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Where to find 6000uF 50V replacement cap cans??
by g1
[Today at 04:49:00 PM] -
Topward 6303A power supply proposal
by saturated
[Today at 04:00:17 PM] -
Less Bass
by edvard
[Today at 01:38:34 AM] -
A new book [Op-Amp experiments]
by saturated
[December 06, 2024, 06:36:41 PM] -
Any Randall RX120D or RX120RH owner here? can I plug in without load?
by Tassieviking
[December 04, 2024, 07:28:27 AM]
Recent posts
#11
The Newcomer's Forum / Re: Topward 6303A power supply...
Last post by Jazz P Bass - Today at 12:09:54 PM #12
The Newcomer's Forum / Re: Topward 6303A power supply...
Last post by Jazz P Bass - Today at 12:05:56 PMCan you put up a link to the previous posts?
#13
Amplifier Discussion / Re: Where to find 6000uF 50V r...
Last post by RG100ESROX - Today at 11:07:24 AMQuote from: Miyagi_83 on Today at 02:49:37 AMQuote from: RG100ESROX on December 07, 2024, 09:50:39 PMHere is the result of the signal input into the FX return, biased just out of xover at 16mV, at the highest resistor sub box setting (1M) with a 10K in series with the sub box.The oscilloscope is hooked up to the speaker output / dummy load box, right? YES.QuoteAs you can see, we have clipping at the highest resistance setting with a .1mV/1KHz injected signal.Highest or lowest? I'm asking because the file name says 'lowest'. SORRY. IT'S THE HIGHEST. RESISTOR SUB BOX WITH THE 10k RESISTOR IN SERIES IS SET TO 1M OHM. SO, WE'RE MAXED OUT ON HOW MUCH WE CAN ATTENUATE THE SIGNAL USING THE RESISTOR SUB BOX. I DO HAVE A 5W 220K RESISTOR I COULD USE IN PLACE OF THE 10K THAT IS IN SERIES WITH THE SUB BOX.
#14
The Newcomer's Forum / Topward 6303A power supply pro...
Last post by saturated - Today at 08:03:26 AMI have a topward dual power supply the left side doesn't get up to full voltage.
If you look in the swap meet section there is some discussion pictures and schematics.
I had an idea that maybe since there aren't that many parts just order some stuff and shotgun it.
However after reading about these units I saw a few instances where some transistor replacements fixed the problem(s).
So for the sake of clarity the focus of this discussion is to simply focus on transistors for the preliminary investigation.
Reading some old threads I saw where I can probe the collector and emitter of said devices in circuit and check for shorts.
-if there is no short then move along
-if there is a short it may be good because of the circuit but remove and test
If I have interpreted this correctly I like this plan
because for starters the power is OFF. 
Also it will give me some experience discerning a voltage regulator from a transistor
So if you like that then that is my plan nothing more or less. Just check every transistor in circuit for C-E short and report back.
If you look in the swap meet section there is some discussion pictures and schematics.
I had an idea that maybe since there aren't that many parts just order some stuff and shotgun it.
However after reading about these units I saw a few instances where some transistor replacements fixed the problem(s).
So for the sake of clarity the focus of this discussion is to simply focus on transistors for the preliminary investigation.
Reading some old threads I saw where I can probe the collector and emitter of said devices in circuit and check for shorts.
-if there is no short then move along
-if there is a short it may be good because of the circuit but remove and test
If I have interpreted this correctly I like this plan
because for starters the power is OFF. Also it will give me some experience discerning a voltage regulator from a transistor
So if you like that then that is my plan nothing more or less. Just check every transistor in circuit for C-E short and report back.
#15
Amplifier Discussion / Re: Where to find 6000uF 50V r...
Last post by Miyagi_83 - Today at 02:49:37 AMQuote from: RG100ESROX on December 07, 2024, 09:50:39 PMHere is the result of the signal input into the FX return, biased just out of xover at 16mV, at the highest resistor sub box setting (1M) with a 10K in series with the sub box.The oscilloscope is hooked up to the speaker output / dummy load box, right?
QuoteAs you can see, we have clipping at the highest resistance setting with a .1mV/1KHz injected signal.Highest or lowest? I'm asking because the file name says 'lowest'.
#16
Amplifier Discussion / Re: Less Bass
Last post by edvard - Today at 01:38:34 AMQuote from: Tassieviking on December 05, 2024, 11:06:33 PM...
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.
...
Yep, the manual says so: https://www.farnell.com/datasheets/1712767.pdf
I'd dare say that input impedance that low is actually chopping off a bunch of treble, which translates to more bass when you turn things up. I'd build a small simple buffer to put in front of it; FET Source follower or non-inverting op-amp circuit powered by 9V, then see what happens. Or if you have an overdrive pedal around, turn the gain down and the volume up, adjust to taste.
#17
Amplifier Discussion / Re: Where to find 6000uF 50V r...
Last post by RG100ESROX - December 07, 2024, 09:50:39 PMQuote from: Miyagi_83 on December 07, 2024, 08:55:17 PMQuotehow do I do that since the front panel controls do not function while we're plugged into the FX return jack. Do I just increase the signal level? If so, to what level? How many volts? I'm not clear on thisFirst, bias should be right so there's no crossover. Once that is done, and, if I remember well, it is, move on to the next steps.
Btw, did you place that resistor in series with the signal generator like I suggested earlier, in reply #258?
Do this experiment:
Unplug your signal and resistor box combo from the amplifier. Disconnect your scope from the amp too, just in case.
Now, hook up your scope probe to the output of the SG / resistance box, the point where it says 'to plug' on the diagram I posted in reply #258.
Set the signal level on your generator to, say, 1V. What can you see on the scope screen?
Now change the resistor value on the substitution box. What can you see on the scope? Try again and look at the scope.
This is your makeshift volume control now. Use it to adjust the signal going into the amp's return jack. Then, on your oscilloscope, watch the waveform coming out of the speaker jack and see when clipping starts. Full clean power is just before the onset of clipping, as I understand it. Then post the signal voltage needed to get there, as requested by g1.
Here is the result of the signal input into the FX return, biased just out of xover at 16mV, at the highest resistor sub box setting (1M) with a 10K in series with the sub box.
As you can see, we have clipping at the highest resistance setting with a .1mV/1KHz injected signal.
(I didn't notice this until just now looking at the large image of the sine wave that is supposed to be out of xover, and there appears to be just a tad bit of xover still. Hope this isn't an issue.)
#18
Amplifier Discussion / Re: Where to find 6000uF 50V r...
Last post by Miyagi_83 - December 07, 2024, 09:09:15 PMQuote from: RG100ESROXSine wave (is it just me, or does this sine wave look pretty bad? Is that cover distortion we're seeing?)Yeah, it does look bad. AFAIC there is crossover and clipping. Reduce the signal perhaps?
#19
Amplifier Discussion / Re: Where to find 6000uF 50V r...
Last post by Miyagi_83 - December 07, 2024, 08:55:17 PMQuotehow do I do that since the front panel controls do not function while we're plugged into the FX return jack. Do I just increase the signal level? If so, to what level? How many volts? I'm not clear on thisFirst, bias should be right so there's no crossover. Once that is done, and, if I remember well, it is, move on to the next steps.
Btw, did you place that resistor in series with the signal generator like I suggested earlier, in reply #258?
Do this experiment:
Unplug your signal and resistor box combo from the amplifier. Disconnect your scope from the amp too, just in case.
Now, hook up your scope probe to the output of the SG / resistance box, the point where it says 'to plug' on the diagram I posted in reply #258.
Set the signal level on your generator to, say, 1V. What can you see on the scope screen?
Now change the resistor value on the substitution box. What can you see on the scope? Try again and look at the scope.
This is your makeshift volume control now. Use it to adjust the signal going into the amp's return jack. Then, on your oscilloscope, watch the waveform coming out of the speaker jack and see when clipping starts. Full clean power is just before the onset of clipping, as I understand it. Then post the signal voltage needed to get there, as requested by g1.
#20
Amplifier Discussion / Re: Where to find 6000uF 50V r...
Last post by RG100ESROX - December 07, 2024, 08:32:03 PMQuote from: Miyagi_83 on December 07, 2024, 07:56:09 PMQuote from: RG100ESROX on December 07, 2024, 06:41:02 PMI measured the DC at the speaker output jacks, and it read -.88mV...Did you take this reading just now? If so, I understand that you put the theory to the test and it turned out to be true, right?
The DCV reading on the output was earlier today.
Of course you were right about the high bias reading while bringing the supply voltage up, because I did not plug the signal into the FX return until the amp was up to voltage, and it was as expected.
I just now took some readings with the signal injected into the FX Return Jack.
all settings at zero
8ohms dummy load
signal .1mV/1KHz
Sine wave (is it just me, or does this sine wave look pretty bad? Is that cover distortion we're seeing?)
bias reading with signal 9.8mV
bias reading without a signal 3.2mV
When you said to take these readings at "Full Power"....how do I do that since the front panel controls do not function while we're plugged into the FX return jack. Do I just increase the signal level? If so, to what level? How many volts? I'm not clear on this.