I have some very old tube amplifiers, which I used regularly until the
early 1980's for a home made stereo. Because the homemade speakers were
huge, I stopped using this system due to living in a small apartment,
and put this stuff in storage. I recently moved and brought these amps
home. I want to power them up again. There are three identical mono
amps, which have four 6L6 output tubes, two 5U4 rectifiers and several
other tubes. When I used them, I had one amp on each channel L&R, and
the 3rd amp was connected to a center channel output and driven thru a
reverb delay to simulate a large auditorium.

These amps and the huge speaker systems really put out excellent sound,
and I loved that "tube sound". The output transformers were HUGE and
could really cover those low bass notes.

Anyhow, I'm ready to power up these amps once again. First I checked
each amp for any possible shorts, where some wires may be frayed, but it
does appear that anything has gone bad in that regard. The tubes should
all be fine, since they generally do not degrade with time. But I am
concerned about the filter capacitors.

I should note that the filter caps were unsual, in the fact that they
were electrolytic cans with an OCTAL base (plugged into a octal tube
socket). Each of them have 3 caps in one can. I recall somewhere in
the early 1970's, I found an electronics store that still had three of
them, so I bought them and replaced all of them. But that's close to 40
years ago.

While I suppose replacement might be a good idea, I'll never find
anything to match, and I am aware that many of those older caps seemed
to last forever, unlike these poor quality newer ones. So, the urge
exists to just plug them in and see what occurs.

However I am aware that a bad filter cap can ruin a rectifier tube
quickly, and possibly do other damage. Therefore, as a precaution, I am
considering putting a fuse on each of the B+ wires where they exit the
power transformer. I'm taking a wild guess that a ONE amp fuse should
be sufficient, or maybe uit should be smaller?????

Or, can I just put ONE fuse on the center tap?

From the best of my recollection, the power transformer is around 500
volts center tapped.

The fuse(s) would be right at the secondary of the transformer, before
the 5U4 rectifier tubes.

I'm asking this to get opinions on both if this is practical, and will
protect the rect tubes as well as other parts, and also what size fuse
to use. I'm also not sure if it's best to fuse both high voltage leads,
or just the center tap.

Thanks for all feedback!