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807 Sound Quality?
807 Sound Quality?
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Old 2nd April 2017, 06:16 PM   #1
FullRangeMan is offline FullRangeMan  Brazil
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Default 807 Sound Quality?

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
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Old 2nd April 2017, 06:27 PM   #2
JonSnell Electronic is online now JonSnell Electronic  United Kingdom
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The 807 is a higher voltage 6L6GC. Excellent work horse that does like to be pushed.The 6SN7 is a good all rounder but the 6SL7 has slightly higher gain and less dissipation.
Should work well but 94db is not very efficient.
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Old 2nd April 2017, 07:06 PM   #3
Eli Duttman is offline Eli Duttman  United States
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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.
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Old 2nd April 2017, 10:52 PM   #4
FullRangeMan is offline FullRangeMan  Brazil
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Thankyou boys for your expert advices.
I have decided for the 1625 cause 30W dissipations.
?To 10W output how much plate voltage and load Bias I will need?
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Old 2nd April 2017, 11:06 PM   #5
sser2 is offline sser2  United States
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Quote:
Originally Posted by Eli Duttman View Post
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.
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Old 3rd April 2017, 12:14 AM   #6
Eli Duttman is offline Eli Duttman  United States
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Originally Posted by sser2 View Post
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?
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Old 3rd April 2017, 12:21 AM   #7
Eli Duttman is offline Eli Duttman  United States
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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.
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Last edited by Eli Duttman; 3rd April 2017 at 12:22 AM. Reason: added ICAS
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Old 3rd April 2017, 12:29 AM   #8
FullRangeMan is offline FullRangeMan  Brazil
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Quote:
Originally Posted by Eli Duttman View Post
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.
OK understood.
?With 20W dissipation in Pentode a 1625 should last how many hours?
Driving my 94dB FR driver;
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Old 3rd April 2017, 12:56 AM   #9
Wavebourn is offline Wavebourn  United States
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807 Sound Quality?
What sound of 6L6-oids, especially in SE, especially with no feedback?
Well, like a porridge of intermodulations.
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Old 3rd April 2017, 01:23 AM   #10
Eli Duttman is offline Eli Duttman  United States
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Originally Posted by Wavebourn View Post
What sound of 6L6-oids, especially in SE, especially with no feedback?
Well, like a porridge of intermodulations.

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.
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