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 was not being able to
fit direct replacements.
Having searched in vain without success,
I resorted to fitting components found in my Junk box as a compromise.
Having replaced the faulty components and performing a complete realignment,
the Transceiver is now working fine.
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.
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
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 couldn't
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.
the power output was still down on the h.f. Bands.
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 tried and
find a single resistor without success, as there is limited space in the
screened compartment. Also, heat
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.
valve with an old one in the Junk box, and a complete realignment, completed
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.
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
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.
|It is a pity that
more of this Old Equipment cannot be recycled, but today, we live in a
Of course, Radio
Amateur's have always shown great pleasure in using the Equipment of 'Yesteryear'.
today with modern equipment using 'Surface Mounted Components' and low
voltages, the components needed to repair older equipment are simply not