Eico HF-85 or Fisher 400-C Preamp?

[NOSValves]

Most of you AK members are far more knowledgable about electronics then I am and I
only do this for a hobby but I like to experiment and modify to improve the sound of
my small collection of audio electronics I have.

I got this Precision power supply as seen in the pic below for free and it works good,
I have another DC power supply so the model 4010 sits in storage not being used.

Can I use this 4010 precision power supply for the Eico HF-85 tube filaments and use
a AC. power strip to switch both units on at the same time or maybe turn the power on
to the tube filament's first using the external DC supply then the AC. power to the Eico
HF-85 on second?

Sure you could do that! But I would leave the rectifier tube heated with the AC from the EICO transformer then heat all the 12xx series tubes with DC from the external supply. I would also check how much residue AC ripple that supply has on its 12V DC tap if its anything over 100 mV cobble in some more filtering inside the HF-85 to get it that low. Also keep in mind that you will have to rewire the 12xx series tubes for 12V DC heaters. Also make sure the 12V tap is capable of delivering the 150mA "each" the 12XX series tubes will require with some headroom to spare.

 

[BrokenHill]

That's interesting, it looks like rewiring the 12xx series tubes heaters to operate on 12
volts is easy, could a computer power supply be used as a external 12 volt power source
for the tubes?
The Precision power supply that I had did not put out enough current to work for the
heaters so all the tube heaters are still using AC, I have gotten the pre very quiet but
you can hear a slight hum if you turn the volume all the way down put your ear right
next to the speaker.

I have been wanting to do some more mods to the HF-85 but I got involved in rebuilding
a couple of Heathkit AA-13 mono amps and have been amazed at the sound
improvements I am getting out of the work I have been doing to them.
I do plain to try some more mods to the Eico HF-85 and these last two post have given
me some new ideas.
Thanks.

 

[zekk]

My HF85's phono stage removed, componants and wiring re-arranged.
AC for heaters and hum pot removed. Dead quite ... fabulous!

Next, contemplating to reduce gain, but don't know how.

 

[BrokenHill]

Did some more work on my HF-85 over the weekend, rewired the tube heaters with
better wire and twisted the wire very nicely, I did find that if I remove the on/off power
switch from the circuit the preamp got even quieter.
When I used the pre amp with my Magnavox tube amp the hum was hard to hear, I
do have a 60 watt per channel SS amp that I had tried to use the HF-85 before but
it is more sensitive to the hum problem and it was noticeable, but the stereo imaging
that I was getting with that combo was excellent and now that I removed the power
switch and moved some wires around I can now use it with that SS amp and get that
HF-85 awesome sound and not generate as much heat as I got from the Magnavox
tube amp, summer is comming I do like the far less heat from the SS amp during the
hot weather season.

I routed the power cord right under to the power transformer directly to it keeping the
AC wiring as short as possible and away from everything else, I now just plug the power
cord into the switched receptacle on the back of the SS amp so when I power up the
amp the pre powers up too.
when you get the HF-85 quiet it truly is a very nice sounding preamp.

Still using AC to the tube heaters.

When you use DC to the tube heaters does the wires need to be carefully twisted also?
Some people have claimed that changing the tube heaters to DC affected the sound
and it was not for the better, I don't know how true that is.:headscrat

 

[sansuisanta]

A few years ago I inherited a Fisher 400-C Phono Preamp and a Harmon Kardon Citation II power amp, both of which had been in storage for several decades. The Citation II worked like a champ after I installed a new set of tubes, but I wasn't that lucky with the Fisher, which had all sorts of strange behaviors. Since the Fisher wasn't functioning properly I bought a new Bellari PA550 phono preamp and hooked that up between a Pioneer PL-530 and the Citation, driving a pair of Phase Tech 8.5 speakers. That system sounded great.

Now I'm considering getting the Fisher refurbished, and the estimate from my local vintage stereo repair shop is $1100.

That's not going to put me in the poorhouse, but it's not pocket change, either, so before I authorize this repair I'd just like to get some feedback, if anybody cares to weigh in. Any thoughts out there?

 

[NOSValves]

$1100......maybe if the knee I'm about to have replaced goes well I'll have to start taking new client again. That is one lucrative price! For the shop that is, of course it depends on what all is included.