Marshall Guitar Amp Transistors overheating - help

[Neil]

On Oct 17, 7:02 am, "Stephen Cowell" <scow...@sbcglobal.net> wrote:

"Phil Allison" <philalli...@tpg.com.au> wrote in message

news:6lqa43Fdbmt7U1@mid.individual.net...



"William Sommerwanker "

Solid state amp: Ok with no load. Tube amp: not ok.

Very few tube amps had this problem.

** Wrong -  the majority of tube guitar amps ARE  at risk when driven with
no load.

This amp is designed for no load... there's a headphone
jack that changes the output, you don't do that unless
you're prepared for all kinds of load shenanigans.

Basically, too much bias current... best thing is to
test every component in the final circuit.  If they
all check OK, then start shotgunning them.  You'll
get there eventually... and it won't be that expensive.
__
Steve
.

Firstly, I'd like to say a big thank you to everyone who posted a
reply, especially within minutes of the original posting.

In summary:

Speaker is connected and impedence was the first thing I checked when
it happened the first time.

Going to check the diodes later today when I get home from work.

It worked perfectly well immediately before it blew.

I have an 'scope that I used for my work, however I'm no electronics
expert and use it only for checking PSU noise & Lissajous signals on
counting devices.

I'll take the T6 MJF122 out of circuit later today to see if it looks
suspect later today

BDV's available at Farnell about Ł2.40 each + vat (you may have to pay
a minimum order value). Also on eBay about the same price.

All heat sink clips are firmly in place.

Fortunately I bought a couple of extra BDV's just in case. If I can
identify the MJF122 as the culprit and replace it I'll monitor the
heat sink temperature every few minutes and power down if it gets too
hot.

Does anybody know what the normal operating temperature of the
darlingtons is?

 

[Phil Allison]

"The Natural Wanker "

I reverse engineered a couple of marshals. Triumph of overrunning
components and cost reduction over correct design.

The marshal 100W valve is based on an overrun Mullard 50W design,

** Nonsense.

The first Marshalls were clones of the Fender Bassman of 1959, the 5F6-A
schematic.

Subsequent models all followed a very similar pattern.

Pus a preamp that closely follows the mullard design,

** Pus is right.

Don't get me wrong. I like the Marshall sound and Ive got one.

** ROTFL ....




..... Phil

 

[The Natural Philosopher]

Phil Allison wrote:

"The Natural Wanker "

I reverse engineered a couple of marshals. Triumph of overrunning
components and cost reduction over correct design.

The marshal 100W valve is based on an overrun Mullard 50W design,


** Nonsense.

The first Marshalls were clones of the Fender Bassman of 1959, the 5F6-A
schematic.

Subsequent models all followed a very similar pattern.

Well just look at the Mullard 50W circuit with 4xEL34 and compare and
contrast.


American tube amps were all based on different valves entirely..beam
tetrodes mainly, not pentodes.

Pus a preamp that closely follows the mullard design,

** Pus is right.


Don't get me wrong. I like the Marshall sound and Ive got one.


** ROTFL ....




.... Phil

 

[Phil Allison]

"The Natural Wanker "

I reverse engineered a couple of marshals. Triumph of overrunning
components and cost reduction over correct design.

The marshal 100W valve is based on an overrun Mullard 50W design,


** Nonsense.

The first Marshalls were clones of the Fender Bassman of 1959, the 5F6-A
schematic.

Subsequent models all followed a very similar pattern.


Well just look at the Mullard 50W circuit with 4xEL34 and compare and
contrast.

** No relevance to Marshall whatever.

American tube amps were all based on different valves entirely..beam
tetrodes mainly, not pentodes.

** All the early 60s Marshalls used beam tubes, 5881s and KT66s.

Marshall Majors used 4 x KT88s.

USA models used mainly 6550s.

EL34s were later substituted with a bias change and little else, as an a
economy measure.

Read the Wiki & check out the schems.

http://en.wikipedia.org/wiki/Marshall_Amplification

http://www.drtube.com/marshall.htm

You are totally WRONG.




....... Phil

 

[The Natural Philosopher]

Phil Allison wrote:

"The Natural Wanker "
I reverse engineered a couple of marshals. Triumph of overrunning
components and cost reduction over correct design.

The marshal 100W valve is based on an overrun Mullard 50W design,

** Nonsense.

The first Marshalls were clones of the Fender Bassman of 1959, the 5F6-A
schematic.

Subsequent models all followed a very similar pattern.

Well just look at the Mullard 50W circuit with 4xEL34 and compare and
contrast.

** No relevance to Marshall whatever.


American tube amps were all based on different valves entirely..beam
tetrodes mainly, not pentodes.


** All the early 60s Marshalls used beam tubes, 5881s and KT66s.

Marshall Majors used 4 x KT88s.

None of the marshalls I ever saw used KT88's

All EL34s.

Maybe that was a US export model you hade.

USA models used mainly 6550s.

EL34s were later substituted with a bias change and little else, as an a
economy measure.

They are not cheap, and never were.

Read the Wiki & check out the schems.

http://en.wikipedia.org/wiki/Marshall_Amplification

http://www.drtube.com/marshall.htm

You are totally WRONG.

Or teh Wiki is..

...... Phil

 

[Phil Allison]

"The Natural Wanker "

Well just look at the Mullard 50W circuit with 4xEL34 and compare and
contrast.

** No relevance to Marshall whatever.


American tube amps were all based on different valves entirely..beam
tetrodes mainly, not pentodes.


** All the early 60s Marshalls used beam tubes, 5881s and KT66s.

Marshall Majors used 4 x KT88s.


None of the marshalls I ever saw used KT88's

** Then you have never seen a Marshall Major

Too damn lazy too look up the schem as well.

USA models used mainly 6550s.

EL34s were later substituted with a bias change and little else, as an a
economy measure.


They are not cheap, and never were.

** Philips /Mullard EL34s were much cheaper than either KT66s or US made
5881s.

You pig ignorance is showing.

Oink, oink.....

Read the Wiki & check out the schems.

http://en.wikipedia.org/wiki/Marshall_Amplification

http://www.drtube.com/marshall.htm

You are totally WRONG.



Or teh Wiki is..

** Fuuuuck ooofffff

- you know nothing PISS HEAD.




........ Phil

 

[jh]

The Natural Philosopher schrieb:

Phil Allison wrote:
"The Natural Wanker "
I reverse engineered a couple of marshals. Triumph of overrunning
components and cost reduction over correct design.

The marshal 100W valve is based on an overrun Mullard 50W design,

** Nonsense.

The first Marshalls were clones of the Fender Bassman of 1959, the
5F6-A schematic.

Subsequent models all followed a very similar pattern.

Well just look at the Mullard 50W circuit with 4xEL34 and compare and
contrast.

** No relevance to Marshall whatever.


American tube amps were all based on different valves entirely..beam
tetrodes mainly, not pentodes.


** All the early 60s Marshalls used beam tubes, 5881s and KT66s.

Marshall Majors used 4 x KT88s.


None of the marshalls I ever saw used KT88's

All EL34s.

Maybe that was a US export model you hade.


USA models used mainly 6550s.

EL34s were later substituted with a bias change and little else, as an
a economy measure.


They are not cheap, and never were.

Read the Wiki & check out the schems.

http://en.wikipedia.org/wiki/Marshall_Amplification

http://www.drtube.com/marshall.htm

You are totally WRONG.



Or teh Wiki is..




...... Phil

Hi Mr Philosopher,

it's very remarkable that you don't recognise one of the most polite
answers Phil.A ever made.

Let me assure you - his statement's correct, yours' not so...

There also were KT88 Marshalls, although they are a completely different
story. IIRC the indeed evolved from generic Mullard or the GEC designs.
But - the bread and butter Marshall began 1962 with the 5881/6L6/KT66
equipped JTM45 - an almost 100% copy of the 5F6-A - and they (Ken Bran)
have publicly admitted that they were clearly aware of that fact. The
evolvement to the usage of pentodes (EL34s) was mainly driven by
economical reasons. The similarities to the mullard designs may come
from the fact, that there ain't so many possibilities to connect a
pentode or a beam power tetrode to a circuit - and - the 5F6-A was also
based on a common available basical circuit (from WE or RCA IIRC).

The preamp of the marshall *was* the same as a 5F6-A and the future
evolvement was only incorporated by the addition/alteration of some
components to fit the sonic tastes of the upcoming rock musicians
(cathode Cs, mixer Rs, bypass Cs, different B+ filtering etc). Even the
MV Marshalls just rewired the existing preamp circuit to a cascaded
design. OK some Rs and Cs were added but that was all. Up to the generic
JCM800 the circuit still clearly showed it's origins.

regards

Jochen

 

[JJTj]

Marshall Majors used 4 x KT88s.


None of the marshalls I ever saw used KT88's

Almost all UK Majors had KT88's. The first few
Major's (via Rose Morris n UniCord) had 88's,
then they switched to 6550's. This allowed the
amps to loft along, due to the less demanding
needs of 6550's. A Major with 6550's sounds very
little like one with KT88's. Of course, bias needs
to be tweeked. Alot of folks who dislike Major's
only heard them with 6550's. And today's KT88's
are not the same. Thank God I have a good supply
of real GEC's. Put aside for old age, ya know.

Besides, a Major on a slant 4-12 cab looks awesome.

Head is as deep as the cab top (11" I believe)

Last killer Major 1/2 stack I saw, because he paid me
danger $ for the KT88's ($200 each in 98) had a cab
full of old white cap'ed SRO speakers. He had to put
bricks behind the wheels, because the amp would roll
backwards when played. He liked the cab being off the
ground, but hated to chase it every other song.

Newest GP shows 'KRANK' amps using surface mount resistors
in the POWER AMP stage ?????????? Flocking wanker design.

Major's had chassis mounted round power resistors.

Transformers that weigh more then today's amps, cab n all.

Guess the times, they are a changing...

JJTj









FS: Old press/Fan Club kit for The GrandMothers,
(Mothers of Invention original members) by
'Panda Records' SIGNED by Band in 2000 !

#522 of about 700 made

About as RARE as it gets, boyz n girlz..


http://www.usaelectron.com/GM







She's 200 years old
So mean she couldn't grow no lips
She's 200 years old
So mean she couldn't grow no lips
(Boy, she'd be in trouble if she tried to grow a mustache . .)

She's 200 years old
Squatting down
And poppin' up
In front of the juke box
Like she had true religion

Boy

She's 200 years old
Squattin' down
Poppin' up
Front o' the juke box
Just like she'd had true religion, now,

Boy

Boy, boing,, it's 200 years
Half of this, none of that
Was 50 . . .
Oh squat, yeah, oh, now, yeah!

She got religion now, boy

Oh, she's 200 years old
Oh, she told me
She just, she just can't grow no lips

Squat

Down

So mean she
Can't grow no lips

200 years old
Whaddya mean she can't grow no lips . . .

Squattin' down
Poppin' up 'n down at the juke box

OWW!

She got the true religion, boy

Boing!!!!!!!!!!!!!!!

 

[JP]

On Fri, 17 Oct 2008 01:31:01 -0700 (PDT), Neil
<group_stuff_etc@hotmail.com> wrote:

On Oct 17, 7:02 am, "Stephen Cowell" <scow...@sbcglobal.net> wrote:
"Phil Allison" <philalli...@tpg.com.au> wrote in message

news:6lqa43Fdbmt7U1@mid.individual.net...



"William Sommerwanker "

Solid state amp: Ok with no load. Tube amp: not ok.

Very few tube amps had this problem.

** Wrong -  the majority of tube guitar amps ARE  at risk when driven with
no load.

This amp is designed for no load... there's a headphone
jack that changes the output, you don't do that unless
you're prepared for all kinds of load shenanigans.

Basically, too much bias current... best thing is to
test every component in the final circuit.  If they
all check OK, then start shotgunning them.  You'll
get there eventually... and it won't be that expensive.
__
Steve
.

Firstly, I'd like to say a big thank you to everyone who posted a
reply, especially within minutes of the original posting.

In summary:

Speaker is connected and impedence was the first thing I checked when
it happened the first time.

Going to check the diodes later today when I get home from work.

It worked perfectly well immediately before it blew.

I have an 'scope that I used for my work, however I'm no electronics
expert and use it only for checking PSU noise & Lissajous signals on
counting devices.

I'll take the T6 MJF122 out of circuit later today to see if it looks
suspect later today

BDV's available at Farnell about Ł2.40 each + vat (you may have to pay
a minimum order value). Also on eBay about the same price.

All heat sink clips are firmly in place.

Fortunately I bought a couple of extra BDV's just in case. If I can
identify the MJF122 as the culprit and replace it I'll monitor the
heat sink temperature every few minutes and power down if it gets too
hot.

Does anybody know what the normal operating temperature of the
darlingtons is?






Dig up the data sheet...it should tell max operating temp

 

[Kevin Aylward]

Jon Slaughter wrote:

"Dave Curtis" <dbaudiotech@roderunner.com> wrote in message
news:ankff45sufvr1r99gst3k1cecg4sqiii2k@4ax.com...
On Thu, 16 Oct 2008 18:05:06 -0500, "Jon Slaughter"
Jon_Slaughter@Hotmail.com> wrote:

In any case I replaced the component and it worked fine. I believe
it blew because I had no load hooked up(it was in a dorm and I
didn't have the cab and was running the line out to my comp).

Solid state amp: Ok with no load. Tube amp: not ok.


Thats not completely true.

Of course it is. The only way a transistor amp can blow up with no load, is
if it is designed incorrectly. Like, it oscillates off load, or the power
supply has such bad regulation that it raises its voltage etc....

Kevin Aylward
kevin@kevinaylward.co.uk
www.kevinaylward.co.uk

 

[Eeyore]

JP wrote:

Does anybody know what the normal operating temperature of the
darlingtons is?

It's not that simple. It depends on the dissipation and thermal resistance.

The *junction* or die temperature may be as high as 150C in plastic devices or 200C
in metal can and still be reliable but that's NOT the heatsink temp.

Google Motorola AN1040 (that's twice this week now I've mentioned that) !

Graham

 

[The Natural Philosopher]

Kevin Aylward wrote:

Jon Slaughter wrote:
"Dave Curtis" <dbaudiotech@roderunner.com> wrote in message
news:ankff45sufvr1r99gst3k1cecg4sqiii2k@4ax.com...
On Thu, 16 Oct 2008 18:05:06 -0500, "Jon Slaughter"
Jon_Slaughter@Hotmail.com> wrote:

In any case I replaced the component and it worked fine. I believe
it blew because I had no load hooked up(it was in a dorm and I
didn't have the cab and was running the line out to my comp).
Solid state amp: Ok with no load. Tube amp: not ok.

Thats not completely true.

Of course it is. The only way a transistor amp can blow up with no load, is
if it is designed incorrectly. Like, it oscillates off load, or the power
supply has such bad regulation that it raises its voltage etc....

Well that is what I SAID, and in the context of MARSHALL, its quite
possible.


Ive seen power amps blow from having transistors unable to handle the
rail to rail voltage they saw off load before.

First job in one company was to work that out and select transistors
that COULD.

Kevin Aylward
kevin@kevinaylward.co.uk
www.kevinaylward.co.uk

 

[Eeyore]

Neil wrote:

"Phil Allison" <philalli...@tpg.com.au> wrote:
"Neil"

I'll take the T6 MJF122 out of circuit later today to see if it looks
suspect later today

BDV's available at Farnell about Ł2.40 each + vat (you may have to pay
a minimum order value). Also on eBay about the same price.

** So which ones did ** YOU ** buy ??????

Your evasiveness is SUSPICIOUS ....

((((( not evasive Phil, I just refered to them as BDV's as you did in
your question - and to be brief. BDV64 & 65 are discontinued at RS &
Farnell so I fitted BDV64a & 65a. Given that the failure is exactly
the same as when I carried out the FIRST repair using pucker BDV64 &
65's I assume suffix 'a' is compatible or adequate. Farnell p/nos
1208581 & 1208579 )))))

IIRC and I'm pretty sure I do, the letter suffix indicates the working
voltage, A being the lowest. That's certainly the case with some BDXs I
used. Then they deleted the BDXxxD and we had to have devices selected from
BDXxxCs. Not my choice of device I'm glad to say, so I could say "told you
so" !

Graham

 

[Eeyore]

Kevin Aylward wrote:

Jon Slaughter wrote:
"Dave Curtis" wrote

Solid state amp: Ok with no load. Tube amp: not ok.

Thats not completely true.

Of course it is. The only way a transistor amp can blow up with no load, is
if it is designed incorrectly. Like, it oscillates off load, or the power
supply has such bad regulation that it raises its voltage etc....

Wouldn't put it past the Indian factory that makes them these days (I've seen
the line) to achieve that. Usually by substitution of inferior components.

Graham

 

[Kevin Aylward]

Eeyore wrote:

Kevin Aylward wrote:

Jon Slaughter wrote:
"Dave Curtis" wrote

Solid state amp: Ok with no load. Tube amp: not ok.

Thats not completely true.

Of course it is. The only way a transistor amp can blow up with no
load, is if it is designed incorrectly. Like, it oscillates off
load, or the power supply has such bad regulation that it raises its
voltage etc....

Wouldn't put it past the Indian factory that makes them these days
(I've seen the line) to achieve that. Usually by substitution of
inferior components.

Graham

Just watching BBC 4 right now. Its the story of les Paul and the 1st
electric...

Kevin Aylward

www.kevinaylward.co.uk

 

[Neil]

On Oct 17, 9:43 am, "Phil Allison" <philalli...@tpg.com.au> wrote:

"Neil"

I'll take the T6 MJF122 out of circuit later today to see if it looks
suspect later today

BDV's available at Farnell about Ł2.40 each + vat (you may have to pay
a minimum order value). Also on eBay about the same price.

**  So which ones did  ** YOU **   buy  ??????

    Your evasiveness is  SUSPICIOUS ....

((((( not evasive Phil, I just refered to them as BDV's as you did in
your question - and to be brief. BDV64 & 65 are discontinued at RS &
Farnell so I fitted BDV64a & 65a. Given that the failure is exactly
the same as when I carried out the FIRST repair using pucker BDV64 &
65's I assume suffix 'a' is compatible or adequate. Farnell p/nos
1208581 & 1208579 )))))

Does anybody know what the normal operating temperature of the
darlingtons is?

**  About 10 degrees C above room ambient.

((((( thanks Phil )))))

.....   Phil

 

[Dave Curtis]

On Fri, 17 Oct 2008 15:04:19 +0200, jh <jh-audiop_NOSPAM@t-online.de>
wrote:

the bread and butter Marshall began in 1962 with the 5881/6L6/KT66
equipped JTM45 - an almost 100% copy of the 5F6-A

Which is why the switches are (still?) upside-down, and the inputs are
on the opposite side.

 

[Phil Allison]

"Neil"
"Phil Allison" "

I'll take the T6 MJF122 out of circuit later today to see if it looks
suspect later today

BDV's available at Farnell about Ł2.40 each + vat (you may have to pay
a minimum order value). Also on eBay about the same price.

** So which ones did ** YOU ** buy ??????

Your evasiveness is SUSPICIOUS ....

((((( not evasive Phil, I just refered to them as BDV's as you did in
your question - and to be brief. BDV64 & 65 are discontinued at RS &
Farnell so I fitted BDV64a & 65a. Given that the failure is exactly
the same as when I carried out the FIRST repair using pucker BDV64 &
65's I assume suffix 'a' is compatible or adequate. Farnell p/nos
1208581 & 1208579 )))))


** Just one more try:

Did YOU buy the BDVs from Farnell or off eBay ???????

I ask because there are so many **fake** devices offered on eBay.

Never buy semis from eBay.



...... Phil

 

[Phil Allison]

"Neil"

The amp (Valvestate VS100R with ECC83 Glass Valve) packed in a few
months ago. Two of the 4 darlington transistors (2xBDV64 & 2xBDV65)
had gone short circuit, also taking out the 1A anti surge fuse. I
replaced them (using heat sink paste as well) and it happened again,
so I replaced them once more and left the amp on (guitar & effects
unit unplugged / overdrive off) to eliminate external possibilities.
After about 15 mins I measured the temperature of the transistor heat
sinks - 3 were 40-50deg C and 1 was cooler. After an hour I went out
of the room for 5 minutes and returned to find it had blown again. The
heat sinks were hot - one of them was 100 deg C. Any ideas what could
be causing this?

** Have a very careful look at R29 ( 0.33 ohms 7 watt ) and make sure the
soldering of the legs is OK.

This resistor is CRITICAL as it conducts speaker current to ground and
supplies a take off point for the POSITIVE feedback loop.

If the soldering is cracked, the amp will oscillate at supersonic
frequency - probably intermittently.



...... Phil

 

[Eeyore]

boardjunkie wrote:

You likely have leaky drivers.

Made of silicon ? !!!!!

Bwahahahahahhahahhaa !

Graham