Tube preamp question

[phantombox]

Hi.
I was wondering what type of pots do you need to build a tube pre-amp.
I am building a classic Alembic F-2B 2 channel pre-amp. It's not completely finished jet but after some testings it sounded great. But after a while the EQ stopped working. If I mess around a little bit with the pots (pushing and pulling) the sound changes sometimes to clean and sometimes to not so clean with a burst in volume. I used standard 1/4 W pots for EQ-ing and master volume. Master volume still works OK.

Another question is: how do I use both channels in parallel with just one instrument and/or amp connected (a bass guitar in my case)?

[Steve Conner]

You probably have a loose connection or bad solder joint somewhere.

[phantombox]

There was one loose solder joint. Also, I changed the pin connection on the pot a few too many times so the carbon coating got dirty and/or damaged. Have to get new ones...

I still have no idea how to use both channels of the pre-amp in parallel. I want to go into both channels simultaneously with a bass / guitar and then go out into either a single channel power amp (SUNN Beta Lead Head, which sounds great, btw) or a 2 channel QSC USA 900 power amp which has some matching issues...