This ^
They can test the tubes and see which ones are going out, if it's a good tech. Could save you a lot of waiting and guesswork if they can narrow down the core issue.
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6550 Tubes for Ampeg SVT
- Thread starter Slpbass81
- Start date
This ^
They can test the tubes and see which ones are going out, if it's a good tech. Could save you a lot of waiting and guesswork if they can narrow down the core issue.
This is interesting and/or amusing. S.F. Bay area SVT listing:
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Ninety dollars per tube doesn't seem very cheap to me.
SVT's are lucky to put out 300 watts, they need good tubes, early ones with 6146B power tubes were close to 350 watts but not the ones with 6550's. I've had mine checked and they're usually around 300.
At what level of distortion. Vintage spec says:
From what I have seen, it's rare for an SVT to meet this spec.
Also, AFAIK 300W at 3% to 20hz is total BS
I believe the current spec is 300W at 5%...but even that may be a bit optimistic.
Can't speak for the 6146B but, for 6550 and KT88 it doesn't matter too much which ones are used.
It was even possible to mix both of them with good success.
SVT calibration procedure,
see note at the bottom regarding sufficient power handling of resistive load at calibration procedure.
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Not necessarily. Once the test signal (sinusoidal waveform) starts to saturate (slight clipping) a FFT analysis tells that THD is in the range of ~3..5%
Once my SVT starts slight saturation then its output power is easily 360 Watts rms.
RMS output voltage measured with True RMS multimeter Fluke 185.
edit, by the way, meant as supplement.
line voltage at the wall socket reads 235 VAC on my voltmeter (I'm living in Germany as you know).
Even in LT-Spice simulation its quite easy to gain about 300..330 Watts with HT anode voltage that was equal to 580 Volts, and something more in the range of 330..360 Watts output power with HT voltage equal to 600 Volts, at THD number in the range of about 3..5%
Besides OT tolerance, some tolerance of load impedance may also affect output power at some content.
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Yes, that calibration procedure came from the 6146B chassis's, one of which I own. Even the internal tube charts on them have both 6550's and 6146B tubes on them.
My 69 says 74mV on the chassis. Other than that, the procedure is the same as later amps.
True, but the stated spec is 300W minimum at <3% from 20hz to 20khz, not +/- 3dB.
Also your SVT seems a bit extraordinary if it makes over 300W at 3%. Some do meet spec, but AFAIK many do not.
Are you really sure?
The pic I posted above was taken from a 12AX7 preamp version SVT at Ampeg website support.
My original schematic in paper print form reads (as well) exactly the same, its a Magnvox SVT made in ~1978
If 6146B tubes shall gain some more of power, the only way doing it was some improved conductance from plate to cathode at full throttle.
Are you really sure that it works this way with 6146B?
Without any additional provided specification done by the manufacturer, the common standard is -3dB
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Personally I think its kinda form of unlucky words rather than "specific".
While any number of bandwidth limits is very specific, and this common standard is applicable to anything, electronics, acoustics, video/audio, science in general, nearly to anything.
Its even valid for bandwidth specification of your scope, if you have one.
I'll take "300W minimum" as intentional and specific until you can provide official documentation from Ampeg that states otherwise.
Ampeg continues to use the same word, "minimum".
Here are the current specs from the 50th AV SVT:
Output Power Rating: 300W RMS minimum continuous @ <5% THD into @ 2 or 4
Ref: Ampeg :: Heritage 50th Anniversary SVT
No frequency response is specified, so the current spec leaves a bit more room for interpretation.
