Benson Monarch

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pamaz67
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Benson Monarch

Post by pamaz67 »

Sunday I had the chance to test briefly a Benson Monarch Reverb amplifier. I've tried a lot of stuff in my life and usually I prefer Hi powered amplifiers due to their dynamic capabilities. But This amp, with its 15ww 2x6v6 power amp has killed me. Such a warm and rich tone that nothin' both old than new, can be compared in my personal opinion.
Seems that is an original design.
Anybody can give any indication on which are the technical particularities on this jewel?
Thanks and bye.

Paolo
Ciao from Italy.
Paolo
carlosaugustine
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Re: Benson Monarch

Post by carlosaugustine »

I'm gonna +1 and bump this as well (since it's been a while too!); I've seen chassis layouts of it as such:

https://www.guitarplayer.com/.image/c_l ... -title.jpg

https://www.premierguitar.com/ext/resou ... -1-WEB.jpg

It's a Volume/Tone only sort of deal but I'm interested in the topology of it, as there have been so many rave reviews of the amp. Chatting with email with him, he said he got a lot of inspiration from Ampeg and Supro circuits. The circuit looks lots more unfettered than a D-Style/Two Rock Circuit from looking at the pictures.

If anyone can actually chime in on the particulars of what they see I'd be happy to learn more!
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Tony Bones
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Re: Benson Monarch

Post by Tony Bones »

The Guitar Player review of the amp confirms that the 6V6's are cathode biased and that the two 9 pin tubes are 12AX7.

The Premier Guitar review offers some info on the American/British switch.

Zooming in on the image from Premier Guitar, it looks like the second 12AX7 has a jumper between pins. It could be a gain stage direct coupled to a concertina PI, but it looks more like a LTP. Hard to tell without more pixels.

The first 12AX7 might have both sections paralleled. Can't really tell from the photos, but if that's the case then it might be a Marshall 18 Watt / Matchless Spitfire with 6V6's instead of EL84's.

The 12AX7 heaters are DC.
Doppler
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Re: Benson Monarch

Post by Doppler »

I think you're right about LTP, not sure about the rest but it sure is a fascinating design yet simple. I'd love to get inside one for a better look and maybe adapt some ideas for a Hammond AO-35 or AO-39 conversion. It's a bit tricky finding any decent pictures let alone a schematic of a Benson Monarch - IIRC he mentioned in an interview once that he started out playing around with modifying a Hammond organ reverb amp a bit like Dr. Z did
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Doppler
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Re: Benson Monarch

Post by Doppler »

The DC filament supply doesn't appear to have any regulation, just bridge and filter cap is all I can see but there's possibly a dropping resistor in there too I guess. Standard 68K & 1M resistors on the input. First gain stage looks to be using a 56K plate resistor, maybe...with a 1K2 cathode resistor and chunky little bypass cap that looks bigger than 25µF. The coupling caps to the output valves are 0.1µF and grid input caps maybe look like 1K5.

Anyone spot other design features? Got any thoughts about the rheostat wired into the middle of that thing?
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alkuz1961
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Re: Benson Monarch

Post by alkuz1961 »

Doppler wrote: Mon Sep 23, 2019 10:13 pm ... Got any thoughts about the rheostat wired into the middle of that thing?
I think it will be something similar
2019-09-24_20-28-32.jpg
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Doppler
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Re: Benson Monarch

Post by Doppler »

Yes that looks like what it might be for, signal balance for the outputs of the phase inverter. I've often wondered about doing something like that but as usual life gets in the way. I note the Benson one is wired as a rheostat (one lug of the pot not connected) as distinct from the version you post there. I'm real curious to get inside one of these Bensons to better understand the design.
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pompeiisneaks
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Re: Benson Monarch

Post by pompeiisneaks »

That likely just means that the wiper isn't the 'output' but it's being used simply as a variable resistor in line, and output is either above or below it so the reference to ground is adjustable, but the output stays at the same point in the chain.

~Phil
tUber Nerd!
Doppler
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Re: Benson Monarch

Post by Doppler »

Yes, simply a rheostat in series with resistor to ground. The full design of the amp is what I'm curious about. No schematics seem to be available, so I'm guessing I'll need to find a Benson Monarch owner to get inside for a closer look. Preferably the reverb version of the Monarch.
pamaz67
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Re: Benson Monarch

Post by pamaz67 »

Trying to revive the subject. Any more info on this jewel?
Thanks
Paolo
Ciao from Italy.
Paolo
turbofeedus
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Re: Benson Monarch

Post by turbofeedus »

pamaz67 wrote: Thu Nov 14, 2019 10:14 am Trying to revive the subject. Any more info on this jewel?
Thanks
Paolo
Maybe you can buy one and trace it for us? It's only 2 large and a 7 month wait :mrgreen:
Doppler
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Re: Benson Monarch

Post by Doppler »

I'm trying to think of any of my 'wealthier' customers who might be persuaded to get a Monarch Reverb for me to look at! :lol:
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pompeiisneaks
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Re: Benson Monarch

Post by pompeiisneaks »

Hehe, I posted a link to a local band here from Seattle that I really like "Deep Sea Diver"

She plays a Benson, not sure if it's a monarch. I guess I need to find a way to get access to that one no? :)

My guess is she knows the owner/builder. She played guitar for The Shins for a while and he's based in Portland OR where the builder is based as well.

Just a guess though.

~Phil
tUber Nerd!
pamaz67
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Re: Benson Monarch

Post by pamaz67 »

I would like to buy one. But unfortunately this is not the time for acquiring anything. On the other side I've got a bunch of transformers, tubes, potentiometers in my drawers.....
Ciao from Italy.
Paolo
Aaron
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Re: Benson Monarch

Post by Aaron »

Have one of these on the bench at the moment. Just finished tracing it. This one has a paraphrase inverter.

Thanks,
Aaron
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