Building an F5 Turbo v2 (in-Progress)

[6L6]

The 100W incandescent light bulb goes in series on the live lead of a powercord. It's a resistor this way, and if there is a big current draw, it will limit the current by lighting up, which also indicates that there is a problem.

 

[PKI]

6L6, would you be so kind to post a link(mouser/digikey) on these pink silpads you use, please? I can't find them in this(big) size... :-( I use aluminum oxide and I do not like the result, the transistor is noticeably hotter than the sink next to it. Maybe, you can even measure this temperature difference? Thanks!

 

[oneplustwo]

I got these: Q3-0.005-00-51 Bergquist Company | Mouser

 

[PKI]

are those sold in sheets or not? I need them for Fairchild's — TO-247-3, I guess.

 

[oneplustwo]

They're individual pieces sized to fit TO-247 at 0.687"x0.562"

You can look for different options here:
Mouser Electronics - Catalog Viewer

 

[PKI]

Thanks I see!

 

[6L6]

You really want the pink ones - the black have about 4 times less thermal conductivity...

The pink can be found here - SP900S-0.009-00-104 Bergquist | BER178-ND | DigiKey I assume Mouser has the same in stock.

 

[PKI]

In this case these should be the best: SP2000-0.015-00-104 Bergquist | BER200-ND | DigiKey

 

[6L6]

Yes, that looks great!

The ones you linked are TO-220, do they have any in TO-247?

 

[buzzforb]

Haven't looked closely, but thickness plays into it as well.

 

[PKI]

They are TO-220 but size is: 25.40mm x 19.05mm, the same as yours, 6L6.
Regarding thickness:
SP900 has 1.6 W/(mK) @ .23mm thickness
SP2000 has 3.5 W/(mK) @ .38mm thickness

So, Therm cond./pad: SP900 0.37 vs SP2000 1.3 in whatever units

 

[PKI]

btw, why have you decided not to cascode?

 

[6L6]

Two reasons -

1) For illustrative purposes I am trying to build a V2 as close to the schematic as I can.

2) If all goes well, once the V2 is done, a cascode V3 will be made in the same chassis.

 

[PKI]

I see . It will be a very hot amp

 

[AudioSan]

oh. i've missed this tread 6L6 you will reach the chassis max before the amp's max

with +/-32V and 1.9A bias(standar V2) thats about what that chassis can handle without external cooling of some sort.
for +/-45V+ even a monoblock will have broblems when you bias it up to "full" power.

 

[toxic ingestion]

6L6,

Any update on your build? Are you able to keep MOSFETs from shorting out?

Thanks,

Steve

 

[6L6]

I've only just received (in todays mail) some different parts to try again. There is a place for a compensation cap on the output boards, and I needed to get some of those to try. I am also going to a much bigger value gatestopper.

 

[Rixsta]

Hi, nice build
Is there any reason to use the Thermal pads over Mica & grease ?
ive had best results with the mica

 

[AndrewT]

There is one brand of Thermally conductive pad that significantly outperforms 1thou mica.

So far I have not seen any Members posting details of any competitor product that can match Keratherm's Kerafol 86/83.

If the others don't catch up quickly, they can only go broke.

 

[PKI]

Some experience about thermal pads:
we discussed earlier these two:
SP900 has 1.6 W/(mK) @ .23mm thickness
SP2000 has 3.5 W/(mK) @ .38mm thickness

To not be speculative I bought two of them and tried. SP2000 are much better pads. I do not trust my thermocouple from DMM in terms of super accuracy, but with SP2000 TO-247 case of F5 is about 5C cooler.