You could place a HP filter on it, or a preamp with tone controls.
A simple High Pass filter with a drop off slope of 6dB is just a capacitor and a resistor, I have read somewhere that those small amps have an input impedance of 50k ohms so just a capacitor on the input might be enough.

Try placing a 22nF capacitor between the guitar and the amp and see what happens, you will have to find a value you like by experimenting.
The smaller the capacitor the more bass you cut off.

Try using this simple calculator to work out different values:
http://www.learningaboutelectronics.com/Articles/High-pass-filter-calculator.php#answer1

Are you plugging the guitar straight into it? No other preamp with tone controls at all or is there a pedal inbetween.

NO
do not connect them in parallel because you will get 2 ohms and destroy the amp.
You want them connected in series/parallel to get 8 ohms.

2 - 8ohm speakers in series is 16 ohm (make up 2 of this)
2 - 16 ohm in parallel is 8 ohm

Look at example 4 on this page:
https://www.amplifiedparts.com/tech-articles/speaker-impedance-power-handling-and-wiring

I imagine it's some sort of 2 part epoxy glue like Araldite.
I would have used a couple of screws myself.
Maybe they glued it down so it got some thermal contact to use the case as a heatsink, but I would think a small 30 watt class D amp would not generate much heat anyway.

The module is only 22mm x 26mm and under $10, 20 watts at 12V @ 4 ohm and 10 watts at 12V @ 8 ohm.
That is plenty for a practice amp, 10 watts into 8 ohm most likely means you run it easily on a wall wart if not a pedal supply.
Want an amp when you go camping ?, you could run it on a small solar panel with some rechargeable batteries.

Quote from: Tassieviking on November 05, 2024, 09:42:19 AMI have not had any problems with it, I just havent used it since I blew up the last laptop power supply, I think the amp is still fine.
If you want to see an even smaller one there is a company selling tiny 30 watt poweramps that are 25mm x 25mm x 100mm.
Even their 50 watt pedal is nice with a VU meter on it.
https://svisound.com/index.php/products/amps-cabs

I found a picture of this tiny amp, it is just a basic 30watt amplifier module glued inside the metal box.
It would be really easy to make one the same.

I just had another look at that power supply you have, there are 2 switches on it.

IND would mean the 2 outputs are separated from each other, not connected to each other at all.

SER would mean in series, I presume that this links the 2 outputs so you have a +,0V, - output.
SER will give you  double the voltage of one output but no more amps.

PAR would mean parallel and the two outputs will be joined up with + to + and - to -, you get double the amps compared to one channel but also only the volts of one channel

Try it with the switches set to SER and then measure the voltages of the 2 outputs, I imagine the plus on one side is equal to the minus of the other side.( they will be linked by the switches internally)

If you have two 9V batteries and you want 18V you connect the plus of on battery to the minus of the other battery, result is 18 Volts.
Where the 2 batteries meet is what we normally call ground, and then you have plus 9 volts and minus 9 volts on either end compared to the ground.
From the minus 9V to the plus 9V will be 18V

On some schematics they just say 0V, 9V, 18V instead of -9v, ground, +9V.

There are so many variations but after some time you just know what they are with a quick glance.

I find having a positive and a negative supply with a ground much easier to trace and understand  a circuit because sine waves have positive and negative sweeps, just think of that oscilloscope waveform where the middle is 0V or ground.

Here is another calculator design tool place thingy, it can be a little bit harder to use:
http://sim.okawa-denshi.jp/en/

You most likely know about the tone stack calculator:
https://www.guitarscience.net/tsc/eseries.htm#RIN=1300&R2=220k&R3=100k&RB=1M&R5=220k&RT=1M&C1=10n&C2=250p&C3=100n&C4=5n&RB_pot=LogA&RT_pot=LogA

If you like to play with tubes here is one I like to use for simple stuff:
https://www.ampbooks.com/mobile/amplifier-calculators/
https://www.vtadiy.com/loadline-calculators/loadline-calculator/

The 100pF cap with the Gain pot form a Low Pass filter.
The 15nF with the 27k resistor form  a High Pass filter at 393 Hz
The 470nF with the 120k resistor for a High Pass filter at 2.8Hz
When 2 filters overlap the fall or rise of the filters change.
( as far as I remember)

This is a good link to read up for you:
https://www.electrosmash.com/proco-rat
I like the calculators on this site because I'm lazy:
http://www.learningaboutelectronics.com/Articles/High-pass-filter-calculator.php

Is this the right schematic ?
It looks very simple to make a pedal from that.

I think it looks like the tube sockets are soldered onto the PCB so it would be hard to relocate anything.

I think we will try this again.
Turn the amp off and unplug from power point.
Measure resistance between terminal 1 to 2
Measure resistance between terminal 3 to 4
Measure resistance between terminal 5 to 6.

We need to know if those are the 3 output windings on the output transformer.
You should have very low ohm readings on those terminals.
If the readings are very close to each other then it is likely you have 3x 25V output windings, I have seen that setup on other Dukane amps.

Join terminals 1, 2, 3 together
Join terminals 2, 4, 6 together
Connect an 8 ohm speaker to terminal 1 and terminal 2.
turn on and put a signal into the amp.

Here is the picture you posted last year when you first got that amp, you can clearly see that 2,4,6 are linked and 1,3,5 are linked.
There is also a wire connected as if it is going to a speaker in the picture.
If you right click and save the picture or open in new tab you can see better.

I found the post from December last year, I wrote this:

"I looked around at some Dukane amps and it seems some of them you could link terminal 1-3-5 and 2-4-6 and then you have the output for 8 ohm speakers.
I think they had 3 different coils that ran at 25 volt output, possibly 1-2, 3-4, 5-6 were the separate coils.
When you run them in parallel like I said above they became right for 8 ohm.
If you run them in series they form a 75 volt (70volt) output for PA speakers.

I think I can see a link between terminal 1-3-5 on your photo so it was running an 8 ohm speaker, there will be links between 2-4-6 as well.

Plug it in and see if you hear anything"

You should be able to check with a multimeter if you have 3 output coils on the back of those terminals.
Check for resistance between terminals 1-2, 3-4, 5-6.

If you look at the speaker in the other unit you will see it has 2 output transformers that is the type you need to drive 8 ohm speakers with the amp.
I am guessing that the speaker might have 2 voice coils or something to be needing 2 transformers.
Take a good look at those transformers and see if you can work out the input voltage, then you can use them to drive 2 separate 8 ohm speakers.

From memory I found a connection diagram for that PA system, PA systems do not use a speaker output but they use a voltage output that feeds into a transformer at each speaker.
It is done that way so you can have really long cable runs with less losses at the speakers.
If you look for audio transformers you will find the correct type of transformers to use since they are rated at 100V, 70V, etc on the input and the output is rated at watts (usually for an 8 ohm speaker)
I have 2 small transformers like that that I can use as an output transformer in a 1-2 watt tube amp, even though they are not meant for that.
Here is a link to the ones Mouser have for sale:

https://au.mouser.com/c/power/transformers/audio-signal-transformers/?m=Visaton&secondary%20impedance=4%20Ohms~~8%20Ohms%2C%204%20Ohms&rp=power%2Ftransformers%2Faudio-signal-transformers%7C~Secondary%20Impedance

The selector switch is most likely so they could send the sound to the right department, office, workshop, dispatch canteen etc.
they could also select the different wattage taps on the speaker transformers so it suited that area, I imagine the office would be less noisy then the workshop floor.

I think they could have used that unit almost anywhere since they were/are common in factories, shopping centres, train stations, clubs, and many more places.