I’ve tried a lot if different combinations as well. Most types except all KT88.
I find the power section of Herbert very clean, to an extreme compared with the VH4.
With very clean tubes ( little harmonics & overtones ) it gets flat and a bit anemic.
These are all based from my personal tone point of view.
I didn’t like any 6L6’s in it. I love 6L6’s in the VH4 , the amps are that different in how the power section works.
Same goes for GL KT77 , just too clean. I do like these a lot in the VH4 and other amps.
The SED 6550’s are good. Dynamics to the extreme. It makes the amp very full & powerful sounding.
Not much in the way of offensive frequencies. Nor does it have that
Marshall bite that I like.
The current recommended JJ KT77 is IMHO a good tube.
Also dynamic, and full but not to the extreme amount that the SED 6550 is.
It has A Lot of low end and low mids. , so much so that almost chokes the amp. I find I need to roll back the deep and use mid cut to get a sound I like.
There’s a frequency that my ears don’t like in the JJKT77 , they seem a little bit unmusical.
The amp doesn’t squish much with these.
JJ el34L is a good tube , my second favourite.
There’s some squish and a more traditional Marshall like eq to the amp.
Cleans are ok but not great.
Ruby / TAD el34 bstr.
My favourite tube in the Herbert.
Dynamic while retaining a more Marshall flavour.
The attack seems to bloom and build. As opposed to the tightness / on-off response of the KT77’s.
Cleans are also beautiful.
Honestly I didn’t get the Herbert hype until I tried this tube.
