Dual Bias Panel Mounting

wdelaney72 · Post by **wdelaney72** » Mon Apr 10, 2006 12:24 pm

Dan (or anyone else that's added a dual bias to a 100W),

I'm going to ready to get started on my 12xxx series and was going to get some parts to add dual bias controls to the rear panel.

Will the following parts work?
Pots
http://www.newark.com/NewarkWebCommerce ... 3F3892&N=0

Dial
http://www.newark.com/NewarkWebCommerce ... 6F9386&N=0

Bias test contacts
http://www.newark.com/NewarkWebCommerce ... 35F844&N=0

Billy Batz · Post by **Billy Batz** » Mon Apr 10, 2006 1:06 pm

I dont think you want binding posts. Look at the probe sockets that hoffman sells. You should be able to find them at newark. As far as the 10-turn pots go, if you use locking dials you should be able to get away with normal pots just fine. But if you want to use them knock yourself out. I just think therye cool. Some super booteekers use them but as I was told many times about my using them- its overkill 1000x over. But hell I think theyre a nice touch.

Billy Batz · Post by **Billy Batz** » Mon Apr 10, 2006 1:18 pm

I think these may be waht your looking for.
http://www.newark.com/NewarkWebCommerce ... =gensearch
Theyre called tip jacks. Theres 6 colors there.

wdelaney72 · Post by **wdelaney72** » Mon Apr 10, 2006 2:21 pm

So, the Bourns locking dial would work with a regular 100K alpha pot that George sells?

BrownSound1 · Post by **BrownSound1** » Mon Apr 10, 2006 2:35 pm

I'll tell you something..those Bourns locking dials are not the most reliable things. We use them on some equipment where I work, and they get replaced quite often. Now having said that, since you won't be tweeking it all the time it will probably be ok. I personally don't trust them to hold.

wdelaney72 · Post by **wdelaney72** » Mon Apr 10, 2006 3:36 pm

BrownSound1 wrote:I'll tell you something..those Bourns locking dials are not the most reliable things. We use them on some equipment where I work, and they get replaced quite often. Now having said that, since you won't be tweeking it all the time it will probably be ok. I personally don't trust them to hold.

Is this limited to Bourns? They have similar dials by Vishay/Spectrol, ETI, and Clarostat. You are correct, though, they would have fairly limited use.

Billy Batz · Post by **Billy Batz** » Mon Apr 10, 2006 4:42 pm

I havent used any yet so I cant comment on either problem but I assumed the dials would work with an alpha pot. They work with all the different bourns and vishay precision which seem to mount the same way

wdelaney72 · Post by **wdelaney72** » Mon Apr 10, 2006 4:59 pm

Dan,
After looking at the store, George doesn't have 100K pots, which is the value you had specified in your dual bias mod. Typically, stock value for the bias pot is 25K. I assume you increased to value to 100K to give a wider bias range, which would allow you to install 6CA7 tubes without chaning resistor values.

George has 25K or 250K. Assuming the locking dial does it's job and holds the pot value in place, is 250K too much?

Billy Batz · Post by **Billy Batz** » Mon Apr 10, 2006 5:15 pm

Also because the 2 voltage dividers (of which the pot is part of the ground leg) both their paths to ground are parallel which reduces their actual resistance in a sense. With the 100k and careful dialing I can dial within .1mA bias on each side. With a 250k I doubt youll have that resolution but you can try it. BTW- 6CA7s really shouldnt be that hard to bias with other EL34s. Its like biasing 2 different sets of EL34s. What I want is more to bias any 2 types of tubes period. But its the same thing. But yes I wanted more range with the pot which seems crazy to me that noone cares about. I understand that the cheapy trimmers wont have any resolution at 100k but theres decent precision trim pots out there that will fit on the board.

wdelaney72 · Post by **wdelaney72** » Mon Apr 10, 2006 6:45 pm

Billy Batz wrote:Also because the 2 voltage dividers (of which the pot is part of the ground leg) both their paths to ground are parallel which reduces their actual resistance in a sense. With the 100k and careful dialing I can dial within .1mA bias on each side. With a 250k I doubt youll have that resolution but you can try it. BTW- 6CA7s really shouldnt be that hard to bias with other EL34s. Its like biasing 2 different sets of EL34s. What I want is more to bias any 2 types of tubes period. But its the same thing. But yes I wanted more range with the pot which seems crazy to me that noone cares about. I understand that the cheapy trimmers wont have any resolution at 100k but theres decent precision trim pots out there that will fit on the board.

Then, I'm going to stick with the 100K precision pots, even if it is overkill. Thanks for the knowledge, Dan.

BrownSound1 · Post by **BrownSound1** » Mon Apr 10, 2006 11:17 pm

wdelaney,

Yes I was referring to Bourns exclusively. The locks seem to wear out quickly on those things. Another brand might be just fine.

wdelaney72 · Post by **wdelaney72** » Wed Apr 12, 2006 4:47 pm

BrownSound1 wrote:wdelaney,

Yes I was referring to Bourns exclusively. The locks seem to wear out quickly on those things. Another brand might be just fine.

I went with the Vishay / Spectrol. We'll see how it works.

rip · Post by **rip** » Thu Jan 28, 2010 10:44 pm

sooo....

how did this work out, was kicking around the idea of using a 10 turn pot for bias adj.

any opinions?

rip

wdelaney72 · Post by **wdelaney72** » Tue Feb 16, 2010 3:36 pm

I gave up on panel mounting. I do use dual bias on most of my builds, but just the on board trimpots. I literally split the bias signal right out of the PT amd run seperate paths for complete independence.

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