Carlsbro Marlin 6-300 Mk II

[cozytowel]

I am a new member to the forum and this is my first posting looking for help. I know that schematics for Carlsbro amps circa 1980-90s are like hen's teeth. The Carlsbro Marlin 6-300 Mk II amp I have has been "got at" by a previous owner and several resistors have been replaced after an earlier fire on the main board. Resistors numbered R10, R11 and R15 have been replaced with flame-proof variants rated at 6.9Kohms.

I am reliably informed that R15 is rated at 2.2 ohms and serves to protect the 0volt rail from damage. If that is the case then it would appear that R10 and R11 serve a similar purpose protecting the +ve and -ve rails from damage. I would like to find out what values are correct for R10 and R11. I f anyone has a schematic or is prepared to take at look at their Marlin 6-300 Mk II main board I can hopefully get the amp back up and running.

Thanks for any help you can offer

[Vaughan]

Carlsbro schematics

I am a new member to the forum and this is my first posting looking for help. I know that schematics for Carlsbro amps circa 1980-90s are like hen's teeth. The Carlsbro Marlin 6-300 Mk II amp I have has been "got at" by a previous owner and several resistors have been replaced after an earlier fire on the main board. Resistors numbered R10, R11 and R15 have been replaced with flame-proof variants rated at 6.9Kohms.

I am reliably informed that R15 is rated at 2.2 ohms and serves to protect the 0volt rail from damage. If that is the case then it would appear that R10 and R11 serve a similar purpose protecting the +ve and -ve rails from damage. I would like to find out what values are correct for R10 and R11. I f anyone has a schematic or is prepared to take at look at their Marlin 6-300 Mk II main board I can hopefully get the amp back up and running.

Thanks for any help you can offer

Hi Cozytowel
Try this site, I found the guy who runs it to be very helpful
Carlsbro Info
Hope this helps

[Jazz P Bass]

Carlboro Marlin 6-150 MK3 Schematic

Where are these 'protection resistors' located in the circuit.

Output section?
Power supply?

I have not heard of resistors that protect zero volts.
Or the power rails.
Quite frankly, 2.2 ohms is not going to put up much of a fight.

I have attached the 6-150 MK3, as this all that I have.

[cozytowel]

Thanks to Vaughan and Jazz P Bass for your input. I've contacted the Carlsbro expert at HNC Electronics and await a reply. Thanks also for the schematic for the Marlin 6-150 Mk 2. No sign of a 2.2 ohm resistor on the output section of the Marlin 6-150 Mk II or III.

I was told by an ex-Carlsbro service/repair engineer that the 2.2 ohm resistor protected the 0volt rail. I agree that it would not put up much of a fight and so explains why it is a very common failure in the Marlin 6-300. I have read elsewhere (AudioKarma.org) that low ohm fusible (flame-proof) resistors are used in the power supplies of some amps (Sansui).

[Lostfollicles]

Hi Cozytowel, I have just been asked to look at a non working Carlsbro Marlin 6-300 ii PA amp for a friend and it has the same problem R15 has burned, I wanted to replace the resistor with the correct size and rating but like you cannot find a circuit diagram anywhere on the net!
Did you manage to find out any more information? I can't find any info on why this resistor is there apart from the normal reason of currant limiting of Z1 & Z2 Zener's but that is normally done on the + volts side???
Thanks for any help or suggestions in advance!
Lostfollicles

[cozytowel]

Carlsbro Marlin II - resistor burn out

Hi Cozytowel, I have just been asked to look at a non working Carlsbro Marlin 6-300 ii PA amp for a friend and it has the same problem R15 has burned, I wanted to replace the resistor with the correct size and rating but like you cannot find a circuit diagram anywhere on the net!
Did you manage to find out any more information? I can't find any info on why this resistor is there apart from the normal reason of currant limiting of Z1 & Z2 Zener's but that is normally done on the + volts side???
Thanks for any help or suggestions in advance!
Lostfollicles

Hi Lostfollicles, I spend quite a bit of time looking for information on the values of resistors R10, R11 and R15 but without success and had to do a little trial and error. Eventually, I replaced R10, R11 and R15 with 6.8Kohm 0.5 watt metal film resistors. R10 and R11 ran a little warm so I mounted them on long legs with ceramic insulators to limit heat damage to the board. I can't recall if I did the same for R15 but I bet I did the same. The amp ran fine and as far as I know the owner hasn't reported any problems. Good luck with your repair. I hope this helps.
Cozytowel

[J M Fahey]

FWIW in the posted schematic R15 is 100 ohms, and is a classic casualty after blown output transistors.
R10 = 10 ohms ; R11=2K2 .

I guess the former owner got tired of having those 3 resistors ("the only fault he could see") burning time and again and put those 6K8 ones which donīt, and flame proof to boot.

Pity he didnīt realize these were a symptom and not the main problem.

As of:

like you cannot find a circuit diagram anywhere on the net!

as they say in my hometown: "if it were a snake it would be biting you !!! "

Just 2 posts above yours

[cozytowel]

FWIW in the posted schematic R15 is 100 ohms, and is a classic casualty after blown output transistors.
R10 = 10 ohms ; R11=2K2 .

I guess the former owner got tired of having those 3 resistors ("the only fault he could see") burning time and again and put those 6K8 ones which donīt, and flame proof to boot.

Pity he didnīt realize these were a symptom and not the main problem.

As of:


as they say in my hometown: "if it were a snake it would be biting you !!! "

Just 2 posts above yours

Hi J M Fahey, I thank you for pointing out that the schematic posted by Jazz P Bass shows that R15 is 100 ohms, R10 = 10 ohms and R11 = 2K2 ohms. However the schematic posted by Jazz P bass is for a Carlsbro Marlin 150 watt MkII and NOT for the Marlin 300 watt MkII. Thanks to Jazz P Bass I was able to compare his posted schematic with the amp I had in front of me. They were not the same and so I had to find out for myself what would get the amp up and running. Extrapolating information derived from the schematic of one amplifier to another model will certainly get you snake bitten.
Cozytowel

[Cordwangle]

Hi all - this post may be a little late for you guys but it might help someone in the future.
My Carlsbro 300w (5-channel pa) amp has burned resistor at R15 on o/p (0-volt) line; this value is 2R2 while the other two dropper resistors, R10/11, on +/- supply are both 6K8 (all 1/4w)
Power transistors read ok on meter & both dc fuses ok; when/if I have more info I'll update this post
Cheers, Paul