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SurfGuitar101 Forums » Gear »

Permalink 73 Quad Reverb hatchet job

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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).
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He who dies with the most tubes... wins

Surf Daddies

Last edited: Nov 29, 2017 22:05:24

Bad ass project.

Looks like a fun project that is in the right, capable hands.
Keep us posted on the progress.

Cheers,
Jeff

http://www.facebook.com/CrazyAcesMusic
http://www.youtube.com/user/crazyacesrock
http://www.reverbnation.com/crazyacesmusic

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

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)
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He who dies with the most tubes... wins

Surf Daddies

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!

Great project. Let us know how it sounds when you connect to a cab.

Craig Skelly
www.thebreakaways.com
www.thecurlriders.com

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.

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He who dies with the most tubes... wins

Surf Daddies

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

I'm a tool freak and I don't own 7 different meters. Smile Note I said "different". Smile

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

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

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 sill like big blonde amps?

Indeed, the high voltages are why I use test clips. Smile 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

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 sill like big blonde amps?

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

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?
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He who dies with the most tubes... wins

Surf Daddies

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