12DW7 in Princeton Reverb PI...

[dang!]

"do any other parts of the circuit need to be changed to accomodate the difference"

that's what this whole thread is about...just read the earlier posts.

fyi/ after going through all the mods i listed above for the 12dw7, i've reverted my 71 PR to stock with the exception of a bias pot and a new speaker. happy with it again. it is what it is

sorry if my question seems redundant.

my concern, as was yours in your initial post, was if 12au7 in v4 is in any detrimental to the amp, or if anything else needed to be changed to accomdate this different tube. there were some suggestions about possibly changing resistors. unfortunately, i'm a gtrst but not an engineer, so that part was over my head. i'm asking if those changes are necessary for the safety/well-being of the amp when using 12au7/12dw7 reverse in v4 for pi?

my experience, like you initially wrote, is that the pi sounds better with 12au7 than the 12ax7. since you've reversed the mods, is it possible for you to say how the bias pot affects your sound now? does it give you something similar to the sound of the 12au7 that you liked? also, which spkr do u like now?

thanks for your help

i found a reverse 12dw7 so i wouldn't have to mod the amp. right now i like the sound with 12au7 in v4, but would like to have the vibrato back too.

[tubeswell]

Hi dang, JJ makes the ECC823, go and see one of their agents near where you are. As for a 12AU7 in V4, that will make the PI sound good, but you will lose out on the trem, as the LFO stage ideally needs triode with an amplification factor of around something like 29 minimum IIRC, and a 12AU7 only has an amplification factor of 19 (hence why some guys use a 12DW7)

[dang!]

Hi dang, JJ makes the ECC823, go and see one of their agents near where you are. As for a 12AU7 in V4, that will make the PI sound good, but you will lose out on the trem, as the LFO stage ideally needs triode with an amplification factor of around something like 29 minimum IIRC, and a 12AU7 only has an amplification factor of 19 (hence why some guys use a 12DW7)

yes i know about the trem, so i just bought a ecc823 on ebay. this way i won't need to mod the tube socket, and will still have trem. my only concern is: are any other changes needed in the amp to accomodate using the 12au7 side in the pi? there was mention of changing resistors, but it was not clear to me from reading those posts if changing resistors was necessary or optional. is the increased current of a 12au7 a problem? i just don't want to damage the other components in the amp.

the sound seems a bit cleaner, sweeter, less raspy with the 12au7 to me. is that other folks' experience?

do u use this yourself?

thanks!

[MWJB]

There are no components that NEED changing to accomodate a 12AU7 or 12DW7 in a Princeton PI. the 12AU7 does draw more plate current than 12AX7, IF you were especially concerned you could measure the voltage drop across the plate resistors, square it, then divide by resistor value in ohms to ensure that you were not running them over dissipation. The half watt, carbon comp, plate resistors in old Fender are pretty bullet proof though, plenty off guys have run 12AU7 in long tail PIs at higher dissipations than you'll find in a Princeton, with very few issues.

[dang!]

There are no components that NEED changing to accomodate a 12AU7 or 12DW7 in a Princeton PI. the 12AU7 does draw more plate current than 12AX7, IF you were especially concerned you could measure the voltage drop across the plate resistors, square it, then divide by resistor value in ohms to ensure that you were not running them over dissipation. The half watt, carbon comp, plate resistors in old Fender are pretty bullet proof though, plenty off guys have run 12AU7 in long tail PIs at higher dissipations than you'll find in a Princeton, with very few issues.

thanks very much for your reply! i'll experiment with it more now that i know it's safe.

anybody here tried the 12au7 or 12dw7 in v4 of a princeton? i'm interested in hearing other perspectives...

thanks again for sharing your expertise... (especially considering that i'm rather electronically challenged!)

[lookah]

dang! read this thread from the beginning. i spent a considerable amount of time looking into this and eventually posted my results with a giant picture, graphs and some explanation with all the mods i did.

12DW7 in Princeton Reverb PI...

and prior to my posting there is some info from other folks here too.

ultimately, although the bass was a bit clearer, the amp didn't sound all that much better cranked and it wasn't quite as sweet at lower volumes. plus the tremolo seemed to lose a bit of mojo even after i'd adjusted resistors to make it stronger.

as i said earlier, i recently reverted back to stock and concluded that the princeton is a great for what it is. the mods folks do to the PR basically just seem to lead to the design of a deluxe reverb. prob the best thing you can do is find a speaker you like for it. i currently have a celestion g10 which sounds great. i've also tried a eminence copperhead which is a bit more "american". also good. the stock oxford speaker sounds real nice and vintage up until 3.5 or 4 on the volume and then farts out. i recorded a cd recently at a studio with a silverface PR that had a emi rajun cajun speaker and it sounded fantastic. might also want to consider a wgs ceramic 10" or jensen neo 10". and weber makes a great 10" too.

as far as the bias pot goes, that has nothing to do with the 12dw7 mod. you can google that subject and find heaps of info.

i should add that i too am namely a guitar player and only started modding about 3 years ago after dealing with nyc amp techs got tiresome. i've fussed around with 4 different amps so far and, other than speaker changes, have basically always ended up with stock circuits. which isn't to say that i regret modding them. it's fun and i've learned a lot about how to get the sounds i want from an amp. good luck...

[dang!]

thanks very much to lookah, tubeswell, and mwjb for your replies.

dang! read this thread from the beginning. i spent a considerable amount of time looking into this and eventually posted my results with a giant picture, graphs and some explanation with all the mods i did.

12DW7 in Princeton Reverb PI...

and prior to my posting there is some info from other folks here too.

ultimately, although the bass was a bit clearer, the amp didn't sound all that much better cranked and it wasn't quite as sweet at lower volumes. plus the tremolo seemed to lose a bit of mojo even after i'd adjusted resistors to make it stronger.

as i said earlier, i recently reverted back to stock and concluded that the princeton is a great for what it is. the mods folks do to the PR basically just seem to lead to the design of a deluxe reverb. prob the best thing you can do is find a speaker you like for it. i currently have a celestion g10 which sounds great. i've also tried a eminence copperhead which is a bit more "american". also good. the stock oxford speaker sounds real nice and vintage up until 3.5 or 4 on the volume and then farts out. i recorded a cd recently at a studio with a silverface PR that had a emi rajun cajun speaker and it sounded fantastic. might also want to consider a wgs ceramic 10" or jensen neo 10". and weber makes a great 10" too.

as far as the bias pot goes, that has nothing to do with the 12dw7 mod. you can google that subject and find heaps of info.

i should add that i too am namely a guitar player and only started modding about 3 years ago after dealing with nyc amp techs got tiresome. i've fussed around with 4 different amps so far and, other than speaker changes, have basically always ended up with stock circuits. which isn't to say that i regret modding them. it's fun and i've learned a lot about how to get the sounds i want from an amp. good luck...

actually, i did read the entire thread, more than once. and, i appreciate the fact that lookah, tubeswell, and mwjb put time/effort into replying, so thanks again to all of you.

my question was basically a simple "yes/no": is the reverse 12dw7 a safe, drop-in replacement or not? the answer to that question was still a bit vague. as i stated earlier, i don't know anything about changing resistors etc. this is why i don't go poking around the inside of my amps with a soldering iron. i realize that i unfortunately don't have the knowledge that appears to be the norm here. and i certainly don't want to annoy posters with my lack of knowledge. thanks mwjb for your concise reply.

lookah, like you, i also find dealing with amp techs tiresome, which is why i was asking for help here. i see mwjb says the reverse 12dw7 is a safe drop-in replacement, so i'll try it for a while; if it doesn't do what i need, i'll move on, because i'd rather practice than solder. you may think that i didn't read the post adequately. i re-read it several x's. but since you posted that you did several changes to your amp (including the stokes mod, which from what i read lately, is no longer considered as helpful as initially believed by many) the simple answer i'd been seeking was not clear, at least to me.

also, i understand that the bias pot "has nothing to do with the 12dw7 mod". i was just asking for your perspective on how you feel it affects your sound.

your info on spkrs was very helpful, as was your idea that the amp is what it is. it was very interesting to read that you've wound up usually going back to having your amps more or less stock. i for one, am not looking to turn my pr into a deluxe. but i grew up on a '69 sfpr that i remember as sounding a bit different ie more headroom, smoother distortion. i'm chasing that sound in whatever simple ways i can without going too deep into re-configuring the amp circuit.

i again thank you all for sharing your knowledge and taking your time to reply to a total newb.

best wishes,
dang