Carlsbro GLX150T schematic

Psygoat

I have a Carlsbro GLX150t in for repair.
It's blowing the internal fuses so I am expecting a power stage fault.
Can anyone hook me up with a schematic?
Thanks.
Mark

DJH83004

I think you may struggle to find one to be honest. I looked at one a few years ago which had blown output transistors TIP ??? And it was a load of trouble, so suspect it may end up as beyond economic repair, since they are not worth that much even when working, but good luck anyway.

Psygoat

I'm going to try them on monday, anyway. It's got one blown output transistor at least and the all the semiconductors are very cheap, so I can probably rebuild it and it won't cost much,

ICBM

From memory it’s a bog-standard discrete-transistor power stage, shouldn’t be too difficult. Most likely one or more blown power transistors and possibly the driver transistor and a resistor or two.

Psygoat

It is. Its fairly obvious, from the layout. I reckon its going to be more of a reliable amp than the mode 4, which was also part of this batch. Just requires a bit if patience.
Use of an output transformer quite unusual for a tranny amp.
I miss my 50 top.

ICBM

Psygoat said:

I reckon its going to be more of a reliable amp than the mode 4

*Anything* is going to be...

The older solid-state Carlsbros are near enough bombproof - these later ones less so but still good.

Psygoat said:

Use of an output transformer quite unusual for a tranny amp.

I wonder if it’s part of the cause? At very low frequencies it will have almost no resistance.

This was part of the reason the 1970s Marshall Lead & Bass 100 was unreliable, they had an auto-transformer so they could be used better with the standard 4x12” cabinets.

Psygoat

As far as the tranformer goes, I think I'm going to have to find out the hard way.
Best I can do is run a signal on the primary and see what I get on the output.

Psygoat

Looks very clean, actually. Just off a signal generator. Gonna go for the rebuild I think.

DJH83004

I'm absolutely certain you will be able to get it up and running, the issue is will it stay that way long term, or will the customer be bringing it back to you in a couple of weeks time with the same fault   

Psygoat

Well, who knows.
These people are friends of mine, so as long as I get covered for parts, then it's ok.
we work together on loads of different projects so it's not a straight up commercial job.

ICBM

I didn’t mean the transformer might be faulty - just that even when working perfectly it’s not really a great idea to load a SS output section with a transformer - at least without a coupling cap as well - because the DC resistance is close to zero.

If there’s room it might be a good idea to fit a big cap...

Psygoat

Interesting idea. I've given all the semiconductors the once over and it looks like only one power transistor has failed.
Seems a bit too good to be true, but there you have it.
I don't seem to have any in the spares box which is a shame.

ICBM

Psygoat said:

Interesting idea. I've given all the semiconductors the once over and it looks like only one power transistor has failed.
Seems a bit too good to be true, but there you have it.
I don't seem to have any in the spares box which is a shame.

What type is it?

ecc83

I don't know how many transistors there are in that amp but I found when fixing HI FI amp blow ups that it was better to just replace the whole lot and check resistors. One 'leaky' CB junction and the whole thing blows again! (Sony used to send us 'kits' of all the trannies!) .

Transformer OP stage? Two ways to do it. Could be like a big Mother tranny radio*, i.e. OPTrasistors DC coupled to a PPull traff . Not a lot you can do to save that  but there should be 'flyback' diodes to protect (ha!) against an OC load, check 'em.

Could be a split rail with traff 'in the middle'. Bit daft if DC coupled because the OP offset will drift and as IC says, thermal runaway will bugger things...NEVER connect  a low R traff to a transistor amp NO matter how expensive it is.

Push come to it? Stuff in a 'Module' ?

* See the Deacy Amp schematic.

Dave. (BTW I have a very old sstate head  100W 8R can't get at it to see the name. Uses a class A 2n3055 transformer driver. I have bashed the buggery out of it with a bass, seems ok. Free to collect it anyone is interested?  Ah! TUAC?

Psygoat

Hi Fi amps are a lot less forgiving, I found,
I've had a few guitar amps, Class A/B, where one side of the push pull is dead and it will still play.
I'm like 'uh there's nothing wrong with it'
Ha haha

Psygoat

ICBM said:

Psygoat said:

Interesting idea. I've given all the semiconductors the once over and it looks like only one power transistor has failed.
Seems a bit too good to be true, but there you have it.
I don't seem to have any in the spares box which is a shame.

What type is it?

The op transistors are MJ15024

ICBM

Psygoat said:

The op transistors are MJ15024

Just had a look in my box of 'pulls' - only a couple of 23s, sorry!

The 24 is basically the same as a 22 but with slightly higher voltage spec - 250V as opposed to 200V. Is the voltage in the amp high enough to warrant a 24?

Psygoat

Thanks for looking. I just need a couple from cpc, gonna to replace the emitter resistors as well, even though they measure ok.I have to order a load of stuff anyway.
They didn't skimp on the thermal paste, it's now bloody everywhere.
It just all seems a bit odd, as I'm used to total destruction, we shall see.

ICBM

Highly unlikely the emitter resistors are dead - I don’t think I’ve ever seen that. They’re usually 5W wirewounds - they should take up to 50W briefly, the fuses will go first.

Excessive thermal paste everywhere is a right pain... and totally unnecessary. Plenty of kitchen roll is the only solution!

Psygoat

I'm sure the resistors are fine, It's a force of habit thing from doing power amps.
There has to be something else wrong, I haven't checked the small resistors, but usually you can see that they're blown, and all the driver transistors seem fine, so going to go with that I think.
this is where not having a schematic really doesn't help.
My guess about the whole thing is that it's had a cab plugged in without matching the impedance.

ICBM

Psygoat said:

There has to be something else wrong, I haven't checked the small resistors, but usually you can see that they're blown, and all the driver transistors seem fine, so going to go with that I think.
this is where not having a schematic really doesn't help.
My guess about the whole thing is that it's had a cab plugged in without matching the impedance.

This is the other problem with those old Marshalls - the transformer was intended to give the full power from a typical 4-ohm amp, at 16 ohms into a standard Marshall 4x12", but then if someone connects it to an 8-ohm cab set like that, it's equivalent to a 2-ohm load...

Too clever for their own good. It's now very rare to find one of these amps in both working order and with its original transistors!