Matchless DC-30 - Black Sparkle - 2020 De-doped Greenback Era - **See Tubes

Matchless DC-30 - Black Sparkle

When I bought this amp, I did a lot of research (I'm very detail oriented as evidenced by my tube data below) I chose this 2020 because my understanding is that this was during a sweet spot where all internal specs are true to Sampson design and they used proprietary, deliberately Mismatched Celestion Greenbacks which they manually dedoped the cones on, like was done on the V30's in the 90's. Matchless no longer does this as the process involved solvents that were deemed to be a health risk (which evaporate long before it leaves the factory, no no lasting issues for amp owners)

So, for collectibility - Sampson Era is great but they're 30 years old and components are drifting by this time, so in many cases that vintage Sampson is out of spec compared to more recent builds and requires servicing. For amp quality, reliability and speaker selection, I consciously chose to go with this 2020 model and it delivers everyhing you'd want out of a DC-30.

This amp is something like 82lbs of quality, so prepare for it. The big iron transformers, heavy speakers, beefy chassis and thick hardwood cabinet are done for a reason.

Matchless DC-30 — tube complement as listed
Every tube measured on an eTracer curve tracer (Sep 2026), 3-minute heater soak, tubes selected and paired from the measurements. Test points: EL84 triode-strapped 250 V / −7.3 V; 12AX7 250 V / −2 V per triode; EF86 triode-strapped; GZ34 0–20 V both plates.

• V1 (Ch1 gain): Tung-Sol 12AX7 — gm 1976 / 2097 µmhos, 1.22 / 1.34 mA, mu 95 / 97 (hottest tube in the amp, placed in V1 on purpose)
• V2 (Ch1 second stage): Tung-Sol 12AX7 — gm 1738 / 1785 µmhos, 1.02 / 1.19 mA, mu 101 / 99
• Ch2 EF86: Amperex Bugle Boy (Heerlen, Holland) — 2.59 mA, gm 1852 µmhos, mu 36.5
• Phase inverter: JJ ECC83S gold pin — gm 1659 / 1654 µmhos, 1.15 / 1.14 mA, mu 98 / 99 — triode sections balanced to 0.3%, selected for the PI on that basis
• EL84 power quad, pos. 1 (outer): RCA 6BQ5 USA — 52.2 mA, gm 11,116, mu 18.6, rp 1676 Ω
• EL84 pos. 2 (inner): RCA 6BQ5 USA — 51.5 mA, gm 12,341, mu 18.7, rp 1514 Ω
• EL84 pos. 3 (inner): RCA 6BQ5 USA — 50.7 mA, gm 12,092, mu 18.7, rp 1550 Ω
• EL84 pos. 4 (outer): RCA 6BQ5 USA — 49.5 mA, gm 12,743, mu 18.9, rp 1484 Ω
• Rectifier: JJ GZ34 — 181 / 181 mA, diode halves identical across two runs

Quad notes: all four RCAs within 5% on plate current (49.5–52.2 mA), gm 90–103% of datasheet; selected from eight measured RCAs. Inner pair (the two that stay on at half power) matched to 1.6%; push-pull sides balanced to within 2–3.5%. A vintage Mullard GZ34 was measured for this seat and rejected: its halves read 299 / 214 mA against the JJ's 181 / 181.