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March 04, 2024, 09:14:27 AM

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#1
The Newcomer's Forum / Re: saturated's all encompassi...
Last post by Tassieviking - March 03, 2024, 09:01:33 PM
You can buy leads that have fuses in them, but they are not really cheap if it is for home use.
If you get the Fluke ones you still have to buy expensive fuses.
My set has a ceramic 3AG fuse in them and they are ok to use, they are a bit bulky though.
https://au.rs-online.com/web/p/multimeter-leads/0204583
#2
Schematics and Layouts / Re: Fender Champion 40 DSP (PR...
Last post by g1 - March 03, 2024, 09:00:05 PM
This is the schematic for a Champion 40.  Not sure which PR, but it has DSP and the output IC is TDA7294.
PR number is 'production release' and does not necessarily mean it uses a different schematic.  Schematics go by model name and revision number.
Check if this schematic matches your unit.  If not, what is the output IC in yours?
#3
The Newcomer's Forum / Re: saturated's all encompassi...
Last post by g1 - March 03, 2024, 08:42:31 PM
When the fuse voltage rating is less than the circuit requires, the possible arcing is more likely after the fuse has blown.
Your probes have a voltage safety rating as well, and that would be lost with any modification of the probes, no matter how high the fuse rating.
#4
The Newcomer's Forum / Re: saturated's all encompassi...
Last post by saturated - March 03, 2024, 06:35:01 PM
So I got to thinking why don't I just put a fuse in my test lead that is less than 2 amps.

It should be plenty for my little Micky 🐭 Mouse 🐁 experiments.  It's not like I'm in a plant or industrial commercial setting poking around.

So I looked around my collection of glass and blade fuses to see what I could come up with.  I was sure that I could scare up a few fuse holders that never got used and accumulated but couldn't find any.

So now that is the plan.  I would have liked to find a 1.5 A fuse but I only found stuff like 0.5 A and much larger.
And all in glass none of the blade automotive fuses were less than 5A maybe 10.

So I had always wondered about voltage ratings on capacitors and fuses and I'm guessing that a component with a lower voltage ratings will be shorted like arcing by a higher voltage.

For example if I have a 250v fuse and I apply 1500v it will short/arc/jump across it?  Rather than open as intended.....idk just thinking out loud maybe I'm wrong.

I know when I had a HV probe and tried to check some HV on an oscilloscope it didn't help it arcd and sparks flew like crazy.

 :'(
#5
Schematics and Layouts / Fender Champion 40 DSP (PR4222...
Last post by Fritter - March 03, 2024, 07:01:35 AM
I just picked up this Amp for a great price and it's all working but I'm considering some modifications (I'm a retired EE) and I would like to get the correct schematic for it.

I have searched all the links and sites for this* and found schematics but they all are for PR2432 version (made in Indonesia I think) but mine is a PR4222 and is made in China.

Can anyone provide a schematic and/or comment on the differences between the PR2432 and the PR4222 versions?

Thanks in advance.

Ted (aka Fritter)

[EDIT] I did find a small sticker inside the speaker area that says 092022 which means this is pretty new, less than 2 years old so I think the PR4222 model is the latest?

* The Fender Schematics link in this forum sends me to a generic Fender page but there's no list of schematics - I did find a Fender list of schematics but, again, they are not for the PR4222.
#6
Amplifier Discussion / Re: Marshall VS100R transistor...
Last post by Tassieviking - March 03, 2024, 03:04:41 AM
If they are fully encapsulated in plastic then you just need some thermal grease.
A thin layer of grease and try to move the transistor around  a bit against the heatsink to spread the grease evenly, clamp it and solder in.
Just poke the legs through the PCB enough to solder them in, it keeps the transistors more towards the center of the heatsink.
#7
Amplifier Discussion / Re: Marshall VS100R transistor...
Last post by markorock37 - March 02, 2024, 02:12:47 PM
It originally had transistors with the metal tab. Only held to the heat sink with a surface clamp. The replacements I have are the newer type.
#8
The Newcomer's Forum / Re: saturated's all encompassi...
Last post by g1 - March 02, 2024, 12:15:07 PM
Lots of modern electronic equipment has standby circuitry that is always running unless you unplug it from the wall.
#9
Amplifier Discussion / Re: Marshall VS100R transistor...
Last post by g1 - March 02, 2024, 12:09:37 PM
The metal tab type has not been made for over 10 years, if you found some they are old stock or possibly fake.
Like Jazz said, you don't need the spacers for the plastic backed type.
Attached datasheet shows both types.

If you do happen to have found some old style metal tab types, you not only need the mica spacers, but also special plastic washers for the screws.
#10
Amplifier Discussion / Re: Marshall VS100R transistor...
Last post by Jazz P Bass - March 02, 2024, 11:07:40 AM
Not to beat a dead horse but if the TIP 142/ 147 transistors are plastic enclosed at the collector then you do not need the mica. Just grease.
As a matter of fact, it may hinder the transfer of the heat.
It would be nice if you would indicate what you have as both the BDV & the TIP transistors come both ways.