Newbie help with F5

[Russellc]

As 6l6 has said several times here, look at the build guides....all of them. He uses different colored wires, takes excellent pics. All the First Watt amps have basically the same power supply. Each of the guides shows a slightly different take and different photos. Careful study will show you where all these wires go.

Then as you keep building amps you will get to where its first nature, get over confident and make a silly mistake. Or at least that is how I did it!

Showing pics of your work here as you have done is also a good move, and has saved me from my own bonehead mistakes a few times!

Russellc

 

[Tuberoller]

Purple wire to chassis ground.

Use a bulb tester, not a variac. The bulb tester will save you from almost all faults automatically, where the variac needs a much deeper understanding of what’s going on and what to look for and how.

Thanks, I will need to build one then.

So the purple wire from the transformer goes to chassis ground. Can I just pin it anywhere on the chassis? Is the main chassis ground you refer to the star washer-cl60 combo near the PSU and power cord connections?

 

[Tuberoller]

Hi Tuberoller,

Please have a look at the few posts around here:

https://www.diyaudio.com/forums/pass-labs/335350-f5-build-11.html#post5770961

Also, please verifying the zero-ing out of P1 and P2 by actually measuring the
resistance across R5 and R6. They should be close to zero.

Dennis

Thanks
The 4 pots were zeroed; the multimeter was lowest and clicks were heard across the resistors.

Will have to work on the middle pots😮 I think the link describes 12 or 5 turns from one end of the dial?

Nice link to Dirk's method. Will read again

 

[Dennis Hui]

I suggest leaving the P3 pot in its mid position. You can use it to adjust
the distortion characteristics but it really requires the use of distortion
analyzer.

Our friend 6L6 produced a video illustrating the P3 adjustment:

YouTube

 

[Lo_Tse]

Darn, I swear I saw 6L6 pointed out in a post where to get the TH1 and TH2 but I could not find it!! Is it in this thread or another one? Both TH1 and Th2 are PTC, right I would be grateful if someone would explain what is their function. Thank you very much in advance.

Regards,

 

[6L6]

They are negative tempature coefficient.

NTCLE100E3472GB0 Vishay / BC Components | Mouser


Long story short, they help keep the bias stable as the amp warms up from cold after power up.

 

[Lo_Tse]

6L6

Thank you very much !!

Regards,

 

[Tuberoller]

Almost finished! All DBT's were successful. And initial bias going pretty good, about test again after warm up. 0.6 is the final bias with zero offset, if I remember correctly.

Thanks to all those who chimed in with help🙂
Especially 6L6 who has contributed so much to this wonderful hobby and it's forum. I'm hooked!!

 

[ColinA123]

Proper blue LEDs

 

[cubicincher]

I lke the blue shine of the LEDs too!


Nice build. Enjoy the sound!


Cheers
Dirk

 

[Zen Mod]

take care of isolating xformer clamp against front plate , to avoid short

even better , remove L bracket and mount a Donut directly on base plate.... that L element looks flimsy

 

[Tuberoller]

Good point, the L bracket is pretty solid but the transformer is “soggy”, just held by a bolt that doesn’t grab the transformer with enough surface area. Could not find a good alternative solution at the time. There are rubber gasket pads on both sides of the bolt and hexnut.

ZenMod, is it the faceplate and some unexpected conducting connection to the transformer that could be a problem. The faceplate is I think aluminum and attached to the aluminum chassis floor grid , and the chassis floor is connected by ground to the purpl transformer the foil which covers the transformer.

thanks for everyone’s input. this amp sounds ******* incredible. I am floored by the sound quality and listened to it nonstop for hours yesterday. Also, there is no need for more power it is plenty loud without a turbo. It is all about the firat watt - right , and the F5 succeeds wonderfully.

 

[McQuaide]

Very nice, you'll love it!!

 

[Attila I]

@Tuberoller
if the bolt, bracket, baseplate and frontplate form a closed loop (i.e. conducting)
then you get a welding machine.
even if the loop is not tight closed (small gap) you will notice hum and rapid warming
I did it once - its no fun
cheers
A.

 

[tooppy]

I am building the F5 right now and have mostly the same questions as anyone who isn't an electronician.

Are the LED on the PSU compulsory ? I don't see the necessity to light up the amp's inside so for the time being I haven't planned to put any.

In return I bought LED and 15K resistor for the F5 boards and will place these LED through the front plate, ACA style.

Would these be adequate ?
- for the 15K resistor N° Mouser : 71-CPF3-F-15K
- for the LED N° Mouser : 78-TLHG6405

 

[6L6]

On PSU are not necessary. They fall into the "nice to have" category, but you may omit them.

Your selected parts are perfect.

 

[tooppy]

On PSU are not necessary. They fall into the "nice to have" category, but you may omit them.

Your selected parts are perfect.

Thank you Jim for your quick reply.
Here is where I stand with the boards

An externally hosted image should be here but it was not working when we last tested it.

An externally hosted image should be here but it was not working when we last tested it.

Hope you can open these pictures.

 

[tooppy]

It seems the pictures cannot be opened, lets try something else

F5-board---Soldering-nearly-accomplished-back.jpg - Google Drive

F5-board---Soldering-nearly-accomplished-front.jpg - Google Drive

 

[6L6]

Looking good! Carry on.

 

[tooppy]

Looking good! Carry on.

Thanks Jim, can I set P1 & P2 to zero right now ?
Before soldering I put them all to mid value, I know P3 must stay this way.