Topics

Consolidated Murania Mods


Jim WB2LHP in MI <jmarco1955@...>
 

I've been asked to re-post my list of mods to the Murania receiver...This is the updated list with corrections to previous typos...Please feel free to ask any questions...Jim WB2LHP

Detector Gain Control...

FLOAT the wiper lug of R3
Place a jumper between the PADS for the R3 wiper and the high side of R3
Lift the leg of R1 that intersects with R2 and R3
Connect a jumper between the floated leg of R1 and the wiper of R3
 
This allows R3 to control the gain of the detector stage in the TA7642...The audio amp runs wide open...Adjust R3 for the best sounding audio...R3 now acts similar to a regenerative control where there is both volume and gain reaction...
 
Reduced audio distortion...
 
In addition to my previous post regarding the change in use of R3, change R2 from 1K to 2.7K...This biases the output stage of the TA7642 for linear operation...
 
Frequency coverage and dial mapping...
 
Increase L1 from 37 turns to 61 turns...Remove C8...This centers the frequency coverage and makes the dial tracking spot on...
 
Overall Performance...

The Murania now presents with crystal clear audio and sharper tuning...Remember, this is not a superhet receiver...It is a simple TRF front end, detector and audio amplifier...Careful adjustment of the gain and tuning controls will give excellent results...The battery life is excellent...This is my favorite AM BCB receiver...Enjoy!


K0WDO Will Osborn
 

Thanks Jim! This is fantastic. These mods will be added to my Murania file! I’ve completed most of them with success. 

73, Will 
K0WDO 


On Feb 15, 2019, at 2:53 PM, Jim WB2LHP in MI <jmarco1955@...> wrote:

I've been asked to re-post my list of mods to the Murania receiver...This is the updated list with corrections to previous typos...Please feel free to ask any questions...Jim WB2LHP

Detector Gain Control...

FLOAT the wiper lug of R3
Place a jumper between the PADS for the R3 wiper and the high side of R3
Lift the leg of R1 that intersects with R2 and R3
Connect a jumper between the floated leg of R1 and the wiper of R3
 
This allows R3 to control the gain of the detector stage in the TA7642...The audio amp runs wide open...Adjust R3 for the best sounding audio...R3 now acts similar to a regenerative control where there is both volume and gain reaction...
 
Reduced audio distortion...
 
In addition to my previous post regarding the change in use of R3, change R2 from 1K to 2.7K...This biases the output stage of the TA7642 for linear operation...
 
Frequency coverage and dial mapping...
 
Increase L1 from 37 turns to 61 turns...Remove C8...This centers the frequency coverage and makes the dial tracking spot on...
 
Overall Performance...

The Murania now presents with crystal clear audio and sharper tuning...Remember, this is not a superhet receiver...It is a simple TRF front end, detector and audio amplifier...Careful adjustment of the gain and tuning controls will give excellent results...The battery life is excellent...This is my favorite AM BCB receiver...Enjoy!


John - KD5EJA
 

Thank you, Jim! I'll be making the mods tomorrow and will report my work. I know they should make a 'cool' little radio into a 'super cool' little radio!

73,
John, KD5EJA


Jim WB2LHP in MI <jmarco1955@...>
 

Thanks John...Let me know if you need any assistance...Jim WB2LHP

On Sun, Feb 17, 2019 at 11:33 AM John L. Porter <jjbbl2@...> wrote:
Thank you, Jim! I'll be making the mods tomorrow and will report my work. I know they should make a 'cool' little radio into a 'super cool' little radio!

73,
John, KD5EJA


John - KD5EJA
 

Well Jim, I completed the mods yesterday and wanted to wait until I had a chance to listen to the Murania at night before reporting back.

These mods definitely improved dial linearity, selectivity/sensitivity and overall sound quality on my radio! I am hearing stations now that previously were not detected all through the tuning range. The radio does seem to be more directional now. Positioning is important when listening. I saw your post from 12/1/2018, explaining this.

Anyone having trepidations about installing the mods need not worry. The improvements to an already neat little radio where worth the time!

I have one question, Jim. How important to winding the antenna is wire size. I had to use smaller copper wire and in doing so the 61 turns ended up in the center of the ferrite rod. I don't think this is too much of a concern, but thought I'd ask.

Thanks again for the mod information!

73,
John, KD5EJA


Jeff Logullo N0̸MII
 

Gee, I hope there's going to be another run of these kits!


On Feb 19, 2019, at 3:49 PM, John L. Porter <jjbbl2@...> wrote:

Well Jim, I completed the mods yesterday and wanted to wait until I had a chance to listen to the Murania at night before reporting back.

These mods definitely improved dial linearity, selectivity/sensitivity and overall sound quality on my radio! I am hearing stations now that previously were not detected all through the tuning range. The radio does seem to be more directional now. Positioning is important when listening. I saw your post from 12/1/2018, explaining this.

Anyone having trepidations about installing the mods need not worry. The improvements to an already neat little radio where worth the time!

I have one question, Jim. How important to winding the antenna is wire size. I had to use smaller copper wire and in doing so the 61 turns ended up in the center of the ferrite rod. I don't think this is too much of a concern, but thought I'd ask.

Thanks again for the mod information!

73,
John, KD5EJA
_._,_._,_



Jim WB2LHP in MI <jmarco1955@...>
 

Glad to hear you are pleased with the mods John...

In my case, I still had the leftover wire from the build...I just soldered the wire on and would the coil out to 61 turns...I had the help of an inductance meter...The target value of the inductor is 200 uH...Variations in wire size will mean more or less turns...If you don't have an inductance meter, it's kind of a leap of faith...But in general, you can fill your ferrite form and cut off turns experimentally until your dial lines up with known stations...

If you're doing a brand new build, there is enough included wire to get to the 61 turns...I hope this helps...Jim WB2LHP

On Tue, Feb 19, 2019 at 4:49 PM John L. Porter <jjbbl2@...> wrote:
Well Jim, I completed the mods yesterday and wanted to wait until I had a chance to listen to the Murania at night before reporting back.

These mods definitely improved dial linearity, selectivity/sensitivity and overall sound quality on my radio! I am hearing stations now that previously were not detected all through the tuning range. The radio does seem to be more directional now. Positioning is important when listening. I saw your post from 12/1/2018, explaining this.

Anyone having trepidations about installing the mods need not worry. The improvements to an already neat little radio where worth the time!

I have one question, Jim. How important to winding the antenna is wire size. I had to use smaller copper wire and in doing so the 61 turns ended up in the center of the ferrite rod. I don't think this is too much of a concern, but thought I'd ask.

Thanks again for the mod information!

73,
John, KD5EJA


Johnny AC0BQ
 

Hello Jeff
When we get the parts from our supplier, we will be back in business.
73
Johnny 

On Tue, Feb 19, 2019 at 9:09 PM Jeff Logullo N0̸MII <jeff@...> wrote:
Gee, I hope there's going to be another run of these kits!


On Feb 19, 2019, at 3:49 PM, John L. Porter <jjbbl2@...> wrote:

Well Jim, I completed the mods yesterday and wanted to wait until I had a chance to listen to the Murania at night before reporting back.

These mods definitely improved dial linearity, selectivity/sensitivity and overall sound quality on my radio! I am hearing stations now that previously were not detected all through the tuning range. The radio does seem to be more directional now. Positioning is important when listening. I saw your post from 12/1/2018, explaining this.

Anyone having trepidations about installing the mods need not worry. The improvements to an already neat little radio where worth the time!

I have one question, Jim. How important to winding the antenna is wire size. I had to use smaller copper wire and in doing so the 61 turns ended up in the center of the ferrite rod. I don't think this is too much of a concern, but thought I'd ask.

Thanks again for the mod information!

73,
John, KD5EJA

--
Check out the 4SQRP website at 4sqrp.com


Johnny AC0BQ
 

Gm Group
I found a few minutes to implement Jim's mods this  morning.
Excellent results!
The Muriana is now better than ever!
Thanks Jim!
73 Johnny AC0BQ


On Fri, Feb 15, 2019 at 2:53 PM Jim WB2LHP in MI <jmarco1955@...> wrote:
I've been asked to re-post my list of mods to the Murania receiver...This is the updated list with corrections to previous typos...Please feel free to ask any questions...Jim WB2LHP

Detector Gain Control...

FLOAT the wiper lug of R3
Place a jumper between the PADS for the R3 wiper and the high side of R3
Lift the leg of R1 that intersects with R2 and R3
Connect a jumper between the floated leg of R1 and the wiper of R3
 
This allows R3 to control the gain of the detector stage in the TA7642...The audio amp runs wide open...Adjust R3 for the best sounding audio...R3 now acts similar to a regenerative control where there is both volume and gain reaction...
 
Reduced audio distortion...
 
In addition to my previous post regarding the change in use of R3, change R2 from 1K to 2.7K...This biases the output stage of the TA7642 for linear operation...
 
Frequency coverage and dial mapping...
 
Increase L1 from 37 turns to 61 turns...Remove C8...This centers the frequency coverage and makes the dial tracking spot on...
 
Overall Performance...

The Murania now presents with crystal clear audio and sharper tuning...Remember, this is not a superhet receiver...It is a simple TRF front end, detector and audio amplifier...Careful adjustment of the gain and tuning controls will give excellent results...The battery life is excellent...This is my favorite AM BCB receiver...Enjoy!



--
QRP....."More smiles per Watt"
72
JOHNNY AC0BQ  ..



Jim WB2LHP in MI <jmarco1955@...>
 

Great news Johnny!

On Sun, Feb 24, 2019 at 10:49 AM Johnny Matlock <jomatlock@...> wrote:
Gm Group
I found a few minutes to implement Jim's mods this  morning.
Excellent results!
The Muriana is now better than ever!
Thanks Jim!
73 Johnny AC0BQ


On Fri, Feb 15, 2019 at 2:53 PM Jim WB2LHP in MI <jmarco1955@...> wrote:
I've been asked to re-post my list of mods to the Murania receiver...This is the updated list with corrections to previous typos...Please feel free to ask any questions...Jim WB2LHP

Detector Gain Control...

FLOAT the wiper lug of R3
Place a jumper between the PADS for the R3 wiper and the high side of R3
Lift the leg of R1 that intersects with R2 and R3
Connect a jumper between the floated leg of R1 and the wiper of R3
 
This allows R3 to control the gain of the detector stage in the TA7642...The audio amp runs wide open...Adjust R3 for the best sounding audio...R3 now acts similar to a regenerative control where there is both volume and gain reaction...
 
Reduced audio distortion...
 
In addition to my previous post regarding the change in use of R3, change R2 from 1K to 2.7K...This biases the output stage of the TA7642 for linear operation...
 
Frequency coverage and dial mapping...
 
Increase L1 from 37 turns to 61 turns...Remove C8...This centers the frequency coverage and makes the dial tracking spot on...
 
Overall Performance...

The Murania now presents with crystal clear audio and sharper tuning...Remember, this is not a superhet receiver...It is a simple TRF front end, detector and audio amplifier...Careful adjustment of the gain and tuning controls will give excellent results...The battery life is excellent...This is my favorite AM BCB receiver...Enjoy!



--
QRP....."More smiles per Watt"
72
JOHNNY AC0BQ  ..



John - KD5EJA
 

Jim, I do have a meter, but forgot to check the inductance when I increased the turns to 61. I tweaked it some more over the weekend by decreasing the turns to 51 turns. Can you believe it, but I still forgot to use my meter to check inductance! hi . Never-the-less, it improved the tuning to very close indications on the dial as compared to another old AM receiver I have. I'm happy with that.

73,
John, KD5EJA


Jim WB2LHP in MI <jmarco1955@...>
 

Certainly, the wire size will vary the number of turns needed to get the right inductance but there's nothing wrong with experimenting to get the best results...Congratulations!

On Mon, Feb 25, 2019 at 12:04 PM John L. Porter <jjbbl2@...> wrote:
Jim, I do have a meter, but forgot to check the inductance when I increased the turns to 61. I tweaked it some more over the weekend by decreasing the turns to 51 turns. Can you believe it, but I still forgot to use my meter to check inductance! hi . Never-the-less, it improved the tuning to very close indications on the dial as compared to another old AM receiver I have. I'm happy with that.

73,
John, KD5EJA


AndyH
 

Assembly's not yet complete but wanted to share some numbers from the coil wind.  I decided to include the coil mod/C8 delete from the start.  The inexpensive M4070 LCR meter's been reasonably accurate in the past.  I went with 54 turns.  The following is from the Creamsicle...er...M4070:

62T: 243 µH
57T: 213 µH
55T: 209 µH
54T: 202 µH
53T: 194 µH

72/73, Andy, KG5RKP


ohwenzelph
 

Using the wire that comes with the kit I reduced mine to 52 turns and the dial seems to be accurate, at least at with the local 1400 kHz station. Fwiw my AADE meter measured ~210uH. 

I changed Q1 to a BC550C and it works ok, the “beta” on my transistor tester was 483 for the BC550C and 212 for the 2N3904. It might have been a little bit louder but it was certainly not striking (the body of the BC550 has to be turned 180 degrees to get the leads right).

Jer aa1of


ohwenzelph
 

Update re tuning with 52 turns, 880 comes in when the dial is on 9, so it is probably not yet ideal and might need a couple or a few more turns to be spot on.
(I get pretty much just one local station at 1400 during the day but many many more at night)


Rich ¥Weeds¥ Nagel
 

Hi folks, first post here in the forums. I stumbled on a schematic of the modifications to the Murania AM radio elsewhere on the internet, and dressed it up a bit... I figured that I'd post it here :) Also, the last one is a simple idea that I thought of, a switch to enable/disable the R3 modification.