Marshall MA 100C 100 Watt All Valve Amplifier

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Re: Marshall MA 100C 100 Watt All Valve Amplifier

Postby peterc » 16 Aug 2016, 11:47

BB

Awesome post, thanks for that

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Re: Marshall MA 100C 100 Watt All Valve Amplifier

Postby blackbunny » 18 Aug 2016, 16:07

You are most welcome. The countless hours I spent testing and fixing my 2000 Marshall TSL100 has taught me a lot, some of which I was able to use on Dr Nomis' amp.

One thing it taught me is never buy a Marshall made after 1985. The TSL100 has got to be the worst valve amp I've ever owned, whereas I had a 1982 JCM800 50 watt 4 input Model 1987 that was superb - reliable, great sounding and loud. Wish I still had it, yada yada :slap:

I eventually fitted a JCM800 series 50 watt output transformer to the TSL100, lowered the HT and other power supply voltages with some 10 watt ceramic resistors and now it runs beautifully with 4 x JJ 6V6 output valves fitted for around 44 watts, or I can take the 6V6's out and get a raunchy 50 watts of Brit rage with a pair of EL34S and a change of bias. The primary impedance of the Marshall 50 watt output tranny suits both options beautifully, :applause:

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Re: Marshall MA 100C 100 Watt All Valve Amplifier

Postby DrNomis » 20 Aug 2016, 04:47

I would like to once again thank Blackbunny for fixing my Marshall amp for me, you're a Legend mate....... :D :thumbsup


I played the amp yesterday and it is still running well without any problems whatsoever.


On other things:


A good mate of mine has left his Peavey Triumph 60 Watt Valve amp with me so I can do some mods to it as suggested by Blackbunny, one of the mods involves changing out the stock screen-grid resistors for higher value ones, the stock screen-grid resistors are 100 Ohm/5 Watt Ceramic Wire-Wound types (going by what I can read on the schematic I was able to find on the internet), Blackbunny's suggested mod is to up the value from 100 Ohms to 220 Ohms, so, I'm going to visit my local Jaycar Electronics store on Monday to buy the needed 220 Ohm/5 Watt Ceramic Wire-Wound resistors, my mate popped-by for a visit yesterday and he gave me all the parts he had ordered online which were needed to do the other mods to his amp, I'll see if I can get some of the mods done later on today, I may even start a new thread about it too.


One other mod that my mate wants to do to his Peavey Triumph amp is to replace the stock 6L6 Power Tubes with a pair of KT66 Power Tubes, I think this will be an interesting mod because I am curious about how the KT66 Tubes will sound, I'm guessing that they will probably have a similar tone to the stock 6L6 Tubes because the 6L6 and KT66 are both what are called Beam-Power Tetrodes, so the transfer-curves should be similar, the amp may need re-biasing after switching over to the KT66 Tubes.

Incidentally, I seem to recall reading somewhere that the Marshall Bluesbreaker Amp used two KT66 Tubes and two 12 Inch Celestion Greenback speakers, or I could be wrong.
Genius is not all about 99% perspiration, and 1% inspiration - sometimes the solution is staring you right in the face.-Frequencycentral.
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Re: Marshall MA 100C 100 Watt All Valve Amplifier

Postby phatt » 20 Aug 2016, 11:57

blackbunny wrote:You are most welcome. The countless hours I spent testing and fixing my 2000 Marshall TSL100 has taught me a lot, some of which I was able to use on Dr Nomis' amp.

One thing it taught me is never buy a Marshall made after 1985. The TSL100 has got to be the worst valve amp I've ever owned, whereas I had a 1982 JCM800 50 watt 4 input Model 1987 that was superb - reliable, great sounding and loud. Wish I still had it, yada yada :slap:

I eventually fitted a JCM800 series 50 watt output transformer to the TSL100, lowered the HT and other power supply voltages with some 10 watt ceramic resistors and now it runs beautifully with 4 x JJ 6V6 output valves fitted for around 44 watts, or I can take the 6V6's out and get a raunchy 50 watts of Brit rage with a pair of EL34S and a change of bias. The primary impedance of the Marshall 50 watt output tranny suits both options beautifully, :applause:


LOL, well if you have owned and fixed a TSL100 then you obviously were well qualified to help DrNomis. :applause:

Those TSL100's are a wiring nightmare.
IIRC, 5 pcb's and I stopped counting Conn blocks at around 50. [smilie=thumbdown2.gif]

Even after all the overvoltage problems and bias creep was fixed I did not like the sound. The Amp was extremely brittle when on Ch2 or Ch3 (Jezz my worst SS amp rigs sound more Marshall that that crap)
After much tweaking,,, I found changing the HT for PI made a night and day difference. I settled on 18k/5W.
I may not be the most qualified amp nerd but at 60 I've heard enough REAL Marshall's to know what they Should sound like.

Owner is very happy with the result,, completely different amp now.

Phil.

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Re: Marshall MA 100C 100 Watt All Valve Amplifier

Postby DrNomis » 20 Aug 2016, 14:34

The thing I like most about my MA100C amp now is how well the clean channel takes pedals, definitely sounds way better than the little Peavey Backstage Plus i had been using while the MA100C was being fixed, I've soon discovered that I'm quite partial to both clean and overdrive amp tones with lots of mids in them, my Gibson USA LP Studio guitar naturally has a lot of mids in it's sound already, but the MA100C seems to accentuate them a bit so I get a classic rock sound.


Yep, mids are where it's at, that's where your loudness frequencies tend to be, and it just so happens that the human ear is most sensitive to midrange frequencies, and the response drops off for lows and highs, that's why you need mids to cut-through in a live band mix.
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Re: Marshall MA 100C 100 Watt All Valve Amplifier

Postby DrNomis » 23 Dec 2016, 03:40

Hey Everyone,

Thought I would post an update so here it is.


Anyway, it is now December and my Marshall amp has been going strong without skipping a beat or blowing any more fuses ever since I got it back from being fixed...... :D 8)
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