sets. In the 12ax7 Pins 2 and 7, I already have 47k Caddock TF020 Ultra precision Film resistor soldered into the pins. I wonder if I solder the 1k Carbon comp would it be a problem? This would be where I would put the grid Stoppers for the 12ax7. Maybe someone can steer me in the right direction? Pins 7 is a little Confusing. I know I should place it after the Grid to ground resistor. So does this mean I put it from pin 7 to the first connection and cut the pcb trace there or add it down after the 2M resistor?
Red, I would cut the pcb trace
Blue = Where is would connect the 1k Carbon Comp.
Red, I would cut the pcb trace
Blue = Where is would connect the 1k Carbon Comp.
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Hi Migkiller ,
the first 1k resistor looks good to me , mean i can understand , because the
resistor is in series to the 47k one .
But the second resistor on the second half of the tube is not in series , its
paralell , to my limited understandig about tubes , thats not the same as in
the first example .
Juergen
the first 1k resistor looks good to me , mean i can understand , because the
resistor is in series to the 47k one .
But the second resistor on the second half of the tube is not in series , its
paralell , to my limited understandig about tubes , thats not the same as in
the first example .
Juergen
On the second (pin 7) I think I have two options:
1. Cut the PCB trace to Pin 7 and add the 1k resistor from pin 7 to that connection. (Right)
2. Run the 1k Resistor from pin 7 down passed the 2M Grid to Ground Resistor. (wrong)
I guess the 2nd option would be Parallel and the first Series. Let me read some more..
1. Cut the PCB trace to Pin 7 and add the 1k resistor from pin 7 to that connection. (Right)
2. Run the 1k Resistor from pin 7 down passed the 2M Grid to Ground Resistor. (wrong)
I guess the 2nd option would be Parallel and the first Series. Let me read some more..
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Hi Juergen,
I can't measure the old resistor because this preamp came with no grid stoppers which is kind of odd for tube amps.. So I'm actually adding resistors (grid stoppers). I've been running this preamp non stop for two days now and I get no whistling.
I have added bypass caps, cleaned up some flux and used Cardas tri EUTECTIC to redo some of the soldering. It sounds amazing. Very Clear and tight especially the bass. I can hear the toms, cymbals and snare especially on Copelands(The Police) drums. WOW..I can hear three people playing instruments instead of mush. it still would not hurt to add grid stoppers and I just have to figure out the resistor size I need for the 12ax7...I ran it for 8 hours yesterday and no whistling on the 12au7 Telefunken smooth plate.
The tubes are fine. Right now I have NOS GE JG-5814WA (1957) in. I don't think I'll hear any oscillation with these tubes in there. I'm still going to put 1k Carbon Comp on the 12au7 and I guess its trial and error on the 12ax7. I'll start off with 1k and work down and up. Too high a values will probably cut off some High freq.
I had whistling problems with my Yaqin and I found that using 5814 tubes in the second stage made a big difference. All the other tubes I tried there were very microphonic. A gentle tap on the tube with a fingernail could be heard coming strongly through the speakers. (Warning: Don't try this with the volume turned up high!)
I had whistling problems with my Yaqin and I found that using 5814 tubes in the second stage made a big difference. All the other tubes I tried there were very microphonic. A gentle tap on the tube with a fingernail could be heard coming strongly through the speakers. (Warning: Don't try this with the volume turned up high!)
I put the Tele's smooth plates back in today, I got Mr Neil Young's Zuma right now...WOW... and I get no Whistling and its been 4 hours. So weird since these tubes were the one giving me all the trouble. I'm not completely sold on the tube sockets either. Here is a review for this Preamp.
AAAVT SM-12B phono pre-amplifier [English]
Note: Check out the second paragraph in "Sound Quality"
I have multiple Carbon Comp Resistors coming in this week. So I guess the problem might be in the 12ax7.
Hi,
I want to thank everyone for helping me with this mod. I've been running my yaqin with the grid stoppers and no whistling so far. I will repot if it occurs again. Unfortunatley, I ran it for two days in musical bliss and my Denon poa 1500 gave out. man, it sounded sweet but right now I have a sony amp in there and its just not the same. I'm over in the solid state froum now. Thanks again and Happy Holidays! Oh and to Audiotux. My friend from Heidelberg sent me some gluwein.
I want to thank everyone for helping me with this mod. I've been running my yaqin with the grid stoppers and no whistling so far. I will repot if it occurs again. Unfortunatley, I ran it for two days in musical bliss and my Denon poa 1500 gave out. man, it sounded sweet but right now I have a sony amp in there and its just not the same. I'm over in the solid state froum now. Thanks again and Happy Holidays! Oh and to Audiotux. My friend from Heidelberg sent me some gluwein.
The best wine? I used to get drunk off a Neuwein,,HAHA...We have cars here too but guess what?
I used to work for a Printing company in Germany. Nothing like a heidelberger press! I miss going to Dusseldorf for Drupa and getting drunk. Those were the day.I had whistling problems with my Yaqin and I found that using 5814 tubes in the second stage made a big difference. All the other tubes I tried there were very microphonic. A gentle tap on the tube with a fingernail could be heard coming strongly through the speakers. (Warning: Don't try this with the volume turned up high!)
That gentle tap is how I knew I finally got it. I can give it a really "REALLY" good tap on the metal shields and I get no Feedback whatsoever thru the speakers. I had to go back and really cut the pcb trace to my back left 12au7 and check for continuity. On the Back right 12au7 was diffcult because in order to cut the PCB trace to pin 7, You have to desolder it down because the 510K resistor is right on the pin. I have no idea why they did it like that. I cut the pcb trace to pin 7 and be really careful soldering it back with the grid stopper. Its been running beautifully with no whistling ever since. Again I'll report back if I hear anything but I doubt it.. Happy Holidays!!!
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