F5 power amplifier

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#6,362
I guess you'll have to be patient and wait until Nelson tested these, and endorse them to the Fairchilds, even though a handful few has followed my advice (and published measurements) and built the F5 with Toshibas to their satisfaction. I bet you'll be sold out in a day after Nelson's endorsement.

I still have people PM me for matched Fairchilds a year after our GB, even they are not true complementaries, and are becoming obsolete.

😉


Patrick
 
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#6,365
drifting bias

Hi All,
I just hooked up the F5 with Peter Daniel boards but I notice that the voltage across the 0. 47 ohm is drifting . I can adjust it to 0.6 V when the heatsink is warm to touch but it ranges from 0.59 to 0.61 V.
When first powered on, the voltage across R11 and R12 can reach about 0.68V and slowly drifted down to around 0.6 V over 5 minutes.
However, the incoming Ac voltage is also fluctuating between 200V in the evening to 235 V Ac in the morning. Of course the incoming AC only drift about 5V during the hour that I was testing it.
The transformer is 220V in and about 19.5 V out. All my caps are rated at least 50 V.
I have bend the TH 1 and TH2 to touch the drain of IRPF 9240 and 240.
Is this normal?
Looking forward to sort this out and compared to the Truepath Class D amp !1
Thanks

kp93300
 
#6,367
DC output offset at speaker terminal

Hi all.
I need some guidance.
I can adjust the dc offset to zero when the circuit reach relative stability in about 10 minutes. . However, during power down the offset reach 0.4 V for a few seconds before it reach 0. !
On power on, the dc offset remains about 0.05 V.
Please advice
Thanks

kp93300
 
#6,368
kp93300

I experienced the same drift upward and then settled around .60. .59 to .61 is not bad at all.

I would set it to close as .60 as possible, make sure there is no DC at output and run it thru a set of test speakers. Later after a few days go back and recheck the DC off set and bias.

Vince
 
#6,370
"You should be able to get the output DC offset down to 10 mV or so, and I would consider 50 mV the highest acceptable
figure for this amplifier when warmed up. After the amplifier has been operated for a few weeks, it is a good idea to check
and adjust the offset again after the parts have been burned in."

These are Nelson's words from the PDF.
 
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#6,376
Zen Mod said:
this amp is piece of cake ;

offset is stable - it's just did you follow procedure or not ;

pardon moi - considering your previous posts - seems that main problem with this amp is that it isn't French ;(
Click to expand...

well it s device dependant...
not french!? not a problem, in fact i once had great admiration
for behind of the curtain ingeneers..they had the skill to make
more with less...
 
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