[LectronFanModerator]

Hi all,

When experimenting with some legacy blocks, I noticed that the amplifier module 8054 was not working properly.

In fact, it didn’t amplify at all !

After removing the white cover, I noticed that the emitter of the 2nd transistor was grounded via a 10K resistor instead of 1,5K.

Also the 2 resistors of 2,7K were replaced by 10K.

And the input capacitor of 0,1µF was missing !

Now to be sure, I replaced and mounted these components.

I did some measurements and the 2,7K resistors should be 10K or the amplifier is not working. The 10K values are also printed in the manual on page 195, experiment 89.

I had another amplifier module and checked these components. It seems that the input capacitor and the 1,5K resistor were also wrong.

Perhaps did Lectron made some updates to this module but placed the wrong resistor at the emitter and forgot the capacitor ?

Can anyone take a picture underneath their legacy amplifier block to compare ?

Now, I added a small change which has an enormous impact on the performance : a gain setting output.

It’s very easy, in fact. Just add a magnet and connector plate at the bottom right connection. Connect this contact to the emitter of the 2nd transistor.

When connecting a capacitor to ground at this connection, you can set the gain of the amplifier.

I will provide example circuits soon with great results.

Here’s the label with the modification implemented.

Just resize it to 5,4 x 5,4 cm and stick it on top of the white cover.

I use self glossy adhesive sticker paper for this. Works great !

Greetings

 

[MichaelKeymaster]

Wow Frank, so many issues with these legacy blocks!  I am surprised and disappointed that the quality control was so poor with changed components, missing components, and incorrect labeling.  Are the three or four I gave you all mismarked and/or incomplete?

The amplifier block was continued by LectronRWO, I wonder what their version of the block is like.  I should have one in my storage area.

Thank you for your research and updates!  I wonder who many other multi component blocks have issues 😥 

[LectronFanModerator]

Hi all,

With the amplifier module modified and working, let’s rebuild experiment 89 on page 195 of the legacy Lectron manual.

This circuit is an audio meter which displays the loudness of audio picked up by the speaker.

But now, with the added gain control connection, the device is so sensitive that even my typing on the computer keyboard is registered and also the bird tweets are shown on the meter !

I’ve modified the original circuit a bit to make it perform better and it can be build with legacy blocks or a mixture of old and new. Both examples are included here and they perform equally.

The advantage of using the legacy Germanium transistor is that the 100K resistor is already built in which saves blocks and precious space.

Just pay attention when putting the earphone in your ear ! Since this circuit has such a large amplifying gain, feedback may occur ! Keep the earphone and the speaker as far as possible away from each other.

This is version 1 with the combination of modern and legacy blocks :

And here version 2 with a legacy Germanium transistor :

A bit of tech info :

The amplifier module with no attached load has a gain of about 180. This means that the output signal is 180 times stronger then the input signal.

With a 100µF capacitor attached at the gain connection (C1 in our circuit), the gain is about 1200 !

The input of the amp module is low ohmic, which means it has a low input resistance.

The output is high ohmic, so the following stage should pose no load to obtain maximum performance.

This is why we use a transistor stage T1 with a 220 Ohm resistor at the emitter to retain this high resistance and which also sets the amplification rate of T1.

The use of the earphone as an inductive load helps to maximize the performance of T1.

Many greetings

[LectronFanModerator]

Hello Michael,

Indeed, all four amp blocks have the same erratic components.

And since I like to tweak a bit, this gave me the opportunity to add the gain control connection,

It’s a pity that the corners of the white covers are glued and so the tabs break off.

With a few small drops of glue, the cover can easily be reinstalled after the modification.

I also made a few measurements this evening.

Without external capacitor, the gain is about 180.

With a capacitor of 100uF, the gain is a whopping 1200 !

I believe that this amp module has a lot to offer.

This is great for amplifying very weak audio signals like in project 89 of the legacy manual.

And with the higher gain, even a tiny whisper from about 1 meter, the meter needle moves a lot. Even the background noise is readable !

So, I hope that readers who have the malfunctioning amp module will find their way to this thread. It’s an easy fix to do.

And even good working amp modules will perform better with the gain control connection.

I will publish a circuit tomorrow which blends new and legacy parts !

Till then !

[MichaelKeymaster]

Hi Frank,

What a shame.  Thanks for your investigation and subsequent solutions.  Very helpful for the Lectroneer community!

Why were the original designs so underwhelming and the implementation so erratic and inconsistent?  

Guenther:  Do you think that Mr. Guerth was aware of these issues?  He was Mr. Greger’s go to person to fix problems with circuit designs.  Or did Mr. Guerth only focus on digital logic?

Best regards,
Michael

[GuentherParticipant]

Hi all,

Max Guerth had accepted to help Egger since 1968 for solving the problems with the digital blocks in the evening hours (after his work at Siemens, developing the full automatic sorting system for letters etc.) and sometimes on the weekends. Furthermore he designed and developed lots of new scenarios for more Lectron business, experiments and sets, as we all know now after studying his many photos, diagrams and scripts.

His test equipment – as already mentioned – was exclusively developed for the tests of the critical digital blocks – not the “standard” ones.

As I know several of the blocks (simple connections, transistors, etc.) were defect, because it seems that no quality control had taken place. Therefore EVERY block has to be checked: if nearly new (NOS), if from 2. hand, 3. hand, schools (!) or what ever: NEVER use it unchecked!

Why did I construct a Lectron block tester? Because I purchased some thousands of (used) Lectron blocks – and >20 % were defect!

Braun AG knows about that problem: “…please send back defect block(s) and we will free deliver the replacement(s) …”

Coming back to the 2-stage amplifier : yes – the amplification is low, therefore I used 2 discrete transistors as AF amplifier, e.g. in my SW receiver versions. I never tried to increase the performance – but there are good hints to do it now, thank you, Frank!

[GuentherParticipant]

Today I opened and “updated” three of my oldest and yellowed 8054 blocks, which covers were completely (!) glued – no tabs, this came later… hard work, sometimes this old blocks will crash while trying to open – like an oyster 😥

The electrolyte capacitor I placed inside, too –  then there is no need for me to add it as extra block(s).

In this moment I cannot remember any change in construction over the years. I will try to varify it in the next weeks.

G.

• This reply was modified 5 years, 2 months ago by Michael.

[GuentherParticipant]

Today I looked up my 8054 blocks and was rather astonished: 6 blocks and 4 different versions!

My findings are placed in the photo so that everybody might see what I mean:

So I have to work some hours to repair all of my 8054 blocks and use this new cover:

Best,

Günther

[MichaelKeymaster]

Wow, this is really sad that quality control seems to have been so bad and inconsistent!

Thank you both for adding such clarity to the situation.

Best,
M.

[GuentherParticipant]

I had a closer look to the inner side of the newer blocks and was quite speechless:

Rather terrible which manipulation was required to get function of a new designed PCB (right) – but the examination of the wired version (left) was the “summit”:

I still struggle with words – and will close for today…

Best,

Günther

• This reply was modified 5 years, 2 months ago by Michael.

[MichaelKeymaster]

So these are LectronRWO blocks?  Very disappointing indeed.  I guess Mr. CvS did not do spot checking of the work the RWO personnel did. One has to wonder what other disasters may exist with other multi-part blocks like the gene block.

• This reply was modified 5 years, 2 months ago by Michael.

[LectronFanModerator]

Hello Michael and Günther,

Thanks for the close up pictures of the modules.

And what a weird cover you put as last, the emitter as input !

The 2,7K resistors were probably used with an older type of transistor. I’ve tried with the AC125 and 10K works best.

Good idea to mount the 100uF cap inside the cube ! But with an external connection you’ll be able to control the gain with external components.

I found a transparent glue which looks like silicone. It sticks very good and can also be removed when needed. I use this for glueing the covers.

I believe that the improved amp has lots of possibilities yet to be discovered, let’s build experiments with it !

 

Many greetings

• This reply was modified 5 years, 2 months ago by Michael.
• This reply was modified 5 years, 2 months ago by Michael.
• This reply was modified 5 years, 2 months ago by Michael.

[LectronFanModerator]

Hello Michael and Günther,

Today I found some time to finish the amplifier modules and make them work as intended.

I have also the “wired” versions and this is an easy way to fix these.

I drilled an extra hole for the emitter of the 2nd transistor and used a different wiring.

I also inserted a 100nF capacitor at the input and removed wrong 10K resistor.

I also made a 2nd amplifier module with 100µF capacitor inside for easy setup.

Many greetings

 

Here are some pictures :

• This reply was modified 5 years, 2 months ago by Michael.
• This reply was modified 5 years, 2 months ago by Michael.

[MichaelKeymaster]

Hi Frank,

Thanks very much for these updates!  We will perhaps need to create a new page/topic/post to reflect these excellent block revisions and updates.  These are very important and unique, particularly for legacy component owners.  

What do you and Günther think is the best way to capture these block corrections to make it easier for other Lectroneers to find?

Best,
Michael

[GuentherParticipant]

Hi All,

today I tried to build the 8054 circuit with the transistors AC173 and AC125 to compare both in amplification, current and collector resistor values.

As input I used a Cassette Deck output (DIN), as “control”  a headphone. After varying the resistor values (via pot) and changing the transistors I – subjectively – decided that 10 kohms (with 1.5 mA current over-all) gives the best result.

I really don’t know why the values of 10 kohms (Egger) had been changed (Braun) to 2.7 kohms – and this  not only in the #8054 blocks, also in the realized and planned BASTELSATZ PCBs!

Best,

Günther

• This reply was modified 5 years, 1 month ago by Michael.
• This reply was modified 5 years, 1 month ago by Guenther.
• This reply was modified 4 years, 7 months ago by Guenther.

[GuentherParticipant]

For a current occasion, I have today easily converted an – already updated – doublette block to NPN Germanium.

I used the Romanian version EFT373 (licence of the French  SF.T373) with the same outline (and hfe) of the PNP version AC173 – and is working with big success!

The new cover:

Best,

Günther

 

• This reply was modified 4 years, 7 months ago by Guenther.

[LectronFanModerator]

Hi Guenther,

What a great idea to use the NPN transistors.

The amplifier module can now be used in the new sets.

I believe there exists also a AC127 NPN version. I will check it out and report later.

Greetings

[GuentherParticipant]

Hello Frank,

You may use AC127 or any other available Ge NPN Transistor (early Japanese types started with 2SD..). I checked the hfe values of my NPN transistors and decided to use the above mentioned ones because of their hfe >220 – my AC127 etc. as low power / switch types had around hfe 100.

Good luck,

Guenther

[Author]

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