Vietnamese Marshall
Phil Allison
** A rather new looking Marshall " MA100H " valve head landed on my bench
today - but it looked a bit different. On the back it says " Made in Vietnam
" - so this is the first non UK made ( ie assembled) Marshall, at least
that I have ever seen.
The amp was silent, valves all lit up but no output whatsoever and no extra
current draw when the Standby switch was closed. OK - so where is the damn
HT fuse ? Nothing on the back so it must be inside - another first for a
Marshall valve amp. On the PCB is a 630mA delay fuse - very blown -
fitting a new one got the amp running.
Bit of poking about finds that both 1/4 inch QCs on the PCB used for output
valve grid drive are very loose - easy fixed. But was this the cause of
fuse blowing? Nope.
That 630 mA HT fuse should be 1 amp at least, since it is fitted in the
secondary of the PT. On test, the fuse had to pass just over 1 amp rms when
the amp is over-driven. The primary AC current draw is 2 amps rms at the
same time ( ie 480VA) .
On sine wave test, there is significant crossover distortion on the CRO
screen at 1/2 output and above. The bias setting seemed OK - there are two
trims inside and a pair of 1 ohm resistors in each pair of output valve
cathodes.
On checking the screen B+ supply, the cause is simple. There is no filter
choke of course ( what are they ?) and instead a 470 ohm ,7W resistor. So
the screen B+ supply falls like a rock soon as the amp is driven. Guess
this helps the crappy Chinese EL34s to survive overdriving.
Besides the above bad points, there are lots more.
The AC tranny is undersized - it looks like a 250VA type and needs to be
400VA to withstand hard use in this amp. Even sitting on the bench with a
605mA idle current from the AC supply, the internal temp rise is almost 40
degrees C. A couple of hours of heavy metal on a warm night will see it off.
The same * ridiculously fragile* plastic shaft pots as used on other recent
Marshalls have been fitted - one light bump on the knob = nasty
intermittent fault.
There is no AC voltage selector fitted and no internal option either,
another first in a Marshall valve head. All the fasteners are metric too,
not one single concession in sight to the brand's UK origin.
There ARE two small screw-in bulbs ( labelled 12V ) fitted inside the
cabinet that illuminate the whole chassis and the "Marshall" logo through
the open weave cloth. These are not ordinary 12 volt dial lamps but special
dual, orange LEDs - one chip connected for each polarity when fed with AC.
Next the these is a non Accutronics ( Belton ?) reverb tank.
All the jack sockets ( 7 of them ) are very fragile, PCB mount types.
Every single part in the amp looks like it came either from China, Korea or
Taiwan and then assembled in Vietnam.
Good points:
--------------
The 4 x EL34 output valves and the 12AX7 PI are on ceramic sockets, hand
wired to the two trannys and the PCB.
The main PCB looks like it is easy to get lose and invert for servicing.
The amp is pretty cheap to buy.
But a used example from the 1980s is a way better product, full of UK made
transformers and other parts that have proved their ability to survive in a
Marshall.
.... Phil
boardjunkie1
Good info. Haven't had one of these cross my path yet. Just finished
up on a DSL100 that had to have the main pcb replaced due to the bias
instability issue caused by crappy board material. The replacements
look to be FR4 or similar good quality stuff.
Gareth Magennis
"Phil Allison" <phi...@tpg.com.au> wrote in message
news:91t5gt...@mid.individual.net...
I've an Ampeg SVT Classic here thats "manufactured in Vietnam".
Have to say the build quality seems good. The pots and sockets even seem to
be the retro style chunky Western parts.
I've seen quite a few of these now, never noticed the Vietnam connection
before, but they have always seemed to be solidly built.
I got 340 Watts out of the 6 x Sovtek 6550's today.
Gareth.
Phil Allison
"boardjunkie1"
Good info. Haven't had one of these cross my path yet. Just finished
up on a DSL100 that had to have the main pcb replaced due to the bias
instability issue caused by crappy board material. The replacements
look to be FR4 or similar good quality stuff.
** Seen that problem a few times - it's an absolute nightmare.
Marshall should make new PCBs available for free.
.... Phil
Phil Allison
"Phil Allison"
> ** A rather new looking Marshall " MA100H " valve head landed on my bench
> today - but it looked a bit different.
** Anyone located a schem for this POS on the net ??
... Phil
Phil Allison
"Phil Allison"
>
> On the PCB is a 630mA delay fuse - very blown - fitting a new one got the
> amp running.
>
> secondary of the PT. On test, the fuse had to pass just over 1 amp rms
> when the amp is over-driven.
** Just for clarity - the 630mA delay fuse was as fitted in the factory and
as labelled on the PCB.
.... Phil
Arfa Daily
"Phil Allison" <phi...@tpg.com.au> wrote in message
news:91uvn5...@mid.individual.net...
I have three different issue numbers of schematics for the MA100, but none
seem to identify specifically an MA100 "H". If they are any use to you,
contact me off-group.
Arfa
Phil Allison
"Arfa Daily"
>
> I have three different issue numbers of schematics for the MA100, but none
> seem to identify specifically an MA100 "H". If they are any use to you,
> contact me off-group.
** Marshall sell ( note not make) an MA100H and an MA100C.
H = head and C = combo.
Decades ago, H-H made an amp called the MA100.
..... Phil
Arfa Daily
"Phil Allison" <phi...@tpg.com.au> wrote in message
news:91vtv0...@mid.individual.net...
So are my schematics for the Marshall MA100 any use to you ? If so, contact
me and I'll send them to you ...
Arfa
Phil Allison
"Arfa Daily"
"Phil Allison"
>
>>> I have three different issue numbers of schematics for the MA100, but
>>> none seem to identify specifically an MA100 "H". If they are any use to
>>> you, contact me off-group.
>>
>> ** Marshall sell ( note not make) an MA100H and an MA100C.
>>
>> H = head and C = combo.
>>
>> Decades ago, H-H made an amp called the MA100.
>
> contact me and I'll send them to you ...
** You can send them to " ro...@sound.au.com " if you like.
..... Phil
Arfa Daily
Phil Allison
"Arfa Daily"
>>> So are my schematics for the Marshall MA100 any use to you ? If so,
>>> contact me and I'll send them to you ...
>>
>>
>> ** You can send them to " ro...@sound.au.com " if you like.
>>
>
> Done.
** Thanks.
I'll let you know if they are for the same amp.
..... Phil
Arfa Daily
"Phil Allison" <phi...@tpg.com.au> wrote in message
news:921htm...@mid.individual.net...
OK. Noted.
Arfa
Boris Mohar
wrote:
Would this contain the schematic? It is not a service manual if there is
such a thing.
http://cgi.ebay.com/MARSHALL-MA100H-MA100C-MA50H-MA50C-OWNERS-MANUAL-/290517800721
--
Boris
Phil Allison
>>
>>>> ** You can send them to " ro...@sound.au.com " if you like.
>>
>>> Done.
>>
>> ** Thanks.
>>
>> I'll let you know if they are for the same amp.
>
>
** I have all the schems now and they are certainly for the same amp.
Only thing I can spot different is that 630mA HT fuse shown in the output of
the bridge rectifier where I see it fitted in the AC input. Makes no
difference to the rms current flow in the part.
.....Phil
Arfa Daily
"Phil Allison" <phi...@tpg.com.au> wrote in message
news:923t5f...@mid.individual.net...
Fair enough. I'll know if one crosses my bench ...
Arfa
Phil Allison
"Arfa Daily"
> "Phil Allison"
>>>>
>>>> I'll let you know if they are for the same amp.
>>>
>>> OK. Noted.
>>>
>>
>> ** I have all the schems now and they are certainly for the same amp.
>>
>> Only thing I can spot different is that 630mA HT fuse shown in the output
>> of the bridge rectifier where I see it fitted in the AC input. Makes no
>> difference to the rms current flow in the part.
>>
>
** Update: On careful perusing of the schems, I see a more differences
compared to the Vietnamese one I have.
1. The Vietnamese have used 12V LED bulbs instead of 12 volt filament
lamps.
2. The power and output transformers carry quite different numbers.
3. The EL34s have their heaters wired in parallel rather than series
parallel.
The Vietnamese Marshalls seem to be special versions or clones of the
similar UK models.
.... Phil
Arfa Daily
"Phil Allison" <phi...@tpg.com.au> wrote in message
news:926ac3...@mid.individual.net...
Interesting. As Vietnam is your end of the world, I wonder if they are a
version specially assembled there for the Oz market, to avoid the costs of
shipping such heavy items all the way from the UK. I'll see if I can probe
around any Marshall contacts to find out if they know anything.
Arfa
boardjunkie1
Mind beaming a copy of that schemo in this direction?
Phil Allison
"Arfa Daily"
>
>> The Vietnamese Marshalls seem to be special versions or clones of the
>> similar UK models.
>>
> version specially assembled there for the Oz market, to avoid the costs of
> shipping such heavy items all the way from the UK.
** No way.
Vietnam made MA100H and MA100C amps are sold world wide in 235V and 120V
versions - as Google search will proves.
Far more likely, initial assembly began the UK a couple of years ago and
then was shifted to Vietnam cos they could do it cheaper even than the
Chinese.
.... Phil
Phil Allison
"Arfa Daily"
>
> Interesting. As Vietnam is your end of the world, I wonder if they are a
> version specially assembled there for the Oz market,
** See the "Overview" on page 2 of the pdf.
http://www.marshallamps.com/downloads/files/ma-handbook.pdf
Also note the pic of the back panel and the specs on page 4 of the pdf.
.... Phil
Arfa Daily
"boardjunkie1" <boardj...@gmail.com> wrote in message
news:89bc0cb9-a8e5-4e7c...@m10g2000yqd.googlegroups.com...
'Tis beamed ... Let me know if any probs
Arfa
boardjunkie1
> "boardjunkie1" <boardjunk...@gmail.com> wrote in message
Right ahn...got it. Thanks bud...
Arfa Daily
"boardjunkie1" <boardj...@gmail.com> wrote in message
news:dc9462c0-dc48-419a...@q30g2000vbs.googlegroups.com...
Welcome ...
Arfa