TW type 3 master volume control

[Mac Dillard]

I installed a type 3 master volume control on a Princeton Reverb build and it is not working..When I turn the pot counter clock wise from the 12 position nothing happens until I get to full travel then it shuts all the sound off. The pot checked good. Any ideas how I messed this simple mod up? Thanks. One lead comes off of the pot center pin and the other comes off of the left (looking at the back of the pot) pin. The right is not connected to anything. I will double check the pot when I get the amp back...Thanks for any suggestions.

[sluckey]

Where did you connect the two wires from the pot?

[Mac Dillard]

One each at the junction of the Power tubes 220K grid leak resistors and the coupling caps.

[sluckey]

Connect the right pot lug to the wiper lug. Any better?

[Mac Dillard]

Alligator clipped the right lug to the wiper and no change...And thanks for the help Steve...This is the first time I have tried the type 3 and it is so simple that one can hardly mess it. seems that I have. Checked the pot and it is good. Noticed that when I sweep it (installed) it goes up to 305K. It is a 1meg pot. Guess that is parallel with another resistor. I have a picture on my phone but don't know how to post it. also it does cut down the volume when it is between say 1 and 0.

[Ten Over]

Alligator clipped the right lug to the wiper and no change...And thanks for the help Steve...This is the first time I have tried the type 3 and it is so simple that one can hardly mess it. seems that I have. Checked the pot and it is good. Noticed that when I sweep it (installed) it goes up to 305K. It is a 1meg pot. Guess that is parallel with another resistor. I have a picture on my phone but don't know how to post it. also it does cut down the volume when it is between say 1 and 0.

That is exactly what I would expect with a cross-cut MV on a cathodyne. The output impedances are very low on the cathodyne so that you're not going to hit -3dB until the MV is down to 20K or so. The 1M pot is in parallel with two 220K resistors which calc's out to 306K.

[sluckey]

I've only tried that cross line MV on one amp, Matchless Lightning. I hated it. My operation was not as extreme as yours but the MV is just worthless IMO.

[Mac Dillard]

Thanks for the help guys. I'll take it out tomorrow and see what I can do pre PI. I'll follow up and let you know how that works.

[Colossal]

I've only tried that cross line MV on one amp, Matchless Lightning. I hated it. My operation was not as extreme as yours but the MV is just worthless IMO.

This has been my experience as well.

[norburybrook]

I've only tried that cross line MV on one amp, Matchless Lightning. I hated it. My operation was not as extreme as yours but the MV is just worthless IMO.

This has been my experience as well.

and mine.

Personally the LAR-MAR type 2 is the only master volume that works OK on a TW amp.


M

[Mac Dillard]

Replaced the TW type 3 master control with, not sure what you call it. It is pre PI. I replaced the PI 1 Meg grid leak resistor with a 1Meg analog pot. It does work though leaves some to be desired. It will control but the control range is pretty small. Maybe 0 up to 3. But at least it is usable. Would have liked to have done the Lar-Mar type 2 but just couldn't justify paying the shipping cost on a dual gang pot and a couple of resistors. Again, thanks for the help and the input. Take Care. Be Safe

[Ten Over]

Replaced the TW type 3 master control with, not sure what you call it. It is pre PI. I replaced the PI 1 Meg grid leak resistor with a 1Meg analog pot. It does work though leaves some to be desired. It will control but the control range is pretty small. Maybe 0 up to 3. But at least it is usable. Would have liked to have done the Lar-Mar type 2 but just couldn't justify paying the shipping cost on a dual gang pot and a couple of resistors. Again, thanks for the help and the input. Take Care. Be Safe

If you happen to have a 47K resistor, connect that from the wiper to the bottom of the 1M pot for more useable range. Don't worry about the frequency response with such a small grid leak because the bootstrapping makes it look like 800K or so at worst case. Even a 100K resistor between wiper and bottom helps if you don't have a 47K. If you have an extra coupling capacitor lying around, you can put a standard voltage divider master volume in as shown.

Cathodyne Princeton MV.png

[Mac Dillard]

Thanks Ten Over. I ended up going to the old stand by of the voltage divider master volume control...It works best for me for sure... Would have liked to have tried the Lar Mar type 2 while I was at it just to see how it performed. Well, maybe next time.

[pdf64]

I can’t think of any benefit from putting a master volume after a cathodyne; the circuit adds no gain, and due to its high degree of negative feedback, distorts abruptly and harshly.
But then clipping diodes are pretty common, and the same can be directed at them