Looking to replace hard to get Germanium Transistors with Silicon ones, is this possible please?

Thread Starter

specmaster

Joined Nov 14, 2017
14
Felt like playing around a bit. The given circuit actually responds fairly well to Si substitution. Needed to raise RV4 outside its adjustment range to 15K. RV3 adjusts at 8K/42K.

At an output level of 1 W, distortion at 1KHz is <1%. The circuit does have a significant peak around 80 Hz, and the tone control network kills the high frequency response, but that might be to compensate for the small built in speaker.
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Wow, thank you this, it's excellent work, saved me drawing it up and running the simulation, what was the software that you used, was it ElectricVLab by any chance as I believe that program also has problems drawing and showing potentiometers.

I attach in case your interested the complete service manual for the radio.
 

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Thread Starter

specmaster

Joined Nov 14, 2017
14
Thank you for the link, I've installed LTSpice and have redrawn the drawing slightly (circuit still the same just changed the numbering to fit the hacker layout)
Please could I ask if you could explain to me how I change the input parameters to reflect different input frequencies etc as I wish to examine in more detail the tone controls to see how much effect I can have on the tonal quality of the sound by tweaking the values of the components in the tone control circuits.;)

I've never used LTSpice before so I have zero idea on what I have to do your function table above C1 and also by V2 and how they interact with each other.:confused:
 

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Alec_t

Joined Sep 17, 2013
10,746
I wish to examine in more detail the tone controls to see how much effect I can have on the tonal quality of the sound by tweaking the values of the components in the tone control circuits
The AC analysis (which it seems you've already tried) shows the audio spectrum. You can re-run it using altered component values to see their effect. The re-run can be automated using the .step command. For example: set the Bass control pot value as {rb}. Add the dot command text .step param rb 1k 50k 5k on the schematic . (**Note the use of curly brackets)
 

Ylli

Joined Nov 13, 2015
878
Thank you for the link, I've installed LTSpice and have redrawn the drawing slightly (circuit still the same just changed the numbering to fit the hacker layout)
Please could I ask if you could explain to me how I change the input parameters to reflect different input frequencies etc as I wish to examine in more detail the tone controls to see how much effect I can have on the tonal quality of the sound by tweaking the values of the components in the tone control circuits.;)

I've never used LTSpice before so I have zero idea on what I have to do your function table above C1 and also by V2 and how they interact with each other.:confused:
Looks like you picked up the basics quickly. I am really an amateur in LTSpice, and since I don't use it enough, I always will be. You can find a bit of light reading here: https://www.diyaudio.com/forums/software-tools/260627-installing-using-ltspice-iv-including-ltxvii-beginner-advanced.html
 

Thread Starter

specmaster

Joined Nov 14, 2017
14
The AC analysis (which it seems you've already tried) shows the audio spectrum. You can re-run it using altered component values to see their effect. The re-run can be automated using the .step command. For example: set the Bass control pot value as {rb}. Add the dot command text .step param rb 1k 50k 5k on the schematic . (**Note the use of curly brackets)
Maybe I'm a bit thick but I'm not following this at all the only thing I seem to be getting is a sine wave and the only thing that changes is the amplitude. I want to be able to feed in signal of say 50hz and then see the what happens with the bass control set to 1K and then at 25k and again at 50k and repeat this at other input frequencies for the treble and bass to see how much cut and lift I get over the flat response .
 

Ylli

Joined Nov 13, 2015
878
You can look at the output in either the time domain (Transient) or frequency domain (AC Analysis). Right click in the schematic and select "Edit Simulation cmd". In the box that pops up, select "AC Analysis". Fill in Type of sweep - Decade, number of points -1000, Start frequency - 10, Stop frequency - 20,000. Click OK. If a .ac command is not already on the page, you will get one that you need to place somewhere on the schematic.

Now run the sim and look at the output. You'll see a plot of gain and phase over 10-20000 Hz. Go back and change whatever component(s) you want and rerun.

There is a way to step a value and have LTSpice make multiple plots as suggested by Alec_t above.
Capture0.JPG Capture1.JPG
 

Alec_t

Joined Sep 17, 2013
10,746
Maybe I'm a bit thick
Not at all. LTspice has a steep learning curve (well worth the climb) and you seem to have got a good way up the hill in a short time.
the only thing I seem to be getting is a sine wave and the only thing that changes is the amplitude.
That is the result of a transient analysis, not an AC analysis. Ylli shows in post #27 how to do the AC analysis.
 

Thread Starter

specmaster

Joined Nov 14, 2017
14
Not at all. LTspice has a steep learning curve (well worth the climb) and you seem to have got a good way up the hill in a short time.

That is the result of a transient analysis, not an AC analysis. Ylli shows in post #27 how to do the AC analysis.
Yes, I've done of these simulations now and the results are favourable and I've ordered the transistors and a new 15k trimmer to modify one of the amps over to Si devices for experimentation. If its good then I'll just have to search for higher output transistors for the audio output to bring it back into line with the original which is 1.5 watts.
 
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