| Home |
| Search |
| Today's Posts |
|
#1
Posted to rec.audio.tubes
|
|||
|
|||
Using 12AZ7's
The tube books show the 12AZ7 as a direct sub for the 12AX7. Out of
curiosity, I put 4 RCA 12AZ7's in my Dynaco PAS-2. Could not tell any difference in sound compared to the the Telefunkens that were in there. Any comments on this tube or has anyone used them ? Thanks, Dave |
|
#2
Posted to rec.audio.tubes
|
|||
|
|||
|
Using 12AZ7's
|
|
#3
Posted to rec.audio.tubes
|
|||
|
|||
|
Using 12AZ7's
On Dec 6, 8:03�pm, keithr wrote:
You can't post that here, this is Il Jute's personal anti global warming news group. Stay on topic please. Hi RATs, The only consistent topic is how dumb other posters are  Ha! Al |
|
#4
Posted to rec.audio.tubes
|
|||
|
|||
|
Using 12AZ7's
On Dec 6, 3:21*pm, wrote:
The tube books show the 12AZ7 as a direct sub for the 12AX7. Out of curiosity, I put 4 RCA 12AZ7's in my Dynaco PAS-2. Could not tell any difference in sound compared to the the Telefunkens that were in there. Any comments on this tube or has anyone used them ? Thanks, Dave At Lasts!! Something on tubes! OK, a few things. Others have noted the lower gain and higher filament current. However, in my limited experience the 12AZ7 is slightly less prone to microphonics which can be a good thing given how sensitive 12AX7s can be and those Telefunkens in particular (again in my experience). In the PAS from modern sources you will not notice the lower gain. As far is you are concerned, you probably did not notice that you had to put the volume control slightly higher than with the Teles, and you will probably have no problem with the extra current. But, if you are into swapping tubes, hunt down some Sylvania Mil.Spec. 5751s and see how you like them. I think you will notice that difference, particularly in that pre-amp. Also, do the X mod if you have not already. Peter Wieck Melrose Park, PA |
|
#5
Posted to rec.audio.tubes
|
|||
|
|||
|
Using 12AZ7's
Hi Peter,
You mentioned to the OP to do the "x mod". What is that? I'm curious because I have an PAS 3. Thanks, Eddie "Peter Wieck" wrote in message ... On Dec 6, 3:21 pm, wrote: The tube books show the 12AZ7 as a direct sub for the 12AX7. Out of curiosity, I put 4 RCA 12AZ7's in my Dynaco PAS-2. Could not tell any difference in sound compared to the the Telefunkens that were in there. Any comments on this tube or has anyone used them ? Thanks, Dave At Lasts!! Something on tubes! OK, a few things. Others have noted the lower gain and higher filament current. However, in my limited experience the 12AZ7 is slightly less prone to microphonics which can be a good thing given how sensitive 12AX7s can be and those Telefunkens in particular (again in my experience). In the PAS from modern sources you will not notice the lower gain. As far is you are concerned, you probably did not notice that you had to put the volume control slightly higher than with the Teles, and you will probably have no problem with the extra current. But, if you are into swapping tubes, hunt down some Sylvania Mil.Spec. 5751s and see how you like them. I think you will notice that difference, particularly in that pre-amp. Also, do the X mod if you have not already. Peter Wieck Melrose Park, PA |
|
#6
Posted to rec.audio.tubes
|
|||
|
|||
|
Using 12AZ7's
On Dec 7, 1:55*pm, "Edward Morris" wrote:
Hi Peter, * * You mentioned to the OP to do the "x mod". *What is that? *I'm curious because I have an PAS 3. You will find the modification described in later amp manuals such as the ST-80/120 and so forth. It is to match the output impedance to 'modern' solid-state amps (and doesn't hurt with tube amps). It consists of changing one resistor and cutting another on each channel - not a big deal. It will make the pre-amp a bit less noisy and tubby- sounding with SS equipment. Also, the true X tone-controls were out-of-circuit when flat - a thing that modern 'enthusiasts' attempt to duplicate by taking them out of the circuit altogether. Those controls were specially made for Dynaco and are almost unobtanium these days. But the output matching mod is simple and worthwhile. I will try to remember to look it up some evening and post the "how" here. Peter Wieck Melrose Park, PA |
|
#7
Posted to rec.audio.tubes
|
|||
|
|||
|
Using 12AZ7's
Hi Peter,
Thanks for replying. How would I know if my PAS has the X tone controls? Thanks again, Eddie "Peter Wieck" wrote in message ... On Dec 7, 1:55 pm, "Edward Morris" wrote: Hi Peter, You mentioned to the OP to do the "x mod". What is that? I'm curious because I have an PAS 3. You will find the modification described in later amp manuals such as the ST-80/120 and so forth. It is to match the output impedance to 'modern' solid-state amps (and doesn't hurt with tube amps). It consists of changing one resistor and cutting another on each channel - not a big deal. It will make the pre-amp a bit less noisy and tubby- sounding with SS equipment. Also, the true X tone-controls were out-of-circuit when flat - a thing that modern 'enthusiasts' attempt to duplicate by taking them out of the circuit altogether. Those controls were specially made for Dynaco and are almost unobtanium these days. But the output matching mod is simple and worthwhile. I will try to remember to look it up some evening and post the "how" here. Peter Wieck Melrose Park, PA |
|
#8
Posted to rec.audio.tubes
|
|||
|
|||
|
Using 12AZ7's
On Dec 8, 1:54*am, "Edward Morris" wrote:
Hi Peter, * * Thanks for replying. *How would I know if my PAS has the X tone controls? Thanks again, Eddie "Peter Wieck" wrote in message ... On Dec 7, 1:55 pm, "Edward Morris" wrote: Hi Peter, You mentioned to the OP to do the "x mod". What is that? I'm curious because I have an PAS 3. You will find the modification described in later amp manuals such as the ST-80/120 and so forth. It is to match the output impedance to 'modern' solid-state amps (and doesn't hurt with tube amps). It consists *of changing one resistor and cutting another on each channel - not a big deal. It will make the pre-amp a bit less noisy and tubby- sounding with SS equipment. Also, the true X tone-controls were out-of-circuit when flat - a thing that modern 'enthusiasts' attempt to duplicate by taking them out of the circuit altogether. Those controls were specially made for Dynaco and are almost unobtanium these days. But the output matching mod is simple and worthwhile. I will try to remember to look it up some evening and post the "how" here. Peter Wieck Melrose Park, PA Eddie: To do the impedance mod - per the Dynaco literatu 1. Obtain two 100,000 ohm, 1/2-watt 10% tolerance resistors. 2. Unsolder and discard the two 510,000 ohm (green-brown-yellow) resistors connected to the audio-output sockets on the back panel of the preamplifier and replace them with the 100,000 ohm resistors. Solder all connections. 3. Snip out and discard the two 62,000 ohm (blue-red-orange) resistors on the PC-5 circuit board adjacent to eyelets 8 & 18. This completes the modification. Given the relative difference in cost, I would use 5% resistors and screen them as well. As to how you can tell if you have the X tone-controls: 1. with your VOM go to either element terminal and the wiper. 2. Operate the control through its range. At/near the center-point there should be a signficant drop or a significant increase in resistance. If that happens, you have the X controls. If the resistance change is approximately linear to the control and with no change at the center-point you have the pre-X controls. Hope this helps. Peter Wieck Melrose Park, PA |
|
#9
Posted to rec.audio.tubes
|
|||
|
|||
|
Using 12AZ7's-thanks Peter
Hi Peter,
Thanks so much for the mod instructions and the explanation of the X controls. Regards, Eddie "Peter Wieck" wrote in message ... On Dec 8, 1:54 am, "Edward Morris" wrote: Hi Peter, Thanks for replying. How would I know if my PAS has the X tone controls? Thanks again, Eddie "Peter Wieck" wrote in message ... On Dec 7, 1:55 pm, "Edward Morris" wrote: Hi Peter, You mentioned to the OP to do the "x mod". What is that? I'm curious because I have an PAS 3. You will find the modification described in later amp manuals such as the ST-80/120 and so forth. It is to match the output impedance to 'modern' solid-state amps (and doesn't hurt with tube amps). It consists of changing one resistor and cutting another on each channel - not a big deal. It will make the pre-amp a bit less noisy and tubby- sounding with SS equipment. Also, the true X tone-controls were out-of-circuit when flat - a thing that modern 'enthusiasts' attempt to duplicate by taking them out of the circuit altogether. Those controls were specially made for Dynaco and are almost unobtanium these days. But the output matching mod is simple and worthwhile. I will try to remember to look it up some evening and post the "how" here. Peter Wieck Melrose Park, PA Eddie: To do the impedance mod - per the Dynaco literatu 1. Obtain two 100,000 ohm, 1/2-watt 10% tolerance resistors. 2. Unsolder and discard the two 510,000 ohm (green-brown-yellow) resistors connected to the audio-output sockets on the back panel of the preamplifier and replace them with the 100,000 ohm resistors. Solder all connections. 3. Snip out and discard the two 62,000 ohm (blue-red-orange) resistors on the PC-5 circuit board adjacent to eyelets 8 & 18. This completes the modification. Given the relative difference in cost, I would use 5% resistors and screen them as well. As to how you can tell if you have the X tone-controls: 1. with your VOM go to either element terminal and the wiper. 2. Operate the control through its range. At/near the center-point there should be a signficant drop or a significant increase in resistance. If that happens, you have the X controls. If the resistance change is approximately linear to the control and with no change at the center-point you have the pre-X controls. Hope this helps. Peter Wieck Melrose Park, PA |
Linear Mode
