| From experience,
the main problem area has been the Driver 12BY7A stage.
I assume that this is due to design, although I cannot complain as the
Transceiver is over thirty years old.
In my opinion, the problem is caused by 'Heat'. Most of the components
associated with the Driver are enclosed
in a small screened box section. The screen grid power resistors
get appreciably hot, and this ages the capacitors
in this section after a few years. My problem
at this time is not being able to fit direct replacements.
Having searched in vain without success, I have resorted to fitting
components found in my Junk box as a compromise for the moment.
Having replaced the faulty components and performing a complete realignment,
the Transceiver is now working fine.
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The initial problem was reduced power output on the h.f. Bands (14MHz,
21MHz and 28MHz).
The l.f. Bands (1.8MHz, 3.8MHz and 7.0MHz) worked fine giving an output
power of 100Watts.
As I only used the l.f. Bands, I didn't bother to investigate why the
h.f. Bands were giving reduced power output.
Recently, whilst calling 'CQ', on eighty metres, the power output suddenly
reduced from 100Watts to zero.
This required prompt action, and the problem (that I should have investigated
earlier) was solved.
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Having removed the covers from the Transceiver and checking some voltages,
I discovered that the 300Volt supply
was missing from the Anode of the 12BY7A driver valve.
Resistor R40, a 1.5Kohm, 5Watt Metal Film Resistor in the main feed
had gone open circuit.
I had to replace R40 with two 3.3Kohm,
3Watt Wire wound resistors wired in parallel.
The reason for R40 burning out was due to C11,
a 200pF Moulded Mica capacitor rated at 1KV going leaky.
This de-couples the tuned circuits in the output
of the driver stage and also forms part of the Neutralizing network..
When measured on the multimeter, C11 had a resistance
of 200ohms, and so removed the 300V supply.
I replaced this capacitor with a 200pF
Television type Pulse Capacitor rated at 4KV.
I just cannot obtain a 200pF moulded Mica
capacitor rated at 1KV type.
At this point the Transceiver started working
again with a full output on the l.f. Bands.
Unfortunately, the power output was still
down on the h.f. Bands.
Further investigation found that the Screen Grid
Resistor R5, 5.1Kohm Metal Film resistor rated at 3Watts,
had increased in value to 10Kohms.
I replaced this R5 with a 4.7Kohm resistor
wired in series with a 470Kohm.
I must try and find a single resistor,
as there is limited space in the screened compartment. Also, heat
produced from the resistors causes the
tuned circuits to drift slightly, therefore, reducing the drive on the
h.f. Bands.
When power was restored, the Screen Grid voltage
of the 12BY7A valve measured ZERO. Smoke
emitted from the new resistors. The reason
was a Screen Grid short circuit within the 12BY7A.
Replacing the valve with an old one in
the Junk box, and a complete realignment, completed the job.
I am sure that the Screen Grid resistor
R5 went high in value, due to the anode of the 12BY7A Valve running on
reduced voltage. This meant that the Screen Grid took over from the Anode,
and consequently the Valve was damaged. When 'full screen grid voltage'
was applied, the screen grid shorted internally.
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I have read many requests, made
by Radio Amateurs, for help in finding 'Low Drive' and Low Output Power
in the FT-101E. I do hope the information that I have provided above will
help them with their problem.
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Three other faults to add:
Intermittent switching (Transmit
/ Receive) can be due to dirty contacts on the Main Relay RL1.
The relay can be unplugged, the
cover removed, and the contacts cleaned with Servisol Switch Cleaner.
Failure of drive on one band can
be due to a faulty Pre-set 50pF tuning capacitor.
The Pre-set tuning capacitors are
in 'Banks'. Problems have been experienced with the connection
between the adjusting screw of the
capacitor and 'Silver Plate'. The 'Silver Plate' is soldered to the adjusting
screw. If this connection isn't made (due to a dry joint), the capacitor
becomes open circuit.
Simply, make sure that the original
solder (on the screw) is over the 'Silver Plate', then resolder the
screw to the plate. (It must be
in contact with the Silver plate).
When the screw is rotated, the Silver
capacitor plate should rotate.
It has been experienced, that C151,
the 10µF, 315V decoupling capacitor, (Screen Grid of 12BY7A Valve)
goes open circuit (due to heat in
the screened compartment). I have been told with authority, one can just
remove it, as it reduces the space inside the 'screened box', and it doesn't
appear to be needed.
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It is a pity that more
of this Old Equipment cannot be recycled, but today,
we live in a throw-away
society. Of course, Radio Amateur's have always
shown great pleasure
in using the Equipment of 'Yesteryear'.
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