id like to improve but keep true, my 66 ST-70

this is where i am at.
i was going to save up and get a VTA-st70
AND THEN!! this 66 great condition dynaco st-70 fell in my lap for $440.
i thought i was taking a chance because it was powered on,but untested,
so i was considering using it to finance the VTA-st70
HOWEVER
the unit is quiet, no hiss or hum.
my transformers are good, old,cloth wire and are in good shape.
power cord is in great shape.
the housing is great,cover is in good shape, all the connectors seem to be ok, no burn spots, or traces lifting off the boards, all solder connections look good.
the choke has heated a bit and melted the wax out onto the bottom cover a bit, but its yellow not brown.
ALL the original DYNACO branded tubes are in it and work good.
i ran my HK-730 preamp outputs into it and it sounds SPECTACULAR!!

BUT*the bios jumps around* so im not using it anymore till i "rectify" the situation :p
the quad cap and rectifier have to go, just because they are old sketchy and hazardous.i get that!

NOW! maybe this is asking alot, or too much at once. BUT! there are so many upgrades/kits/mods.
id like to know which ones may deface it, or cause its value to degrade.
which serve a safety purpose and are absolutely imperative.(besides the bios diode/res's/caps).
which will change it for the better( in keeping with the idea of its original intent- (wigiwig)a flat "what you give is what you get"output response.

i KNOW the bios kit is a must, as is the quad cap, but do i keep the quad cap similar with a slightly higher voltage?
or should i get one with a higher uf and much higher voltage. like 600v 80/40/20/20.

RESISTORS,ALL? with metal film? or just a few(besides the ones covered in the bios kit).

CAPS,ALL? with film,electrolytic,poly? or just a few.

wire?
power cord / grounding?
the boards?
pots?
sockets?
switches?
connectors?
retain the oem driver tube type. or not?(adapters obviously don't degrade value)

triode mod?
auto-bios addition?

also ive seen addressing's toward fluttery low bass response, limited high response, and references to the solid state recto,

there is SOOOO much to consider.
Im trying to wrap my head around improving it, while retaining its value, keeping it true to its nature, or even fixing what they didn't have the technology or ability to pull off back when it was designed.

so many of you have been down this road already, i hope to gain from you. and thanks if you allow me to do that.
thank you all in advance for your knowledge in getting me to my end result.

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thanks peter capo.
very good advice.

BIOS
the bios when i got it, was 1.78 and 1.65
i turned the pots up and down rapidly a 1/4 turn or so centering the original position,then i zero'd them in to 1.56 - i noticed 1 effects the other by 2 or 3 hundreths, (.0x)x being the effected)
i was putting music through it, giving it a light push, id seen the bios's both were fluctuating between 1.44 and 2.11
i then set the bios's to 1.56 with the signal running.
i then turned off the input signal(music) and noticed the bios's went down to 1.44 and 1.48
they were coming up ever so slowly- a 100th of a volt every 2-5 seconds,
so i set the bios's yet again to 1.56, and left it alone but id noticed the bios's were still moving and differentiating from one another.

i definitely want to keep it sounding true to its design

i ordered a dynaco selenium recto swap kit. it has a diode, couple resistors and a couple ceramic(i think) caps.
i was lookin at the 525v 30/20/20/20 quad cap. so ill go for that next.
today ill gingerly clean and re-tension the tube sockets.
i will gingerly clean the driver board with a old toothbrush,and some tuner cleaner.
while i have the cleaner out ill get the switches and pots.
i will check the voltages as you say

after all that i think ill opt for some tube adaptors for the 7199 sockets, so i can use alternatives.
and ill be keeping the rectifier tube.

my concerns for safety was for the amps power supply,and tubes as i do push it.
id like to be assured its going to be reliable with no sketchy overheating issues.
considering voltage difference's between when it was designed and now.

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thanks pete
bios.
glad that was acting all fairly normal
as to the kit. it was $8 and supposedly new old stock
i cant post links yet, just joined, i tried that initially.
but this is the description.
(1) Diode Kit for the Dynaco Stereo 70 Tube Amplifiers; this kit replaces the original outdated selenium rectifier with a modern diode.  We consider these NOS as they came from the SV / SCC inventory which dates back to the 1980's.  These are not Dynaco brand "kits", rather they are aftermarket kits that were offered by SCC back in the 1980's.  These are a simple and inexpensive way to replace your old crusty selenium rectifier; included are a very basic instruction sheet, diode, terminal strip, and hardware.  The parts are sealed in a small paper envelope with the instructions folded around it; some have dust from warehouse storage but perfectly usable.  (D544042R)

and holy crap. that number?!D5540942R...might be the rectifier itself! i just found it online at
double u double u double u. dot.thermionic.de/tdyna5.html as part 5540942

and the cap 525v 80/40/30/20 - duly noted.
tranny
how would i know if mine was a 120v primary tranny?i do know its probably year 66-67
i can tell you now, my mains run from 118-125, ive seen that in the past on the display of a battery backup i had.

.

yes! thats it.
i saw the dynaco kit, that was first on my list, i saw they were out till july, so i looked for it on ebay to get it faster. maybe that was a bad idea, i took it from the post that it was a dynaco part.. my bad thinking.
incidentally, you think there is any use to keeping the parts i am replacing?
also today my service mains are L1 122 AND L2 119 the lug running my amp and other stuff like my guitar amps are the lower voltage lug, the lower lug seems to have changed from the high position to the lower position since the tornadoes(in new fairfield, ct

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hey hey pete
here. i posted pics
https://dynacotubeaudio.forumotion.com/t3755-just-got-this-puppy
i will be studying into that manual, ive downloaded it (both) to my computer.
thanks for putting that up.

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they are pete
ALL dynaco branded tubes
yea, 3a fuse it is, its a littel USA(old rounded type set text) fuse, wouldnt be surprised to find it was oem also,looks like a quick blow style spring type,with copper flat wire on one side for the actual fuse link.and solid thin wire on the other connecting the spring to the end

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well there it is! believe me, id like to be able to do minimal changes if possible, but i want to be able to sleep at night.lol knowing its running well.. thing is, i will push it.

incidentally, i have a variac, but its only protected as 2A.

on another note, look at the extreme lengths this young man went through to mimic the selenium diode.
youtube.com/watch?v=r5fquGccuSk
YYYEA. no....not doin that!! lol