Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Hoffman Turret and Eyelet Boards => Topic started by: EL34 on July 31, 2014, 10:47:14 am
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The layout Diagram, Schematic and BOM and other build information can be found on the library page here
http://el34world.com/schematics.htm (http://el34world.com/schematics.htm)
Layout and Schematic
http://el34world.com/Hoffman/files/Hoffman_PrincetonReverb.pdf (http://el34world.com/Hoffman/files/Hoffman_PrincetonReverb.pdf)
BOM - Parts list
http://el34world.com/Hoffman/files/Hoffman_PrincetonReverb_BOM.pdf (http://el34world.com/Hoffman/files/Hoffman_PrincetonReverb_BOM.pdf)
Hoffman Board install instructions (http://el34world.com/Hoffman/instructions.htm)
Build page link - http://el34world.com/Hoffman/Princeton_Reverb_Board_Build.htm (http://el34world.com/Hoffman/Princeton_Reverb_Board_Build.htm)
Hoffman Turret Boards are on this page
http://hoffmanamps.com/MyStore/catalog/TurretBoard.htm (http://hoffmanamps.com/MyStore/catalog/TurretBoard.htm)
Hoffman amps Public parts list page is here
http://hoffmanamps.com/MyStore/catalog/PartsListIndex.htm (http://hoffmanamps.com/MyStore/catalog/PartsListIndex.htm)
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I discovered that my Original board was too long for the repro Princeton reverb chassis
I removed the two 100 ohm resistors from the right end of the board and the board fit perfectly into the chassis
The 100 ohm resistors can be installed on the back of the Fender lamp assembly just like in vintage Fenders
I made detailed notes as I did this build
The new Layout, Schematic and BOM has been uploaded to the library page
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Here's some videos of the Hoffman Princeton reverb in action
I did not have a Princeton Reverb cabinet with a 10 inch speaker
I used my 4 x 12 Marshall cabinet with vintage 30's
The cabinet was set to 8 ohms stereo, so only 1/2 of the cabinet was used
http://youtu.be/JdVN5TdOk1k (http://youtu.be/JdVN5TdOk1k)
http://youtu.be/0ShPbbuZs18 (http://youtu.be/0ShPbbuZs18?list=PLVvDFekIYJjflOUPVAV9ENuznt6IgBF4_)
http://youtu.be/TKV2Z4ievOU (http://youtu.be/TKV2Z4ievOU?list=PLVvDFekIYJjflOUPVAV9ENuznt6IgBF4_)
http://youtu.be/IiZzRmvTbco (http://youtu.be/IiZzRmvTbco)
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That's a fine sounding amp! Good player drivin it too!
Bias trem has plenty of swamp to it.
Brad :bravo1:
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The trem could probably be deepened.
The new owner can decide if he needs more trem or not.
Anyone have a mod already worked out for that?
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Doug,
I've got the board and chassis assembled, but I have a couple questions before I fire it up. Am I correct that pin 6 of the phase inverter connects to D not C?
One end of the bass pot does not connect to anything in the layout diagrams, but appears connected in the wiring schematic. Does it have to be connected in order to function as a rheostat?
The schematic seems to show shielded cable being used to connect the reverb (send/return). The RCA cables I was planning to use were salvaged from the reverb of a a Fender Frontman. Will they work?
Do you recommend insulating the input jack(s) from the chassis with the fiber washers, or is that overkill?
And finally: Bias. Apparently the Princeton was fixed bias and you've modified it to be adjustable. For those of us with a limited concept of bias, where should we set it a.) to start with, and b.) why would we want to ever change it from that?
Thanks.
-MAX-
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Am I correct that pin 6 of the phase inverter connects to D not C?
D is correct, Nothing connects to C except a filter cap
The layout diagram shows that C is just a middle point between two filter caps
One end of the bass pot does not connect to anything in the layout diagrams, but appears connected in the wiring schematic. Does it have to be connected in order to function as a rheostat?
It is used as a variable resistor. The top lug connects to nothing or you can connect the top lug and the wiper together. It is the same thing either way
The schematic seems to show shielded cable being used to connect the reverb (send/return). The RCA cables I was planning to use were salvaged from the reverb of a a Fender Frontman. Will they work?
I don't know what you have but reverb cables need to be shielded cables
Do you recommend insulating the input jack(s) from the chassis with the fiber washers, or is that overkill?
No need to do that. The input jack is grounded via the buss that connect all the pots to the chassis so it would not do anything isolating the metal jack
And finally: Bias. Apparently the Princeton was fixed bias and you've modified it to be adjustable. For those of us with a limited concept of bias, where should we set it a.) to start with, and b.) why would we want to ever change it from that?
They both are fixed bias
A stock princeton reverb is Fixed bias
Mine is Fixed adjustable bias
There is a document right above all the hoffman boards on the library page
http://el34world.com/Hoffman/instructions.htm (http://el34world.com/Hoffman/instructions.htm)
Step 16 and 17 tell you how to fire up the amp for the first time
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I'll split off any troubleshooting post into new post and post the links here
See the post below
http://el34world.com/Forum/index.php?topic=17807.0 (http://el34world.com/Forum/index.php?topic=17807.0)
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I uploaded a new PDF file
The power supply page now shows 40x20x20x20 for the filter caps
http://el34world.com/Hoffman/files/Hoffman_PrincetonReverb.pdf (http://el34world.com/Hoffman/files/Hoffman_PrincetonReverb.pdf)
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Here's an example of a successful build by one of our forum members
http://el34world.com/Forum/index.php?topic=19006.0 (http://el34world.com/Forum/index.php?topic=19006.0)
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A couple videos of Mike's PR using my PR turret board