Hoffman amp build pictures (princeton reverb)

[wetdog]

Hello, I am starting my second build which is a Princeton Reverb using the Hoffman board. I am following the layout and schematic provided on the website but would really appreciate a picture of the completed innards of the Hoffman Princeton layout. I have installed the turrets and am ready to wire up the busses and connections between the turrets, and a picture of complete Hoffman builds, preferably the Princeton Reverb, would really help with guiding the neatness of my build. Of all the useful info I have gathered on the websites (el34 and Hoffman amps), I haven't come across a picture of a complete Princeton Reverb on a Hoffman board. I attached a picture of my turret board I made using a dowel centering tool and turret setting tool.   

[Madison]

Here ya go.
One I rebuilt.

[stratele52]

Madison ,

 How it sound ? No buzz , hum , parasitic oscillation at any volume ?

[Ed_Chambley]

Here is a link to a thread where I built a princeton.  Photos along the way.
http://www.el34world.com/Forum/index.php?topic=13855.msg130876#msg130876

It is a Hoffman, but it has many little added features.  There is a photo of the loaded board, but keep in mind it is dual bias, so the bias section is duplicated.  This amp took me longer than any amp I have ever made, but I did make everything except for rolling my own caps.

Reading the thread will help mistakes to minimum because I made as many as possible.

[Madison]

Madison ,

 How it sound ? No buzz , hum , parasitic oscillation at any volume ?

No probs.
Sounded fantastic.

[wetdog]

Great! Thanks for the pictures. They will help with starting to lay out my components and wiring. Even though I have started to understand schematics, turning a schematic into a neat wiring layout is another thing. I will post back when I make more progress.

[stratele52]

Madison ,

 How it sound ? No buzz , hum , parasitic oscillation at any volume ?

No probs.
Sounded fantastic.

Great , congrat.

[wetdog]

I have almost finished laying out the busses and wiring turrets together on my board but have a question about the layout.
My understanding is the lower buss wire (the power rail) should extend from the lower left side of the board with the first connection going to pin 1 of V1 and the wire buss continuing to pin 6 of V3.
Question: Is the end of this buss wire at the connection with the 100k resistor going to pin 6 of V3 or does the power rail extend across the bottom of the whole board to (A)?
The layout seems to have the power rail buss wire depicted as a solid horizontal line extending all the way across to (D) the 3 watt 18K resistor.

[sluckey]

My understanding is the lower buss wire (the power rail) should extend from the lower left side of the board with the first connection going to pin 1 of V1 and the wire buss continuing to pin 6 of V3.

That's how it is on the original layout. But then an under board jumper continues on to (D) the 18K/3W.

The layout seems to have the power rail buss wire depicted as a solid horizontal line extending all the way across to (D) the 3 watt 18K resistor.

That's Doug's new and improved layout. It's electrically identical to the original.

I would stick to the layout that you used to drill and install the turrets. There are some slight differences in physical layout. The board in the pic that Madison posted was made using the original layout, not the layout you just posted.

[wetdog]

Brief progress report on my princeton build. I finished weaving the buss wires onto the board and soldering them into place. My next step is to mock up the resistors and capacitors, bending the leads into the turrets, and then soldering them. 

[wetdog]

This is my progress on my second amp. I started with the Hoffman Princeton Reverb board many months ago and have since acquired a drill press and drilled an chassis Al chassis (0.09') (16.5*6.5*2.5).  The dimensions are slightly smaller than a stock PR chassis. There is about 50 holes required of various sizes.     

[TIMBO]

LOOKIN GOOD

[andyfromdenver]

Man, i'm so jealous of guys with an actual garage! (wipes off the table in music studio...).  You seem to have a great attention to detail!  Best wishes with your build!
Your benchmark, Fender's own fantastic creation, which when in perfect order, is superbly quiet :)  you can do it!
Andy

[wetdog]

Thanks for the comments. I have currently shifted from soldering to woodwork, and plan on building a head unit and 12" speaker cabinet. I'm a novice woodworker and am trying to learn dovetails and/or box joints, which is a whole other story:) I attached a few more pics, but this project is slow go due to finances, family, and work. I appreciate any feedback or suggestions!
 
I have 2 questions:
I am using a Deluxe Reverb output transformer (classic tone #40-18038) that has 4 and 8 ohm taps and would like to wire both taps without using an output selector rotary switch. How do I wire the 2 outputs to be separate 4 ohm output and 8 ohm outputs? Specifically, how to I connect the NFB wire to the 2 output jacks? I understand the NFB resistor value will be different for a 4 ohm output and plan on installing a NFB switch (on/off/on).
Also, after getting the board into the chassis, I noticed there is little space between the board and the tube sockets. I am using 1/2" standoffs but am a little worried about the cramped space could cause wiring the board to the sockets to be cramped. I can work with the current spacing but want to avoid unfavorable AC vs. DC wiring or getting components too close. Should I shift board forward ~1/2" toward the potentiometers or does the spacing of the board in the chassis look good?

[Ed_Chambley]

Yea buddy, keep it going.

[Willabe]

Yeah, very, very nice. Very neat and tidy work. Nice tightly, evenly twisted wire pairs on the PT.


             Brad     

[HotBluePlates]

I have 2 questions:
I am using a Deluxe Reverb output transformer (classic tone #40-18038) that has 4 and 8 ohm taps and would like to wire both taps without using an output selector rotary switch. How do I wire the 2 outputs to be separate 4 ohm output and 8 ohm outputs?

You already have 2 speaker jacks. In your pictures, the one on the left has 3 lugs (a Switchcraft type 12A jack), while the one on the right has 2 lugs (a Switchcraft type 11 jack).

- You need 2 type 11 jacks instead of one of each (which is how the original amp was set up).
- The black wire of you output transformer connects to the ground lug of each jack. Run the black wire to one of the jack grounds, then have a jumper wire from it to the other jack's ground. "Ground" will be the lug not connected to the arm which contacts the plug's tip.
- The yellow wire goes to the 4Ω jack's hot (tip) lug.
- The green wire goes to the 8Ω jack's hot (tip) lug.
- The wire to the 2.7kΩ feedback resistor goes to the 8Ω jack's hot (tip) lug.

That's it.

Specifically, how to I connect the NFB wire to the 2 output jacks? I understand the NFB resistor value will be different for a 4 ohm output and plan on installing a NFB switch (on/off/on).

You don't.

If you have only one secondary tap, and it's not the stock value, you'd need to adjust the feedback resistor value to get the stock amount of feedback.

But if you have more than one tap, you only need to connect the feedback resistor to a single tap. That's because there is output voltage present at all taps, all the time. So even if you're only plugged into the 4Ω jack, the 8Ω tap is still sending a voltage back through the feedback resistor.

You can prove this to yourself by looking at a Marshall schematic with switchable output impedances: the feedback resistor is attached to a single tap and is never switched.

[Ed_Chambley]

I missed you were using a Classictone #40-18038 OT.  YOu may be aware of this, but I thought I would mention it.  I have used these in princeton builds 3 times.  Each time the amps would have a large amount of speaker flab when turned up a little.  Initially they all sounded great at low volumes.

One I simply changed the first 2 bypass.  First one was 8uf/50 and the second was 4.7uf/50.  They dude was happy as he likes a full sound with solid bass notes in a practice amp.

The second one reduced all the caps very similar to Tubenit revised values he posts from time to time.  In this one these values removed a lot of the bass and made it a great recording amp. Maybe he may add it to this thread.  He good about sharing.

Just thought I would mention this so when you do fire it up you can be expecting to tweak here and there till you get what you want.

The 3rd one I am currently doing.

[wetdog]

I shelved this project for a few years and had forgotten this thread. I plan on making a head cabinet for the amp and also making an extension cabinet with 1x12 or 2x10. Until I scrounge the funds for new speaker(s) and a set of tubes for my PR, I plan on cannibalizing my 5e3 for any transferable tubes and using the speaker to test the PR.


I was hoping for someone knowledgeable to give some confirmation that things are wired correctly. In particular, I choose to omit the standby switch and wired the cap can directly to the OT and the wiring of the independent 4 and 8 ohm jack (to be used separately, of course:)


   

[sluckey]

Looks fine to me.

[EL34]

One of the documents on the library page under the princeton reverb section is a link to my build

Please read this post first
http://el34world.com/Forum/index.php?topic=19361.0