philly 148 gtl low am power help.???

[1iwilly]

hello to all
i have a philly made 148 gtl that i've change the pre-driver the driver and then the final and still with vr-10 wide open the best the radio will do is 4 1/2 watts and only swings to 5 1/2 the voltage regulatpr was upgraded. on ssb she does 18 bird watts. but on am she sucks any suggestion besides volting to get a little more out at least to make it swing to 7 or 8 watts.?? thanks

 

[loosecannon]

post your personal transmitter tuning procedure for this radio.
its possible that something in your method is keeping the full output from being realized.
just an idea.
LC

 

[1iwilly]

post your personal transmitter tuning procedure for this radio.
its possible that something in your method is keeping the full output from being realized.
just an idea.
LC

i bought and downloaded the sams manual for this radio thats the procedure i used.

 

[loosecannon]

ok, well then ill just assume that you knew what you were reading and did the alignment correctly. seeing as you are getting 18 watts PEP on SSB, you probably did ok.

if you have the sams manual, look at the voltage readings for all the transistors and ic's involved in your issue. some of these would be the driver and final, TR41 and TR42, and the voltage regulator.
be sure to measure them on RX and TX, as you might have a voltage drop on TX somewhere that could lead you to the bad part.

also be sure that your power supply is adequate. 5 amps constant should be plenty.

if you are getting 18 watts on SSB, then your driver and final are fine, i only mention taking their voltage readings as a way to see if something weird is happening on AM mode.

a guess would be that you are not getting enough voltage to the collectors of the driver and final in AM mode. look for cold solder joints or shorted parts if you have been working in this area.

low power problems can be very hard to determine.

one thing you can try is hooking up an ammeter to the input of the radio.
if the radio draws 2 amps on SSB when modulating it to 18 watts, and also draws 2 amps on AM when you are only modulating it to 5.5 watts, then you know you have a short somewhere in the radio that is drawing your precious current away from the driver and final.

good luck,
LC

 

[1iwilly]

thanks i'm using a 30 amp power supply yes ssb is fine
i'll check the voltages as you stated in tx&rx on am i even change the pre voltage regulator.

ok, well then ill just assume that you knew what you were reading and did the alignment correctly. seeing as you are getting 18 watts PEP on SSB, you probably did ok.

if you have the sams manual, look at the voltage readings for all the transistors and ic's involved in your issue. some of these would be the driver and final, TR41 and TR42, and the voltage regulator.
be sure to measure them on RX and TX, as you might have a voltage drop on TX somewhere that could lead you to the bad part.

also be sure that your power supply is adequate. 5 amps constant should be plenty.

if you are getting 18 watts on SSB, then your driver and final are fine, i only mention taking their voltage readings as a way to see if something weird is happening on AM mode.

a guess would be that you are not getting enough voltage to the collectors of the driver and final in AM mode. look for cold solder joints or shorted parts if you have been working in this area.

low power problems can be very hard to determine.

one thing you can try is hooking up an ammeter to the input of the radio.
if the radio draws 2 amps on SSB when modulating it to 18 watts, and also draws 2 amps on AM when you are only modulating it to 5.5 watts, then you know you have a short somewhere in the radio that is drawing your precious current away from the driver and final.

good luck,
LC

 

[1iwilly]

ok today i had a few minutes to spare voltage at tp8/tp7=13.77 on RX on TX with out audio=3.60 volts with audio= 5.45 volts accourding to sams those are normal i just can understand if i replace the voltage regulator with the upgraded one i use the nte one the pre driver was change 2 times so was the driver=2166 and the final was change 3 times. why only 4 1/2 watts wide open and 5 1/2 on swing with r131 cut with r131 in circuit it barely swings.???

 

[radiohobby]

ok today i had a few minutes to spare voltage at tp8/tp7=13.77 on RX on TX with out audio=3.60 volts with audio= 5.45 volts accourding to sams those are normal i just can understand if i replace the voltage regulator with the upgraded one i use the nte one the pre driver was change 2 times so was the driver=2166 and the final was change 3 times. why only 4 1/2 watts wide open and 5 1/2 on swing with r131 cut with r131 in circuit it barely swings.???

To see the swing everyone loves to talk about, you have to be using a pep meter not an average reading meter. If you had a pep meter you would see the same power on am that you see on ssb or within a watt or two if you don't have the carrier cranked up too high.

 

[loosecannon]

the voltages going to the collectors of the driver and final look a bit low.

in AM mode with a 4 watt carrier, you should measure around 7 volts on them.

this voltage is provided by TR41 and TR42 and is the place to start looking for problems.
in AM TX you should measure this on TR41:
E-5.8v
C-13-13.8 volts
b-6.8 volts or so.

if its a new 148GTL (front mic) make sure VR501 is turned up.

if its an old 148GTL (side mic) check TR42 and if bad replace it with a 2SC945.
also look for old dried out electrolytic caps around the audio amp and TR41.
LC

 

[1iwilly]

thanks loosecannon will look in to that what is a better regulator to use??? i think i can get a replacement from ratshack.???can't remember the tip number

the voltages going to the collectors of the driver and final look a bit low.

in AM mode with a 4 watt carrier, you should measure around 7 volts on them.

this voltage is provided by TR41 and TR42 and is the place to start looking for problems.
in AM TX you should measure this on TR41:
E-5.8v
C-13-13.8 volts
b-6.8 volts or so.

if its a new 148GTL (front mic) make sure VR501 is turned up.

if its an old 148GTL (side mic) check TR42 and if bad replace it with a 2SC945.
also look for old dried out electrolytic caps around the audio amp and TR41.
LC

 

[loosecannon]

if you are talking about TR41, i like to use the 2N6487. if you cant find that, the NTE152 or the NTE291 will both work just dandy.

its not like with a final where one transistor might make the radio louder than another; in this case its about being adequately rated for its purpose.

the three transistors i mentioned are more than adequate for what their purpose is.

LC

 

[1iwilly]

hey loosecannon
somebody when they wire vr-10 to the rf gain pot. inline with the middle leg they added a resistor+diode i remove it now the radio dead keys 7 watts and from 2 watts it swings to 6 1/2 on a bird meter. now i need a good modulation mod heheehh thanks

the voltages going to the collectors of the driver and final look a bit low.

in AM mode with a 4 watt carrier, you should measure around 7 volts on them.

this voltage is provided by TR41 and TR42 and is the place to start looking for problems.
in AM TX you should measure this on TR41:
E-5.8v
C-13-13.8 volts
b-6.8 volts or so.

if its a new 148GTL (front mic) make sure VR501 is turned up.

if its an old 148GTL (side mic) check TR42 and if bad replace it with a 2SC945.
also look for old dried out electrolytic caps around the audio amp and TR41.
LC

 

[loosecannon]

i have done pretty much all of the audio mods available to a 148 style chassis, and i have to say that just clipping R131 which is the AM mode modulation limiter makes the radio sound great!

the other mods do work, and may give different audio qualities, but after all my fiddling, just removing R131 works just fine.

yes, you can make the radio sound like crap by doing this.
if you are the type who just HAS to run the Dynamike at maximum, and you use a power mic, then you can distort the heck out of the audio.

if however you are sparing with the dynamike (i like about 2 O'clock) and just turn the power mic's volume up enough to get full modulation from the radio, then you will sound great.

just a couple of sidenotes. if you have removed TR24, or modified it in anyway; put it back the way it was with a 2SC945 transistor.
it will make SSB sound bad if its messed with.

also, if you have done the mod that tells you to change the values of R124 and R126, put them back the way they were.
you dont gain anything by changing these transistors because you just have to turn the mic gain down more to keep from distorting.

changing R114 to a 10K resistor will give you some more audio bandwidth on transmit.

so, just give the radio a good alignment, remove R131, and change R114 if you want to.
it will sound great.
LC

 

[Robb]

. . . changing R114 to a 10K resistor will give you some more audio bandwidth on transmit.

so, just give the radio a good alignment, remove R131, and change R114 if you want to.
it will sound great.
LC

Just how "broad-banded" does it get with this mod? Can it be moreso if another value us used? Just what value can be used effectively to get wider? OR is a change in the cap (C46; value ??) in order also to get more width?

Are there any mods to widen the TX bandwidth, as well as the audio?

I'm interested in what you have to say here, LC!

 

[loosecannon]

i found that mod on the old grant xl owners club site.
the guy that owned the site came up with that mod as far as i know.
he came on here a while ago for a short while.
didnt stay too long. too bad.

the way i figure it, C46 and R114 form some sort of high pass filter, and changing their values lowers the cut off freq.

i went with 10K and .22uF and people really seem to like the sound, but thats the only data i have to offer on it.

i do believe that if you went lower than 10k that you would lower that freq even more.
LC

 

[1iwilly]

ok i also found a diode resister combo in heat shrink from the leg of tr41 to a small solder pad on the solder side of the board if i remove it the radio only swings to 5 1/2 if i put it back then it swings to 8 watts. also i did the r114 change and a friend recorded me talking when he played it back it sounded clean and natural voice quality. also they change the 5 pin mike jack to 4 pin
they tide the sw-common wire with the shield wire does that sound right. or should it be just the shield wire to pin 1 or just the sw-common if i turn the amp on i have to run the mike gain at 10 oclock anything higher and she squeals.???

i have done pretty much all of the audio mods available to a 148 style chassis, and i have to say that just clipping R131 which is the AM mode modulation limiter makes the radio sound great!

the other mods do work, and may give different audio qualities, but after all my fiddling, just removing R131 works just fine.

yes, you can make the radio sound like crap by doing this.
if you are the type who just HAS to run the Dynamike at maximum, and you use a power mic, then you can distort the heck out of the audio.

if however you are sparing with the dynamike (i like about 2 O'clock) and just turn the power mic's volume up enough to get full modulation from the radio, then you will sound great.

just a couple of sidenotes. if you have removed TR24, or modified it in anyway; put it back the way it was with a 2SC945 transistor.
it will make SSB sound bad if its messed with.

also, if you have done the mod that tells you to change the values of R124 and R126, put them back the way they were.
you dont gain anything by changing these transistors because you just have to turn the mic gain down more to keep from distorting.

changing R114 to a 10K resistor will give you some more audio bandwidth on transmit.

so, just give the radio a good alignment, remove R131, and change R114 if you want to.
it will sound great.
LC