Do all tube preamps leak DC?

Actually, if you wanted to get a very nice bypass cap, here's one

https://www.parts-express.com/audyn-true-copper-cap-010uf-630v-copper-foil-capacitor--027-150

You'd put it in parallel with your existing caps. Give 48 hours of play time.

I've not tried them in electronics but in speakers they are excellent. :)

Hi Paul,  you could have called me on the phone with these concerns,  however,  I see Eric_squires  has answered you as thorough as I would have,  cheers. 

Hello Keith, I'm going to call you anyway, we have some catching up to do, Paul.

Almost all preamps and amps have a tiny bit of DC offset. Maybe 5 mV or less for a pre, 60mV or less for an amp.

A preamp with 5 mV of DC at its output is rare. Our preamps have direct-coupled outputs and they have less DC Offset than that!

With **any** preamp, tube or solid state, it is advisable to turn on the preamp first and let it stabilize before turning on the amplifier. All preamps can exhibit turn-on thumps unless the manufacturer installed a mute relay.

Krell started the 'DC at the output' rumor with tube preamps; it was entirely false. Tube preamps usually have less DC at their outputs than solid state! This is mostly due to the output coupling capacitors used; tube preamps usually use a film cap at their output as stated earlier; solid state preamps often use electrolytic capacitors which are far more prone to leakage and failure.

It's been a very long time since I touched a tube preamp, but as I recall, the film caps do have a smidgen of DC leak. Maybe 50uV was closer to the truth, and yes, film caps will tend to have less DC than SS state pre's.

I've never seen an AC coupled solid state preamp in the high end, certainly not one with an electrolytic coupling cap. 

I _HAVE_ seen lots of bi-polar electrolytics as coupling caps in pro gear though, especially amps. 

But my experience is all pretty random, and from a small sample. I'm sure examples of all of these exist. 

Best,


Erik