Hoffman Princeton Reverb boards with Mallory

[bnwitt]

NOTE:  this thread goes with the other archived thread on Hoffman Boards for Princeton
Reverbs



For those of you wishing to use the Mallory caps, here is a mask that moves the three turrets so the .1uf Mallory caps will fit.  I couldn't post this on the orginal thread as it is an archive now.
Barry

[bnwitt]

Here is the loaded board

[bnwitt]

Here is the wiring layout.

[bnwitt]

By the way, if you're going to use the 20/20/20/40 uf multicap can, make sure you put the 40uf terminal on the very first turret of the power rail where the OT red wire and the wire from the standby switch are connected.

[mick]

Barry,
Maybe a dumb question, but why do you show the bias feed comming fromt the rectifier tube (pin 8).   Is there an advantage to using a dc feed for your bias circuit??

Mick

[bnwitt]

Mick,
I answered your email too and the answer is that is a mistake on the layout. Thanks for catching it.  I will post the new wiring layout.
Barry

[bnwitt]

MResistor brought to my attention that none of the files in the posts above would download.  For some reason the links went to an error page.  I have reloaded each file in each post.  They should download again.  Also, here is the schematic with notes.

[EL34]

I found a wiring mistage on the PDF layout diagram
See the area in the image below with the red box

The wire should go from the top of the .1 cap to the top of the 56K resistor
The 1.5K resistor should be a 1K resistor if you are using the original value from the AA1164 princeton reverb

here's a image file showing the changes

[sluckey]

As you say the resistor value shoud be 1K. But the cap connects to the top of the 1K, not the junction of the 1K and 56K. See the original Fender diagram...

http://www.el34world.com/charts/Schematics/files/fender/princeton_rev_gz34_aa1164.pdf
http://www.el34world.com/charts/Schematics/files/fender/PRINCETON_REVERB_AA1164.pdf

Barry's schematic in reply #6 is wrong. It'll work either way.

[EL34]

Hmm,
This is cathode section of V4b shown in my gif file below

barry's schematic and my CAD drawing layout

I have double check it several times and it still looks right
What am I missing?

[sluckey]

That ain't the original schematic. That's Barry's redrawn schematic and it is in error. Look at the schematic from the library that I posted above. Or look at the clip of the original schematic below. The cap connects directly to the cathode of that tube, not the junction of those resistors.

Barry's layout agrees with the original schematic except that he shows a 1.5K resistor on the layout for Mallory caps. His original layouts correctly show a 1K.

[EL34]

yeah, I had Barry's schematic in front of me

I'll go sort it out again cause I am drawing up a layout drawing for a Hoffman princeton reverb

[sluckey]

Take a look at Barry's layout in reply #2 above. It's correct (I think) and may save you some time doing your style layout drawing.

[EL34]

I already have my layout drawn up
I just had to change that section

Here it is