[Lincoln]

I started a 6G2 Brownface Princeton build the other day, using a MojoTone Chassis. I was surprised to find that the Hammond 290AX transformer that fits all the champs and princetons, did not fit this 6G2 chassis. This chassis wants the larger 290BX transformer. The 290BX is the common transformer for Deluxe & Deluxe Reverb.

Anybody encountered this before? Do all 6G2's take the larger PT or is this something Mojo does? Even the common Princeton 12/15 watt output transformer is too narrow for the way this chassis is drilled. It's a perfect fit for the DR output transformer though. 20 watt 6G2? Sounds like fun.

 

[copperhead]

I built a 5e3 last year this time ,I used a mojotone chassis & used the 290ax tranny you are right the PT transformer cutout in the chassis is larger & I had to drill the 4 pattern holes inside the original holes ...The Hammond trannys should be a direct replacement in the amps it claims it's for I have ordered a few of the hammonds them & installed them without having to modify any thing . I have heard the Mojotone chassis are made for some hayboer or something .

 

[Lincoln]

I built a 5e3 last year this time ,I used a mojotone chassis & used the 290ax tranny you are right the PT transformer cutout in the chassis is larger & I had to drill the 4 pattern holes inside the original holes ...The Hammond trannys should be a direct replacement in the amps it claims it's for I have ordered a few of the hammonds them & installed them without having to modify any thing . I have heard the Mojotone chassis are made for some hayboer or something .

Ah, I figured it must be something like that. Not having the luxury of real 6G2 to check out.....I was wondering what was up. Hope the higher voltages aren't going to be a problem

 

[copperhead]

What are you calling higher voltage ? my build ended up being 357v at the plates & I thought it was within reason

 

[Lincoln]

What are you calling higher voltage ? my build ended up being 357v at the plates & I thought it was within reason

I'm not there yet, I was just thinking of the last DR I built. It was running at just over 400 volts. I can always use a 5Y3 instead of a GZ34. That should hold it back a bit.

 

[keithb7]

Yup the mojotone tranny is cut out for a 6G3 power transformer. Its kinda dumb. Not sure why.

I encountered the same thing. I also used the Hammond 290CAX. Low primary option. I have a solution I will share shortly.

You’ll also notice the fuse and power cord cut outs are mixed up and in the wrong spots. Fuse is aupposed to be on rear of chassis. However rear has D ring cutout for power cord strain relief.

 

[keithb7]

I built an adaptor plate and bolted it in, for the smaller 290CAX transformer.

Here you can see it reads fuse. However fuse hole is supposed to be round. The fuse folder is in the rear corner of the bottom of the chassis. Where the power cord is supposed to be.

 

[Lincoln]

I found out about the fuse holder cutout last night. I had 4 different fuse holders, some vintage Bakelite & brass, some just plastic, all of them were round and too small for the hole. Thought it was time for my medication again, but when I checked a few other chassis', they had way smaller, round holes. Never occurred to me that they had mixed up the fuse & power cord holes. Way to go Mojo.
Nice looking plate you made @keithb7 . I had a 290BX transformer laying around for future DR build, so I just plugged in the bigger transformer. The 20 watt Deluxe/Deluxe reverb output transformer went in too. It lined up with the holes in the chassis perfectly. Only thing that worries me is voltage. Schematic says 325 B+ for the 6G2. The 6G3 I just finished, using the same transformer set, came out a little hot with 445 volts and 65 to 70 milliamps.

The whole thing kinda bumbed me out, cause I had a 291AX transformer with the CT on the heater circuit I had saved just for a 6G2.

 

[dtsaudio]

Actually, the fuse and ground switch holes are not mixed up. Notice the key on the ground hole. The needed switch will have a matching key slot. Also, you can buy fuse holders with one or two flatted sides. Keeps them from rotating when you undo the cap.

 

[keithb7]

The ground switch hole is not the problem @dtsaudio . It's the fuse and the mains power wire hole that are mixed up. I never said the fuse and ground switch were mixed up.

You can see my fuse far bottom left of this photo. You can see my mains wires entering the chassis where the rear face plate is labeled fuse. As per above photo.

 

[dtsaudio]

Must have been half asleep when i read your post. Regardless, looks like they supplied the wrong fuse holder. My comment still stands that you can buy fuse holders to fit the marked hole. Or you could just file two flats on the fuse holder to fit.

 

[Lincoln]

A very nice & neat build @keithb7 ! Now I can't post pics of my 6G2 build cause it will look like dog-sh1t compared to yours. B#(*

 

[keithb7]

Dude....If you have not done this yet, and you like to rock, you NEED to sever the NFB circuit permanently on this 6G2 circuit. Then add a 2.2uF e-cap across the V1 second stage triode, 1500 ohm cathode resistor. OMG this turns the 6G2 into a rock machine. Soo good. Run don't walk, and get this done! I highly recommend.

 

[dtsaudio]

That'll bump up the gain significantly and without the feedback loop, distortion will rise too.
Definitely making for a harder rock sound.
If you add the extra bypass cap, you must open the feedback loop.

 

[Lincoln]

Dude....If you have not done this yet, and you like to rock, you NEED to sever the NFB circuit permanently on this 6G2 circuit. Then add a 2.2uF e-cap across the V1 second stage triode, 1500 ohm cathode resistor. OMG this turns the 6G2 into a rock machine. Soo good. Run don't walk, and get this done! I highly recommend.

I already put a toggle switch into the NFB loop so I could shut it off. I might just give that other mod a whirl. Thanks.

Here's my build, just getting ready to start hooking up the board.

 

[keithb7]

Looks good brah! I don’t see any dog sh1t! Gonna be killer. I love mine!

 

[Lincoln]

This is another one of those "check the date" posts. This build wasn't going well, and I shelved it for over a year.
Main thing was the chassis I got from Mojo Tone had the wrong cut-out size for the power transformer and the fuse hole and power cord hole locations were switched. Also, I didn't have a 30/30/30 filter cap can, so I used a 30/30 and added another 30 inside the chassis. I just wasn't happy with the whole thing. Mojo has stopped selling the 6G2 chassis now btw.

So I dug it out yesterday, blew the dust off it (kidding) and started working again. This time I had an OEM style 30/30/30 cap can, which I installed. Also put in a pot for adjustable bias. I wanted that should the larger transformer become an issue. Pretty simple amp, shouldn't take long to finish it off. It will be a 22 watt brown-face Princeton. I'm thinking 12" speaker rather than a 10".

 

[keithb7]

Keep the updates coming Lincoln. No matter how far apart they are!

We’re all still here.

 

[Lincoln]

Update on the 6G2 Princeton. I got it all wired last night and fired it up. To my surprise, I didn't get feedback and I didn't have to swap the brown/blue wires on the OT!
Only issue I had was the tube bias a little high. The lowest I could get it was 48 mA at 385 volts. I had installed the "standard" 10K fender bias pot, and it wasn't enough. This morning I swapped out the 10K for a 100K and now I've got lots of adjustment. Probably could have done alright with a 50K. I set it for 27 mA with a plate voltage of about 398 (call it 400). I think its going to be a nice little amp. Wife is home so I haven't cranked it yet to explore the breakup.

 

[Lincoln]

For somebody "Frenderish" looking at doing their first amp build, I would suggest either one of these or a blackface Champ as a first build. Why? Room to build. Sure, tweeds are great, but those narrow chassis's are a biotch to work in.