# Not the usual tube amp output impedence matching question



## Granny Gremlin (Jun 3, 2016)

So, I have a Bogen Challenger PA head with LoZ inputs that I really like for my instruments with LoZ pickups. The OT has multiple taps for 4, 8, 16 and constant voltage PA speakers, but also a 600 Ohm tap. I was thinking, 600 Ohms is old school line level.... so can I effectively use this as a preamp for recording my LoZ instruments, feeding a line level input on a recording device instead of a speaker?

Now the line level input is modern and therefore 10k. Would I need to terminate the amp output with a 600 Ohm resistor like you have to with some vintage recording gear or?


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## jb welder (Sep 14, 2010)

For sure the OT will have to be loaded somehow. Is there an owners manual available for it?


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## Granny Gremlin (Jun 3, 2016)

Good point .... a quick search shows manuals exist for the CHA-10 and 75 (mine's the 33) but all pay to download. Will have to look around more later.


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## Paul Running (Apr 12, 2020)

Is the PN legible on the output transformer?


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## jb welder (Sep 14, 2010)

I would put a 560 ohm resistor between 600ohm tap and common. Then you should be safe with the OT.


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## Granny Gremlin (Jun 3, 2016)

Thanks that's what I thought, but I may have brain farted - it's not a 600 Ohm out but a 3rd option for constant voltage lines. Was looking over the amp at the back, reading upside down and got me hopes up.


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## Paul Running (Apr 12, 2020)

Are they 7868s or 7591s in the output stage?


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## Paul Running (Apr 12, 2020)

Sorry, barking up the wrong tree, probably better off to tap-off the preamp for a line-out.


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## jb welder (Sep 14, 2010)

Granny Gremlin said:


> it's not a 600 Ohm out but a 3rd option for constant voltage lines.


I think both can be true. Is it still a tap off the OT? What is it labelled as?
I think 600ohm out is designed for driving phone lines. So it would be lower level out, and if it's a tap on the OT, terminating it with 560R would provide proper load for OT safety.


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## Granny Gremlin (Jun 3, 2016)

That would be great, but no. I've been the victim of me own dyslexia again.


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## Paul Running (Apr 12, 2020)

Not to worry man, sometimes seeing something the other way reveals things that other do not notice.


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## Paul Running (Apr 12, 2020)

There are ideas in this ball that only you may see


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## bolero (Oct 11, 2006)

Some original Marshall amps had a 600v OT tap too, used for driving long runs of PA speakers at ballparks, factories & things, I believe?


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