Princeton Reverb

[purpletele]

The next scheduled project I have is a standard Princeton Reverb.  This is my reverb circuit learning phase.

I have a couple of question's, one  regarding the Hoffman Bias Tap as it relates to the TP25 transformer, and the other about the Transformer and Rectifier.

The TP 25 has a Red/Green 50V Bias tap.  David Allen notes that that wire should not be used for a Princeton Reverb (Classic Fender only I assume),

However Hoffman's circuit is designed for a Bias Tap.


1. Should I utilize the bias tap and then reduce the 100K 3Watt Bias Tap Resistor to 470?

2. Or should I tuck the bias tap away and proceed as designed?

3. The TP25 has a note to Not use 5U4G rectifier.  I assume I would drop to a GZ34 or a SS Rectifers Cap, correct.

4. It was recommended to use a choke and a SS rectifier.  I haven't used a SS Tube plug, is there a recommended unit for this amp?

Thank you


The heater voltages at this stage are as follows:

V6 = 6.68 V
V5 = 6.69 V
V4 = 6.66 V
V3 = 6.66 V
V2 = 6.62 V
V1 = 6.62 V

I like these readings much better than the AB763 Science Project.

[sluckey]

Hoffman's circuit is not designed for a bias tap. Just tape off that bias tap wire on your PT and tuck it away. Hoffman uses the high voltage winding for his bias 'tap'. Just run a wire from pin 6 of the rectifier socket to the board just as Hoffman shows. You must use a 100K bias range resistor.

Just follow Hoffman's layout exactly and you will be successful. You will find that this amp has a lot of similarities with Hoffman's single channel AB763. I would use the GZ34 from that possessed amp. Hoffman sells a SS plugin rectifier but I really recommend the GZ34.

Look at the build page for Hoffman's PR. Make your amp look just like his.

PS... Just looked at your chassis. You are already started down a bad rabbit hole with your grounding. Put that black wire from your reverb transformer where it belongs. It has no business being connected to a speaker jack. Look at Hoffman's PR build page. Lots of good pics showing how to do this stuff right.

[purpletele]

Hoffman's circuit is not designed for a bias tap. Just tape off that bias tap wire on your PT and tuck it away. Hoffman uses the high voltage winding for his bias 'tap'. Just run a wire from pin 6 of the rectifier socket to the board just as Hoffman shows. You must use a 100K bias range resistor.

Just follow Hoffman's layout exactly and you will be successful. You will find that this amp has a lot of similarities with Hoffman's single channel AB763. I would use the GZ34 from that possessed amp. Hoffman sells a SS plugin rectifier but I really recommend the GZ34.

Look at the build page for Hoffman's PR. Make your amp look just like his.

PS... Just looked at your chassis. You are already started down a bad rabbit hole with your grounding. Put that black wire from your reverb transformer where it belongs. It has no business being connected to a speaker jack. Look at Hoffman's PR build page. Lots of good pics showing how to do this stuff right.

It's all about grounding and I want to get it right, thanks!

[purpletele]

This amp went really smooth.  Here are a few photos.

I made a quick sound test as well.  I have a little hum issue that I have to work out, you can hear it at the beginning of the sound audio.  It's not bad, I bet its just wires that can me manipulated.

The amp sounds just as I had imagined.  Very pleased with the results so far.

[sluckey]

That looks much better than the other amp! Those Xicon caps look good on the Hoffman board. Did you know that most of Hoffman's boards were designed for Xicons? Orange drops are just too big to fit comfortably.

That hum may just be picked up by the guitar. Could be fluorescent lights? Does the buzz go away with guitar cable unplugged from the amp? With the lights off?

[purpletele]

That looks much better than the other amp! Those Xicon caps look good on the Hoffman board. Did you know that most of Hoffman's boards were designed for Xicons? Orange drops are just too big to fit comfortably.

That hum may just be picked up by the guitar. Could be fluorescent lights? Does the buzz go away with guitar cable unplugged from the amp? With the lights off?

The hum is constant in different locations of my house.  It might be a tube selection, I have JJ 6 v 6's and JJ preamps.  Also I left my control wires long based on my troubleshooting issues on the Deluxe, so those are sitting near the B+ leads and may cause some noise.

Question, I have some reverb cables from Antique Electronics, red and white tips with a sealed dual cable.  Not sure if that is a shielded cable, I would assume so, but it may not be.

The Deluxe is make a comeback,  new caps to replace the goofy orange caps.  Still issues but getting closer.

I have determined that my audio probe is not working correctly, I got the same results on the Princeton.  I loose signal at V-1.  This test is just signal running through, no power.

I have a photo of my probe with a 100K resister in series with a .01 400V Cap.  The 100K resister has a parallel tail that is a 10K resistor and it ties to the ground sleeve. 

Any ideas and suggestions on the probe would be well received.  I just plan on taking the resistors out at this time, that is how it was originally. 

Thanks,

BV

[mresistor]

I built mine like Hoffman diagrams and discusses.. it works well.. I made mine in a electrical jiffy box.. i use a Champ Amp as the listening amp.





 This a visual layout of how the components would look as you go from probe tip to the listening amplifier.
I have drawn it this way because you probably could install the blocking cap and the trim pot in a small metal box and not use a dedicated listening amp.
The signal probe would go to the metal box and then the metal box would go to a listening amplifier by way of a two conductor shielded cable.
You could use one of the small aluminum pedal boxes that I sell on my web site.
It's about the size of an old MXR pedal.
The pot needs to be grounded to the same surface that the alligator clip grounds to.
The cable leaving the metal box going to the listening amp needs to be a two conductor shielded cable.

[bnwitt]

The amp sound great!

Here is a link to an audio probe diy:

http://billmaudio.com/wp/?page_id=1254

[mresistor]

The amp sound great!

+1

[sluckey]

Tremolo sounded very subtle. You should be able to get a very strong tremolo effect with intensity turned up.

[tubenit]

Great looking amp!  Minus the buzz, it sounds excellent.  Thanks for sharing!

With respect, Tubenit

[tubeswell]

The buzz could possibly be partly lead dress, but more likely to be grounding I'd say. Its quite tricky to get rid of ground loop hum if you're relying on a cap can for filtering, especially in an amp with reverb. There are multiple stages with different ground return currents (including the reverb recovery stage, which is quite sensitive to noise because of its high S:N ratio). Read Merlin Blencowe's chapter on grounding thoroughly - you may get a few ideas there.

[purpletele]

Tremolo sounded very subtle. You should be able to get a very strong tremolo effect with intensity turned up.

The tremolo seems weak.  That is on my list to check out.

Otherwise not bad

[sluckey]

Could just need a bias tweak.

[purpletele]

I built mine like Hoffman diagrams and discusses.. it works well.. I made mine in a electrical jiffy box.. i use a Champ Amp as the listening amp.





 This a visual layout of how the components would look as you go from probe tip to the listening amplifier.
I have drawn it this way because you probably could install the blocking cap and the trim pot in a small metal box and not use a dedicated listening amp.
The signal probe would go to the metal box and then the metal box would go to a listening amplifier by way of a two conductor shielded cable.
You could use one of the small aluminum pedal boxes that I sell on my web site.
It's about the size of an old MXR pedal.
The pot needs to be grounded to the same surface that the alligator clip grounds to.
The cable leaving the metal box going to the listening amp needs to be a two conductor shielded cable.

This looks interesting. 

Question:

What is the address of your website.
Do you use the Pot to make the Cap more or less sensitive?
How do you avoid using a listening Amp?

I am running signal through the amp without power on.  Please tell me otherwise.

Thanks for the ideas and design.

[purpletele]

The amp sound great!

Here is a link to an audio probe diy:

http://billmaudio.com/wp/?page_id=1254

Barry, I had that set up and upgraded to the resistor mod.  I am going to try it as BillM has it designed.

Thanks,

BV

[2deaf]

Question, I have some reverb cables from Antique Electronics, red and white tips with a sealed dual cable.  Not sure if that is a shielded cable, I would assume so, but it may not be.

Those are shielded cables.  Does the hum get worse if you turn up the reverb?

[purpletele]

Question, I have some reverb cables from Antique Electronics, red and white tips with a sealed dual cable.  Not sure if that is a shielded cable, I would assume so, but it may not be.

Those are shielded cables.  Does the hum get worse if you turn up the reverb?

Indeed, the noise gets louder when the reverb is turned up.

[sluckey]

I am running signal through the amp without power on.  Please tell me otherwise.

Think about this for a microsecond...

Time's up. Clue. Do you need the power on for your guitar signal to run through the amp and be heard?

[purpletele]

I am running signal through the amp without power on.  Please tell me otherwise.

Think about this for a microsecond...

Time's up. Clue. Do you need the power on for your guitar signal to run through the amp and be heard?

Well I answered my own question.  You were correct on the operator procedures.  I think I found my lost signal at the top of a 470K resistor that heads to the middle of the reverb pot.

I have to resume later.  Glad to get over that hump. 

[sluckey]

I think I found my lost signal at the top of a 470K resistor that heads to the middle of the reverb pot.

That may just be a missing or faulty under-board jumper.

[purpletele]

I have my standard Princeton Reverb working quite well.

I have the amp very quiet according to colleagues, but it still seems like it has a just a tad to much hum at idle.  I will be working on that, it is very nice and I am trying for very very nice.

The question I have is how can I get a little more hump in the thump of the intensity.  It is working quite well, but I am told that the intensity should be like a a loud heart beat or metronome. 

Can anyone make a recommendation for a stronger intensity?  There is always a possibility that I don't have something wired correctly, but the speed and intensity are working fine, the intensity is just a little weak.

That is sounding really nice, I am very pleased.

BV

[tubenit]

Have you looked in ARCHIVES under tremolo mods to see if there is something useful to you in this regard?

http://el34world.com/Forum/index.php?topic=604.0

With respect,  Tubenit

[purpletele]

Have you looked in ARCHIVES under tremolo mods to see if there is something useful to you in this regard?

http://el34world.com/Forum/index.php?topic=604.0

With respect,  Tubenit

I have not.  Good call

Thank you

[purpletele]

Princeton Reverb Update:

Running on all cylinders, very quiet after a few minor grounding changes.

This circuit/amp sounds fantastic!  Thanks to all that worked on the original re-design and Tremolo upgrade.

I will post a video to get an opinion as to whether I got the amp to be as quiet as possible. 

Very pleased with this amp and it's tone in the 112 cabinet.

[MFowler]

Very nice and a great circuit for sure.


Mark

[tubenit]

You did a great job with it!  Thanks for sharing your success with us!

 

With respect, Tubenit

[mresistor]

What is the address of your website.
Do you use the Pot to make the Cap more or less sensitive?
How do you avoid using a listening Amp?

this should answer the questions about the listening amp tool..     scroll to the bottom of the page          your amp looks nice .. 
I used an old japanese battery powered transistor radio as a signal to inject into the amp being probed.  A signal generator 1Khz would probably be better.

http://el34world.com/Hoffman/tools.htm

[purpletele]

What is the address of your website.
Do you use the Pot to make the Cap more or less sensitive?
How do you avoid using a listening Amp?

this should answer the questions about the listening amp tool..     scroll to the bottom of the page          your amp looks nice .. 
I used an old japanese battery powered transistor radio as a signal to inject into the amp being probed.  A signal generator 1Khz would probably be better.

http://el34world.com/Hoffman/tools.htm

That looks like a great tool!

Thanks for the info!

[purpletele]

Here some links to the demo's I made of the Hoffman Princeton Reverb.

What a great sounding amp! 



http://www.youtube.com/watch?v=pCbLE6jcEzY

http://www.youtube.com/watch?v=hk5kBvwKjuw

https://www.youtube.com/watch?v=fic5Qud_bqI

[purpletele]

Here some links to the demo's I made of the Hoffman Princeton Reverb.

What a great sounding amp! 



http://www.youtube.com/watch?v=pCbLE6jcEzY

http://www.youtube.com/watch?v=hk5kBvwKjuw

http://www.youtube.com/watch?v=fic5Qud_bqI

Here is a voltage chart for the two Princeton Reverb amps that I am completing for anyone that needs that info.

[purpletele]

Advice on Tremolo Thumping

I'm getting a thumping from the tremolo bleeding through as I increase the speed control.  It stops when I max out.

Does that sound like a familiar symptom? 

When chopsticking I can get the right wiper on the speed knob to stop making the noise.  I re-flowed the connections without any change.

Wondering if I should change the Pot?

any suggestions?

BV

[sluckey]

See if tweaking the bias pot will stop the thumping.

[purpletele]

See if tweaking the bias pot will stop the thumping.

I'll give it a whirl, thanks

[pdf64]

Is the thumping issue only at high trem intensity settings, or does it occur even with the trem intensity at min?

[purpletele]

Is the thumping issue only at high trem intensity settings, or does it occur even with the trem intensity at min?

It's interactive with the Intensity knob.

If both knobs are dimed then there is a heavy thump and sometimes a weird squeal.

If the Intensity is set on say 8, then the thumping occurs when the speed approaches 10

Don't know if that makes sense, but it is a finicky problem.

[pdf64]

There was mention made previously of mods to increase trem intensity; were any done?

[purpletele]

There was mention made previously of mods to increase trem intensity; were any done?

Good point, I have not modified anything on the tremolo circuit on this amp. I did on another Princeton and Deluxe. I considered trying to see if that would help.

Thanks,

BV

[pdf64]

For me, the most likely suspect then is a bad power supply cap (bias or HT), or related connection. Is it a can cap, if so are its 0V common tabs properly soldered to the chassis using a 'big bertha' iron?
Tack a suitable cap (eg 4.7 - 10uF 450V) across each each in turn; if no improvement then move on to the next.

[purpletele]

For me, the most likely suspect then is a bad power supply cap (bias or HT), or related connection. Is it a can cap, if so are its 0V common tabs properly soldered to the chassis using a 'big bertha' iron?
Tack a suitable cap (eg 4.7 - 10uF 450V) across each each in turn; if no improvement then move on to the next.

I do not have anything soldered to the chassis, and it is a steel chassis.  I have the ground for the Cap Can going to the main ground which is bolted to the chassis.


I'll try the bleeder cap method as described.


Thanks,

BV

[dennyg]

For stronger tremolo, replace the 1M res at the junction of the 220K and plate.  Can't tell you why it works but was recommended to me and does improve the depth.  Sorry if this already suggested - i didn't read the entire post in detail.