Amp/Preamp Asylum: REVIEW: EICO AF-4 Amplifier (Tube) by Richard CWY

Model:	AF-4
Category:	Amplifier (Tube)
Suggested Retail Price:	$200
Description:	Single-end EL84 stereo integrated amp
Manufacturer URL:	EICO
Manufacturer URL:	EICO

Review by Richard CWY ( A ) on February 08, 2003 at 04:26:17
IP Address: 210.3.46.44

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for the AF-4

**vintage EICO AF-4 Single-ended EL84 stereo integrated amp**

Purchase

After listening to so many push-pull EICO amps, I always find it
attractive to have a tiny single-end EL84 stereo amp as the EICO AF-
4 to audition and compare. But AF-4 rarely appeared in eBay and
when it appeared, the ending price always fetched up to US$200 or
over. In the past 2 or 3 years, AF-4 has appeared only for a few
times.

In October 2002 I found the eBay auction but this AF-4 had an ugry
look - oversized cannister capacitor (the multi-sectional power
supply filter cap) emerged from a large hole cut through the golden
metal cage! (see the first picture in "Photos"); brass faceplate was
dirty, etc. Moreover, the seller mentioned problems here and there
and did not give any guaranty except the transformers. I could win
the auction easily at US$79.90!

Cosmestic

It took more than 2 months for the amp to arrive at my door by USPS
surface mail. I replaced the can cap with one pulled from an EICO HF-
12, cleaned and lacquer sprayed the brass faceplate, and replaced
the golden metal cage with one pulled from an HF-85 (Yes, HF-85 and
AF-4 has the same size and use a same golden metal cage).

Electronic

My AF-4 was obviously a kit - no EICO QC stamp on the chassis and
the soldering was done only up to an 'amateur' standard. It has all
original ceramic disc coupling caps (0.025 uF) same as in original
HF-81, HF-86 etc. All resistors are original and fortunately within
tolerance. However, 1 cathode bypass electrolytic capacitor (see
photo) was found burst. I replaced this and the other to make both
channels matching. Other than this, I need make no more change.

A point to note: AF-4 does not use the same type of output
transformer as 2510 receiver, though both are EICO single-ended EL84
amps. AF-4's output has this part number "32018" whereas 2510
has "32038" and the latter looks very slightly larger in size.

Testing

1) Measured the power transformer first without any tubes in. Normal
AC voltage and normal heater AC supplies at all tube sockets.

2) Then with the rectifier tube (6CA4) in, normal DC voltage at B1
position. Voltage at other positions is not reliable because no
loading to the DC supplies.

3) After putting in 4 tubes (1x EL84 + 1x 7247 for each channel),
measured and found the DC voltages normal, plate voltages also
normal. Voltages compared normal with each channel. Measured the
output transformer taps (with loading resistors) and found no AC
voltage out. (Later on I shall put these voltage data to this site
for members' reference.)

4) Given the limited space on the back of the chassis, AF-4 uses 3
small-sized round sockets on the back of the chassis for giving
power supply (back view: right most) to a device (turner, etc.)
which is not self-powered, and 2 for speaker connections (instead of
screw broads).

5) Be careful NOT to mistakenly plug a speaker connector plug into
the power supply socket! If you did, 300VDC would fry your
speakers. Be warned all AF-4 users! (I always keep the power supply
socket occupied by a redundant plug to avoid any mistake.)

Audition

The amp must have been in storage for many years. At first nothing
sounded right to my ears even after I 'upgraded' EL84 and 7247 tubes
to vintage Amperex D-getter and Mullard respectively.

After running the amp for some more days, particularly when it works
with a pair of JR149 (which has higher efficiency and deeper bass
than BBC LS3/5As), the sound becomes amusing. Violin, guitar and
vocal are so real. The bass is not bad at all despite it has only 4
Watt output per channel. It is really incredible that big sound
does come from such a small amp. With high efficiency speakers,
e.g. Lowther, Altec, the sounding could be even better.

When compared to other integrated EICO amps, I would say its
sounding is close to HF-81 although it lacks a little detail in the
high and punch in the bass. Overall, it is acceptable in view of its
low wattage and, running within the rated output power, music is
dynamic and really adorable.

To conclude, AF-4 does not sound like a single-ended amp, but more
like an EL84 push-pull amp. It clearly does not sound like any
singled-end pentode amps like 6L6 and KT66 or a triode 300B amp that
I have heard.

Richard CWY

Please visit the EICO Tube Amp Fans Club in Yahoo!:
http://groups.yahoo.com/group/eico/

Product Weakness: Work better with high efficiency speakers.
Product Strengths: Tiny tube amp, has EL84 sweet but does not sound like single-ended!

Associated Equipment for this Review:
Amplifier:	AF-4
Preamplifier (or None if Integrated):	None
Sources (CDP/Turntable):	CD
Speakers:	Jim Rogers JR149
Cables/Interconnects:	DIY
Music Used (Genre/Selections):	Female vocal, Yo-Yo Ma Silk Road Journeys, etc
Room Size (LxWxH):	NA x NA x NA
Room Comments/Treatments:	NA
Time Period/Length of Audition:	Regularly in 1 Week in February 2003
Other (Power Conditioner etc.):	N.A.
Type of Audition/Review:	Home Audition

Product Weakness:	Work better with high efficiency speakers.
Product Strengths:	Tiny tube amp, has EL84 sweet but does not sound like single-ended!