F5 power amplifier

[udailey]

Great Thanks Mr. Pass.
Uriah

just got these and will use .5oz stuff for any preamps
http://cgi.ebay.com/20-lbs-Copper-Cl...742.m153.l1262
Thanks again

[ChuckE]

1) Is it possible to raise the F5's input impedance so as to make it even friendlier to a delicate tube preamp? (Mine likes a 470k ohm input impedance on an amp). What would be the effect on the F5's performance of doing this?

2) Could one use paper-in-oil caps in the power supply? I know a diy'er who swears by them, even in the power supply, for imparting a rich, full, warm sound.

Thanks.

[AMPMAN]

its the fairchild set that increases the output ,I mentioned that for the sake of completness.whether that is material is moot, I should mentionwhen I put a cap on the front the output goes to zero. Even so I am still not satisfied and will investgate further

[enzedone]

Could someone please confirm if these are the correct thermistors that are to be placed in series with R15 & R16.

http://newzealand.rs-online.com/web/...duct&R=1912257


Regards

Brett

[enzedone]

I have also found a site for the following. Which has a minimum order of 20.

http://www.ampslab.com/trans_2sj74bl.htm

What I'll do with 40 of these, but if that's what it takes to get this amp built.


Sorry for asking so many questions, but I'd rather check with someone who know's more than I do.

[jacco vermeulen]

Brett,

if you are only after 2 pairs of J74/K170 you could ask if someone has some spares for you.
PayaPalling a few dollars is easier on the wallet than shelling out $40 and be stuck with $36 in parts you don't have a destination for.
Maybe you should ask the right question.

[enzedone]

I have purchased a couple of chips from here before, and just happened to go back to have another look. I found a good deal on some parts for the F5.

http://tech-diy.com/inside_tech_diy.htm

I couldn't get get these here for this price and matched as well great stuff........




Brett.

[udailey]

ChuckE,
You might consider building the supply on the last page of the F5's operating manual.
http://www.firstwatt.com/downloads/F5-om_sm-080527.pdf
If you go to www.apexjr.com you can get 12,000uf caps for 1.99 each. The PIO caps will NEVER have enough capacitance to work well in the power supply for this amp unless they are the size of a broom closet. You could use them to snubber the supply though.
Uriah

[udailey]

Brett,
I had similar questions about TH1 and TH2. From the answers I received I think that the thermistor you found will work fine. It seems that the wattage it is capable of really doesnt matter much and you are at 4.7k so that should work fine. I have mine 90% built for some reason and not 100% so I cant say that mine fired right up no problem yet. However, I could also add that Nelson says in his paper on the F5 that the Thermistor is not necessary and a few people have left it out of their amp, replaced by a resistor. So I think you can count yourself safe with that Thermistor.
Uriah

[estman]

I measured IRFP244/SFH9240 @ 1,15A. And the results are good news: the tempco is negative for both.
Happy building without thermistors !