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Messages - aoresteen

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Amplifier Discussion / Re: Mod a Squire SP-10 amp.
« on: March 05, 2018, 02:06:48 PM »
I fixed all the broken links due to PhotoBucket shutting down posting images to forums.  I now host the photos on my own domain.

Amplifier Discussion / Re: Marshall Lead 100 MOSFET 3210 Head
« on: June 14, 2017, 02:21:56 PM »
Just a quick update.  I'm still working on the 3210 but a number of higher priority projects have jumped in front of it.  I did invest in a new ESD soldering station :) and I love using it.

I hope to get back on it in a week or two.  Thanks for all the help.

Amplifier Discussion / Re: Marshall Lead 100 MOSFET 3210 Head
« on: April 25, 2017, 11:35:25 AM »
Thanks all for your responses.  I am away in Alabama for a vacation with family and will not be able to post any new pictures of the 3210 until next week.

Please understand that the amp will ONLY be use with a 4 ohm load.  The two cabs are Marshall 1965A 4x10" and a Marshall 1965B modified with a 15" Weber California.  I currently use a Carvin VT50 head with it.

So I need to have the head able to drive a 4 ohm load without failure.

When I said that I have 6 other amps it meant that I am in no rush to use the 3210.  I don't have to have the 3210 working tomorrow.

When I get back home I will post some more photos of the interior & the heat sink.

Amplifier Discussion / Re: Marshall Lead 100 MOSFET 3210 Head
« on: April 21, 2017, 12:22:01 PM »
Make sure I understand, you bought a used amp that at least was claimed to work.  You have not even plugged it in, and you are proposing to tear it apart and replace half the insides?


Online discussions may demonstrate that WHEN these amps fail, it is more often blown outputs than other parts, but how many of these worked flawlessly their entire lives?  Those amps never get mention online.  SO it is like hanging around a hospital emergency room to decide what your life is going to be like.   There is a difference between "these blow up" and "this is what burns on the ones that blow up".

You measured a couple caps in circuit, and they both are within 10% of value.  They could have measured the same the day they were new.  it isn't the value that wears out, it is the ESR and leakage inside.

A beefier rectifier bridge would just mean that someing else burns up when you have an output failure.


Why?  Because I'm cautious.  I have no idea how long the amp has set or the past history of the amp.  In the tube world techs never just plug in an amp that they know nothing about.  They put them on a variac and bring the voltage up  s l o w l y.

The 3210 has a past history of failure that is well documented here and elsewhere.  So let's do this again:

I'll just plug it in and see what happens. 

Me: "I bought an amp I knew nothing about it and plugged it in and now it doesn't work.  Help! "

Enzo: "You bought an amp that you knew nothing about and plugged it in without checking to see the history of these amps?  Their failures are well known and had you been a bit more cautious we could have helped you avoid a catastrophe".

Sometimes Enzo you can be a real PITA.  In spite of your electrical genius.

I have 6 amps floating around here and I don't need the 3210 right away.  And yes I will replace known components that have a history of failure.  Before I even use them.  Like the brakes on my 1990 Ford Ranger I bought used and had dropped off at my mechanic and had them overhauled right away. I don't like catastrophes.

So I will replace the output MOSFETs and then run the 3210 at 4 ohms and see what happens.

Also, I've been sick for the past year due to my injuries in Iraq and I have not been able to do much like I used too.  So the 3210 had to wait a while.

Amplifier Discussion / Marshall Lead 100 MOSFET 3210 Head
« on: April 21, 2017, 11:10:29 AM »
Hello all!  The Marshall 3210 MOSFET amp was my first decent amp that I bought around 1990 with the Marshall 1965B 4x10 cab.  Never had an issue with it. I sold it in 2000 to my nephew (who I understand still has it) but recently acquired another 3210 (vintage 1990, Y0xxxx) a few months back off of the local Craig's list.  I have yet to plug it in although the seller said he had been using it regularly and had verified that all functions work.

I have both the Marshall 1965A & 1965B cabs that I use with my Carvin VT-50 tube amp head.

The Marshall cabs are 8 ohms each so using them both would put a 4 ohm load on the 3210 amp.

Last night I did a bit of research on the 3210 head's past problems and found out that they have a tendency to blow the MOFETs taking out the rectifier & a few other parts with them.  This seems to occur when you put a 4 ohm load on the 3210.  I always ran my old 3210 with a single  8 ohm cab so I never had the problem.

1. Before I plug it in, should I put a 16ohm speaker load on it first?  Or should I give it a shot with an 8 ohm load?  No way will I start out with a 4 ohm load.

2. As a preventative measure should I replace the MOSFETS with a pair of Exicon 10N20 & 10P20 before I run it with a 4 ohm load?  They are cheap at $35 for a pair.

My current MOSFETs

3.  While I am at it, should I replace any caps that have been problematic in the past?  Or just replace them all?  I checked the filter caps.  One read 1980 mf, the other read 2160 mf.

Filter Caps

4.  The board looks clean an un-modded.  No sign of a previous repair.  The ICs are not in sockets - they are soldered to the board.  Should I socket them and stock some replacements?

My 3210 board

5.  Should I beef up the rectifier with an 8 amp one?  Any recommended replacements?

As I plan on keeping this amp for the next 10 years at least, what spare parts should I stockpile?


Amplifier Discussion / Peavey Bandit 112 Silver Stripe Rig Rundown
« on: September 10, 2015, 01:12:44 PM »
For the past couple of years the Peavey Bandit 112 Silver Stripe (1996-1999) has been my main amp.  I like the way the Transtube circuit sounds. I've finally gotten it set up the way I want it.

It's paired with the Peavey 112SX external speaker cabinet.  I've replaced the Peavey 1230 speakers with a Weber 100w Blue Dog in the Bandit and a 100w Silver Bell in the external cab.

Next to it is my rack:

The top half is a Samson power amp driving my 1996 Rocktron Chameleon.  The bottom half is for my MIDI guitar.  The Yamaha MIDI interface feeds the Alesis QSR sound module which is driven by a Samson 1U power amp (120a). The cabinet was custom made by J Designs and holds the two Peavey 1230 speakers from the Bandit & 112SX cab.

 I added a 1U mixer so I can now play backing tracks through the rig.  I had to swap out the 2U Samson amp for a 1U amp to make room for the Peavey LM mixer.

I made a custom snake to run power and signals to my pedal board.  The length is the same as the Peavey foot switch, about 14 feet.  120v AC power, guitar signal to Bandit, effects send and return cables, guitar to Chameleon cable, and a 7 pin powered cable to the ADA MIDI foot switch are all bundled together.  The pedal board has a power master switch on the top and power comes from below.

Overall view:

All my gigging guitars have their own wireless transmitter on them and they all are on Samson VHF Channel 1.  The guitar signal goes from the Samson SR-2 reciever to the Morley ABC box IN.  Channel A goes to the Bandit, Channel B goes to the Rocktron Chameleon, and C is used for mute/Rocktron XTune tuner.

The main pedal  board has all the boost, distortion, OD, and amp sim effects that go into the Bandit front end (normal guitar input).

Time based effects like delay & chorus are on their own sub-board and go to the effects loop of the Bandit (not shown is the NUX Looper that is all the way to the left, the last device in the effects loop chain).

The ADA MC-1 midi foot switch lets me instantly get 10 different sounds from the Rocktron Chameleon.

So that's a rundown of my rig.  It breaks down into manageable parts that I can carry where as my tube gear is way too heavy.

Amplifier Discussion / Re: Mod a Squire SP-10 amp.
« on: March 07, 2015, 09:28:19 AM »
As I mention everywhere, the *main* difference between Tube and SS amps is the kind (meaning $$$$$) of speakers fitted to each.
Day and night.
There even is a You Tube where they plug a 1/2W , LM386 based "Smokey" amplifier into a Marshall 4x12" cabinet.
Only comment: WOW!!

In a Marshall 2x12:

Marshall 4x12:

Good speakers are the key!

Amplifier Discussion / Re: Effects Loop Kit for SS Amps
« on: March 05, 2015, 01:55:56 PM »
Super!!  Thanks so much!  I will get working on it.

OK, I figured out what I will do.  I am buying another Peavey Bandit 112 Silver Stripe.  It has an effects loop and can take a 4 ohm load.  It has more power than I need (100 watts @ 4 ohms, 80watts @ 8 ohms) but that's why there is a vol knob on it  :).  It is the same vintage as my Envoy 110.

I found one on my local Craig s List for $120 and I bought a matching external cab off of eBay for $150 shipped.

I emailed Weber speakers and were are discussing new 12" speakers - A Blue Dog and a Silver Bell seem to be the best candidates thus far.

Here's what the rig will look like when done:

Project Done!

Thanks for all the advice and help!

Amplifier Discussion / Re: Effects Loop Kit for SS Amps
« on: February 26, 2015, 08:29:18 PM »
The Peavey Studio Pro TT of the same vintage has an effect loop and I wonder if it can be lifted and used with the Envoy 110 as they are very similar.  Attached is the schematic for it.


The Newcomer's Forum / Re: Peavey studio 112 hum problem
« on: February 26, 2015, 08:24:50 PM »
Thanks all!  A lot to digest here.  I've got a lot to learn about ss amps.

Thanks guys!  I have done some more research into larger amps and I am now confused.  I found two other amps of the same vintage that have higher power.

1. Peavey Studio Pro 110 silver stripe - 65watts

2. Peavey Bandit 112 silver stripe - 100 watts @ 4 ohms, 80 watts @ 8 ohms

Both amps use the exact same power transistors that the Envoy 110 does - 70473100 and 70483100 (MJ15016 and MJ15015).  This tells me that the Envoy 110 can produce 100 watts if it has the proper power supply components & a speaker that can handle the power.  No need to swap them out (but I will need a much larger heat sink ect).

Both amps are rated at 8 ohms only - 4 ohms are not recommended for either of them. (Edit:  Error!  The Bandit will take a 4 ohm load - external speaker can not be less than 8 ohms,  my bad!)

The Envoy 110 power amp is driven by 15.5v rms.  (15.5^2)/6 yields 40 watts @ 6 ohms as Peavey states.  40w/15.5v yields 2.58 amps of current.  If I do the calculations with a 4 ohm load I get 60 watts and 3.875 amps of current.  I do not know what the Envoy power supply is rated at but I will assume it's less than 3.875 amps and greater than 2.58 amps.

Doing the same calculations for the Studio Pro 110 which is driven by 22.8v RMS I get 65 watts as Peavey states and 2.85 amps being drawn.  At 4 ohms the load would be 5.7 amps for 130 watts.

I hope that so far that my math is correct.

Here's where I get confused.  The Bandit 110 is rated at 80 watts @ 20v RMS @ 8 ohms.  How does Peavey get the extra power?  At 20v RMS it should produce 50 watts with an 8 ohm load but it produces 80.  I've attached the Bandit 110 TT schematic which shows one pair of power transistors.  I must be missing something.

The Envoy's power supply is rated at 75 watts (.625 amps) at 120 VAC, the Studio Pro is 200 watts (1.67 amps) at 120VAC, and the Bandit is 300 watts (2.5 amps) at 120VAC.  Is there anyway to calculate the rated amps at the drive voltages like 15.5v RMS?

Also, if I dropped the Envoy's v RMS from 15.5v RMS to 10.5v RMS, I calculate that at 4 ohms  I would get 27.6 watts and draw 2.6 amps which is in the Envoy's power supply range.  Would this work?


The Newcomer's Forum / Re: Peavey studio 112 hum problem
« on: February 26, 2015, 12:12:38 PM »
I know that this is an old thread but reading through it I have a question that is universal.

Let's assume that the amp was killed by the ultrasonic output of the Fuzz Face. 

If an amp can be killed by a 10KHz oscillation signal, why didn't Peavey put the the 47pF or 100pF capacitor in the preamp input to prevent it from ever getting to the power stage?  Wouldn't that be good design practice to protect the amp?


Amplifier Discussion / SoundTech QM4 PA Head
« on: February 25, 2015, 06:42:24 PM »
I have another project I'd like to get done.  Two years ago I picked up a used SoundTech QM4 4 channel PA amp head for my son-in-law to use for rehearsals.  The first time he used it it worked for 20 minutes and then went dead.  They tried it again a few days later and again after 20 minutes the sound wend dead.  They set it aside and used another amp.  It found it's way back to me  so I would like to fix it. Sounds like a cold solder joint or other heat related issue or perhaps a defective component.

All 4 channels cut out so I think the place to start is in the power amp stage.

I was able to track down the schematics - it is in three parts: preamp, preamp2, and power amp (attached).

While I do have a signal generator I do not have a scope to trace the signal through the circuit.

How would you approach finding the source of the problem?

Many thanks!

I've done a bit more research on the Peavey Envoy 110.  The power amp stage uses Peavey power transistors 70473100 (PNP) and the 70483100 (NPN) in a push pull configuration.  These parts are really Motorola MJ15015/MJ15016 amps:

My thoughts are to replace them with more robust power transistors such as the Motorola MJ15024/MJ15025 power transistors.

Would the MJ15024/MJ15025 transistors be able to handle a 4 ohm load that would produce about 60 watts?  And would I have to upgrade other compoments in the power amp stage?


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