tubeswell
Joined: Sep 24, 2011
Posts: 1424
Wellington, NZ
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Posted on Nov 29 2017 09:58 PM
Scored a cheap 100W MV Quad Reverb amp chassis sans-cabinet that is badly in need of some TLC. It has been severely molested over the years, and has had only patchy maintenance at best. Somebody put a PPMV in it in the past and have also jumpered other components off the problematic wax-impregnated main board.
My aim is to coax it back into form, but as a head for my monster 76 DSR cab. (The 100w MV QR and DSR - and for that matter the 100W MV Twin Reverb etc of the same era are basically the same amp chassis, but with different faceplates and speaker configurations). The chassis and xformer date codes point to late October 1973.
I've been over the basic circuit, including replacing what were the original filter caps, and tested the trannies, and replaced the dodgy 6L6 sockets (one of them was badly charred) and its just about ready to test-fire. Time will tell, whether more electrical restoration/maintenance work is required. I may have to yet put a new main board in - the CBS waxed board has obviously been problematic in the past. And I would like to re-do the less than classy looking bias mods (including wrong bias pot and bias supply bucking tranny), and I'll probably rethink the PPMV.
I've been working on building a new slim-line head cab to house the chassis in. Finished tolexing it yesterday. (still got to do the grille cloth and replace some of the wrong control knobs with 73-era witchhats).
— He who dies with the most tubes... wins
Surf Daddies
Last edited: Nov 29, 2017 22:05:24
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SandBug
Joined: Feb 22, 2016
Posts: 439
California
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Posted on Nov 29 2017 11:29 PM
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CrazyAces
Joined: Jul 31, 2012
Posts: 4052
Nashville, TN.
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Posted on Nov 30 2017 08:19 AM
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ArabSpringReverb
Joined: Jul 13, 2012
Posts: 490
San Diego CA
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Posted on Nov 30 2017 12:37 PM
nice . I hope the circuit board is usable after all . I ve got a mid 70s SFTR I've been using for 30 + years . I had my amp guy remove the MV circuit and its pull-distortion thing ..I never used the pull distorto bit and finally just decided that the whole deal had to go ...channel volume only ;sounds great . So I guess its a partial blackface conversion and I like it. Good luck with this , looks very worthy
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tubeswell
Joined: Sep 24, 2011
Posts: 1424
Wellington, NZ
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Posted on Dec 18 2017 05:38 PM
Grille cloth and badge arrived in the post this morning, so it took all of 1/2 hour to finish the cab (bar the few extra replacement witchhats I still have to find)
— He who dies with the most tubes... wins
Surf Daddies
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JObeast
Joined: Jul 24, 2012
Posts: 2762
Finknabad, Squinkistan
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Posted on Dec 19 2017 12:07 AM
Cool new head you got yourself there. I headized my Twin Reverb (minus the Reverb) and it sits on top my Bassman cab like a true surf beast. Loud as Har Megiddo.
— Squink Out!
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LittleKahunaCraig
Joined: Jan 09, 2008
Posts: 369
Orange County, CA
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Posted on Dec 20 2017 08:15 AM
Great project. Let us know how it sounds when you connect to a cab.
— Craig Skelly
Little Kahuna
www.littlekahunamusic.com
The Breakaways
The Curl Riders
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tubeswell
Joined: Sep 24, 2011
Posts: 1424
Wellington, NZ
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Posted on Feb 10 2018 04:35 AM
Finally got around to matching up some output tubes , plus some shots of the head (spot the out-of-place witch-hats) and DSR cab.
The biggest battleship in my surfin fleet.
— He who dies with the most tubes... wins
Surf Daddies
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CrazyAces
Joined: Jul 31, 2012
Posts: 4052
Nashville, TN.
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Posted on Feb 10 2018 09:13 AM
BIG amp, a gang of multimeters - you win!
I'm not going to help you move that though, LOL.
O.K., it has wheels.
Cheers,
Jeff
— http://www.facebook.com/CrazyAcesMusic
http://www.youtube.com/user/crazyacesrock
http://www.reverbnation.com/crazyacesmusic
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wfoguy
Joined: Dec 11, 2011
Posts: 2090
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Posted on Feb 10 2018 12:23 PM
I'm a tool freak and I don't own 7 different meters. Note I said "different".
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tubeswell
Joined: Sep 24, 2011
Posts: 1424
Wellington, NZ
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Posted on Feb 12 2018 12:26 AM
I keep different ones in circulation at different times, depending on what I feel like buying when I'm waiting in the queue at the local electronics shop. The cheapies are perfectly adequate for basic jobs like measuring tube current and they are about US$8 with a 12-month warranty and a fresh battery. No-brainer.
— He who dies with the most tubes... wins
Surf Daddies
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CrazyAces
Joined: Jul 31, 2012
Posts: 4052
Nashville, TN.
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Posted on Feb 12 2018 10:09 AM
After my Fluke died after being well taken care of, shop use only, and they refused to cover it under warranty I spend much less on multimeters now.
Funny, I had a Fluke clone made by Radio Shack on the road with me for years. It got smashed (road cases don't always work) and Radio Shack replaced it for free.
Still dig that big ass amp!
Cheers,
Jeff
— http://www.facebook.com/CrazyAcesMusic
http://www.youtube.com/user/crazyacesrock
http://www.reverbnation.com/crazyacesmusic
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eddiekatcher
Joined: Mar 14, 2006
Posts: 2764
Atlanta, GA
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Posted on Feb 13 2018 08:43 AM
Can you say "Caution High Voltage?"
I got tired (and scared) of doing it with multimeters and bought a four tube bias meter which allows me to have all the tubes in place, monitored at the same time and just select which tube to address with a four way rotary switch.
Trick, and a bit less spooky.
Nice project. It's been a while since I cut down my Dual Showman Reverb head cabinets to "official" piggy-back cabinet height. On several I actually routed out a pocket in the bottom for the pan to clear the output transformer and still keep the modified cabinet the height of the non-reverb piggy-back heads. On one I just built an outboard cabinet to house the pan. Ended up never using any of that as we all had reverb units.
ed
— Traditional........speak softly and play through a big blonde amp. Did I mention that I still like big blonde amps?
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tubeswell
Joined: Sep 24, 2011
Posts: 1424
Wellington, NZ
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Posted on Feb 13 2018 12:05 PM
Indeed, the high voltages are why I use test clips. Bias probes are handy for when you just want to bias the amp, and I have a few in my stash. For this session I was taking other voltages throughout the amp, so I had the meters handy.
— He who dies with the most tubes... wins
Surf Daddies
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eddiekatcher
Joined: Mar 14, 2006
Posts: 2764
Atlanta, GA
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Posted on Feb 14 2018 04:03 PM
I did notice the healthy B+.
Were you custom tuning for a low 30's mA on the bias? I couldn't tell from the pix if that amp had a true bias adjust or the CBS hum balance control.
One tube appears to be a bit on "tired" side.
Just curious.
ed
— Traditional........speak softly and play through a big blonde amp. Did I mention that I still like big blonde amps?
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tubeswell
Joined: Sep 24, 2011
Posts: 1424
Wellington, NZ
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Posted on Feb 14 2018 11:48 PM
The tubes I'm trying out are rated at 20.5W, so 30ishmA @458V is around 67%. This will not deliver 100W output, but it will still be loud and clean. I'm still fooling around a bit with the matching (have another 12 tubes I'm subbing in one by one) and hope to get them a bit more balanced within 1mA of each other.
— He who dies with the most tubes... wins
Surf Daddies
Last edited: Feb 14, 2018 23:49:27
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tubeswell
Joined: Sep 24, 2011
Posts: 1424
Wellington, NZ
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Posted on Mar 06 2018 01:26 AM
I gave it an inaugural run at a gig on Sunday. You can hear every nook and cranny in the sound with this setup - huge bass. Sounds amazing with flatwounds on my JM. We ripped through a bunch of Ventures tunes during our 1st set and this nice tourist lady from the USofA walked up to us and introduced herself - said she was Mel Taylor's younger sister, and she had another brother called Larry who was the bass player in Canned Heat. So we got a group selfie - does anyone here recognise her?
— He who dies with the most tubes... wins
Surf Daddies
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