Another thought on the ice pick tone...... :|
I was looking at the schematic to better understand how the EQ effects tone of the amp (Also compared to the Mark IVB schematics). You have to consider that the EQ circuit is last tone control of the signal path before the phase inverter. Also, the EQ is not tube driven, it is solid state (considering the matrix of NPN and PNP transistors along with the passive components of inductors and capacitors that make up the filters). Once the signal enters the EQ the distorted signal will gain some higher order harmonics of the input signal which adds to the ice pick effect. Two things, shape your overall tone of each channel with the tone, gain and presence controls with the EQ turned off, and then use the EQ as the final shaping tool. Since the EQ circuit is effectively the front end of the PI, select a tube that has good low end and improved high frequency roll off for the phase inverter. The exception here is, if you are using the FX loop for the master volume control, half of V6 will insert another tube driven gain stage used as a return to shift the voltage level back to the amplitude of the EQ signal. In essence, V6 could be used to tone shape the EQ signal as well as V7 (PI). For some time I have battled the ice pick tone but did not realize I was actually making it worse with different preamp tubes. I finally abandoned my tone quest with the Mark V and resorted back to stock tubes and could not be happier. Since the phase inverter circuit is not fully balanced (due to the Simul Class and 10W circuit which is class A) there is an offset so using a matched triode tube probably will not make any difference. I found the Mesa 12AX7A (current production) serves the PI position quite well. For some time I have been using a matched triode Sovtek LPS for the PI position of all of my amps. I tried one in the Roadster and discovered it brightened the amp up too much. After that, I am no longer using the Sovtek LPS and much prefer the Mesa 12AX7A as the PI tube. My Mark V was an ice pick from the start so I thought changing preamp tubes would be the way to go. I could not be so wrong. Power tubes and speakers can also enhance the top end too. I had found the Tung Sol 7581 and Svetlana 6L6GC increased the ice pick tones, even the SED =c= 6L6GC did the same thing to the point it was intolerable. Going back to stock preamp tubes for me was the cure. Now I can enjoy the SED =C= tubes and retain my hearing. I am one that is hyper sensitive to high frequencies. For me, if the amp sounded like thin window pane glass shattering in my ears (and the Mark V did just that) just no point in going any further. It will make a difference what type of speakers, size of the cabinet, and their characteristic at high volume vs low volume that could make or break your desired tone and or gain characteristic. The presence controls are very influential to the overall tone of the Mark V. Going back to stock Mesa tubes in the preamp, I can now raise the treble and presence controls in all three channels and most of the voice configurations (except tweed and edge which require major adjustments in order to sound good and keep them out of the brittle zone). Extreme and the EQ preset is no longer an issue for me with the Mark V. I generally play at elevated levels and want to feel it as well as hear it and enjoy it at the same time without wads of cotton in my ears. Changing speakers may help but it will not cut the high frequency out unless it has a considerable drop in frequency response. EV, Celestion (V30, MC90) and others can be bright, but what matters most is to remove the undesirable top end in the signal before you convert it to mechanical energy (speaker).
I was looking at the schematic to better understand how the EQ effects tone of the amp (Also compared to the Mark IVB schematics). You have to consider that the EQ circuit is last tone control of the signal path before the phase inverter. Also, the EQ is not tube driven, it is solid state (considering the matrix of NPN and PNP transistors along with the passive components of inductors and capacitors that make up the filters). Once the signal enters the EQ the distorted signal will gain some higher order harmonics of the input signal which adds to the ice pick effect. Two things, shape your overall tone of each channel with the tone, gain and presence controls with the EQ turned off, and then use the EQ as the final shaping tool. Since the EQ circuit is effectively the front end of the PI, select a tube that has good low end and improved high frequency roll off for the phase inverter. The exception here is, if you are using the FX loop for the master volume control, half of V6 will insert another tube driven gain stage used as a return to shift the voltage level back to the amplitude of the EQ signal. In essence, V6 could be used to tone shape the EQ signal as well as V7 (PI). For some time I have battled the ice pick tone but did not realize I was actually making it worse with different preamp tubes. I finally abandoned my tone quest with the Mark V and resorted back to stock tubes and could not be happier. Since the phase inverter circuit is not fully balanced (due to the Simul Class and 10W circuit which is class A) there is an offset so using a matched triode tube probably will not make any difference. I found the Mesa 12AX7A (current production) serves the PI position quite well. For some time I have been using a matched triode Sovtek LPS for the PI position of all of my amps. I tried one in the Roadster and discovered it brightened the amp up too much. After that, I am no longer using the Sovtek LPS and much prefer the Mesa 12AX7A as the PI tube. My Mark V was an ice pick from the start so I thought changing preamp tubes would be the way to go. I could not be so wrong. Power tubes and speakers can also enhance the top end too. I had found the Tung Sol 7581 and Svetlana 6L6GC increased the ice pick tones, even the SED =c= 6L6GC did the same thing to the point it was intolerable. Going back to stock preamp tubes for me was the cure. Now I can enjoy the SED =C= tubes and retain my hearing. I am one that is hyper sensitive to high frequencies. For me, if the amp sounded like thin window pane glass shattering in my ears (and the Mark V did just that) just no point in going any further. It will make a difference what type of speakers, size of the cabinet, and their characteristic at high volume vs low volume that could make or break your desired tone and or gain characteristic. The presence controls are very influential to the overall tone of the Mark V. Going back to stock Mesa tubes in the preamp, I can now raise the treble and presence controls in all three channels and most of the voice configurations (except tweed and edge which require major adjustments in order to sound good and keep them out of the brittle zone). Extreme and the EQ preset is no longer an issue for me with the Mark V. I generally play at elevated levels and want to feel it as well as hear it and enjoy it at the same time without wads of cotton in my ears. Changing speakers may help but it will not cut the high frequency out unless it has a considerable drop in frequency response. EV, Celestion (V30, MC90) and others can be bright, but what matters most is to remove the undesirable top end in the signal before you convert it to mechanical energy (speaker).
