Brown Princeton vs Tweed Harvard

Ronno25

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Is there anyone out there who owns a vintage example of each of these? I'd really appreciate a description of the difference in sound. I understand the technical differences (higher B+ in Brown Princeton, 12ax7 vs 6at6 preamp, tremolo in Brown Princeton, etc). I've read through many threads comparing the two amps and most people simply say "they're the same but one has tremolo", "one has higher B+", "the same but with different preamp tubes", or just list the technical differences. There aren't many descriptions of any tonal, headroom, or character differences between the two and I'm curious: What are the sound differences? If you put a 6av6 tube (approximately half a 12ax7) in the preamp of a tweed Harvard are you getting the sound of a Brown Princeton sans the tremolo, or is the lower B+ changing the character of the amp a lot? I have a tweed Harvard clone and do get a dirtier sound out of it when I plug in a 6av6 for the 6at6. Am I getting the Brown Princeton sound just by swapping the preamp tube? The Harvard is such a killer amp and I find myself asking how it could get any better than this? But then I see tons of threads praising the Brown Princeton and I wonder, maybe it can?
 

King Fan

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I bet our wise friend @Wally could help out here. FWIW I think the 5F11 is in that lineage, too; you might Google ”5F10, 5F11, 6G2 site:TDPRI.com.”

My only experience comes from playing my 6G2 on a bucking transformer at different B+ values. The difference between approximately Harvard (?305) and 6G2 (nominal 315?) isn’t huge, but as you get upward toward 330, it gets a little cleaner but a little colder — sorta what I've come to expect from increasing B+ in tweed and brown amps. Of course I can’t comment on the V1 question.

FWIW *some* owners of vintage 6G2s say their actual B+ was never as low as 315 even on vintage wall current. OTOH I like mine at that level. Also, if you ever use trem, the trem in these slays…
 

Wally

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The preamp plate voltage is higher in both the 5F11 Vibrolux and the 5F10 Harvard compared to the 6G2. That affects the biasing in the preamp. Otherwise all three amps are very similar in basic sound since the bias vary trem in the Vibrolux and Princeton does not affect the gain in the signal path As does the later opto-isolator trem introducedinthe the BF era.
ime, the Vibrolux and the Princeton yield similar sonics. I have never been around a 5F10 Harvard. Yes, a 6AV6 will yield a hotter signal than the 6AT6.
 

King Fan

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FWIW, here's a thread from a couple years back about the same question.

https://www.tdpri.com/threads/5f10-vs-6g2.1016390/

Doesn't get into the V1 thing much, and has speaker content that isn't directly relevant here, but at a minimum I like Wally's hint there that if you build one with adjustable bias, you can kinda dial in the heat. And if you don't need trem, you can vary that bias over the whole useful range by ear. BTW also, a bucking transformer is a simple, fun build, and super useful for comparing B+ in tweed and brownface, IME.

I'm interested in this cuz I have that nice 6G2, which I love, but I'd love to play a Harvard. Part of that is the dumb fallacy that it'd make ya sound a little like Steve Cropper (as if, duh) but part is just that 6AT6 and the funky 3-hole inputs and the mystique -- and simple curiosity...`
 

peteb

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The preamp plate voltage is higher in both the 5F11 Vibrolux and the 5F10 Harvard compared to the 6G2
The plate voltages on my 63’ 6G2 are far higher than the schematics show for either amp, like slightly over 100 volts over the 6G2 schematic. 245 to 135.

I think the amp has a quick transition from clean to crunch. 6 is clean and 7 can crunch depending on pick attack.

i think the breakup is harsh. The type of breakup someone would never design a pedal to emulate.

I thought the cathodyne PI caused the harsh breakup. Could it be the high plate voltages in the pre amp?
That affects the biasing in the preamp.
let me check my pre amp bias.

ok, the cathodes of v1a and v1b are sitting at 1.7.

I think that is an ok bias.


what are your thoughts on acceptable pre amp bias Wally?
 

Ronno25

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I'm interested in this cuz I have that nice 6G2, which I love, but I'd love to play a Harvard. Part of that is the dumb fallacy that it'd make ya sound a little like Steve Cropper (as if, duh) but part is just that 6AT6 and the funky 3-hole inputs and the mystique -- and simple curiosity...`
I can assure you I sound nothing like Steve Cropper through the Harvard :). I've been playing it through a JBL D130f and it's probably the best sound I've ever had. It actually reminds me in some way of that semi-broken up Keith Richards rhythm tone. I was originally playing the Harvard through a typical 12" Alnico Jensen-like speaker and it sounded mediocre enough compared to my 5e3 that I was regretting building the thing. Amazing how much difference a speaker makes. Also the 5e3 doesn't sound great at all through the D130f.
 

Wally

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Pete, I don’t have a 6G2 at this time. I wish I did because I would like to see the preamp voltages. That 245vdc on the V1 plates is a lot of voltage. We generally don’t see preamp voltages that high until we get into the BF era.????

As for that cathode voltage, that is part of the bias. The Plate voltage is another part.
 

Ronno25

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I just found this from another thread:

"The circuit is near identical. The main difference is a bigger output transformer (125A1A/022640) in the 5F11's - same as a 6G3 Deluxe and Deluxe Reverbs. The 6G2's have the smaller OT (022913/125A10B) - same as Princeton Reverbs"

Edit: After a bit more research it appears the OPT's changed some through the years of manufacture of the Harvard and Tweed Vibrolux when they switched from Triad to Schumacher around 1960. Not sure about the Brown Princeton.
 
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King Fan

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The plate voltages on my 63’ 6G2 are far higher than the schematics show for either amp, like slightly over 100 volts over the 6G2 schematic. 245 to 135.

I think the amp has a quick transition from clean to crunch. 6 is clean and 7 can crunch depending on pick attack.

i think the breakup is harsh. The type of breakup someone would never design a pedal to emulate.

I thought the cathodyne PI caused the harsh breakup. Could it be the high plate voltages in the pre amp?
Pete, I don’t have a 6G2 at this time. I wish I did because I would like to see the preamp voltages. That 245vdc on the V1 plates is a lot of voltage. We generally don’t see preamp voltages that high until we get into the BF era
Interesting. My 6G2 plate voltages are fairly close to schematic. I can't give you exact numbers, but my old notes say within 10%. OTOH, my amp also acts very differently from yours; very *slow* onset of crunch, just rides the lip from like 5 to 8. Likewise, that breakup isn't harsh, tho it can get a bit gnarly above 8. So in answer to your question, I do wonder about your voltages. Note my B+ ran as high as 330V on full wall voltage, but even then the preamp voltages weren't way out, and the breakup was very controlled.

@King Fan, you could run a 5751 in V1 of that 6G2 to clean it up a bit.
Thanks, Wally. I just noticed this morning the 6at6 and 5751 have the same mu, around 70. I bet I still won't sound anything like Steve Cropper, but it'd be a fun easy experiment.
 

peteb

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We generally don’t see preamp voltages that high until we get into the BF era.????
Good point Wally.
AA864 bassman shows 250/1.8
super reverb shows 270/2.1

the 12ax7 spec calls out max plate voltage 300 and max power dissipation of one watt.

the super reverb is still well below 50% of max plate dissipation.
this is a class A gain stage.

I think the idea in fender amps is to keep the pre amp as clean as possible.


OTOH, my amp also acts very differently from yours; very *slow* onset of crunch, just rides the lip from like 5 to 8. Likewise, that breakup isn't harsh, tho it can get a bit gnarly above 8.
Thanks Kingfan. That sounds fairly similar to mine. 5 to 8 versus 6 to 7. There is definitely a tipping point some where around 6 or 7. I really like the sound and volume at 6.5 and I generally feel like Fenders sound the best in the middle range.
 

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I have played all 3, but not comparing them or even at the same time period, so pretty hard to identify much. I will say my impression is they are close enough sounding that speaker selection and cabinet size will probably make more change in tone than anything in the circuit really.
 

King Fan

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@King Fan, you could run a 5751 in V1 of that 6G2 to clean it up a bit.
@King Fan If you do end up trying the 5751 I'd be interested to hear what your impression is.

Hey, Wally, you da man. Thank you. I had a couple GE JAN 5751s in my stash. Bingo -- the amp is even nicer to my ear. It may partly depend on the speaker, since I have a fairly bright crisp ceramic in there now, and missed some of the mellow I got from my older alnico. But altho I still don't sound anything like Steve Cropper, I hear a little of that Stax/Memphis/Otis thing I always hoped I could coax out of my 6G2. :)
 

ballynally2

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@King Fan If you do end up trying the 5751 I'd be interested to hear what your impression is.
My impression is that the 5751s are excellent substitutes for 12ax7 valves in non MV Fender style amps if the amp is set for those. An 12at7 will alter the bias point if everything remains the same. Some like it.
Everytime i replace an 12ax7 with a 5751 it improves the amp. Clearer, more transparant whatever you call it. It has a lower output but that actually improves the way the volume equation and the pot work in non MV amps.
A more gradual onset of crunch and more clean output which i initially didnt expect but makes sense as you use more of the output section.
One caveat, ive never tried nos 12ax7, only used ones (uos). But i do use nos 5751s.Bought a bunch of them when they were cheap about 20 odd years ago.
GE and RCAs mostly.
 




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