These
notes were sent to me before I had a schematic or information
about the EICO which explains why they are rudimentary.
Roger and I had exchanged several emails regarding mods
to the EICO HF-81 and this is one of them along with
a full-size shot of my relatively stock interior with
corresponding numbers to parts referred to in the text.
I added some of my own opinions below Roger's comments/suggestions
- kh
#1
Stock it's about a 30mfd@350vdc electrolytic. I used a
new axial electrolytic I obtained form AES (www.tubesandmore.com),
and went to a 47mfd@450vdc cap. The make is probably a
Nichicon or Xicon - They're equivalent. A step-up would
be a Sprague Atom (see latest on this), also available
from AES.
[If it were me, I would go the extra route and at least
put some Sprague Atoms (see at left) in here; personally,
I am going to go for ELNA Cerafine which are extremely
fast and transparent sounding - they are supposed to improve
the tightness of bass and give the amp a more open sound
- Regardless, like Stephen, I would tie these caps down
in some fashion. The originals were held with clamps.
UPDATE: The ELNA is no longer found cheap coming in
around $45 depending. But from someone whose ears I trust
says the Sprague ATOMS leave a bit to be desired here
- They are a tried and true option by many, however. .
Direct
quote: "Just for your information,
I found the Sprague Atoms suck... Cerafines
where much better. I didn't find a big difference between
the Cerafines and the original ones (the Astron). The
sunds lost a big portin of the guts and the soul is mostly
gone. The transients which were really good before are
now dull.
Not the best report.
The ELNA Cerafines DO fit
- Another cap to consider here is the Nichicon MUSE series
or Panasonic TSHB which will fit within the space limitations
but will not be of the same quality as the ELNA. On the
other hand, the ELNA are no longer made so they are getting
quite hard to find. While Solen might be another option,
thus negating the use of Electrolytics in the power supply,
the size would be a problem. kh]
#2 This is the power supply dropping resistor,
probably a 5K. Leave it alone.
#3 These are the output tube cathode bias resistors,
and are 165 ohms stock, at 5 watts. I'd make them a 180-ohms,
5-watt Xicon, available from Mouser (www.mouser.com) or
DigiKey (www.digikey.com), you have to look. This will
lower the temps a bit and more closely match modern voltages
anyway. Get them as closely matched to each other as possible--order
5 and measure them and select the closest two.
[Once
again, I am not sure about this either. Would this cause
the amp to be biased a bit colder and thus lose some of
the warmth? His idea does make sense and is worth a try.
I would probably elect to get new stock in both values
and might just elect to keep the bias the same as stock
- kh]
#4 These are the line stage coupling caps, and
as stock are .1mfd@600vdc
if I recall correctly. I used 716P Orange Drops of the
same value.
[Another
option here would be Auricaps at near the same
value. These caps are supposed to be relatively neutral
and not too harsh while also fitting within the chassis.
This seems to be a good option to the Orange Drops (If
going with the Orange Drops, make sure you get the 716P
and not the 715p). I sure wish oils could be used here
and in the main coupling caps. I now believe these to
be the smoothest but size is an issue. There is
also a lot of heat down below here - kh]
#5 These are the output tube coupling caps. The
stockers are ceramic and have to go. Space is, however
extremely tight, and anything good would be tough to fit
in there. I started out with no-name polyester film yellow
jobs from AES, and used .1mfd@600vdc units. I later reduced
them to .047mfd@600vdc Orange Drops (type 716P), also
from AES, but they're physically a lot bigger, but usable.
Sound great. 716P Orange Drops are the best overall compromise
between price and performance for these amps. I haven't
tried Illinois like they recommend up onthe Vaccum Tube
Valley website (they sell the beasts).
 [Very
important to sound of amp. Really can affect the smoothness
and transparency. Worth the extra to put some quality
here. I have not made up my mind but most of the guys
say the "Orange Drops" just arent in the same
league as other film/foil caps. As he said, room will
be an issue in stock chassis. Others to consider included
Hovland Musicaps and Oil Filled caps which can be costly
but have the richest sound. NOTE: Probably the easiest
option size wise would be the Auricaps I mentioned
above. And at this stage, I am more inclined to not go
that much bigger than stock. I would go with the 600v
versions at .033 or even .027uf. The 400v are smaller
and easier to fit, however (also cheaper). The reason
is that larger caps can actually slow the amp down and
I believe the bass is already a strong suit in the EICO
HF-81- kh]
#6 These are the output tube cathode bypass caps.
In stock form they are, I think, 25mfd@25vdc electrolytic
caps. I used 100mfd@35vdc electrolytics from Radio Shack.
A step-up would be 100mfd@25vdc Sprague Atoms from AES.
#7 (he missed these in pic - they are phono
preamp)
You don't show the phono preamp over on what would be
the upper right of your picture. In there are additional
parts that need replacement, such as .25mfd@600vdc caps
which are in stock form ceramic but for which I used 715P
Orange Drops (there is no equivalent value available in
716P's). In fact I have probably replaced EVERY cap in
my amp, end to end. Also, in the lower right there is
a cap that as far as I know is not stock. It looks like
an aluminum electrolytic (note: are these vintage oil
caps? kh), and is clearly an addition. What it does
and what it's connected to in your amp I have no idea.
A good soldering implement should be a real soldering
station, such as from Weller or Ungar ie a Weller
971ZX. Any temperature-controled pencil iron with about
a 35-45 watt capacity will be fine; you will need a 140-watt
gun (or bigger) for chassis ground work.
*
SEE EICO HF-81 REVIEW NOTES
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