Converting
FT-101 Rigs From Sweep Tubes to 6146B
Type Finals
Eliminating Additional Below Chassis Heat with an Optional Supplemental Relay
If the user desires, a supplemental relay can eliminate the
additional heat caused by the 5.6K 5 watt resistor and zener diode
'regulator' while receiving.
To free up some below the chassis space, choke T-12 will have to be
mounted above the chassis in the area where the new electrolytic
capacitors have been installed. Just one hole has to be drilled
in the rear of the chassis to mount T-12, as shown here.
Most any relay with a 12 VDC coil and a contact rating of 250
volts can be used. Since I had a new one, I opted for the OMRON
relay shown in the parts list.
It is a DPDT unit and it is mounted where T-12 was located. The
new relay's coil connections are wired to the same feedthrough
capacitors that provide power for the FT-101's antenna changeover
relay, specifically C39 and C40. The connection between the 5.6 K
5 watt resistor and the (low voltage) B+ supply is severed and routed
through the 'make contact' of the relay.
For
good measure, a spark suppresion capacitor is placed across the relay
contacts, and a 470K, 1/2 watt resistor connects the 'break' contact to
ground. This is another failsafe measure in the very unlikely
event that the R30 replacement would ever open up.
Once done, the screen grid supply to the PA tubes will be applied
whenever the FT-101 goes into the transmit mode, and the voltage
'regulator' consisting of the 5 watt resistor and the zeber diode(s)
will be applied to the PA tubes. Here's the schematic drawing.
The relay itself is secured via two heavy nylon cable ties to some under chassis wiring as shown in this picture.
Be sure to use wire that will handle 350 volts for the high
voltage connections and exercise caution when installing the relay