need justin's advice on a 2000gtl mod (all others welcome)

[loosecannon]

hi,

dont really post here very often if at all, but i do sandbag and read the posts.
the reason i am posting this here is that i would like Mr. depolis' opinion of the part change i wish to try.
all other opinions are welcomed, but i am really looking for what justin thinks of it.

here goes:
i have a 2000gtl that i have tried just about every audio mod on, at different times.
most i thought were a degradation in performance instead of a boost.
currently, here are the mods in the audio section.
1k added to TR24
R131 changed to 4.7k
R114 changed to 10k.
NPC cap added to audio chip.
final volted.
i am going to return the radio to a more stock setup, and will be unvolting the final, and returning TR24 to its original state.

my question is should i leave R131 as a 4.7k or go back to 10k?
i want the radio to sound clean on AM and i dont want to cause a bunch of splatter.
i do want the modulation to be at 100% or close to it, and i find that these rigs dont want to get above 80% with the stock R131 in.
just want to know your opinion of what i want to do.
what else would you do?

this is my absolute favorite radio, and i do not hack it.
it has been completely recapped, and all upgrades were done by me.
i handwired an EPROM board and added a three digit LED display.
not my design, i just built one up.

thanks for any and all responses,
loosecannon

 

[Switch Kit]

someone else will have something else to say here but stock is about the best way to go on those radios , Those were good radios out of the boxes for the most part as well as there counter parts the 148 and the Grant XL ,80% audio ? what meter is that ? they should do 100% without any problems , and on those ,that's all you really need, I tend to like different things , I like the NPC's when amps are involved but I really don't see the need on one of those , The audio section on those radios are like none I've ever seen , IM no expert but as far as IM concerned with those radios , a slight tune up and your done, If you want more ? let a amp take care of the rest.

 

[Switch Kit]

Now theres a good tip 55 if you think you can handle it. Very good Justin .

 

[loosecannon]

first of all, thanks so much for responding to my questions justin.
i know you are busy, and i appreciate your time.

i do have a few questions about the mod you suggested, but please dont take it as me questioning your abilities; i am just trying to learn.

1. you mentioned replacing R131 with a 10K and then removing TR26.
doesnt this take R131 out of the circuit?
why does it matter what value it is?


2. you also mentioned jumpering R180, which i did when i volted the final.
if im going back to stock voltage for the final, does this still need to be a jumper even though i will be biasing the driver and final like stock?
should i leave it as a jumper even though i am not interested in the power output increase?

3.the NPC mod i mentioned is where you add a 10uF cap from pin 9 of the audio chip to the junction of R194/D63/R228.
you mentioned removing C174 and adding a 1,000uF cap to the base of TR41.
is this sort of the same thing?
what is the difference with the way you suggest?

4.i run a 680uF at C18.

5.you mention adding a 100ohm resistor to the S042P.
what does this do?
does it broadband the TX mixer, or increase power out or what?
im wondering because i am not interested in increasing the power out of the radio, but a bit more broadbanded TX would be OK.

thanks again for the help, and thanks for the suggestion of the 2N6487. now i dont have to use NTE parts anymore.
loosecannon

 

[loosecannon]

again, thanks so much for your concise and technically adept reply.

i peruse alot of these CB forums and i find that the guys who really know the "how's" and "why's" of this stuff are either too busy, or too fed up with answering the same old questions, and dont bother to explain or reply.
i dont blame them, i just appreciate your attitude.


VERY COOL about the C174 change. cant wait to try it.
got some 2N6487's in the mail last week.

one more question:

if i decided to leave TR26 in place, would i be wasting my time in doing the C174 change?


thanks in advance,
loosecannon

 

[W1R3T4P]

Remove Tr-26, and set the mic gain, you'll be fine, you can leave TR26 in, but you're never going to get 100% modulation.

Removing TR-26 disables the AMC on am.
How much modulation will he get then?

 

[loosecannon]

interesting.

i am ot one who needs to run the mic gain open all the time, but i dont have a scope and i am trying to acheive a clean waveform.

trying to keep nice with the neighbors, and also use my amp on AM.
(i am VERY hip on grounding, good coax, and using low pass filters.
i run LMR400 coax, and learned about it all from a very good broadcast engineer. grounding is good!)

im am going to try leaving TR26 in at first, and if the mod. reports from trusted friends is bad, i will remove it.

thanks for all the help.
when all is done, i will post the results and the reports.
thanks to all who replied to this thread.
loosecannon

 

[loosecannon]

well i am certainly learning from this thead!

thanks justin.

if you ever have the time or inclination to delve deeper into the loopback shunt circuit for the AMC of this chassis, please post it here, and i will do whatever reading is required to understand it.LOL

if i were to remove TR26, and set the radio to key at 5 watts and swing to 20 on my PEP meter, and about 8 on the RMS; would that be about 100% modulation?
basically, turn the external mic gain up until 20PEP is acheived.
would this work?

again, trying to keep peace with the neighbors and not create splatter.
loosecannon

 

[loosecannon]

mod is done.
very happy with the results.
5 watts, swinging about 20PEP, and about 8-9 RMS.

cheapo RS meter, but relatively new.

left TR26 in for now.
getting good reports, but i havent heard it myself.
running a turner +3b.

also added a fast/slow AGC switch using a 22uF cap.
very cool on SSB.


thanks for all the help justin. this is my favorite chassis, and im always trying to learn more about it.
loosecannon

 

[TonyV225]

HATS OFF TO JUSTIN...For taking the time to answer this and most of all for explaining it in laymens terms which he has always done with or for me on the phone when asking him one of the 1000 questions I did ask him LMAO!!! it takes a patient person to do this as said exspecially after answering this question a dozen times.

 

[loosecannon]

hi all,

i too want to thank justin for his patience and willingness to help
someone who is trying to learn about this stuff.

justin, remember that i left TR26 in so my numbers may be a bit off from what you are used to seeing.

i have the driver and final biased at 30 and 60mA if that makes any difference.

i do not own an oscilloscope or a spectrum analyzer, but i have built the test equipment i need to do a pretty proper tune up to my radios.
i own an RF sig. gen., a good freq. counter with probe, a decent wattmeter, a good voltmeter that i built an RF probe for, a homebrew AF wattmeter, a homebrew pulse noise gen., and a homebrew dummyload.

whole radio has been recapped.
all TX coils are tuned for peak modulation.
always happy to receive constructive criticism.

thanks again,
loosecannon

 

[Switch Kit]

7 watts into a TS-500 ? OUCH !!

 

[Switch Kit]

Wow !! my humble apologies here , I had no idea that a Texas Star 500 could handle a 10 watt DK . Shoot !! I run a 4 x 454 and only put 2 watts with a swing of just over 20 into that and see about 100 swing'in 400 ballpark . I think if I put 10 watts into that, it wouldn't be long for this world. Wow !! Had a TS-350 and all it liked was about a 2 watt DK as well , go figure. Good luck with your stuff. Peace

 

[loosecannon]

hi again,

im doing this mod to a 148gtl (old style) and i would like to make TR26 switchable.

is there any lead in particular that would be best to switch out?
as in, E, B, or C?
or will i need to switch out two or all three leads simutaniously?
as in use a TPDT switch.

any help is appreciated,
loosecannon

 

[DTB Radio]

hi again,

im doing this mod to a 148gtl (old style) and i would like to make TR26 switchable.

is there any lead in particular that would be best to switch out?
as in, E, B, or C?
or will i need to switch out two or all three leads simutaniously?
as in use a TPDT switch.

any help is appreciated,
loosecannon

Just put a switch in line with the base lead.