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Post subject: Hot Rod Deville/Deluxe 5w 330ohm or 470 ohm ceramic caps
Posted: Wed Aug 17, 2011 11:50 am
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Just a quick question. I am looking at a lot of information online about Fender using 330's instead of the 470's. I have worked on a Deluxe where the schematic shows 470's being used and I replaced these with new ones of the equivelant value. I have noticed even on the Justin Holton page that it states that changing to 330 is better. My question is has anyone verified weather or not fender is using 330's insted of 470's? and would there be a great change if a 470 was used where the schematic shows a 330 as it is on the HR Deville?


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Post subject: Re: Hot Rod Deville/Deluxe 5w 330ohm or 470 ohm ceramic caps
Posted: Wed Aug 17, 2011 1:13 pm
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The Dvl has a lower voltage from the transformer, and uses the lower value 330 ohm resistors. The voltage in this same supply in the Dlx is higher and needs the higher value 470 ohm resistors. Fender is not using 330 ohm resistors in the Dlx. This use of 330 ohm resistors in the Dlx by Fender, has so far proved to be an unsubstantiated rumor.

It is possible that Fender has recommended this in the past, maybe send them an email and ask. But, any recommendations that I've seen to use the 330s in the Dlx have come from somewhere other than Fender. I don't agree with it, wherever it came from, there is zero advantage in changing from 470 ohm to 330 ohm in the Dlx.

Deja vu!

BTW, these are resistors, not caps. (cap is short for capacitor)

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Post subject: Re: Hot Rod Deville/Deluxe 5w 330ohm or 470 ohm ceramic caps
Posted: Wed Aug 17, 2011 1:19 pm
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As Power = U^2/R. If R is lower consequently there is more power to dissipate in the resistors and more current in the zener diodes. This is a question of SOA design (Safe Operating Area) taking into account worse cases (also named corners) and choise of bias point of this circuit (not the bias of the valves).

Simply --> measure U on R and calculate power. Have a look on resistor specs and apply a derating for an operating temperature at 85 to 90°C, same for the diode and then you will have an good idea on the margin you have with lower resistors.
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Post subject: Re: Hot Rod Deville/Deluxe 5w 330ohm or 470 ohm ceramic caps
Posted: Wed Aug 17, 2011 1:28 pm
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Tis-san wrote:
As Power = U^2/R. If R is lower consequently there is more power to dissipate in the resistors and more current in the zener diodes....


That is exactly what my simulations show Tis-san. The 330 ohm resistors actually dissipate more wattage in the Dlx than do the 470 ohm, so more heat is produced using the 330s in the Dlx, by both the resistors and the zeners. :)

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