Princeton-ish Reverb design - 12AT7's and Sand!

[Joel]

Hello fine people of EL34World!

I've got the bug again...  I don't need another amp y'know?  But I *do* need another build.  So here we are. 

It's predominantly an AA1184 Princeton reverb.  I've re-used the FET-a-Dyne idea I successfully used in my last build (https://el34world.com/Forum/index.php?topic=29299.msg343303#msg343303).   A solid-state Tremolo seemed like a good idea, so I've thrown in one inspired by others on this forum using a pair of LND150's.  These two changes save 3 triode segments.  Nice.  Merlins Transformerless Reverb Driver makes an appearance.  Thanks Merlin!  Saves $80AUD on the iron alone.  I'll be able to afford some McDonalds for dinner!  I've used 12AT7's throughout.  Why?  Because I have soooo many of them.  I used Merlins Load Line Plotter to give what I think will be a good operating point to them all and also provide flexibility to change to most of the common preamp tubes if needed.

Can anyone find any issues or glaring mistakes I may have missed?  Suggestions, comments, queries, and critiques welcomed.  No gripes though. 

[tubenit]

IF you get it built, PLEASE do some soundclips!  This is a very intriguing build and somewhat innovative.


The only critique I would have is using .047 instead of .1 for C24 and C25.


And for V1, I am not a fan of a 12AT7 in that position. It's just a personal preference thing. I don't think that tube is very musical in tone.  I prefer a 5751 or 12AY7 which I think have a better tone. I do use 12AT7's in my amps but just not in V1


I'll be following this thread with some interest.  Thanks for sharing!   With respect, Tubenit

[jbrrrrr]

Following this thread - I'm working on a remodel of a single channel Princeton Reverb-type with LND150 recovery and oscillator stages to free up a few triodes to do some other more interesting things.  I might consider a transformerless-reverb or one of the single tube reverb designs also if I'm not digging how this ends up.

Godspeed!  Build it well and post updates frequently please! 

[pullshocks]

I don't want to hijack this thread, but......JBRRRRR could you post a schematic of your LND150 recovery stage?  Thanks

[jbrrrrr]

I haven't settled on exactly how I want to do mine yet, but here's an example from a Blues Jr. that uses an LND150 for reverb recovery - I might add a source follower to this and tweak the bias a bit but I'll have to do that kind of tuning by ear.  Hope this helps.

I'll post my schematic once I've finished it up in a separate thread for anyone else to mock or find useful.   

[Joel]

IF you get it built, PLEASE do some soundclips!  This is a very intriguing build and somewhat innovative.

The only critique I would have is using .047 instead of .1 for C24 and C25.

And for V1, I am not a fan of a 12AT7 in that position. It's just a personal preference thing. I don't think that tube is very musical in tone.  I prefer a 5751 or 12AY7 which I think have a better tone. I do use 12AT7's in my amps but just not in V1

I'll be following this thread with some interest.  Thanks for sharing!   With respect, Tubenit

You want soundclips of *me* playing?!?  That's like making someone listen to Vogon poetry (and yes, I realise I'm showing my age here.  Fortunately, I identify as 28 years old, so everyone has to treat me as if I am.  So there!). 

Thanks for your feedback.  It's greatly appreciated.  Can you please elaborate on your recommendation for 0.047uF instead of 0.1uF for C24 and C25?  I must admit to simply copying the original and Hoffman's single channel version here. 

5751 is my very favourite tube.  Each of my builds has one in it - replacing a 12AX7 with spectacular results.  Each time I plug on into V1 (when the amp is designed for 12AX7 as V1), the amp is better.  Unfortunately, I don't have many left.  It's worth noting that the AX84 "Clean Preamp" uses a parallel 12AT7 as V1.  My Heretic Woke amp uses "Clean Preamp with added gain" and it's *very* nice.  I'm unsure how a single triode 12AT7 will go, but I think I'm willing to give it a shot, especially since I'm not just subbing it for a 12AX7.  The stage is designed for a 12AT7.  That won't guarantee it sounds good I know.  I can always mod the amp afterwards if it sucks.

[Joel]

I haven't settled on exactly how I want to do mine yet, but here's an example from a Blues Jr. that uses an LND150 for reverb recovery - I might add a source follower to this and tweak the bias a bit but I'll have to do that kind of tuning by ear.  Hope this helps.

I'll post my schematic once I've finished it up in a separate thread for anyone else to mock or find useful.   

Thanks for you input!  Have you seen this: http://www.hawestv.com/amp_projects/amp_solid_tube/fetpreamp_200v1.htm#drain_curves? 

I was also considering using an LND150 as the reverb recovery, but then I'd have 1/2 a triode free.  I could replicate the parallel AX84 Clean Preamp 12AT7 input stage again, but that's designed for DC coupling to the following stage, and I wanted to try a 12AT7 as a stand-alone V1.

[jbrrrrr]

Thanks for you input!  Have you seen this: http://www.hawestv.com/amp_projects/amp_solid_tube/fetpreamp_200v1.htm#drain_curves? 

I was also considering using an LND150 as the reverb recovery, but then I'd have 1/2 a triode free.  I could replicate the parallel AX84 Clean Preamp 12AT7 input stage again, but that's designed for DC coupling to the following stage, and I wanted to try a 12AT7 as a stand-alone V1.

Sorry!  That was just a response to the comment above mine re: my recovery stage - your plans are obviously slightly different.  Any more chat about that side bit can go in a different thread. 

It's kind of fun to think about what to do with free triodes IF you can find a way to be happy with MOSFETs in non-audio-path critical places, or places where tube non-linearity probably isn't being employed much.  Parallel stages, extra cathode followers... that's been occupying my brain for past couple weeks and it's been pretty enjoyable considering it allows taking an old circuit like a PR and giving it a few more possibilities without needing to squeeze any more tubes in there.

[tubenit]

I think with your design a .047 instead of .1 will sound less "woofy" and have a clearer more solid sounding tone.


With respect, Tubenit

[Joel]

I think with your design a .047 instead of .1 will sound less "woofy" and have a clearer more solid sounding tone.

Thanks.  I had reduced the cathode cap on the first two stages from Fenders original 20-ish uF down to 4.7uF for this same reason.  I'll give the 0.047 a try.