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Messages - galaxiex

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Amplifier Discussion / Re: newbie question about cranked amp overdrive
« on: December 24, 2021, 02:20:10 PM »
Trace the circuit.
Draw schematic from that.

It shouldn't be too difficult.

I've drawn quite a few schematics for old, cheap, SS amps where the schem is unobtainium.

Search my threads in "schematics and layouts".

Honey Amp / Re: Power supply suggestions
« on: May 20, 2021, 06:30:21 PM »
I got the kit that came with the 8 ohm speaker.  All assembled and currently powered with a 9-volt battery.  It seems I have to have the volume absolutely cranked to be heard over the guitar strings themselves. Turning the gain up obviously gets past this a bit.
I tried to use a 12 volt DC wall plug but that introduced a ton of hum into the amp.
What are you using as power for this little guy? Would an A23 battery work?

Install a 10uf cap on pins 1 & 8 to maximize the gain.
The pads are on the board so it's easy to do.

Hey Joe, pretty cool amp.  :tu:

I'd back the project but I'm in Canada.
Can you change the kickstarter to allow folks from Canukistan to back it?


I've made the adjustment! Only reason why is that you have to calculate shipping for each country. If anyone else from another country is interested, let me know and I'll add it as an option!

Thanks Joe, I'm in! :)

Hey Joe, pretty cool amp.  :tu:

I'd back the project but I'm in Canada.
Can you change the kickstarter to allow folks from Canukistan to back it?


I would love to hear some sound samples from the amp, demonstrating the tone control and variable distortion.  It might help your kickstarter, too.

The kickstarter page has a video demo.

The Newcomer's Forum / Re: Soldering Station
« on: October 18, 2020, 08:54:51 AM »

A solution looking for a problem?  ???

Schematics and Layouts / Re: Teisco CheckMate 22 schematic
« on: May 24, 2020, 04:34:15 PM »
Bumping this cuz we seem to have reached the limitation of the tiny output transistors.  ::)

The new 18VAC transformer and resulting 25VDC rail is just a bit too much for them.  ;)
Playing the amp for more than 30 minutes at full volume causes the output transistors to go into thermal overload.

At less than full volume I have not reached the limit...
but this thing sounds so darned good at full.  8)

So options are...

1. Better heatsinking on the output transistors
2. Better (higher rated) transistors and better heat sinking.

I'm leaning toward option 2 but might try cobbling up a better heat sink for the originals.

I do have a couple of NOS T0-3 PNP Germanium transistors looking for a home...  ;)

Schematics and Layouts / Re: Teisco CheckMate 22 schematic
« on: April 15, 2020, 08:18:00 PM »

Great job!  I always love seeing people make old gear work / work better.  :dbtu:

Thanks Joe!  :)

This one has been fun for me.
I don't even mind that it's barely 2 watts (if even that) with those tiny germanium output transistors.
I've learned a lot after tinkering with all those other amps that are similar to this one. (still learning! )

I've been running this thru a 12" sealed cab loaded with a 8 ohm Celestion G12H.
Great sounds at bedroom levels with the vol on max.

I did find out it doesn't like 4 ohm loads.
The output transistors go into thermal overload after about 20 seconds.  :o


Schematics and Layouts / Re: Teisco CheckMate 22 schematic
« on: April 12, 2020, 12:12:25 PM »
Ok, more polishing the turd....  ;)

I just can't leave well enough alone.  ::)  :duh

I wasn't happy with the reverb sound of this amp.
It's mostly due to the limitations of the single spring reverb tank.
At almost any reverb setting it sounded more like a metallic "clank" than reverb.

So I thought the way to get a more musical/realistic reverb sound,
was to have some control over the frequency's being sent to the tank.

I first tried the reverb tone network you see in the schematic,
without the trim pot and no buffer.
2 X 51K resistors in place of the trim pot and output taken from the junction of them.

This worked somewhat,
but the tone network loaded down the circuit too much, reverb too quiet.

So I took the volume buffer (from previous schematic) and swapped it to the tone network.
Then adding the trim pot as a reverb tone control.

This works great!

The tone network adds a mid notch and the trim pot lets you roll off the highs.

The boards are supported on solid core stiff wires.

Schematics and Layouts / Re: Teisco CheckMate 22 schematic
« on: April 04, 2020, 02:00:32 PM »
Ok, some more mods.  :)

Added a buffer at the mix point of the volume and reverb.
The high pass filters at the output of the op-amps (C23, R38 and C26, R43) cut unnecessary low frequencies.
Corner frequency of the filters is approx 88 Hz.

The filters helped a lot to get rid of the amp sounding muddy/mushy/smeared sound.

Now... I think the mix point of the vol and reverb could use some help.

The way it is now the reverb sounds like a completely separate signal sort of "riding on top of" the main signal.
IOW it doesn't sound "mixed".
Hope that makes sense...

Any suggestions on how to "more properly" mix the 2 signals?

Thanks for any help!   :)

Edit; connecting the reverb output to the top of the volume pot seems to work better.

Here's the corrected schematic...

Schematics and Layouts / Re: Teisco CheckMate 22 schematic
« on: March 29, 2020, 05:40:02 PM »
Got the coil wound and installed.  :)

4760 turns and 662 ohms.

It's alive!
We have reverb!
(albeit not very good reverb, but I expected that  ::))

Now I'll disassemble the tank and clean it up some,
just to get rid of some of the corrosion.

Edit: This is the output coil that I just wound at 662 ohms.
No idea what it was originally, or what it's supposed to be.
Seems to be working fine.

The input coil measures 1K6 ohms DCR and both coils were/are wrapped with blue tape.
I don't know if the tape color indicates coil impedance/DC resistance like the Accutronics tanks.

Schematics and Layouts / Re: Teisco CheckMate 22 schematic
« on: March 29, 2020, 03:27:00 PM »
Ok, the reverb coil winding has started....  :)

First pic is the bobbin mounted to the winder with the old wire still on it.

Second pic is the new wind started.

Wow this thing is tiny!

Winding going really sloooow cuz I don't want to break the wire and hafta start over...

The new wire is thicker than the old, so I'll over-wind it somewhat.

Old wire measures .015"
New is .025"

I was able to find the end wrap and paid attention to the direction of wind.

New wind is going on the same direction, don't know if it would matter (phase issue, maybe?).

Schematics and Layouts / Re: Teisco CheckMate 22 schematic
« on: March 29, 2020, 12:16:14 PM »
Here's some modifications to the little CM-22.  :)

Pics show the added stuff.

The input buffer is just hung on some stiff wires, right on the input jack.

The added C24 and R39 (see schematic) give a large gain boost,
very "crunchy" germanium transistor distortion, almost Fuzz Face territory.  8)

I tried with just the 100uF cap and it was too much gain, squealing feedback.
The 1K resistor tames it just right.
Thinking to maybe put the C24, R39 "gain boost" on a switch...

Last pic is a size comparison of the power Tx.
The bridge rectifier setup is temporary, I'll make a little board for it.

Can you tell I'm bored with being stuck at home?  ;)

Edit; still haven't fixed the reverb tank, I'll get to that later today... maybe...

Edit 2; schematic removed, mistakes were made, corrected schematic with all modifications in post below.

Schematics and Layouts / Re: Teisco CheckMate 22 schematic
« on: March 28, 2020, 03:52:23 PM »
Here's a layout for the original board.

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