ETI480 help please

peter12 · 25th August 2005, 12:15 PM

Hi. Going through my old junk I've found a couple of ETI480 modules including transofrem I bought 20 years ego so've decided to finally build that amp I intended in the first place.
I've powered up one module and it worked great so to make sure it's ok I've left it running at full blast for 5 minutes. Than suddenly it stopped. I found blown fuse but that also have found both 2N and MJ power transistor blown. I'm about to replace them but can't figure out why it happened in the first place. Any ideas? I can only think if it isn't the trim pot (bias?). I've not touvhed that and it's set at 1/3th.

Also, is it possible to swap the 50W output transistors for onc with more power just by straight swap? For example MJ15003 and 4?
I got another trafo that can handle 200W but don't know if straight transistor swap is possible without any other tweaks.
Thanks for any advice Peter

MikeB · 25th August 2005, 12:32 PM

I've heard that the mj15024/25 is an excellent upgrade for this
amplifier, giving better sound and having more robust bjts.

Mike

Centauri · 25th August 2005, 03:20 PM

Sounds like it probably got too hot - what sort of heatsink was it bolted to, and what impedance was it running into? Is it 50W or 100W version? Note also that if the heatsink is not earthed, this amp can become unstable (especially if it is a Dick Smith kit).

The MJ15004/4 can be used without any other modification, but if you plan to increase the supply voltage, then other mods need to be done as well.

Cheers
Graeme

25th August 2005, 12:15 PM	#1
peter12 diyAudio Member Join Date: Aug 2005	ETI480 help please Hi. Going through my old junk I've found a couple of ETI480 modules including transofrem I bought 20 years ego so've decided to finally build that amp I intended in the first place. I've powered up one module and it worked great so to make sure it's ok I've left it running at full blast for 5 minutes. Than suddenly it stopped. I found blown fuse but that also have found both 2N and MJ power transistor blown. I'm about to replace them but can't figure out why it happened in the first place. Any ideas? I can only think if it isn't the trim pot (bias?). I've not touvhed that and it's set at 1/3th. Also, is it possible to swap the 50W output transistors for onc with more power just by straight swap? For example MJ15003 and 4? I got another trafo that can handle 200W but don't know if straight transistor swap is possible without any other tweaks. Thanks for any advice Peter

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25th August 2005, 12:32 PM	#2
MikeB diyAudio Member Join Date: Apr 2004 Location: Gütersloh	I've heard that the mj15024/25 is an excellent upgrade for this amplifier, giving better sound and having more robust bjts. Mike

25th August 2005, 03:20 PM	#3
Centauri diyAudio Member Join Date: Jul 2003 Location: Newcastle, Australia	Sounds like it probably got too hot - what sort of heatsink was it bolted to, and what impedance was it running into? Is it 50W or 100W version? Note also that if the heatsink is not earthed, this amp can become unstable (especially if it is a Dick Smith kit). The MJ15004/4 can be used without any other modification, but if you plan to increase the supply voltage, then other mods need to be done as well. Cheers Graeme

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