Coming Soon
- Thread starter idsnowdog
- Start date
idsnowdog
Imperator of Indignation
I followed the Hoffman schematic https://el34world.com/schematics.htm#Hoffman_5F2A_Princeton
idsnowdog
Imperator of Indignation
It can be found on the wayback machine. Otherwise it is gone.
marcello252
Well-known member
Nice project, what trannies have you used?
idsnowdog
Imperator of Indignation
The pictures are what it started as and I have no evidence it ever worked in original condition so I gutted it. It had two 6V6s, a 6SN7, and 5U4 tubes. It has a Merit A-2904 transformer, Merit P-3151 transformer, and Merit C-2990 choke. I removed the choke because it was underneath the amp and it took up too much space and was deeper than the chassis. If it's noisy there's enough room for it up top after moving the output transformer and tube sockets around. There were some questions about whether the transformers were big enough to support two 6V6s so I decided to build a SE Princeton and change the 6SN7 to a 12AX7 since 6SN7s are pretty low gain and 6SL7s are expensive and prone to microphonics.
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idsnowdog
Imperator of Indignation
It doesn't take long to build the board. I can build a board in a day as long as I have the parts on hand. It takes much longer if you have to wait for parts. I used the layout from Hoffman amps but built my turret board. It's pretty much paint by numbers.
https://el34world.com/Hoffman/files/Hoffman_5F2A.pdf
idsnowdog
Imperator of Indignation
Coming Soon Pt.2 and Pt.3.
The chassis on top of the combo is a Fender Harvard clone The guy I bought it from said it was a Harvard and was about 75% complete before he quit working on it. However, the board he built was some kind of Deluxe variant that shared no similarity other than a 6AT6 in the V1 position. It probably wouldn't have worked so I gutted the board and built a Harvard circuit from scratch. It has a Volume and Baxandal Bass/Treble control on a concentric knob. It has a 6AV6, 12AX7, two 6V6s, and a solid-state rectifier. The transformers are from a Hammond Organ. I have a bias pot inside and I wouldn't mind running 6K6s instead of 6V6s if it's too loud and bright. I don't have a cabinet for it.
The combo below is the chassis of a 1960s ELK Pro-Sonic that I have built a Fender Deluxe Reverb clone from. The guy I bought it from had completed about 90% of it and quit. I figure he painted himself into a corner. The board he built was a Hoffman Deluxe Reverb and the ELK Pro-Sonic faceplate is the opposite of the Deluxe Reverb layout with the Reverb channel first with Reverb, Volume, Bass, and Treble. That meant he had wires crossing over each other to try and compensate and it became a mess. I believe the final straw for him was when he wired the tube sockets and found out he was missing a phase inverter socket. So I drilled another tube socket and swapped the front panel and tube layout to match the Deluxe Reverb. I moved the reverb control to the end near the pilot light. That allowed me to add a Friedman-style clipping switch and a Middle control to the Normal Channel. I will need to relabel the front panel later. It has two 12AX7s, and three 12AT7s, and a 5U4 rectifier. The transformers and reverb tank are original. I have one MISCO 10-inch Ceramic Hemp Cone and one MISCO 10-inch Alnico Hemp Cone speaker in the cabinet.
The chassis on top of the combo is a Fender Harvard clone The guy I bought it from said it was a Harvard and was about 75% complete before he quit working on it. However, the board he built was some kind of Deluxe variant that shared no similarity other than a 6AT6 in the V1 position. It probably wouldn't have worked so I gutted the board and built a Harvard circuit from scratch. It has a Volume and Baxandal Bass/Treble control on a concentric knob. It has a 6AV6, 12AX7, two 6V6s, and a solid-state rectifier. The transformers are from a Hammond Organ. I have a bias pot inside and I wouldn't mind running 6K6s instead of 6V6s if it's too loud and bright. I don't have a cabinet for it.
The combo below is the chassis of a 1960s ELK Pro-Sonic that I have built a Fender Deluxe Reverb clone from. The guy I bought it from had completed about 90% of it and quit. I figure he painted himself into a corner. The board he built was a Hoffman Deluxe Reverb and the ELK Pro-Sonic faceplate is the opposite of the Deluxe Reverb layout with the Reverb channel first with Reverb, Volume, Bass, and Treble. That meant he had wires crossing over each other to try and compensate and it became a mess. I believe the final straw for him was when he wired the tube sockets and found out he was missing a phase inverter socket. So I drilled another tube socket and swapped the front panel and tube layout to match the Deluxe Reverb. I moved the reverb control to the end near the pilot light. That allowed me to add a Friedman-style clipping switch and a Middle control to the Normal Channel. I will need to relabel the front panel later. It has two 12AX7s, and three 12AT7s, and a 5U4 rectifier. The transformers and reverb tank are original. I have one MISCO 10-inch Ceramic Hemp Cone and one MISCO 10-inch Alnico Hemp Cone speaker in the cabinet.
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idsnowdog
Imperator of Indignation
Coming Soon Pt.4:
Matchless Spitfire 15 clone. Converted from a Voice Of Music Hi-Fi amplifier. 2x12AX7s, 2xEL84s, and 1xEZ81 rectifier. The amplifier originally had a 6AU6A in V1 but I replaced that with a 12AX7. I need to order two capacitors and a 10H choke to finish the power filtering section. There's not much room in the chassis so I will need to run an umbilical cord to the faceplate and controls. I have a Crate 2X12 cab with two 1950s Magnavox Alnico speakers for it.
Matchless Spitfire 15 clone. Converted from a Voice Of Music Hi-Fi amplifier. 2x12AX7s, 2xEL84s, and 1xEZ81 rectifier. The amplifier originally had a 6AU6A in V1 but I replaced that with a 12AX7. I need to order two capacitors and a 10H choke to finish the power filtering section. There's not much room in the chassis so I will need to run an umbilical cord to the faceplate and controls. I have a Crate 2X12 cab with two 1950s Magnavox Alnico speakers for it.
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beaubrummels
Well-known member
The Harvard reminds me of my Emery SuperBaby. Simlar setup.
Fender_Punk
BerriesAndCreamologist
I would love to learn how to do this. It would be so sick to build my own amp. Any resources you can recommend on learning?
idsnowdog
Imperator of Indignation
I started with the Hoffman Amplifiers site. They have layouts that show all the component values so it's easy to duplicate their circuits. Rob Robinette's website for modifications and customizations. Schematic Heaven for inspiration and reference. I like that I can see an amp demo on YouTube and look up the schematic on Schematic Heaven to see what components it uses and how it's built then go to Hoffman Amplifiers and find a board layout then Rob's site to customize the circuit.
https://el34world.com/charts/TubeAmpSchematics.htm
https://robrobinette.com/Generic_Tube_Amp_Mods.htm
https://schematicheaven.net/
