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Ampeg HB15

This project is a custom modification of the original Ampeg Heritage B15. You can download the schematic HB15.pdf.

IMG_20220104_171503_nometa

Warnings

  • Use 6L6GC valves that support 500V at the screen
  • Always checks that all capacitors are discharged
    • Even if the 470k 2W resistor shoud discharged the capacitor

Valves

Valves used in this project:

  • TAD - 6L6GCM-STR REDBASE
  • Philips USA as JAN 12AT7WC (6201) [NOS military grade]
  • JAN 6SL7WGT Philips [NOS military grade]
  • Shuguang 6N9P J level [NOS military grade]

Custom mods

  • The 100K 2W resistor in parallel with the standby switch reduce all the inrush current which is better for the capacitors
  • Boost switches increase the gain of the triode by adding a bypass capactor
  • Enable or disable the bright capacitor (boost in 8kHz)
  • Effects Loop (buffered) is built to be transparent and you can do severals things around:
    • Enable or disable the effects loop
    • Can be used as a buffered preamp out
    • Can be used as an input for a "preamp in a box"
    • Can be used as distortion stage on the cathode follower by increasing the send volume
      • Eventually a clean boost of the preamp
  • Post Phase Inverter Master Volume (PPIMV) allowing to push the preamp while keeping the amplifier not too loud
  • Negative Feedback loop for rumble fix and different voicing (see schematic)
  • Midranges boost is a custom version inpired from Pignose B100V amp
  • Adding a 4.7nF capacitor in series with C1 and C3 to cut sub frequencies
    • It may be a side effect by replacing all 22nF by 47nF in order to support a 5 strings bass
    • It also due to the frequency response of my PF-210HE cabinet which have a greater low frequencies response
    • 3.3nF may be better depending your cabinet (and taste)

Tips

  • Use a rubber seal inside the chassis to easily mount a APEM 644 for example
  • Use teflon tape and rubber seal to insulate metalic jack plug (e.g. Switchcraft 11) from the chassis to avoid ground loops
  • Avoid soldering ground on the potentiometer's cover (gound loops enabler)

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