Tips on keeping your vintage solid state hi-fi working
First, always make sure the fuse is of the correct value. Although vacuum tube audio is somewhat forgiving,
solid state stuff is not. If it takes too big of a current hit, it will go up in smoke in a flash. A lot of solid
state amplifiers are direct coupled form transistor to transistor. So, if one shorts, it takes the entire circuit
with it. This sort of daisy chain failure effect is why most defective solid state units end up in the dumpster.
But, if you have a unit that is presently running, there are precautions you can take to keep it that way.
One very important thing to remember is that these early units got hot! Proper ventilation is paramount if
you hope to keep the unit in good working order. Never EVER place anything on top of a receiver
unless it is at least 3" above any vents or openings. This is critical. Once you fry it, you loose it!
Do not place the amp or receiver on a carpet or soft surface that blocks the vent holes in the bottom of the
chassis. If the amp or receiver has side or rear mounted heat sinks. Insure that there is adequate
space around the unit to insure good air flow around the heat sinks. Now, to the fun part.
Most of these units are crowding 30 years of age. Obviously there are things that should be
done. Since we are dealing with much lower voltages, many of the parts that were a problem
on tube amps are not in solid state ones, but since we deal with a lot of current, wiring
and connectors become more of a problem, especially the power supply wiring and
speaker selector switches. If your amp or receiver has a bad speaker select switch, try
flushing it and cleaning it with DeOxit first. It may take several try's, but usually they will clean up.
If not, you must replace the switch! You can solder wires to bypass the selector
switch. Although this will make it impossible for you to select between different
speakers, at least you will be able to use the unit via one set of speaker connectors on the
back. These speaker select switches are one of the biggest headaches in early solid state amps.
Many a seemingly dead amp, or an amp or receiver with one channel that is dead has nothing
more wrong then a bad speaker select switch. A word of caution
A big solid state amp will put out enough current to
roast the switch if it has enough internal resistance. Also an intermittent switch connection can
over stress the output transistors and cause premature failure. Remember, a receiver like
a Marantz 2270 puts out more power per channel then the biggest power amps of the late 50's and
early 60's. In fact, it puts out as much power in one channel as an entire Dynaco ST-70
with both channels driven at once!
Obviously, any wiring, relay contacts, or switch contacts between those big output
transistors and the speakers is going to spell trouble.
As with a tube amp, you should clean all the controls
with a cleaner / lube like DeOxit. On receivers, I would suggest putting a drop of fine oil
on all the pulleys for the tuning dial and mechanism. Clean the chassis of all dust, bugs and debris.
You do not want a lot of crud blocking air flow or shorting out components on the circuit
boards.
OK, you have her cleaned and lubed, now for the fun stuff. You should remove the socketed
output transistors one at a time, clean them of their old heat sink grease, clean their leads, and
reinstall them with a fresh coat of heat sink grease. If your output transistors are not removable,
leave them alone. But, most vintage solid state units have removable output transistors.
If your unit is equipped with a soft start, or power amp protect relay, and it acts a bit strange
at times, you can use a very fine burnishing file on the contacts. It is best to remove the
relay completely before doing this. In Marantz receivers, these relays are notorious for
causing one or both channels to cut out now and then.
The tuner sections of these receivers have the same adjustments as the old tube ones, but
many have several more RF and IF stages. They do drift out of spec, and unless you
know what you are doing, I'd leave a tuner alignment to a professional. The Oscillator
will let you position the stations on the dial correctly, and the RF will also do this a bit,
especially at the higher end of the scale. But you need to align both so they work together
or your front end will deliver very poor reception. You can do a ball park kind of adjustment
by tuning to a station with a known frequency and setting the thing up for best reception of the
station with the tuning dial pointing to the proper frequency. But if the thing is working good, and your only
complaint is that 94.3 FM is at 94.7, I'd leave it alone.
OK, there are problems with old solid state hi fi that parallels tube hi fi. You can run across a
unit with bad filter capacitors. You will know it by the loud 120 hz hum. Some amps can be ferociously loud!
You do just what you would with a tube amp. Find the proper size and voltage capacitors and replace them.
But a word of caution. Do NOT replace them with capacitors much larger then the originals.
By this I mean, do not replace a 2000uf @ 100V with a 10,000 uf @ 100V. Although you might
get away with it, there is a chance that the inrush current caused by having to charge that huge
capacitor may well do the power supply rectifier in if it was not designed to handle such an initial
load. OK, these amps do tend to have some coupling capacitors and they do go bad too.
You will generally see them on the amplifier boards and the preamp circuit boards. Obviously, if
they are leaking their guts on the circuit board, replace them. Again, use a value as close to the original as
possible. One thing to remember. With solid state circuits, you must be extra careful. If you do not know what
you are doing, you can cause some severe damage. In a tube amp, a small slip with a meter probe might
take out a resistor, or cause a nasty spark, but will generally not totally wipe out the amp. In a solid state
receiver, you can take out a whole circuit just with the slip of a probe. Such things could turn your treasure
into trash in a split second. Also, most solid state amps and receivers are assembled using circuit boards
and are much more complex then their tube counterparts. So repairs and trouble shooting can be a bit more
difficult. If you do not believe there are lethal voltages in solid state receivers you are wrong. My 2270
has a power supply that delivers both a - 48 volts and a + 48 volts. So, the potential is 96 volts.
The other problem is that this 98 volts is at several amps, not miliamps as in a tube amp. Believe me, it
can kill you deader then a door knob! So don't think that the voltages in solid state gear are low
enough to be safe to touch! Also, output transistors can actually have this voltage present on their cases so
be careful. Do NOT touch power transistors when your other hand is on the chassis. Most amps
and receivers are such that the high voltage is not on the outer case of the power transistors, but there are always
exceptions! Again, always make sure ALL cooling vents on solid state hi-fi equipment are free from any
obstructions. Power transistors get hot! The most common reason for transistor failure in vintage
solid state hi-fi is heat, followed by failing components in the transistor's bias circuit. Transistors, like vacuum tubes,
are biased. Usually small low power ones are not as critical, but the big driver and output transistors usually
have special circuits that insure they stay in their normal operating range. These can and usually do consist of
other transistors and zener diodes used as voltage regulators. This bias regulation is critical in these high
current transistors. If one of the regulating components goes south, you can kiss your output and driver
transistors good-bye. Many times you will find adjustment pots by the output transistors. If the unit
is working well and there is no or only a milivolt or so of DC at the speaker terminals with no
audio signal present. Do NOT touch or adjust these controls. If you misadjust them, you will most probably
ruin your output transistors or driver transistors. My advice is to try to find a service manual
for your vintage solid state amp or receiver. As I said. These are generally much more complex then
the old tube amps and receivers. It is easy to get lost in older solid state circuitry. You do NOT want to go
poking around in the unit blind. So, clean the unit physically, look for obvious signs of component failure,
clean all the controls and switches, and if the unit still needs work, get a service manual for it and
trouble shoot it. But, be careful! As I stated, this solid state stuff is not forgiving. You short something
with the slip of a probe and you will see things go up in smoke! Patience is most definitely
a virtue that is needed when working with these receivers and amps, but the end product can
reward you with a fine performing vintage piece that will run trouble free for many years.
Vintage solid state hi fi is rapidly gaining a loyal following and gaining in value as well.
5 years ago, this stuff was relegated to 'give away' status. Such is not the case anymore.
A nice Scott or Fisher 60's and 70's vintage solid state receiver will now set you back over $100.00.
As for Marantz, you can double that for an average unit, and for more rare, upscale units, you
are looking at prices of over $500.00!