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Old 24th September 2013, 10:04 AM   #641
bkdog is offline bkdog  Australia
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Quote:
Originally Posted by georgebrooke View Post
This is really great.. all we now need is someone with time an enthusiasm to put together some PDF files for Pass DIY builds. This would be a great example of how to do it and it would be even better if this thread were referenced from a more central point, say Pass DIY site? It need not mean that they support the build description, but it would give newbies a flying start and the thread could be used for updates.

Thanks for a great piece of work

George
this was first on the list when I just tried searching...
An illustrated guide to building an F5
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Old 24th September 2013, 10:24 AM   #642
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Oh.. well I found Home | F5 Networks as a first search.
it was just a thought.... I assume reading a thread is not the ideal way of presenting a well structured document?

george
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Old 12th October 2013, 04:50 PM   #643
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Wierd f5 bias problem....... Hello, I have a problem with my f5, stopped working due to rectifier bridge which I fixed, and when I reconnected inadvertely reconnected negative to positive and vice versa, with some nice smoke. Blew out R 11 and 12 which instantly turned bright red before fuse blew.

To repair, I changed all transistors and output devices, as well as resistor r11 and 12. However, now, when I try to bias I get a wierd problem,

when I put meters on r 11 and r12 and turn the pots to change bias, when I change one pot, both meters move, such that when one meter is at .4v the other is at .6v or so on, no matter how I change adjustments and no matter what pot I adjust, voltage at both resistors 11 and 12 changes, with about a .2 v difference. one channel offset of 3mv and other channel offset of .65 volt and pots adjustment will not change this at all on this channel.

Even with one pot maxed out showing .4 v on R 11, I cannot get r 12 to follow. the differential stays the same and both r 11 and r12 voltages move in parallel when I adjust either pot, with approximately .2 volt differential. Frustratingly, it is the same for both channels with a little smaller differential on one channel.

Not sure what to do next. Checked orentation of all devices double checked and all good. Both output devices are in the correct positions.

Would this be a problem perhaps due to use of poorly matched devices.

perhaps this is due to bad resistor on the pcb which has no apparent damage.

Any ideas, thought appreciated.
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Old 12th October 2013, 07:41 PM   #644
6L6 is online now 6L6  United States
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Can you adjust to zero offset with any bias amount?
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Old 13th October 2013, 03:26 AM   #645
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no, on one channel I get offset of .6 v and other 3 mv, which stays steady throughout range of adjustment of both pots. For some reason offset does not change when pots are adjusted, only voltages across resistors 11 and 12.

I guess the problem is due to some of the resistors in the board are damaged, without showing apparent damage.

The drain of sj74 and 170 are R2 and r3, both 10R resistors so perhaps there was damage there?
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Old 13th October 2013, 09:42 AM   #646
AndrewT is offline AndrewT  Scotland
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Does the VR resistance (with power OFF) change when you adjust the VR?

With power ON, does the VR voltage change when you adjust VR?
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Old 13th October 2013, 09:46 AM   #647
AndrewT is offline AndrewT  Scotland
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A pair of diodes across the +ve to PG and -ve to PG eliminates the reversed PSU damage.
The bulb lights up full brightness and the worst case reverse voltage on your power amp semiconductors cannot exceed ~800mVdc.
It is also very worth while adding a pair of diodes +ve to speaker and -ve to speaker to protect from back emf from the speaker.
These 4 diodes cost a few pence (1n4002) and potentially save $$$s (£££s).
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Old 13th October 2013, 11:01 AM   #648
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I notice that on the CVILLIER Rev B boards there is no provision for P3 ?

Its not on the boards that 6L6 used at the start of the thread either.
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Old 13th October 2013, 12:23 PM   #649
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Default Another F5 is born.

But where is P3 ?
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Old 13th October 2013, 12:30 PM   #650
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the P3 is not on the Cviller boards. and P3 is useless for most people anyway. you just can not dial it in for optimum performance by ear.
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