F5 power amplifier

[6L6]

Originally Posted by Bksabath

Maybe you can look at the most excellent 6L6 thread

Which can be found here - An illustrated guide to building an F5

As I say in the introduction, this is not the only way of doing it, merely the way I did it. (Heck, if I were to make another I would do it a bit differently! But that is the nature of DIY...) My biggest reason for making the post is because this thread has gotten ludicrously big and unwieldily.

[CeeVee]

Yes threads are big but if you want to learn something...that is good news.

This is not a kit building site ...thank god !

Your effort is very welcome 6L6 and appreciated, after the amp has been discussed here in detail.

...and Bksabath makes a very relevant point....$20 gets you a very easy to view version of the thread !!!

DIY is not like taking a pill...it's the enjoyment of the journey...and there is some great company here for that.

[ClothEar]

Originally Posted by Bksabath

...The most important thing... Mighty Zen Bias guide.

Mighty Zen Bias Guide? Where can this be found?

[6L6]

Originally Posted by ClothEar

Mighty Zen Bias Guide? Where can this be found?

It's in the middle of my build guide. It looks like this -

From Zen Mod:

dial both pots to 0 ohms ( check with ohmmeter )

place one voltmeter across PSU caps ( best between + and - of PSU) to observe max voltage of PSU

place one voltmeter at output - to observe offset

place one voltmeter across one source resistors of output mosfets ; it doesn't matter which one .

for test - slowly dial up Variac ( presuming that you have one , as man with many skills) up to full mains voltage , observing voltage at PSU ....... thinking about max cap voltage ( 25V as in FW ? ) , because with 0 Iq PSU is unloaded and voltage is maxed

if nothing is smelling - leave Variac at full mains ;

what's important - Iq must be very low , offset is irrelevant in this moment .

now turn one pot one turn ( assuming that you have multiturns )

then turn other pot one turn

observe Iq and offset

proceed one then second pot , again just one turn

observe Iq and offset

again one turn + one turn

now you are probably in range when you can see which pot is pulling offset in right direction - to 0 .

proceed iteratively with pots , while you set - say - 75% of desired Iq and zero offset

now - put lid on box and let it cook for a while - until yo get thermal equilibrium on heatsinks

it's best to use wire/clips to leave those voltmeters in place ;

open the lid , up bias to - say - 90% of desired one ,while maintaining offset

put lid on , let it cook

check ;

if all is OK - move voltmeters for Iq and offset to other channel and repeat procedure

use it few days at 90% of desired bias , then check and set to 100%

remember - temp. equilibrium with lid on is important
`````````

[ClothEar]

[QUOTE=6L6;2868635]...It's in the middle of my build guide...

Very Nice.

Merci, eh?

[dvb-projekt]

Originally Posted by crazycody1993

where is the capacitor that goes across mains??

That's the secondary side...

[KatieandDad]

http://www.parttimeprojects.com/audio/diy/F5.php

One DIY-er really hated his F5.

I've just got the building bug, his comments almost steer me away from trying an F5.

I've got a DIY Aleph 4 (100W Class A / Ch) which I am very happy with. I just wondered if the F5 was better.

100W versus 25W might make the A4 an easier amp to use ????

Not quite sure of the sensitivity of my speakers, they are B&W 683's.

[Salas]

He does not discuss the voltage gain though, which at 15dB, is surely more unusual than 25W. Many tube amps of such power live along medium sensitivity home speakers. Another 15 to 20dB of line level gain before the amp is needed for the system to feel normally dynamic on circa 90dB/W speakers. Max SPL could be compromised with 25W on such speakers, but average level ''bounce'' need not.

[AndrewT]

B&W state

90dB spl (2.83V, 1m)

but they don't seem keen on declaring what the nominal impedance of these speakers are

8? (minimum 3.0?)

all available @
Experience the B&W 683 - Bowers & Wilkins | B&W Speakers

They seem to be 4ohms to 8ohms speakers that are 90dB/2.83Vac @ 1m.
The 4 to 8 will effectively reduce their sensitivity to ~ 87dB/W @ 1m.

They are also suggested as being compatible with 25W to 200W amplifiers.
The F5 being ~50W into 4r0 just sneaks into the lower end.

Worth trying, to see/hear how the Aleph compares to the F5.

[KatieandDad]

Hi Andrew T

Yes, I've just found the same site.

Experience the B&W 683 - Bowers & Wilkins | B&W Speakers

As you say 90dB/W

B&Ws are notoriously horrible loads to drive. The A4 does it well.