Hi,
?I would like lots of info on how is the 807/1625 sound?
Likely will be Russian G807 or the 12V G1625, input stage is 1 tube only 6SN7 or 6SL7, tube rectification, output is one single tube in Tetrode Single Ended A1 about 10W w/low NFB to drive one full range 94dB,8 ohms.
Thanks for help:00
?I would like lots of info on how is the 807/1625 sound?
Likely will be Russian G807 or the 12V G1625, input stage is 1 tube only 6SN7 or 6SL7, tube rectification, output is one single tube in Tetrode Single Ended A1 about 10W w/low NFB to drive one full range 94dB,8 ohms.
Thanks for help:00
94 dB. sensitive speakers need 8+ WPC, to satisfy Paul Joppa's 102 dB. rule.
The 807 is not a 6L6GC, with a top cap. Absolute max. plate dissipation is 25 W. and you, most definitely, don't want to go there. 21 W. should be safe enough. At 40% efficiency, power O/P will be 8.4 W., which is sufficient.
Take advantage of the high allowed B+ and regulate g2 B+, at a substantially lower value, say 250 V. Open loop linearity will be as good as it gets.
You will need a fair amount of NFB, in order to obtain a satisfactory damping factor. Given the overall open loop gain requirements, a 6SL7 section voltage amplifier seems right. Fortunately, the full "pentode" mode final exhibits low CMiller, which will not tax the wimpy driver triode.
The 807 is not a 6L6GC, with a top cap. Absolute max. plate dissipation is 25 W. and you, most definitely, don't want to go there. 21 W. should be safe enough. At 40% efficiency, power O/P will be 8.4 W., which is sufficient.
Take advantage of the high allowed B+ and regulate g2 B+, at a substantially lower value, say 250 V. Open loop linearity will be as good as it gets.
You will need a fair amount of NFB, in order to obtain a satisfactory damping factor. Given the overall open loop gain requirements, a 6SL7 section voltage amplifier seems right. Fortunately, the full "pentode" mode final exhibits low CMiller, which will not tax the wimpy driver triode.
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94 dB. sensitive speakers need 8+ WPC, to satisfy Paul Joppa's 102 dB. rule.
The 807 is not a 6L6GC, with a top cap. Absolute max. plate dissipation is 25 W. and you, most definitely, don't want to go there. 21 W. should be safe enough. At 40% efficiency, power O/P will be 8.4 W., which is sufficient.
Take advantage of the high allowed B+ and regulate g2 B+, at a substantially lower value, say 250 V. Open loop linearity will be as good as it gets.
You will need a fair amount of NFB, in order to obtain a satisfactory damping factor. Given the overall open loop gain requirements, a 6SL7 section voltage amplifier seems right. Fortunately, the full "pentode" mode final exhibits low CMiller, which will not tax the wimpy driver triode.
ICAS (intermittent service) plate dissipation for 807 is 30 W. From my childhood experience as radio hooligan, these tubes can take tremendous abuse.
"Fair amount of NFB" would be a difficult proposition in SE.
ICAS is a very different situation than Class "A" audio, with its more or less constant dissipation. Exploiting an absolute maximum rating will lead to a short service life. I guesstimate that 21 W. is a fair approximation of design maximum.
Extracting sufficient gain from the voltage amplifier to support the requisite NFB level is easy enough. In what way is adequate NFB going to be a problem?
FullRangeMan,
The 1625 data sheet indicates that 30 W. is an absolute maximum ICAS rating. Please don't go there, as your tubes will not last.
The 1625 data sheet indicates that 30 W. is an absolute maximum ICAS rating.
Please don't go there, as your tubes will not last.
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OK understood.FullRangeMan,
The 1625 data sheet indicates that 30 W. is an absolute maximum ICAS rating.
?With 20W dissipation in Pentode a 1625 should last how many hours?
Driving my 94dB FR driver;
What Anatoly said is yet another good reason for a substantial amount of NFB. Regulating g2 B+ at a fraction of anode B+ holds the IM distortion down, but doesn't completely eliminate it. NFB is a tool. When used judiciously, NFB is beneficial. Always start with maximizing open loop linearity and then apply the NFB.
Thanks again for explain
How much NFB would be it in a 1625 20W dissipation?
IT would use variable NFB?
Thanks again for explain
How much NFB would be it in a 1625 20W dissipation?
IT would use variable NFB?
It depends on how much your output transformer allows. No free lunch.
As in the discussion about Bruno's paper mentioned, it does not matter how much NFB you have on 1 KHz. What matters, how much do you have on 20 KHz.
Never, ever, put an inter-stage trafo (IT) inside a NFB loop. We only just get away with O/P "iron" inside a GNFB loop.
IMO, variable NFB is not a good idea, but it has been used.
My seat of the pants guess is that approx. 15% of the speaker O/P voltage is a reasonable place to start. In any event, you want O/P "iron" rated for 15 W. or so. Magnetic headroom is needed to keep the deep bass error correction signal from saturating the core.
Another technique for preventing O/P "iron" core saturation is rolling infrasonic noise off at the amp's I/P. A simple RC high pass filter that "corners" in the 16 to 18 Hz. range gets the job done.
IMO, variable NFB is not a good idea, but it has been used.
My seat of the pants guess is that approx. 15% of the speaker O/P voltage is a reasonable place to start. In any event, you want O/P "iron" rated for 15 W. or so. Magnetic headroom is needed to keep the deep bass error correction signal from saturating the core.
Another technique for preventing O/P "iron" core saturation is rolling infrasonic noise off at the amp's I/P. A simple RC high pass filter that "corners" in the 16 to 18 Hz. range gets the job done.
inside a NFB loop. We only just get away with O/P "iron" inside a GNFB loop.
Noted, Thanks.
A simple RC high pass filter that "corners" in the 16 to 18 Hz. range gets the job done
This seems good. It substitute the NFB?
With this filter I dont need a NFB?
For your info:
The 807 Application Report.
SE and PP Operating conditions etc.
http://www.tubezone.net/pdf/807stc.pdf
Cheers,
Ian
The 807 Application Report.
SE and PP Operating conditions etc.
http://www.tubezone.net/pdf/807stc.pdf
Cheers,
Ian
inside a NFB loop. We only just get away with O/P "iron" inside a GNFB loop.
Noted, Thanks.
A simple RC high pass filter that "corners" in the 16 to 18 Hz. range gets the job done
This seems good. It substitute the NFB?
With this filter I dont need a NFB?
You need both the I/P high pass filter and a GNFB loop.
Wow. Thanks boys for your valuable help.
I glad I ask here to made ma less dumb.
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