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Dummy loads across speaker terminals

 
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shedshrine
george martin


Joined: 01 Jun 2004
Posts: 1436
Location: sf bay area

PostPosted: Fri Apr 15, 2016 6:37 pm    Post subject: Dummy loads across speaker terminals Reply with quote

Would like to see if it is possible to use an old 12 watt integrated stereo tube amp
as a stand alone stereo preamp via its tape outs.

With no speakers attached, I've read you need to provide a "dummy load across the speaker terminals".
What exactly does that entail, as far as actual components and configuration?
..And will it harm the amplifier if this load is in place long term.

Thank you and have a nice day.
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Drone
buyin' gear


Joined: 18 Dec 2009
Posts: 584
Location: Uranus

PostPosted: Fri Apr 15, 2016 7:31 pm    Post subject: Re: Dummy loads across speaker terminals Reply with quote

Two ways to do it.

1. Buy two power resistors, probably 8 ohm, and connect one across each set of speaker terminals.

https://www.radioshack.com/products/radioshack-8-ohm-non-inductive-resistor?variant=5717262405

2. It's likely the preamp feed is taken before the power amp section. Remove the output tubes. Run the amp like that.
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Scodiddly
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Joined: 10 Dec 2003
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Location: Mundelein, IL, USA

PostPosted: Sat Apr 16, 2016 10:12 am    Post subject: Re: Dummy loads across speaker terminals Reply with quote

http://www.mouser.com/ProductDetail/Vishay/RE70G8R00C02/?qs=%2fha2pyFaduh437wwzf7efUXcTPiZuJKJ8h1dNhrW04c%3d

Assuming 8-ohm load, that is. Probably totally fine. No problems with long-term use. If you tap off the speaker outputs, say into one of those DIs that have a big pad switch for speaker-level outputs you'll likely see a bit different sound than with a real live speaker connected.

For under $15 including shipping it doesn't seem like a big risk.
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shedshrine
george martin


Joined: 01 Jun 2004
Posts: 1436
Location: sf bay area

PostPosted: Sat Apr 16, 2016 5:09 pm    Post subject: Re: Dummy loads across speaker terminals Reply with quote

Going to order a couple of those Vishays and see how it goes.

Thanks guys for the input.
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Drone
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Joined: 18 Dec 2009
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PostPosted: Sat Apr 16, 2016 5:53 pm    Post subject: Re: Dummy loads across speaker terminals Reply with quote

Be careful with them, as they are inductive being wirewound.

I always try and get non-inductive for dummy loads, yes a loudspeaker is inductive too, but you can predict what happens with a purely resistive load.

If you're not near a Radioshack, which is the easy option, parts express do non inductive dummy load resistors, bigger than you need, but chassis mountable and non inductive.

http://www.parts-express.com/cat/dummy-load-resistors/1535
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supafuzz
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Joined: 07 May 2003
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Location: Beacon NY

PostPosted: Fri Jul 22, 2016 11:28 am    Post subject: ceramic resistors Reply with quote

I used to have these hug he ceramic resistors that looked like a pair of claves and were about 8 inches long and 1-1/2" diameter and they worked great as a dummy load on a fender tube amp. Not sure why I needed a dummy load at the time but I did and it worked.

like the one on the left
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supafuzz
carpal tunnel


Joined: 07 May 2003
Posts: 1720
Location: Beacon NY

PostPosted: Fri Jul 22, 2016 11:29 am    Post subject: ceramic resistors Reply with quote

I used to have these huge ceramic resistors that looked like a pair of claves and were about 8 inches long and 1-1/2" diameter and they worked great as a dummy load on a fender tube amp. Not sure why I needed a dummy load at the time but I did and it worked.

like the one on the left
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