Hallicrafters SR-150, Operation And Maintenance Manual

By Walter Cates WD0GOF (UPDATE 10/30/2013)  

12  

SR-150 REFURBISHING AND REPAIRING CONTINUED:  

1-9. TRANSMITTER TESTING  

1-9-1. TRANSMITTER TESTING EQUIPMENT REQUIRED  

Wattmeter/load 50 ohm 250 watts full scale  
Scope 100 MHz bandwidth  
Microphone dynamic 600 ohm  
Multimeter 2 VDC full scale and 10 VDC full scale recommended 

Optional 

telegraph key  

1-9-2. TRANSMITTER TESTING PROCEDURE  

Back in paragraph the 3 amp slo-blow fuse was replaced with a 3 amp normal delay. It is now time to re-install 

the 3 amp slo-blow fuse. Set the main tuning dial to 7.25 MHz. Set the band switch to 40 meters. Set the rest of 
the controls to the 

STANDARD PRE-POWER UP CONFIGURATION. 

Set your meter to the 2 VDC full 

scale range and plug it into the red (+) and blue (-) test jacks on the power supply chassis (this is to monitor the 
PA plate current). Connect a wattmeter/50 ohm load to the antenna jack of the transceiver. Set the 
OPERATION switch to STBY and allow 15 to 20 minutes for warm-up.  

Earlier in this process the –bias was rough set. Now it needs to be set more precisely. Set OPERATION 

switch to either USB or LSB, ensure MIC GAIN and RF GAIN are at Ø. Attach your mic and key the 
transmitter with the mic. Adjust the BIAS ADJ control on the back of the power supply for a reading of Ø.7 
volts (This indicates 70 milliamps of plate current) on the meter plugged into the power supply. 

WARNING;

keep your eyes on the meter as you key the mic. Quickly un-key the mic if the meter pegs. If you cannot adjust 
the bias or it pegs you have a problem in the PA or bias voltage divider ckt. This may be a tube or a DC 
problem. Check V14 and V15. Then check the voltages on V14 and V15. This fault must be cleared before you 
can continue, go to the TX BIAS FAULT section for more information. If you are able to set the bias to 0.7 
VDC observing the meter and adjust the BIAS ADJ control to see if you can get 1.5 VDC on the meter. 

Quickly

 return the setting to Ø.7 vdc. If you are unable to get 1.5 VDC then one or both of you final tubes are 

weak. Replace them with a matched pair. If replacing the tubes does not clear the fault then you have a problem 
with the HV, B+, screen voltage or bias. This fault must be cleared before you continue.  

The next series of tests will be conducted in the MOX, CW mode. You will need to switch the FUNCTION 

switch from LSB to CW quite often. You MUST keep the transmit duty cycle short. I find it easier to plug a key 
into the key jack on the rear of the transceiver. Then you can set the FUNCTION switch to the CW position and 
leave it there and press the key when you want power. This saves wear and tear on the FUNCTION switch and 
reduces the chances of leaving the transmitter keyed to long. For the remainder of the tests when you are 
instructed to “

key the transmitter

” you will either switch the FUNCTION switch from LSB to CW or press the 

key.  

Assuming you have properly set the 

STANDARD PRE-POWER UP CONFIGURATION 

and are in STBY 

tune the main tuning and band switch for 7.25 MHz. Switch to MOX and key the transmitter. Set the meter to 
the 10 VDC range. Observe the plate current while advancing the RF GAIN. Do not let the plate current exceed 
250 mills (2.5 VDC on the meter). If you do not get an increase in plate current advance the RF LEVEL to the 3 
o’clock position. Adjust the PRESELECTOR and FINAL TUNING controls to find a peak in the current. Keep 
the plate current below 250 mills by reducing the RF LEVEL as needed. If you are unable to get an increase in 
plate current proceed to the TX DRIVE FAULT ISOLATION subsection. This fault must be cleared before you 
continue.