1965 Ampeg B-15N Portaflex – NF Circuit – All Tube – CTS Speaker

For sale is a mid-1965 Ampeg B-15N Portaflex bass amplifier, featuring the highly sought-after NF circuit with fixed bias and 5AR4 rectifier. This is the classic studio B-15 sound—tight low end, warm mids, and excellent headroom.

The amp is fully working, retains original wiring, and is fitted with a period-correct CTS “Custom Ampeg Design” 15” speaker. The cabinet about 20 years ago had been re-covered in period-correct blue check Tolex, new handle installed, presenting very well while maintaining a correct vintage appearance. The cabinet is mounted on a removable base, covered with period correct blue check Tolex. The large casters makes it easy to move this heavy amplifier.

This is an excellent player-grade collectible: authentic, correct, and ready to be used.

Specifications & Details

• Model: Ampeg B-15N Portaflex
• Circuit: B-15NF (fixed bias)
• Year: Mid-1965
• Serial Number: 016088
• Output: ~30 watts, all tube
• Rectifier: GE 5AR4 / GZ34
• Power Tubes: 2 × RCA 6L6GC
• Preamp Tubes: 3 × Tung-Sol 6SL7GT
• Speaker: 15” CTS “Custom Ampeg Design” (EIA 137, 1967)
• Cabinet: Single-baffle Portaflex, period-correct blue check re-tolex

Tube Test Results

(Tested on calibrated Tv-7a/u vintage tube tester modified to measure plate current, photo of tester shown)

RCA 6L6GC Power Tubes

• 47 gm / 37 mA
• 41 gm / 36 mA
  (Minimum spec: 25 gm)

Tung-Sol 6SL7GT Preamp Tubes

• 47 / 49 gm (strong)
• 24 / 29 gm (below minimum)
• 27 / 52 gm (one section below minimum)
  (Minimum spec: 32 gm)

GE 5AR4 / GZ34 Rectifier

• 52 / 53
  (Minimum spec: 40)

All tubes are currently installed and the amplifier is functioning properly. Two preamp tubes test marginal on one or both sections but remain operational; full test data is disclosed for transparency.

Condition

• Electronics: Working and stable; original wiring intact
• Speaker: Era-correct CTS; sounds excellent
• Cosmetics: Very good vintage appearance; period-correct re-tolex
• Modifications: None beyond normal vintage service
• Environment: Smoke-free

Notes for Collectors

• NF circuit is widely regarded as the most desirable “player” B-15 variant
• Fixed-bias design with 5AR4 rectifier offers increased headroom over earlier NC models
• CTS speaker is era-correct and appropriate for this amplifier
• Cabinet re-cover disclosed and reflected in pricing

Shipping / Pickup

Local pickup preferred.