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Messages - Enzo

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1
Amplifier Discussion / Re: Peavey VSS-20 amplifier with chorus noise problem
« on: September 17, 2020, 12:50:41 AM »
U3 and all those caps are the chorus clock circuit, they are not in the audio path.

U2, U7 Q6, Q7 are the chorus path.  MAybe Q5 too but I doubt it.  Turn chorus on, you get hiss.  Power off, remove U2, power on.  His still there?  You won't get a chorus signal with U2 gone but we are looking for the noise now.  Still noise?  Remove U7, same question?

Make SURE not to install ICs backwards.

2
Amplifier Discussion / Re: Help with Crate CR112 Tonestack
« on: September 09, 2020, 01:38:53 PM »
Hamburger claw meat just isn't that good to start with...

3
Amplifier Discussion / Re: Help with Crate CR112 Tonestack
« on: September 03, 2020, 12:07:51 PM »
It is fun to try to tweak an amp for tone, but remember, no matter what you do to a hamburger, you will never make it taste like a lobster.

4
Amplifier Discussion / Re: Trying To Repair a Traynor TBM 25...
« on: September 02, 2020, 01:51:39 AM »
The MJE150xx series are useful in a number of situations.  I use them

I suspect Traynor uses them in some other product, and has them on hand.  The MJE15032 is rated at 250v versus the 60v rating of the 2SC2233,  and 8A versus 4A, so it is overkill.  I am sure it works fine though.

In tube amps, a EL34 will sound different from a 6L6, but transistors don't work the same way, and especially in power amps, you can use pretty much anything that has the minimum specs covered.

5
Amplifier Discussion / Re: Trying To Repair a Traynor TBM 25...
« on: September 01, 2020, 06:54:18 PM »
A guy brings me a 1969 Corvette with a flat tire.  I put a brand new Goodyear (or Michelin or whatever) on it, balance up fine, car drives fine.  Now do I check to make sure the guy doesn't have his heart set on an actual 51 year old tire for it?

6
Amplifier Discussion / Re: Trying To Repair a Traynor TBM 25...
« on: August 31, 2020, 10:41:01 PM »
Quire often, it is just outputs.  I usually replace the drivers too, but if it is working, they may be fine.  And if the two 1/2 ohm resistors are OK, and the 150, 150, and 22 ohm resistors are OK, likely it is fine.

SOlid state amps like this and a million others are massively fed back and self-correcting, so pretty much any transistors that will safely work there will sound about the same.

There is no bias adjustment, so if it works, doesn't get real hot, and sounds OK, then I'd stop fixing it.

7
Amplifier Discussion / Re: Trying To Repair a Traynor TBM 25...
« on: August 26, 2020, 09:44:20 PM »
Those voltages look fine for idle DC levels, but they don't tell us if the parts can conduct current well.

You can probably find 2SC2233, or the common TIP41C would likely work fine too.

8
Amplifier Discussion / Re: Marshall 5005/Lead 12 Hum Source?
« on: August 23, 2020, 01:24:00 AM »
You knew the volume pot worked because you could hear it change things throughout its range.

Determine whether your hum is 60Hz or 120Hz.   Or if not in USA, then 50Hz and 100Hz.

Turn it all the way down and solve that hum first.  I suspect you have two hums going on.  You have some sort of hum coming in from the early stages, and it is out of phase with whatever hum is after the volume control.  SO at some middle setting of that control the two cancel.  That explains your 2 o'clock thing.

A schematic would be nice.

9
Amplifier Discussion / Re: Trying To Repair a Traynor TBM 25...
« on: August 21, 2020, 11:55:26 PM »
Just noticed a drawing error.  The two output transistors are drawn wrong, they have swapped base and collector connections.

Quite possible one of those two parts is bad.

10
Amplifier Discussion / Re: fender ultra chorus distortion
« on: August 21, 2020, 04:35:02 PM »
I used to rebuild Seeburg Juke Boxes.  And in the tube era, there would be two large chassis.  One was the amplifier, the other the control center.  The control center used tubes too.  A 2050 thyristor tube acting like a triac to fire a solenoid, 12AX7s amplifying pulses from the core memory, and other circuits.  Some of those tube circuits ran plates at ground and a -300v supply into the cathode circuits.

11
Amplifier Discussion / Re: Trying To Repair a Traynor TBM 25...
« on: August 20, 2020, 06:50:47 PM »
OK, that tells me the output stage cannot provide the current the load demands.

You have 8v instead of 7.5 on the supplies, well close enough, it is just a guitar amp, not lab equipment.

verify the two 0.5 ohm 5w resistors associated with the output transistors.  And for that matter, the 150 ohm and 22 ohm resistors associated with the drivers.

From the speaker on the schematic, follow the output line to the left and you come to 10 ohm R124.  Is it open or burnt?

12
Amplifier Discussion / Re: fender ultra chorus distortion
« on: August 20, 2020, 03:24:02 PM »
g1, see my post two above your earlier one, is my explanation ffaulty?  I don't think the drawing is wrong.

13
Amplifier Discussion / Re: Trying To Repair a Traynor TBM 25...
« on: August 20, 2020, 02:09:00 PM »
Perfectly normal for the two 330 ohm resistors to get hot.  Hopefully there is about 7.5v across each of the two diodes.

You say it sounds OK through headphones, but does it still sound OK through the phones with the speaker also connected?  Oh wait, you say the phones makes the speaker silent?  The schematic does not show a cutout, but we can deal.  With speaker connected, how does the line out sound?  Run that to some other amp.  Does the line out sound change when speaker is connected or removed.

You soldered some stuff and it came to life then failed again.  SOunds like you have a bad connection or cracked copper trace somewhere.  Not so much a bad part.  Transistors don't generally die and heal themselves.

14
Amplifier Discussion / Re: fender ultra chorus distortion
« on: August 19, 2020, 04:52:16 PM »
Look at the data sheet for the 3101, note it runs on -16v, that is a negative supply.  SO if they connect +15 to ground and ground to the VDD terminal, the IC sees a negative supply.   The VDD terminal is 15v more negative than the +15 supply.

Your MN chips are probably fine.   Remember the chorus circuit path is a lot more than the MN chips.  Certainly U6, and Q6 could be leaky as well.

15
Amplifier Discussion / Re: Woodstock GX-55R SS Amp
« on: August 13, 2020, 01:07:13 PM »
Sounds like someone already uploaded a file with the same name as you want to use.  Try renaming your file first., or resave your file under a new name and upload that.

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