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F5 power amplifier
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Old 17th June 2017, 05:56 PM   #15601
Nelson Pass is offline Nelson Pass  United States
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F5 power amplifier
The F5 design was released to DIYers when production ceased, and
it's fine with me if people want to generate their own artwork.

The IP involved is simply copyright.

There are pc boards available in the store.
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Old 17th June 2017, 06:26 PM   #15602
2 picoDumbs is offline 2 picoDumbs  Australia
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Quote:
Originally Posted by peafarmer View Post
Pico, I'm using the Peter Daniels boards. I might be sqeamish, but the boards are so small that I'm not really looking forward to de-soldering. I might just splice in a 12K like 6L6 did for his bias resistors, though. Thanks, guys! Andy
Alternatively just remove the current limiters altogether.
I personally never bother with them.
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Old 17th June 2017, 10:04 PM   #15603
Nelson Pass is offline Nelson Pass  United States
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F5 power amplifier
I have a nice one where all that stuff is gone, including the Source resistors.

Takes a short while to warm up...
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Old 18th June 2017, 04:11 AM   #15604
2 picoDumbs is offline 2 picoDumbs  Australia
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Me too.


I tweak the source resistors on the input jfets to get around 0.025% 2nd Harmonic on the distortion analyzer.
Extremely bloody good amp like this.
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Last edited by 2 picoDumbs; 18th June 2017 at 04:25 AM.
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Old 18th June 2017, 04:30 AM   #15605
Hikari1 is offline Hikari1  United States
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If I want to take out the current limiting can I simply cut the a resitor lead from r21/r22? My f5 is built with current limiting and its much easier to just snip a resistor lead while it's in the amp instead of taking about the boards and removing the resitors and ZTX devices.
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Old 18th June 2017, 04:43 AM   #15606
2 picoDumbs is offline 2 picoDumbs  Australia
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snip ztx450/550, r17, r18, r19, r20, r21, r22.
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Old 18th June 2017, 05:52 PM   #15607
Nelson Pass is offline Nelson Pass  United States
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F5 power amplifier
Unless you are committed permanently, it is adequate to simply remove
the ZTX parts.
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Old 21st June 2017, 08:48 PM   #15608
Hikari1 is offline Hikari1  United States
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Thanks for the advice and the amp, Nelson.
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Old 29th July 2017, 06:10 AM   #15609
Kosst Amojan is offline Kosst Amojan  United States
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Total nube rube here... I've got sitting on my table a completed F5 but I've got a problem. I've powered the thing up and tried to set the bias.... and nothing. I can crank the pots to their max and absolutely nothing across the resistors.

A little info about this specific build:
I've opted to run 32V rails. I used boards from DIYaudiostore which are laid out according to the F5 Turbo article. I've built the boards to the design except that I've omitted R15-R18. R19-R20 remain. All the transistors are Linear Systems parts.

In probing around I'm getting power to the boards. I've attached heatsinks to the JFETs and they get slightly warm. I have modest amounts of offset at the outputs (15-22mV+) which also doesn't change regardless of how much a turn pots P1 and P2. I'm thinking based on what I've read that R5 and R6 are too low in value and may need to be increased. Would this thinking be correct? Could R19 and R20 be allowing the current limiting to kick in with the higher voltage? This is my first amp and I'm really a bit lost.
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Old 29th July 2017, 09:44 AM   #15610
AndrewT is offline AndrewT  Scotland
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If you have built an F5t then try posting in the F5t thread.

Now supply some measured information attached to a pic of your adopted schematic.
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