Adapt & Build Princeton Head with 6L6s?

[big_teee]

Has anyone adapted a Princeton to run 6L6s.
I am considering building up a Mojo Princeton chasis with bigger PT, & 4.2k OT for 5881s, or 6L6s.
I just want the smaller size and one chan. like the Princeton, I would put it in a Mojo Princeton Head Cab.
Classic Tone sells a bigger 40w PT that is nearly as small as the 20w Princeton PT.
I may have to file the bolt holes some to make it fit.
I would use a 4,8,16ohm 4.2k OT for the 6L6s.
Am I all wet, or would this work ok?
T

[tubeswell]

Weber does one called a 6A14HP Head

[big_teee]

Weber does one called a 6A14HP Head

Thanks a lot!
That is exactly what I'm looking for.
Have you heard how it works?
I can get dealer cost parts from Mojo, so I was wanting to use their Princeton chassis, and Cab.
I think that would work ok?
T

[imaradiostar]

I built one for my brother. It sounds pretty good! I used the Weber chassis, faceplate and PT with a New Sensor output transformer I have laying around. The Weber cabinet uses two diagonal tens. I have some old CTS speakers around that aren't super loud but work well in the amp.

Somewhere on here I have a thread about the one I built. I found the standard Fender style eyelet board to be a bit limiting. I modified the grounding and power scheme a bit and it's dead quiet- even with the reverb cranked up it's really quiet. I used a buss bar at the back of the pots and connected the filter caps directly to the buss bar. Corresponding grounds connect near the cap grounds at the buss bar. I used a JJ 2x50uf 500 volt cap for the plate and screen filters, mounted in the location of the original US style can cap. This way the preamp grounds aren't shared with the power grounds. It made a big difference.

I'd build it again. It's not my favorite amp style but it's very usable and sounds great.

jamie

[imaradiostar]

http://music-electronics-forum.com/t23631/

I'm thinking back to the issues I had- I couldn't find a pilot light to fit the Weber chassis without rubbing on the bottom of the chassis. It still doesn't have one and I have a light to put in it now but I haven't had time to fix it.

I recall using smaller cathode bypass caps in a few places to keep it from getting too flubby. It sounds fabulous cranked up so it must have worked. I don't usually find that to be the case with stock Blackface Fender values. I also used high value grid stoppers on the cathodyne and output tubes. It really does distort in a pleasing way but doesn't lack high end, regardless of what people tell you about large grid stoppers.

I still want to bias it a little colder so it sounds more "Fendery" and the trem works better but it sounds very good. I left the second input open so I could add a front panel reverb/trem footswitch jack. I think the rean/cliff jacks also helped make it quiet because you can ground them easily without fiber washers to isolate them from the chassis.

The Weber transformer had plenty of gusto for the 6l6's but don't expect it to sound like a super or bassman or anything. I'd say at best it's a 35 watt amp, probably less. I'm using some old Sovtek 6L6's I had laying around but I'd like to put some new tubes in it to see how it sounds by comparison- maybe the JJ 6l6?

I think I also used a high value mid resistor. I had briefly considered putting the mid resistor on a footswitchable relay to open it up to 50k or so as a boost- just wired directly so that 5 volts from the footswitch about open up the mid resistor. I guess it's not needed as it's mostly used with an assortment of pedals anyway.

If you like I can open it up and get specifics. I really need to install that light and glue down the caps anyway.

Oh yeah- I only used 4 electrolytic caps in the power supply! It was an experiment but it worked well, possibly because they're twice (or more) the usual Fender value and the grounding scheme is better. I had surplus 47uF radials so I think I arranged them with a verb drive on the screen node, PI on the next node and verb blend/return and V1a/b on the last node. I don't recall for certain but that sounds right.

Jamie

[tubeswell]

http://music-electronics-forum.com/t23631/

I'm thinking back to the issues I had- I couldn't find a pilot light to fit the Weber chassis without rubbing on the bottom of the chassis. It still doesn't have one and I have a light to put in it now but I haven't had time to fix it.

Hi Jamie

I resorted to the crappy fender lamp holder in mine, but I mounted a terminal strip nearby to run the filament wires to (instead of hooking everything up to the tiny holes in the crappy lamp holder). See pic



I also put some insulation between the lamp-holder terminals and the chassis, because everything was quite close.

Cheers
Pete

[big_teee]

Thanks guys for the info.
I notice there is some tube differences between the princeton and the deluxe.
the PR has 4 Preamp tubes, and the DR has 6.
One of the six, is the Norm chan.
The other one is extra stage in the P I., and extra stage in the vibrato chan.
So is the DR a better design with the extra stages than the PR?
T

[JoeM]

Thanks guys for the info.
I notice there is some tube differences between the princeton and the deluxe.
the PR has 4 Preamp tubes, and the DR has 6.
One of the six, is the Norm chan.
The other one is extra stage in the P I., and extra stage in the vibrato chan.
So is the DR a better design with the extra stages than the PR?
T

I don't think the DR is better necessarily. I have both a Princeton and a DRRI, I like them both. I like your idea of a PR with 6l6s, who ever uses both channels anyway on a DR?

[big_teee]

I don't think the DR is better necessarily. I have both a Princeton and a DRRI, I like them both. I like your idea of a PR with 6l6s, who ever uses both channels anyway on a DR?

So do you end up just using the reverb chan?
Like on my Marshall 2204, I always use the Hi gain input.
I never use the low side.
On the PR, it could be built with 5 tubes, instead of 4, if the PI is more efficient with the 2 Stages.
T

[JoeM]

Yeah, I only use the Reverb (Fender calls it Vibrato) channel. I played for years with a Super Reverb and did the same thing. Actually my Princeton is a non reverb model, but stock it had absolutely no balls (you could crank it to 10 and it barely broke up), so I used the half tube for the trem to add an extra gain stage. The circuit looks like a PR just sans reverb and tremolo. Just 2 preamp tubes. Really a nice sounding amp.

Oh, and the baffle was cut for a 12".

[tubeswell]

Yeah my 'PR' has a 12" speaker and a DR spec OT (6k6 Pr Z and bigger iron, which is what the weber 6A14 kits ship with anyhow). My amp breaks up at 7.

The DR is like the 'bigger brother' of the PR (both amps have fixed bias 6V6s, but the DR has a bigger OT @ 6k6 Pr Z and a LTP inverter). But the PR is BF amp at its simplest. With a 12" speaker and a DR OT you won't notice much difference. The plates in mine run at about 430 IIRC (I use JJ6V6S), and if you're using 6L6s with the 12" speaker and the bigger OT it'll sound more like one of the 6L6 BF amps anyhow. With 6L6s, you'll want a 50-80W speaker I guess.

[JoeM]

I too have a DR OT in the Princeton (Magnetic Components Classic Tone), but the speakers I want to use the most with this amp don't clear it, so I may just go back to the stock one. As is it sounds pretty close to my DRRI, and as tubeswell notes, definitely the BF sound.

[big_teee]

Yeah my 'PR' has a 12" speaker and a DR spec OT (6k6 Pr Z and bigger iron, which is what the weber 6A14 kits ship with anyhow). My amp breaks up at 7.

The DR is like the 'bigger brother' of the PR (both amps have fixed bias 6V6s, but the DR has a bigger OT @ 6k6 Pr Z and a LTP inverter). But the PR is BF amp at its simplest. With a 12" speaker and a DR OT you won't notice much difference. The plates in mine run at about 430 IIRC (I use JJ6V6S), and if you're using 6L6s with the 12" speaker and the bigger OT it'll sound more like one of the 6L6 BF amps anyhow. With 6L6s, you'll want a 50-80W speaker I guess.

Sounds good.
I was planning on making it into a head.
I have a 4x12 Cab in the shop and a 1x12 V30 here in the house.
The V30 is rated at 60Watt.
Still thinking it through, what I'm going to do.
I may start by ordering the PR Mojo Chassis, and small parts kit.
That way I could figure out what Iron I could get to fit in it.
Or I may go ahead and buid up the DR with the bigger Iron.
Either way, I would still build a head.
I have the 6l6 amps and really wanted to stay away from the having to buy different 6V6 tubes.
T

[tubeswell]

I forgot to mention that with the DR pre-amp topology, you get a bigger signal swing at the grids on the vibrato channel because there is more gain with 3 stages then the LTP, whereas with the PR there are 3 stages then the cathodyne (and the cathodyne has unity gain, whereas the gain from each triode in the LTP is about 1/2 of what you'd expect from a single triode of the same type - so the LTP has more gain). But you can get more clean headroom by making the cathodyne fixed bias. You cab also re-jig the power rail to get about 400V at the cathodyne node, then use 100k for the plate and cathode resistors, and you get a good swing at the 6L6 grids - I did this with my 6L6 surfin' combo the weekend before last.

[tubeswell]

Well if you haven't tried 6V6s, there's nuthin wrong with JJ6V6S, they're rock solid and they sound good. But don't let that interfere with your 6L6 plan.