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Old 19th June 2017, 12:24 PM   #1
waltube is online now waltube  Italy
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Default Fab Four: 4 x KT150 monoblock

In this month on Audioreview magazine I have presented a pair fo mono who a my old friend ask me to build.
Are used PCC88 ( or 6922) in input, 6H30 as splitter and two pairs ok KT150 for out, Pentode connection.
The trafo is customa made with double C core, it is pottedd and the rating is 130 w at 20 Hz, nominal; the rato is 19:1, single secondary at 5 ohms.
FB selectable from 12 to 18 dB.

The power supply is 520 vdc with 8 x 470 uF /550 v each mono, so the joule are about 510!

Fixed bias, deep selection of tube by Sofia.
Fig. 1 input
Fif. 2 splitter
Fig. 3 out
pdf file the tests on the lab

On the first diagram is possible tosse the performaces with different load with continous signal and impulsive.
More the line is vertical more the amp can delivery current to the load.
In impulsive I reach 290 on 3, 2, it is veru good.

on the second there is a frequency answer, at 1 watt I got -1dB at 200 kHz, and at 100 wat at 150 kHz, -3dB about at 175 KHz.

Very interesting is the THD vs. Freq; for each level the thd is very costant; only for 100 and 125 watt goes upper to 1 % ( up to 2% maz at 20Hz)
At 1 watt is below thw 0,1 % from 20 to 20KHz.

Ciao

Walter
Attached Images
File Type: jpg Fig. 1 stadio di ingresso.jpg (23.3 KB, 289 views)
File Type: jpg Fig. 2 stadio sfasatorer.jpg (71.6 KB, 286 views)
File Type: jpg Fig. 3- OUT.jpg (115.1 KB, 282 views)
Attached Files
File Type: pdf KT150_test.pdf (288.9 KB, 54 views)

Last edited by waltube; 19th June 2017 at 01:43 PM.
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Old 19th June 2017, 03:02 PM   #2
45 is offline 45  Italy
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Hey Walter nice performance. Especially those extra impulsive watts into 4R.

I would rate the output transformer as 125W @28Hz with power bandwidth (-3dB or half power if you like) from 20Hz. They have likely designed it to reach high induction at fuill power @20Hz but it is ok as below 28Hz there is not too much to listen to usually and one saves space, weight and money. I would do the same design choice.
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Old 19th June 2017, 05:45 PM   #3
waltube is online now waltube  Italy
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to 45

thx


The use of 6922 and 6H30 give me a very good swing with low distortion even the gain is not so high; each section of 6H30 has 10 mA of bias and the Vdc is high for this type but it is working fine.
The trafo comes after some tests during last years; I have had an help from KT150 because they can delivery a good Iamax so at the edge of the spectrum they can delivery current also when the L is decreasing.

But the very important test, for me, is the THD vs freq; in this test is possible to see in which way the interaction between tubes and trafo is running.
More straight is the line of THD better is the coupling; in this case the FB is very low for the pentode configuration

Walter
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Old 20th June 2017, 09:08 AM   #4
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depletion type mosfets from IXYS are now available with ratings of 1000v at 6A...
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Old 20th June 2017, 09:19 AM   #5
waltube is online now waltube  Italy
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to Tony

your post is for me?
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Old 20th June 2017, 10:19 AM   #6
waltube is online now waltube  Italy
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The photo of amps.

Walter
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Old 22nd June 2017, 11:32 AM   #7
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Don't they resemble huge suppositories?

Best rfegards!

Last edited by Kay Pirinha; 22nd June 2017 at 11:32 AM. Reason: typo
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Old 22nd June 2017, 12:54 PM   #8
waltube is online now waltube  Italy
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Please can you explain your post?

Walter
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Old 22nd June 2017, 02:16 PM   #9
waltube is online now waltube  Italy
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Yes
But in this case they have a good sound.
When hot they help you about cold!



Walter
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Old 23rd June 2017, 12:22 AM   #10
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Quote:
Originally Posted by waltube View Post
to Tony

your post is for me?
can you use that?
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