Hallicrafters S40-B
 

Recently acquired a Hallicrafters S40-B reciever that was DOA. We made a
few repairs and got it working (including some tube replacement and coil
damage repair). We were a little alarmed when some of the voltages on
the screens & plates were a lot higher than they should be. We then
checked the schematic with actual resistor values and they came close in
agreement with each other. Especially concerned about the higher
voltages on the R.F. AMP tube (6SG7). Any suggestions?

Also; has anyone looked into making a temporary mod to change the BFO
into a Q Multiplier? The idea would be to add a .005, 500WVDC capacitor
from the grid of V5 (6SC7) to the plate of V2 (6SA7), and inserting a
50K variable resistor between pin 6 and ground of V5 (6SG7). The 50K
variable resistor would act as a gain control and affect the "Q" or
bandwith.

John

KE0GG

older receivers usually had a choke input at the PS filter ..if someone
took the choke out or made the circuit a cap input,the voltages would
be noticeably higher..just a thought..There are several schemes that
have been used to create a product detector in the BFO circuit,I am not
familiar with them ,but am interested .. GL W4PQW

older receivers usually had a choke input at the PS filter ..if someone
took the choke out or made the circuit a cap input,the voltages would
be noticeably higher..just a thought..There are several schemes that
have been used to create a product detector in the BFO circuit,I am not
familiar with them ,but am interested .. GL W4PQW

The S-40B doesn't use a filter choke. It uses simple RC filtering.

The voltages are to be measured with the receiver set up as described
in the manual, that is without a signal being received. With a strong
signal present, the AVC voltage will increase the bias on the RF (6SG7)
and IF tubes (6SK7s) and the screen voltage will increase over the
no-signal condition. The B+ will increase a bit also. Another problem
is today's higher line voltages. Most of these old radios are designed
for 115 or 117 volts and when operated on 123-125 volts the B+ will be
15 or 20 volts higher than normal (115 VAC operation).
Best Regards,

Ed

The S-40B doesn't use a filter choke. It uses simple RC filtering.

The voltages are to be measured with the receiver set up as described
in the manual, that is without a signal being received. With a strong
signal present, the AVC voltage will increase the bias on the RF (6SG7)
and IF tubes (6SK7s) and the screen voltage will increase over the
no-signal condition. The B+ will increase a bit also. Another problem
is today's higher line voltages. Most of these old radios are designed
for 115 or 117 volts and when operated on 123-125 volts the B+ will be
15 or 20 volts higher than normal (115 VAC operation).
Best Regards,

Ed

I'll second that! I've found that, given a house line voltage of from
120-127 volts, many of my older receivers used to get very hot. I
installed a 7A Variac on the line dedicated to the BA'a and set it for
110v. No more problems.. at all.

Another problem
is today's higher line voltages. Most of these old radios are designed
for 115 or 117 volts and when operated on 123-125 volts the B+ will be
15 or 20 volts higher than normal (115 VAC operation).
Best Regards,

Ed

I'll second that! I've found that, given a house line voltage of from
120-127 volts, many of my older receivers used to get very hot. I
installed a 7A Variac on the line dedicated to the BA'a and set it for
110v. No more problems.. at all.

Another problem
is today's higher line voltages. Most of these old radios are designed
for 115 or 117 volts and when operated on 123-125 volts the B+ will be
15 or 20 volts higher than normal (115 VAC operation).
Best Regards,

Ed

Thanks for all the input. We found a suspect resistor in the B+, just at
the filter capacitor. It's a 1500 ohm, 10 watt unit that now measures
1400 ohms. We'll try a higher value (say 1800 ohms) based on the
"revised" house line input voltage to bring the overall voltage down a tad.

John

KE0GG

K3HVG wrote:
I'll second that! I've found that, given a house line voltage of from
120-127 volts, many of my older receivers used to get very hot. I
installed a 7A Variac on the line dedicated to the BA'a and set it for
110v. No more problems.. at all.

Another problem

is today's higher line voltages. Most of these old radios are designed
for 115 or 117 volts and when operated on 123-125 volts the B+ will be
15 or 20 volts higher than normal (115 VAC operation).
Best Regards,

Ed

Thanks for all the input. We found a suspect resistor in the B+, just at
the filter capacitor. It's a 1500 ohm, 10 watt unit that now measures
1400 ohms. We'll try a higher value (say 1800 ohms) based on the
"revised" house line input voltage to bring the overall voltage down a tad.

John

KE0GG

K3HVG wrote:
I'll second that! I've found that, given a house line voltage of from
120-127 volts, many of my older receivers used to get very hot. I
installed a 7A Variac on the line dedicated to the BA'a and set it for
110v. No more problems.. at all.

Another problem

is today's higher line voltages. Most of these old radios are designed
for 115 or 117 volts and when operated on 123-125 volts the B+ will be
15 or 20 volts higher than normal (115 VAC operation).
Best Regards,

Ed