The Yaesu FT-101E Transceiver
                                                    The Transceiver shown above was purchased in 1977, and has given very good service.
                                    I have included this Webpage to help those Radio Amateurs who may be finding difficulties in faultfinding.

                               Above is a Circuit Diagram showing the Driver and Power Amplifier stages of  the Yaesu FT-101E.
                        The components circled refer to the ones detailed below and show their location on the Circuit Diagram.
                         Modifications as recommended by other knowledgeable Radio Amateurs.
It has been found that the 'Drive Coupling Capacitors' from the Driver to the Power Amplifier Stage can cause severe damage to the equipment if either become 'Short Circuit'.
There are TWO Coupling Capacitors, C131 (1000pF) for Top Band, and C13 (80pF) for the other bands.
The modification is to wire a 0.01µF Disc Ceramic Capacitor in series with C131 and C13 respectively.
If either capacitor fails, the 0.01 Disc Capacitor will prevent a major catastrophe.
It has been found that if either Power Amplifier Valve (6JS6C) 'flashes over' internally, then severe damage can occur. 
The recommendation is to wire a BY127 Diode in series with the Screen Grid resistor R14. 
                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 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 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. 
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 tried and find a single resistor without success, 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.

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. 

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 throw-away society.
Of course, Radio Amateur's have always shown great pleasure in using the Equipment of 'Yesteryear'.
Unfortunately, today with modern equipment using 'Surface Mounted Components' and low voltages, the components needed to repair older equipment are simply not available.
                    Harmonics as viewed on the G3NGD Spectrum Analyser for the FT-101-E.
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Updated: May 2014