[Theo]

Being relatively new to tube equipments (Cornet2 was my first tube electronics), I've read some old articles about having to re-bias or re-balance the tube or circuit every couple of years.  Does Hagerman tube gears require this procedure?  I don't see any circuitry in Jim's design that accommodate this process.  May be I need some more education on tube gears.

[BobRex]

You typically only have to rebias amplifier output tubes, and not all amplifiers give you the capability to even do that.  Whether or not the tubes need manual biasing is a design choice.  If you are looking at small signal tubes (preamps, phono stages, amplifier input tubes,...) you can't rebias these.

[Theo]

You typically only have to rebias amplifier output tubes, and not all amplifiers give you the capability to even do that.  Whether or not the tubes need manual biasing is a design choice.  If you are looking at small signal tubes (preamps, phono stages, amplifier input tubes,...) you can't rebias these.

Thanks.  Good to know that I don't have this to worry about for my Hagerman pieces. 

[poty]

I think in relation to Hagerman design there are several factors which differs the DIY systems from factory-made devices.
First of all - lower heating voltage in some low-signal devices. It gives the big chance to get bad (unpredictable) results with some tubes . And there is no source of checking the right bias either, because the datasheets for the tubes in this case are useless.
Then for some unknown reason there are either wrong or inconsistent values written on the schemas (for voltage and currents) and no information about the right procedure for tuning the resulting builded devices for correct biasing.
I'll not write the rest differences, but even the mentioned two gives good chance that you will need to rebias the devices in the future!