The TFM-15 is a pretty impressive amplifier when your compare THD ratings at load, the TFM-15 is reportedly very stabile at even down to 2ohms, with a rating of 8(100W)/4(140W)/2(200W) w/ .1%THD. I really like the aesthetics of the meters here too.
Just wanted to show some basic measuring and some photos of a neat Carver we have in for repair.
Initially noted a decreased output in one channel along with erratic, excessive DC parameters. Many, many times DC stabilization correlates to issues with in the first stage differential transistors.
The TFM-15 uses a tied emitter pair of 2SA970 PNP's, which do not have a notorious track record or anything, but swapped to a 992fbu which is a very reliable device. This effectively dropped our working Offset below the initial 36+mV skew. Idle current is recorded at the emitters and confirm through the series of tied emitter .33 ohm resistors for 5mV (%1mV>) Matched differentials also brought the bias a little more in line and more stabile left and right, with appropriate drops to 4.9mv (.5mv>%) after heavy load.
carver tfm-15 bias notzen
punkten emitterwiderstand R824 und 924 für 5mV
bestatligen 5mV beim emitterwiderstanden R824A/825A
bestatligen 5mv beim emitterwiderstanden R924A/925A
Below are some comparisons (P=E(2)/R) (1Khz SINE (500mV) 4.25 (R)
1Khz SINE mit 4.25(R/) beim 3.52(3.51)Vac = 2.93W/CH
1Khz SINE hit 4.25(R/) beim 6.00(6.03)Vac = 8.47/8.55W/CH
1Khz SINE mit 4.25 (R/) beim 9.99(9.997)Vac = 23.48/23.51W/CH
Id love the chance to get one of these in and try some filtering upgrades and TO-3P/Driver stage upgrades, theirs the On-Semi MJL21193/94 devices that would be perfect!
Great work Noah! I've been enjoying this amp immensely since you've repaired it. It once again sounds as sweet and warm as ever.
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