F5Turbo Illustrated Build Guide

[nashbap]

Nicely done 6L6.

Can you tell me what is the hole size for the +, _ and speaker output wires on the board or what is the largest stranded wire AWG that can be inserted? Thanks.

 

[Liliya]

6L6

How the two thermistors are connected is cleary seen from your photos when the primares are divided(2x120V AC), but how should this be connected when it is 1x240V AC?

Does this thermistors have any influence on inrush problems?

Eivind Stillingen

 

[AndrewT]

one Power Thermistor to each 110/120Vac primary.

When the primaries are in parallel the 110/120Vac sees the mains supply through the resistance of one thermistor.

When the primaries are in series the 110/120Vac sees the mains supply through the resistance of one thermistor. Both primaries see twice the thermistor resistance between them and the mains.

 

[Liliya]

Andrew

Thanks for answering. Forgive that I need this explained with "teaspoon".
Is this what you mean? Or must another TH be added on the other side of C1?

Will the use of the thermistor influence on inrush, so I do not need a Soft Start?

Eivind Stillingen

 

[Zen Mod]

NTC of at least 10R

one or two in series

say one CL60 for 110Vac , two in series for 220Vac

 

[AndrewT]

The CL60 works well for 300VA to 600VA primary
If the transformer has two 300VA primaries, then two CL60 are required. One to each primary.

When the primaries are in series the CL60 are also in series.
Two CL60 now work well with 600VA to 1200VA 220/240Vac Primary.

This is the same as Zen states:

two in series for 220Vac

 

[Liliya]

Thanks again. I happens to have a lot of 5 Ohm 5 A. Can I use them, eventually two 5 Ohm in series to make 10 Ohm??

Eivind Stillingen

 

[AndrewT]

For a 230Vac supply with a 1.5ohms primary winding and two 5ohms NTC in series, the peak start up current is likely to be around 230*sqrt(2)/[1.5+5+5] = 28Apk

That will need a big fuse to survive repeated start ups over a period of many months.

 

[AndrewT]

for a 500VA transformer with a 2A close rated fuse I'd try to find the resistance that allows reliable starting over many years.
I would use 40r to 60r of added resistance to get the start up current down to <7Apk
A T2 fuse will likely survive that repeatedly.

 

[Liliya]

The tranformer in this project is 500VA and a ordinary F5 that I build for a friend
(2x18v AC). So I must look for 40-60 Ohms TH? Can you suggest a suitable one.

Eivind Stillingen

 

[AndrewT]

A series combination of 10r 5W wire wound ceramic cased resistors

 

[Zen Mod]

fixed resistors in soft start (relay equipped) are hardly universal solution ( think RC in time domain)

contrary to that , series connection od several NTCs (with even greater value ) are much more universal

 

[Zashoomin]

Is it possible to fit 2 monoblocks in one 5U chassis as to run it in balanced configuration.

 

[Zen Mod]

yup

 

[6L6]

Zashoomin - Possible? Yes, as in 'yes there is enough room'. But it's going to be tight, and definitely not fit on any of the UMS holes.

Also with twice the devices you will almost certainly need a fan for cooling.

 

[AndrewT]

A pair of channels for stereo takes up the same space as a pair of channels for balanced.

Both channels in either configuration will dissipate the same heat.

Why would he need to add a fan?

 

[6L6]

He said 2 monoblocks and balanced. I interpret that (and could be wrong...) as 2 channels balanced, which is twice the output devices.

 

[aeronautical]

Jim,

An amazing job! You are a giver!

Thanks

 

[vdi_nenna]

Is it possible to fit 2 monoblocks in one 5U chassis as to run it in balanced configuration.

I had the opportunity to see the F5T v3 in two 5U cases this past weekend. I was surprised that the 5U case wasn't as big as I imagined it. Not saying it's small, but not over-whelmingly big.

Just saying, plan your build accordingly. 450mm is only ~17.75" deep, 400mm usable!

 

[Zashoomin]

I had the opportunity to see the F5T v3 in two 5U cases this past weekend. I was surprised that the 5U case wasn't as big as I imagined it. Not saying it's small, but not over-whelmingly big.

Just saying, plan your build accordingly. 450mm is only ~17.75" deep, 400mm usable!

Ya I was doing some measurements and decided that a single chassis 4 channel design will be much more reasonable if I build the F4.