Double my portfolio using equity

[Jonathan Seda]

Hello Bigger Pockets, thank you for being there for me any time I needed guidance. I have been on the sidelines for a while now, absorbing all I can while I build my portfolio. I have one question that I have not found an answer to, and hopefully someone here on BP can point me in the right direction.

I am a buy and hold investor, I am currently at 12 doors across various multifamily properties in Philadelphia for which I have acquired mainly through conventional financing. I've leveraged my first house (also a rental) in 2014 into my first duplex and have slowly built up my portfolio from there. I purchased most when interest rates were at their lowest (2014-2017) I am comfortable with all of what my portfolio brings in.  They all perform well. I have paid down my first few properties expecting to keep my portfolio, pay it off and enjoy the cash flow, but I keep looking at my numbers and see all of my equity just sitting there, doing nothing.  

I want to know, is there any possible way, to refinance all of my properties into an umbrella or portfolio type of loan, and use the equity across all of my properties to leverage into an apartment building? Currently, I have about half a million in equity. I'm confident I can easily double my portfolio if I was to come across the right deal. I came across a couple of 10 unit buildings but was hesitant to pull the trigger and couldn't find any solid info on who could help me in this specific situation, financing with the ability to leverage across my entire portfolio. 

Perhaps I'm looking in the wrong places?

If there is anyone out there who was recently in this boat and managed to push through, I would love to hear about it!