New Princeton Reverb no tremolo build

[Stevewdewitt]

I am going to build the Hoffman Princeton Reverb with no tremolo using a 7"D x 15"W X 3"H aluminum chassis and need some suggestions about layout. I am going to use a SS rectifier and one tube reverb.

I have used the one tube reverb on 2 amps now and I really like the concept. It sounds fine to my ears and saves a lot of space.

I have attached a photo of my proposed layout. Please comment.

TIA
Steve

[sluckey]

I'll be following your progress.

[tubenit]

I'd love it IF you would please share a schematic for what you are doing?

I've drawn one up that you can edit.  Not sure about the fixed biased in this?  Maybe Sluckey can offer some edits.  Consider this a DRAFT idea
that may contain errors.  I personally would use 4.7uf/1.5k cathode values for both V1-3 and V1-8. It's my preference.  Note that I lowered the.1 coupling cap after the phase invertor to .047.

The SCH file is editable.  Would you please consider editing it to show what you're goal is.

When I am doing an unproven & somewhat "experimental" design,  I like to use paralleled turret boards similar to HiWatt type idea.  Then IF something goes haywire,  I can still use the same board and modify into something different.  The paralleled turret boards aren't "better" they simply are easier to mod into something else in my experience.

Thanks.  With respect, Tubenit

[Stevewdewitt]

here it is
http://el34world.com/Hoffman/files/Hoffman_PrincetonReverb_NoTremolo.pdf

Thanks tubenit!

[tubenit]

Hoffman's schematic/layout uses 4 12A_7's (with an unused triode) and yours is using 3 12A_7's. 

His layout will work fine for you & the Hoffman style layouts are very quiet and well thought out. And he has the fixed bias values worked out for you.

Having said that, I want to draw your attention to something.   The mixing resistor on a typical Fender reverb is 3.3M/10p with a 100k reverb pot vs.  on the one tube reverb where the mixing resistor is typically more like  150k-220k range with a reverb pot of 1M to 2.2M .

So, IF you use the typical 150k-220k one tube reverb mixing resistor, then note that your attentuation in the signal chain is less.  In other words, that 3rd triode gain stage is getting more signal from the previous stage and you will possibly loose some more headroom (which is sometimes already a complaint on Princeton Reverbs).  You may wish to stay with the typical Fender 3.3M/10p mixing resistor when using the 1 tube reverb?  I have never tried that myself so I am not certain how that will sound?

One way to lessen mud and too much a woofy tone is to lower the 22uf cathode caps to 4.7uf & lower the .1 post phase invertor caps to .047. 

Just a thought for you to ponder.     With respect, Tubenit

[Stevewdewitt]

The mixing resistor on a typical Fender reverb is 3.3M/10p with a 100k reverb pot vs.  on the one tube reverb where the mixing resistor is typically more like  150k-220k range with a reverb pot of 1M to 2.2M .

So, IF you use the typical 150k-220k one tube reverb mixing resistor, then note that your attentuation in the signal chain is less.  In other words, that 3rd triode gain stage is getting more signal from the previous stage and you will possibly loose some more headroom (which is sometimes already a complaint on Princeton Reverbs).  You may wish to stay with the typical Fender 3.3M/10p mixing resistor when using the 1 tube reverb?  I have never tried that myself so I am not certain how that will sound?

One way to lessen mud and too much a woofy tone is to lower the 22uf cathode caps to 4.7uf & lower the .1 post phase invertor caps to .047. 

Just a thought for you to ponder.     With respect, Tubenit

Thanks for that.

I would have room for the standard reverb circuit.

The photo shows the trans and sockets with tube recto and standard reverb tube compliment.

the inside with pots, switch, jacks, and board laid inside for reference


Steve

[Stevewdewitt]

Preamp and reverb section to start with. I am back and forth on the one tube reverb. I am going to give it a shot.

[tubenit]

That looks good to me.  I think it will work.

with respect, Tubenit

[Stevewdewitt]

It has been a while since I posted anything on this build. I have done the fabrication work on the blank chassis today. I forget how much I like doing this kind of work.

[Stevewdewitt]

A few more pics

[Stevewdewitt]

I am going to add a master volume to this build. I was thinking PPIMV. I have attached a schematic of the original power section with a suggested MV option. The MV change is in the black box on the left side of the schematic

[Stevewdewitt]

the board is wired. I added the extra caps for the MV and wire.

[Stevewdewitt]

Question: If the cathode and plate leads from V1a go over the power rail how much if any noise should I expect?

V1 is on the front of the amp near the input and I used V1b as the input half of that tube. In the picture attached I am concerned about noise.

The cathode and plate leads of V1a go over the power rail.

Probably the last time I use orange drops. They are huge.

Thanks very much,
Steve

[sluckey]

Question: If the cathode and plate leads from V1a go over the power rail how much if any noise should I expect?

There should be zero noise. The B+ rail at that point should be just as noise free as the ground rail.

I would be concerned about those 100K plate resistors crossing over that ground rail though. Don't want an accidental short there!. I'd probably put spaghetti tubing on those resistor leads.

I gave up on those huge orange drops for that same reason. Ever notice how neat Hoffman's layout drawings look? That's because his layouts are done with the intent of using his small xicon chicklet caps.

[Stevewdewitt]

I have finished it without the master volume. I had a bunch of trouble with the MV. It was noisy and distorted. After taking out the MV it sounds really good. It is really quiet. Breaks up real nice. I have a 5Y3 in the rectifier.

Happy to be mostly done. A couple of pics.

The MV I used is also attached. The arrows are pointing to the spot where I put it just after C24 and C25 and before R47 and R48. I do plan to put the MV back in at some point. Any suggestions are welcomed.

thanks,
Steve

[Stevewdewitt]

I have added the MV from Rob Robinette’s 5e3 mods to my PR. It does work but I am not crazy about it. It doesn’t turn the volume off when all the way down. There isn’t much sweep in the 1MA pot. Anything past 9:00 seems to be full volume.

Anyone have any luck with this MV?
https://robrobinette.com/5e3_Modifications.htm#Add_Master_Volume

Thanks,
Steve

[sluckey]

This is the MV I prefer. The dual 250KA pot replaces the 220K grid resistors. The safety resistor value is not too critical. 2.2M is more commonly used. Don't know why Rob chose 1.8M unless he was just trying to use up that less common value.

[Stevewdewitt]

Thanks sluckey! I will give this a try some time next week. In the mean time, I did get the current MV working much better. I had it wired incorrectly.

I still don't like the MV much. Seems like a tone sucker to my ears.

Otherwise I am really happy with the results of the build. Very quiet. Great tone. It is going to be a gift to my son. I will of course "tweak" it for a while to get it just right before I give it to him.

Thanks to everyone on this forum!

Steve

[SILVERGUN]

I still don't like the MV much. Seems like a tone sucker to my ears.

Try putting bright caps across the pots like: