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Messages - bry melvin

#122
They probably  will only sell it to an authorized repair center and they want that ID #.

FWIW I've run into that with Marshall parts.

Amp companies sometimes want this as a method to help prevent cloning and wrongful death suits. (particularly from tube amps)




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#123
Are you sure that's an 1875  I THINK that's a TDA 2030  they are USUALLY interchangeable however if you've ordered a new chip

If that's the only thing looking blown... The heat sink tab often needs to be isolated (mica washer and plastic nipple)and not grounded. If the screw loosens they can short and blow the chip...can't be sure without a schematic though.

If there was a thin film square washer under the chip it is to isolate it. Most versions of TDA20xx need to be isolated with a split power supply...which your amp probably has because of production costs(Single sided needs bigger caps and an additional cap on the output)

Also as this is the output chip any short in the output can blow it or even an intermittent speaker connection.

That all said you probably use the application notes for either the TDA or LM to trace out components associated with it...the layout difference is usually only 2 diodes for the TDA which are left out on the LM.


Here's a schematic link:
http://www.amparchives.com/Amp Archives/Marshall/Schematics & Layouts/MG Schematics/Marshall MG15CDR.pdf


Looks like it uses TDA2050.
#124
just some thoughts here...You said you found the amp in a cellar...

Does this noise continue with the reverb tank unplugged?

Do the pots all work smoothly now  (or is it too noisy to tell)?

I've had to replace a lot of pots on my Marshalls due to noise  (they get played about 20 or 30 hours a week; my newest Marshall amp is an 82)

#125
Tubes and Hybrids / Re: Peavey Mace Question ?
June 02, 2010, 01:54:37 PM
I did that mod on my triumph head. It makes the crunch channel quite useful with vintage single coils (~4.7ohm) for a blues tone at low pre settings which it couldn't do before. I use a boss NS2 with that amp for the increased noise.


I also did a jumper cut mod that allows the tone stack to work in the crunch and ultra channels.
There are some on the peavey forums that say not to do this as a capacitor failure might wipe out the tone stack.
I never tried to analyze if that is true or not


link to peavey forum comment: http://forums.peavey.com/viewtopic.php?f=19&t=5232&sid=1ef08c4335d3c863fc2de985ce5febd3&start=15

I am taking my chances as the amp didn't work out for me before the mods and was a closet ornament.

I've also considered putting 5751s in V2 and V3 but haven't tried that yet
#126
Yes you should be able to rewire the transformer as  marked up in the picture, and change to a 3 amp fuse and be good to go.
#127
As far as I know the only wires you would need to change are at the top of the transformer The brown ones and a blue one

consider the pic #14 at the top of the transformer in this pic you have 4 connections

Lets call them 1 2 3 and 4 left to right

I THINK you need to remove the jumper from 2 and 3

place a jumper between 1 and 3
place a jumper between 2 and 4

change the fuse to a 3 amp

You Might want to wait for a second opinion from one of the experts though. I'm a musician that fixes her own not an amp tech.

;)
#128
ok sorry got confused there.  SO that would mean the schematic referred in earlier posts is in fact showing European wiring... and isn't the "export" version after all?

Sorry for the dyslexia.

FWIW that's one of the reasons I usually buy Hammonds...they have nice pictorial instructions for their products.



#129
Thanks for the double check. JM

If the transformer has 4 primary wires, they'd be wired in parallel for Europe. So they'd need to be wired in Series as per the schematic.

If the transformer doesn't and needs to be replaced a hammond 167N70 would work...it's actually 280VA I misread earlier. the choices from Hammond seem to be 140VA (too small) or the 280

Of course other are other brands too

FWIW Mouser has 2 of the Hammonds 167N70s in stock.
#130
Using Hammonds "Design Guide for Rectifier Use" I come up with that you need a 70V CT transformer:

Bridge Rectifier...capacitor filter... So +50 -50 (according to the schematic) DC :

So 100 VDC/ 1.41 = 70

and you'd probably need about 250VA

Hopefully one of the super gurus here will check my math :D

#131
I agree with the inconclusive Greatly.

It is interesting but as a musician doesn't create a Eureka moment for me. I use both SS and tube simultaneously to make sure I can get the sound I need. I usually need it just at the edge of that no man's land of clean but distorted.

I have reservations concerning the tests equipment. It is very likely that the Fender twin was a silverface or Post cbs blackface. I USED to play with pre CBS Fenders ( in the 60s).  Back then no one wanted the CBS versions as the sound changed drastically and they were REALLY prone to self destruction. If so the whole thing is moot as I wouldn't touch one with a ten foot pole.(although today a lot of people love them) A lot of us moved to Marshalls and Sunns etc. back then.
I really liked the mid 60s Guilds,and still hold on to them.

The solid state amp used in the test is unidentifed and nebulous in description. So it's kind of meaningless as there is nothing for the Musician to say...THAT is the SS amp I need.

Lately I buy mostly solid state: they are reliable and much better sounding at low SPL. I AM partial to Carvin's SX series, but use others on occasion. One of the "favorites" I have stayed away from is the Roland Jazz chorus. There were some good ones, but the innards of those have changed multiple times.Recent ones haven't been that popular. A lot of them are sold through past reputation and found wanting. ( I know several musicians with one stuffed in the closet) .I own a couple of big Road Cases of rack gear that let me duplicate just about any sound I need but I still like to play with four 2x12 setups half tube and half solidstate.( usually old Marshalls and Recent Carvins).

I haven't bought a Fender amp since CBS actually. I depend on  Pre CBS and copies (MoJo Weber Torres) for that.

Fortunately for most of my tube amps I have accumulated classics and keep them maintained. My stage tube amps run from early 60s to an 82 Marshall being the newest.

For small Venues I use a Peavey Hybrid (Heritage VTX on the low Watts setting) with a tube preamp and an effects processor in the effects loop, and a 64 Guild Thunderbird (about 40 watts with built in inedependent reverb SE amp [6mb8 and 12ax7])

Back in the 60s I used to use Teneyck SS amps. Used to get a lot of What is that?  Found out about them when the music store that used to supply my rentals  (Usually Solarus, Colleseum, and Sentura amps weren't available for a last minute gig).
#132
Actually I don't think ther was a Carvin SX that used 4558s then. Ithink the first SXs were around 87 and MOSFET.

The current SX isn't all op amps ...couple of Jfets.

That said there isn't really an eq IN an SX... tone stack but not really an EQ. I always DO use an eq on the Carvins here. And after the preamp. It's in the effects loop  along with a effects processor AND a tube Preamp actually.

Not sure why someone would think that they used Carvin for that paper.

To me that paper doesn't mean a whole lot. The amps weren't used in the test in a manner that a musician would use them.

Actually there are "fanboys" that will debate this (tube vs ss) till you can't buy tubes anymore! Musicians use whatever works 'till they get an endorsement, then they get THAT equipment reworked until it does what they want.

Very few recordings are done with what is used onstage. And today onstage EVERYTHING ends up getting miked and put through a PA.

I use Marshalls Peaveys Vintage 60s Guilds Sunn Fender and Ampeg amps depending what I am playing/recording.

In the Studio it is VERY difficult to use high powered tube amps. Often what SOUNDS like a big tube stack is not. Even Hendrix and Clapton have recorded with little Champs and Princetons etc. on occcasion.

FWIW My preference for a Blues overdriven "tube" amp in the studio is a Carvin SX coupled with a JCM 800 on the low input (feeding to both) and outputting both by DI through ART processors for effects. I get four channels to tweak afterwards in the mix.  Everything is not always what you think it is on a record.

#133
Out of the way places are handy for a working/practicing guitarist

This album art was taken in my yard http://sunsets.arivacaart.com/home/back%20cover.jpg?attredirects=0
#134
Have a few questions

1 what impedance are the two sides of your speaker cabinet originally?
2 How did you connect the two sides...series...parallel ?
3 What was your impedance switch on the head set at?

Short answer is yes you can damage your amp with the wrong impedance Rule of thumb is the impedance can double for a short time without damage Very short time.It will run a LITTLE happier on half the impedance set. This is why most good amp setups (tube ones anyway) have two speakers per cabinet in series and the sets then paralleled if you blow one series pair the amp will survive for a little while running on the other.
If they are all series and something goes open the amp will shortly self destruct. Tubes  tolerate shorts better than open. Open usually doesn' t hurt Solid State but they don't tolerate shorts. Your 333 is tubes.

whether you damaged it or not with the speakers is a guess at this point.

For grins plug a cord into the speaker and measure how many ohms you read across the speakers.
(plug it in just like you had done with the amp) This won't give exact ohms of impedance  just DC resistance but it will help figure things out.

Then look to see what your speaker impedance switch was set at.

Let us know the values.

I can't find a schematic ...but you possibly have other fuses inside. It COULD be a fuse on the 6.3 volt heater circuit.
BUT BUT BUT!!!
DON'T stick you hands inside that thing unless you know what you're doing. There are ~500 volts possible in there even if it has been shut off for days.

Actually don't even slide the chassis out you could get bit doing that with a finger in the wrong place/

It can kill you very quickly.

To be honest if you aren't sure about speaker wiring. You are not safe to be opening up a tube amp.

Don't mean to sound harsh but we'd rather you stay alive.

Oh by the way...this is a Solid State forum...but someone here probably can help you.
#135
Actually "tube compression" is most pronounced when it is done with OUTPUT tubes. Also it is very apparent when the amp uses a tube rectifier and it creates a "sag". This can happen with a solid state rectifier but not as pronounced.

You ARE right that the "vintage" tube sound has other factors. These are sometimes deliberate as calculated resonant frequencies of good cabinets. Quality wood in the cabinet and type of speaker materials used.

Some of the "vintage" sound is actually due to deterioration in the type of components used.

You CAN change the sound some by using different capacitors of the same value. Orange drops , oil filled. polyesters all have a slight sound difference. Even Carbon composite resistors contribute toward that.

Some of the vintage sound was due to QUALITY of the tubes. Modern tubes are not manufactured to the same tolerances, and usually use different materials. The most apparent example of this is the 5881. Originally a milspec type there is negligible difference today between that and a "regular" tube.

That all said some of the tube sound stuff is hype. It usually is applied to a 12ax7 preamp. 12ax7s make good preamps, but the BEST tube sounds are from a hard driven OUTPUT 6l6 6v6 el34 7591 etc which is played through a speakers that handle but just barely the power that the amp puts out. Vintage tube amp speakers were designed to just barely handle the amps output. I remember how many I blew apart in the 60s.

When I play live in a large place using rig that includes Peavey Hybrids, Marshall JCMs etc. it ( output tube compression) is apparent. At low levels it really isn't.  In the recording studio I actually use more Solid state with the exception of a couple of 5 watt tube amps. To drive the high power amps into compression would produce sound levels unusable to record. I actually have a work table full of 5 watter experiments to get a tone I want on the album I'm working on.

FWIW I have a Carvin SX amp that can sound more like my (favorite) 64 Guild Thunderbird amp cranked than any of the modern tube amps I own. Of course the Guilds Fenders Sunns and Marshalls are always on stage. Even if the Carvins are doing most of the work :D

By the way there is a caveat with output tube compression:  If the amp is driven to that point you also have lag. The rectifier tube can't recover quick enough and you lose the beginnings of notes if your playing fast. Some amps start producing notes in there that you didn't play too!

Anyway look for that perfect tone that is in your mind...Don't care if it's from a tube or chip or transistor. If you have to go to a music store and play everything there.  Then if you have to find the schematic and make one :D