6G16 Brown Vibroverb build!

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Powdered Toast Man
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6G16 Brown Vibroverb build!

Post by Powdered Toast Man » Thu Aug 12, 2021 5:31 pm

I just completed my build of the Mojotone 6G16 Vibroverb kit! Here's my review of the process:

I purchased the Mojotone kit minus speakers. I ordered a pair of Weber 10A125's separately. I also found a seller online that makes repro faceplates and ordered up the proper Vibroverb style plate.

It took me about a week to complete. Background: I'm not an electronics or amp tech. Just an enthusiastic hobbyist. I've previously built several pedals and a 5E3 kit. I decided to do the Vibroverb because I wanted a challenge and it's not something I have in my amp lineup.

The kit comes with no instructions at all. Just a layout diagram and a schematic. This was my first time building an amp of this layout. I did find that Mojotone had a video series on Youtube where they go through a build of their Deluxe Reverb kit and I used that as sort of a guide as the chassis layouts are very similar so the same principles apply.

THE GOOD:
The cabinet construction is top notch. It's easy to see why Mojotone is such a popular supplier of cabinets around the industry. The whole thing is made of pine and it's completely flawless. Tolex and grill cloth look spot on. The whole construction appears to be vintage accurate. Same goes for the chassis. It's heavy gauge steel and perfectly made. I have owned an actual vintage 1960 Super and honestly the Mojo cabinet and chassis look identical to what was in that vintage amp.

Transformers appear to be well made. (internet says they're wound by Heyboer). Fiber eyelet board is also of high quality. The components are all carbon comp resistors. The caps are orange drop. No, they're not the primo Sozo or F&T's but I can't see it being an issue.

My aftermarket faceplate also looks PERFECTLY vintage accurate and the holes lined up EXACTLY with the chassis!

THE BAD:
To be frank, Mojotone has work to do on their attention to detail when supplying these kits. I ran into missing pieces multiple times. One resistor was missing due to a miscount on the kit. Later I discovered I was missing another resistor entirely. It was on the layout and schematic but it wasn't in the actual parts inventory at all. They also didn't include screws to mount the cap board or reverb pan. And the final kicker was when I went to mount the chassis I discovered that the nuts to secure the chassis strap bolts were missing.

Also, they are really chintzy with the supplied wire. It's funny because in their DR build video their tech manager says, "oh you can make your leads extra long if you want there's lots of wire. I've got a shop full of the stuff." No. Do not be careless with your lead lengths as you will run out of wire. I was very judicious with my leads and I still ran about 8" short of blue wire. I had JUST enough red, green, and brown wire. The only wire I had a little extra left on was yellow. And like I said, I was careful with how much I used. I did very little trimming of the leads in final assembly.

CHALLENGES:
-It took some thinking and figuring on how to drill and mount the boards (they're not pre-drilled).
-Despite the Mojo design being modified from the original Fender schematic to add an adjustable bias pot, I had trouble getting the bias current up high enough. I replaced the 15K bias resistor with an 8.2K and with the pot maxed I still can only get it up to 42ma which ends up being about 60% of plate dissipation.
- Reverb was noisy at first. Ended up reading to try flipping the reverb tank 180 degrees inside the bag and it worked!

VERDICT:
In the end, it sounds GREAT! The amp is very warm and harmonically rich. The reverb might be the best I've ever heard. It's darker sounding that your typical BF reverb and doesn't get overly splashy and incoherent when turned up. The reverb is rich and warm. The tremolo also sounds fantastic because how can you beat tube driven bias wiggle trem?

And finally, here's the pictures of the finished product!

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Re: 6G16 Brown Vibroverb build!

Post by i love sharin foo » Thu Aug 12, 2021 5:43 pm

Beautiful amp and nice work! Your lead dress looks nice and consistent with the original Fender work of the era. I built a Mojo JTM45 about 10 years ago. I sourced a good many of my parts myself for it like Classictone transformers, turret board, and some other parts. It was a great sounding amp and I really enjoyed the build. I've been wanting to pick up one of their Princeton Reverb kits for a while now.
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Re: 6G16 Brown Vibroverb build!

Post by Veitchy » Thu Aug 12, 2021 7:33 pm

I love Vibroverbs and your build looks super-clean. Really well done.

Nice Tele too.

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Re: 6G16 Brown Vibroverb build!

Post by Surfysonic » Thu Aug 12, 2021 9:22 pm

Looks outstanding - great job! :?

I regret letting my '90s reissue Vibroverb go and now they're pretty much double the amount I paid for mine used about 7 years ago. It was a great sounding amp when cranked with my surf/punk band at reheasals and gigs around the Washington DC area.

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Re: 6G16 Brown Vibroverb build!

Post by pacemaker » Fri Aug 13, 2021 1:35 pm

Man, that looks incredible. Well done! I agree with you on the reverb and trem circuit on that amp – it's glorious.
I'm currently seeking speakers for my 90s RI VV – what you got goin' on in there?

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Re: 6G16 Brown Vibroverb build!

Post by JSett » Fri Aug 13, 2021 2:01 pm

Neat wiring like that makes me all warm and fuzzy inside. Bravo
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Re: 6G16 Brown Vibroverb build!

Post by jthomas » Fri Aug 13, 2021 4:18 pm

Great job. I've bought a couple of amp kits, one from Weber and one from Watts Tube audio (a Supro 1624 clone). The Weber kit needed a few screws and nuts from the hardware store, but all the parts were there. I kinda expected that because the Weber kits are for the budget-minded. I'm surprised that Mojotone had missing parts (and no instructions).

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Re: 6G16 Brown Vibroverb build!

Post by Powdered Toast Man » Fri Aug 13, 2021 9:14 pm

pacemaker wrote:
Fri Aug 13, 2021 1:35 pm
Man, that looks incredible. Well done! I agree with you on the reverb and trem circuit on that amp – it's glorious.
I'm currently seeking speakers for my 90s RI VV – what you got goin' on in there?
Weber 10A125. 30w. Light dope.

Best 10's you'll ever buy for late 50s/early 60s Fender amps.

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Re: 6G16 Brown Vibroverb build!

Post by wproffitt » Sun Aug 15, 2021 7:15 am

I’m really impressed with your work! That’s beautiful. I built a 5e9 (Tremolux) clone a few years back and really enjoyed the process, even without directions. From your description, it must sound glorious. Enjoy it in good health!

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Re: 6G16 Brown Vibroverb build!

Post by sookwinder » Sun Aug 15, 2021 9:42 am

The problem with any build as successful as this is that very soon you’ll want to build another amp and in it goes until you have plenty of amps and no room

So we’ll done. What is your next project ?
relaxing alternative to doing actual work ...

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Re: 6G16 Brown Vibroverb build!

Post by NewBuild22 » Thu Mar 03, 2022 3:16 pm

Hello all from a newbie on this site.

Question for the OP (or you can send me a PM if I’m hijacking the thread). I just finished the same kit (but now that I see yours, a proper faceplate is a must!). The amp works well, is quiet and has a really nice Vibrato. But - I’m questioning the overall output/volume. It’s just not as loud as a 40w amp with a pair of tens should be (I used a 10f150 and a 10a125 for speakers).

Can you tell me how hot you’ve got your bias? I’m using NOS RCA Blackplates, an NOS mullard gz34 and nos preamp tubes. My negative bias is correct (-52v) and plate voltage is 450v but initially couldn’t get the tubes biased any higher than about 35-37mA. I changed the bias resistor from 1k to a 1.5k and that helped. I’m now running the idle at about 41mA and the bias pot is dimmed. I’m aiming for 70% (46.6ma) and feel that the sound I’m looking for lies in running the output tubes a bit warmer. I’m going to check my stash and increase the resistor value to 2.4 or 2.7k as to increase the range of the bias pot again. I have gone through my tube stash and this pair has the highest plate draw.

Do you recall how yours is set up? I appreciate any input.

Mike

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