Mojotone Brownface Deluxe 6G3 Build and a Question?

j.doughty

Member
Messages
55
I just finished my 1st amp from a Mojotone kit, a Fender Brownface Deluxe. Luckily, I was able to find some good info and pictures on here to help me out, since the Mojotone kit only comes with a layout and a schematic. Especially found @VJF 's post of his build extremely helpful.

I do have a question for those that I have either built a Brownface Deluxe or own an original. When the tremolo intensity is set beyond halfway should the speaker physically pump in and out?



Here are some pictures along with a video of the tremolo causing the speaker to move. The only thing I have left to do before mounting the chassis when the cab is delivered in a couple of weeks is to replace the temporary bias pot with a true bias pot.

IMG_20161230_081137_zpsbfs290sd.jpg


IMG_20161230_081201_zpsa0prxxik.jpg

IMG_20161230_081206_zpsy5oupd65.jpg
 

Bob Arbogast

Gold Supporting Member
Messages
1,256
Nice work.
And, yes, that "pumping" of the speaker is normal. It's the low frequency oscillator signal being fed to the output stage (actually modulating its DC bias point).
 

j.doughty

Member
Messages
55
There was a recent thread on this https://www.thegearpage.net/board/index.php?threads/6g3-tremolo-issue.1754053
My guess is that the thumping may improve if the HT reservoir cap value is increased above the regular 6G3 spec, eg from 16uF to 32uF.
Is the reservoir cap the 16uF connected directly to B+ ?

I have some 22uF (500V) caps leftover from upgrading a HR Dlx. I could connect it across the 16uF and see what happens. Also, I will try the 47pF caps mentioned in the other post. Thanks!
 

j.doughty

Member
Messages
55
Tried both increasing the value of the first filter cap, and adding the 47pF caps, neither affected the pumping caused by the tremolo. So, I'll take @Bob Arbogast 's word that it's supposed to pump. I noticed when I played through an extension cab that the pumping isn't really noticeable. And in a live situation I wouldn't be using the tremolo anyway, although I do really like the way it sounds.

Thanks everyone!
 

Bob Arbogast

Gold Supporting Member
Messages
1,256
You can try adding a 47uF, 50V e-cap from the top of the bias pot (i.e., the terminal where the bias supply voltage feeds the pot) to ground. Make sure that the positive end of the cap goes to ground!
 

Taller

Gold Supporting Member
Messages
4,067
Beautiful work! I've been considering the purchase of this exact kit. I'll look forward to sound clips/videos.
 

Mattbedrock

A player who collects
Gold Supporting Member
Messages
5,095
Nice work - thanks for sharing. I also answered your pm on this subject with similar advice as above - didn't realize you had posted here already.
 

j.doughty

Member
Messages
55
I tried a couple of the suggestions for fixing the tremolo. Nothing seems to help. From everything I've been told and found the speaker should "pump" at higher settings. So I will just leave well enough alone. I'm enjoying playing the amp while waiting on the cabinet to show up, and trying to fight the impulse to build another amp! Eventually, I want to retrofit something into my Hotrod Deluxe.
 

VaughnC

Silver Supporting Member
Messages
19,051
It's modulating the grid bias...so it is what it is, an LFO signal riding on the DC bias supply. Perfectly normal IMO.
 

j.doughty

Member
Messages
55
Here's some photos of the final results, plus my 2nd project, a slightly modified Tweed Deluxe 5E3. I'm still looking for the right speaker. Didn't like the Cannabis Rex (too much low mid punch), and don't like the WGS 12C/S (no highs).

IMG_20170115_083023_zps9woprgr8.jpg


IMG_20170115_083051_zpsbvdjhnf2.jpg

A "real" bias pot, ground switch wired for standby and shielded cable where I thought it might help:
IMG_20170125_221653_zps82aou7od.jpg

IMG_20170127_171943_zpsrqdxmqgr.jpg
 

jthomas666

Member
Messages
1,070
i don't see the pics... is it just me? Hmm... my browser is trying to still load something from TGP. Maybe that's the pics out in the aether somewhere trying to get here.
 

Rob s

Member
Messages
1,159
Nice build
Surprised you didn't dig the WGS G12.
That usually solves my problems.
Eminence patriot perhaps
Old Jensen .
Stay away from the new Jensen.
 

j.doughty

Member
Messages
55
Nice build
Surprised you didn't dig the WGS G12.
That usually solves my problems.
Eminence patriot perhaps
Old Jensen .
Stay away from the new Jensen.
I have the smooth cone version of the G12. And it doesn't sound bad. But, I'm going to try the G12Q, the light version of the G12, and see what it does. Thanks for the suggestions. I give an update and what I come up with.
 




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