Alron Mosfet 1000 Project (Made in NZ)

Amp tinkerers and people who aren't afraid of 700 volts or so in here....

Moderators: Slowy, Capt. Black

Post Reply
User avatar
Cdog
Vintage Post Junkie
Vintage Post Junkie
Posts: 4364
meble-kuchenne.warszawa.pl
Joined: Wed Feb 07, 2007 3:01 pm
Location: Christchurch
Has liked: 3466 times
Been liked: 711 times

Alron Mosfet 1000 Project (Made in NZ)

Post by Cdog »

Picked this NZ made beauty for my daughter as a project we can work on together. I'd repaired a much smaller one of the same brand a couple of years ago, a neat sounding amp. This is much bigger however... and ridiculously heavy. I'm hoping it'll sound nice for both her bass and guitar. Has a reverb tank! Be interested to hear your thoughts about these, especially from any tex who've poked around in their guts before.

Image
Image
Image
Image
Image
Image

Speaker is blown, with no discernible markings so first port of call is getting a new 15".

Sucky because it had a speaker fuse, but someone had used a 13A instead of a 4A fuse... :thumbdown: Fuse choice makes me think there was a problem before the speaker blew. Not much info online about these, so thought I'd see if anyone here has had experience with them... need to see what power handling my replacement speaker needs.

It has two pair of K135/J50 Mosfets in the poweramp as pictured... so that might put the output at up-to 300-400W? Which seems high, except the sticker says 300W, but methinks that's supply related. 4A (speaker fuse) for 16Ohms (assumed load) could be a clue... P=i^2R = 256W? 128W if 8Ohm. Speaker's coil has gone open circuit, so not sure.

I suppose I could just put a big-ass 8 ohm resistor and some 1kHz through it to see 'watts' going across the load. ;)

User avatar
sizzlingbadger
Vintage Post Junkie
Vintage Post Junkie
Posts: 8241
Joined: Sat Jan 15, 2011 7:12 am
Location: Wire Wrapper
Has liked: 1203 times
Been liked: 1398 times

Re: Alron Mosfet 1000 Project (Made in NZ)

Post by sizzlingbadger »

The wattage will be higher at lower impedance, due to more current flowing. Solid state usually have a minimum impedance rating which is usually the maximum power rating. Example 200W into 4 ohms which would be 100W into 8 etc.

I have 15” speaker in the shed, it’s old and I have no idea if it’s suitable, I’ll check it out tomorrow.
Tube amp and guitar tones straight from 1958… amazing how believable the sounds were back then, even without the modellers...

User avatar
RectifiedAmps
Fender
Fender
Posts: 506
Joined: Tue Jul 22, 2014 7:05 am
Location: Wellington
Has liked: 200 times
Been liked: 240 times

Re: Alron Mosfet 1000 Project (Made in NZ)

Post by RectifiedAmps »

If the speaker is blown and the speaker fuse rating was boosted, then be very suspicious of the output transistors. If any are shorted, they’ll dump the whole power supply’s-worth of DC voltage onto the speaker, hence the open voice coil. Do NOT fire it up again with a new speaker connected before you check the output for DC offset. If you need new K135s (or whatever their complement is - cant read it), I may have some spares in my stash.

User avatar
Cdog
Vintage Post Junkie
Vintage Post Junkie
Posts: 4364
Joined: Wed Feb 07, 2007 3:01 pm
Location: Christchurch
Has liked: 3466 times
Been liked: 711 times

Re: Alron Mosfet 1000 Project (Made in NZ)

Post by Cdog »

sizzlingbadger wrote: Sun Sep 05, 2021 9:42 pm The wattage will be higher at lower impedance, due to more current flowing. Solid state usually have a minimum impedance rating which is usually the maximum power rating. Example 200W into 4 ohms which would be 100W into 8 etc.

I have 15” speaker in the shed, it’s old and I have no idea if it’s suitable, I’ll check it out tomorrow.
Ah...cool, thanks for the reply... that makes sense. And, keen if the speaker is suitable! Cheers :)
RectifiedAmps wrote: Sun Sep 05, 2021 10:14 pm If the speaker is blown and the speaker fuse rating was boosted, then be very suspicious of the output transistors. If any are shorted, they’ll dump the whole power supply’s-worth of DC voltage onto the speaker, hence the open voice coil. Do NOT fire it up again with a new speaker connected before you check the output for DC offset. If you need new K135s (or whatever their complement is - cant read it), I may have some spares in my stash.
Thanks for the reply... great to hear what the fault condition might be. I have a big 8Ohm resistor, I' ll fire it up with that connected and do some probulating to see whats goin on . Appreciate the offer of trannies too, will post when I've had another chance to look at it :)

User avatar
RectifiedAmps
Fender
Fender
Posts: 506
Joined: Tue Jul 22, 2014 7:05 am
Location: Wellington
Has liked: 200 times
Been liked: 240 times

Re: Alron Mosfet 1000 Project (Made in NZ)

Post by RectifiedAmps »

Cdog wrote: Mon Sep 06, 2021 7:47 am Thanks for the reply... great to hear what the fault condition might be. I have a big 8Ohm resistor, I' ll fire it up with that connected and do some probulating to see whats goin on . Appreciate the offer of trannies too, will post when I've had another chance to look at it :)
It doesn’t need a load connected at all- there’s no output transformer and transistors don’t care. You can fire it up without a load and measure for DC across the speaker wires without causing any damage. Note that if a transistor is shorted and you see DC offset, you should switch it off as soon as possible or it’ll strain the power transformer and the shorted transistor(s) will start to smoke! If you have a light-bulb limiter, this is the perfect situation to use it.

User avatar
sizzlingbadger
Vintage Post Junkie
Vintage Post Junkie
Posts: 8241
Joined: Sat Jan 15, 2011 7:12 am
Location: Wire Wrapper
Has liked: 1203 times
Been liked: 1398 times

Re: Alron Mosfet 1000 Project (Made in NZ)

Post by sizzlingbadger »

Here it is, I just checked and its 16ohms, bit dusty too :D

The box is 44x44x24cm and its 8KG, you can have it for free, just arrange the postage if you want it. PM for my address.

IMG_4411.jpeg
IMG_4411.jpeg (309.48 KiB) Viewed 2524 times
Tube amp and guitar tones straight from 1958… amazing how believable the sounds were back then, even without the modellers...

User avatar
RectifiedAmps
Fender
Fender
Posts: 506
Joined: Tue Jul 22, 2014 7:05 am
Location: Wellington
Has liked: 200 times
Been liked: 240 times

Re: Alron Mosfet 1000 Project (Made in NZ)

Post by RectifiedAmps »

What do they mean by ‘70 watt USA’? Is that to account for americans being louder than the rest of us?

User avatar
Slowy
Vintage Post Junkie
Vintage Post Junkie
Posts: 22641
Joined: Wed Sep 09, 2009 4:13 pm
Location: Orcland
Has liked: 1011 times
Been liked: 2466 times

Re: Alron Mosfet 1000 Project (Made in NZ)

Post by Slowy »

RectifiedAmps wrote: Mon Sep 06, 2021 11:59 am What do they mean by ‘70 watt USA’? Is that to account for americans being louder than the rest of us?
American watts are only half as powerful as everyone elses?
Beyond a critical point within a finite space, freedom diminishes as numbers increase. This is as true of humans as it is of gas molecules in a sealed flask. The human question is not how many can possibly survive within the system, but what kind of existence is possible for those who so survive.

User avatar
sizzlingbadger
Vintage Post Junkie
Vintage Post Junkie
Posts: 8241
Joined: Sat Jan 15, 2011 7:12 am
Location: Wire Wrapper
Has liked: 1203 times
Been liked: 1398 times

Re: Alron Mosfet 1000 Project (Made in NZ)

Post by sizzlingbadger »

RectifiedAmps wrote: Mon Sep 06, 2021 11:59 am What do they mean by ‘70 watt USA’? Is that to account for americans being louder than the rest of us?
I think years ago USA used to quote "Music Power" instead of RMS, its was roughly double.
Tube amp and guitar tones straight from 1958… amazing how believable the sounds were back then, even without the modellers...

User avatar
Cdog
Vintage Post Junkie
Vintage Post Junkie
Posts: 4364
Joined: Wed Feb 07, 2007 3:01 pm
Location: Christchurch
Has liked: 3466 times
Been liked: 711 times

Re: Alron Mosfet 1000 Project (Made in NZ)

Post by Cdog »

sizzlingbadger wrote: Mon Sep 06, 2021 10:53 am Here it is, I just checked and its 16ohms, bit dusty too :D

The box is 44x44x24cm and its 8KG, you can have it for free, just arrange the postage if you want it. PM for my address.


IMG_4411.jpeg
That's a mighty generous offer sir... Thank-you! PM incoming :)

User avatar
Cdog
Vintage Post Junkie
Vintage Post Junkie
Posts: 4364
Joined: Wed Feb 07, 2007 3:01 pm
Location: Christchurch
Has liked: 3466 times
Been liked: 711 times

Re: Alron Mosfet 1000 Project (Made in NZ)

Post by Cdog »

Quick update as we had a half hour to work on the amp this weekend. First time power on with Lightbulb in series... And no DC on the speaker wires... Win! Young miss and I did some ohms law equations to set a safety fuse to protect the new speaker from sizzlingbadger. Other than a few crackly pots, it actually sounds pretty good. Haven't tried the spring reverb yet. I'll give it a proper overhaul before we put it back together. Looks like its been worked on at some stage, I'm hoping the filter caps have plenty of life left.

And a bit of hunting has this as a mid to late seventies build. Google search yielded a recently serviced one that looks identical... And only down the road in Rangiora too!

https://m.facebook.com/story.php?story_ ... 3415580131
Screenshot_20211003-193601.png
Screenshot_20211003-193601.png (680.21 KiB) Viewed 2256 times

IMOCD
Vintage Post Junkie
Vintage Post Junkie
Posts: 1744
Joined: Tue May 10, 2016 9:04 pm
Has liked: 480 times
Been liked: 222 times

Re: Alron Mosfet 1000 Project (Made in NZ)

Post by IMOCD »

That's a cool project to do together. Makes me wish I was a bit more receptive to my father when he suggested projects.
Cdog wrote: Sun Oct 03, 2021 6:29 pm Young miss and I did some ohms law equations to set a safety fuse to protect the new speaker from sizzlingbadger.
Curious, though. Why do the speakers need protecting from Mr Badger. What does he do to them? :wink: :)

User avatar
Cdog
Vintage Post Junkie
Vintage Post Junkie
Posts: 4364
Joined: Wed Feb 07, 2007 3:01 pm
Location: Christchurch
Has liked: 3466 times
Been liked: 711 times

Re: Alron Mosfet 1000 Project (Made in NZ)

Post by Cdog »

IMOCD wrote: Sun Oct 03, 2021 6:41 pm That's a cool project to do together. Makes me wish I was a bit more receptive to my father when he suggested projects.
I know right... Me too tbh. It's pretty fun working on something like this together.
Cdog wrote: Sun Oct 03, 2021 6:29 pm Young miss and I did some ohms law equations to set a safety fuse to protect the new speaker from sizzlingbadger.
Curious, though. Why do the speakers need protecting from Mr Badger. What does he do to them? :wink: :)
Ahh my england. Well I hope the fuse will help that too :lol:

User avatar
Slowy
Vintage Post Junkie
Vintage Post Junkie
Posts: 22641
Joined: Wed Sep 09, 2009 4:13 pm
Location: Orcland
Has liked: 1011 times
Been liked: 2466 times

Re: Alron Mosfet 1000 Project (Made in NZ)

Post by Slowy »

Cdog wrote: Sun Oct 03, 2021 6:29 pm Quick update as we had a half hour to work on the amp this weekend. First time power on with Lightbulb in series... And no DC on the speaker wires... Win! Young miss and I did some ohms law equations to set a safety fuse to protect the new speaker from sizzlingbadger. Other than a few crackly pots, it actually sounds pretty good. Haven't tried the spring reverb yet. I'll give it a proper overhaul before we put it back together. Looks like its been worked on at some stage, I'm hoping the filter caps have plenty of life left.

And a bit of hunting has this as a mid to late seventies build. Google search yielded a recently serviced one that looks identical... And only down the road in Rangiora too!

https://m.facebook.com/story.php?story_ ... 3415580131

Screenshot_20211003-193601.png
Rob Magnus! There's a name. Great guitarist, fine bloke. Old neighbour I haven't seen for far too long. :D
Beyond a critical point within a finite space, freedom diminishes as numbers increase. This is as true of humans as it is of gas molecules in a sealed flask. The human question is not how many can possibly survive within the system, but what kind of existence is possible for those who so survive.

Post Reply