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Topics - engelheimer

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Amplifier Discussion / Marshal Amp 7815/7915 swap to 7818/7918
« on: December 18, 2015, 08:41:32 PM »
I posted this on the Marshall Forum last week and they gave me the boot, here is my post:

Here's one have been doing on most of the solid state Marshalls since they came out. From the Valvestate, AVT, MG, Mosfet, 5210, DFX, DSL and MB series. Are you with me now people?

Swap the 7815/7915 TO220's with 7818/7918 TO220's, with the +3 and -3v supply boost you get headroom and crunch out the wazoo.

Should clean the white silicone grease (if any) on the TDA chip, regrease w/clear and tighten it up. Do a continuity czech on the tab to chassis. If you see a short replace the mica insullator and/or plastic washer, grease both sides. czech it again.

On amps w/o a fan, an external heatsink (vertical fins) should be used. Use your noodle to figure this out, be sure to clean and regrease, for maximum heat xfer.

Enjoy!

This was my first post on 3 discussion groups last nite, and got an e-mail asking to introduce myself, and post on the workbench so here goes:

My opinion on Marshall, is they are all superior amps right out of the box.

My fave is the DSL5C
.
Compulsive/obsessive with a bit of ADD thrown in - the crux of the biscuit is who we all are.

My objective here is to entertain, annoy, confuse and send others off on tangents.

At least I know ya’ll are keeping out of trouble and behaving yourselves.
This was my first official post on any forum, and do consider myself a luddite. Every once in a while I visit this one and other sites to get a laugh from the plethora of “google techs”. Many (including myself) can’t leave well enough alone and are just born to tweak.

Do have plenty more updates/revisions for these and many others. Can’t use the word “mods” cuz my definition of it is: (https://en.wikipedia.org/wiki/Mod_(subculture) Just talk’in bout my g g generation. Since everyone’s personal taste/opinion is different, your mileage may vary.

Have been doing this stuff long before the www. My first cohort in crime was Kenny Fischer, then Gerald (El Presidente) Weber. My hearing is gone, have to use an oscope and someone else who is a tone monger to judge improvements.

About my first post: Op-amp data sheets have a maximum voltage to keep the specs in tolerance, noise/gain etc… you can go higher. If one fails, (have yet for one to fail) it means the chip was weak to start with. Will give you an opportunity to update key op-amps in the signal path, (after  8 pin sockets are soldered in). This makes it easier to find one of the many types available, bipolar/jfet/lo noise/high slew etc, as a suitable replacement. 

I always use a 100W light bulb limiter to bring an amp up, but for the anal just use a variac and the limiter. If it holds, burn it in for a while before you plug it in the wall. A shorted op-amp is easy to find by measuring resistance between the +/- pins with a good meter (Fluke 115) and good test leads. The one with the lowest resistance is the culprit.

My visit on this forum may not be long, and might hang around a while to share some experiences and observations. Am busy with many other HD audio/RF endeavors and this was just a temporary diversion. Will use this thread to post, and would like everyone to first review:

 https://en.wikipedia.org/wiki/Hypersonic_effect

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