Plate resistor rating on a svt

[bakerlite]

Got an open plate resistor here on an svt classic (the new one), it's 200 ohms but can't make out the rating? Is it 1 or 3 watt metal? Thanks !

[xm52]

Which tube has the blown plate resistor? If it helps, on the SVT-VR, the 6550A plate resistors are 5 ohm, 3W, 5% flameproof. The screen resistors are 220 ohm 1/2W, 5% flameproof.

Since you are working an a current model, you can request a copy of the schematics from TechnicalSupport@loudtechinc.com . They will want the model and serial number. There is a partial set here http://www.amparchives.com/album/Ampeg/Schematics/Ampeg%20SVT-CL%20Schematics/index.html for the SVT-CL but it does not include the power tube board. There are some updates written on the schematic that you might find helpful.

[RicharD]

When in doubt, err on the high side, especially if it's eaten one already.  A 5 watt resistor will be fine where a 1/2 watt one was but not the other way around.  If you know the voltage across said resistor, divide the voltage by the resistance to find the amps, then multiply it by the voltage to find watts.  Take this value and multiply it by 150% and use the next higher standard size. 

[bakerlite]

  meant screen sorry!

don't know what got plate into my head.

looks like someone used 200r at some point. will replace all 6 with correct 1/2 watt 220r.

thanks again

[Cups]

TUT recommends 1k 5w.

[bakerlite]

Mmmm, does the book specifically reference the svt? 1k 5 watt is a Large jump for stock 220r 1/2 watt or does it refer to kt88's In General? Surely the different operating voltages from amp to amp put different demands on the screen resistor? For example what "takes out" the stock value may not destroy the 5 watter and do a different type of damage?
This is just me being curious as opposed to disagreeing I don't have the knowledge to disagree yet, hopefully one day I will and I can annoy the hell out of the lot of you!
Thanks folks

[RicharD]

I would NOT use 1/2 watt resistors on KT88 screens.  Screen currents rise sharply when rockin it hard.  I'd use at least 2 watt and keep the original 220 ohm value.  1k will give you more current regulation, a little lower voltage at the screens, and therefore probably need to be higher wattage.

[Cups]

Kevin O'Connor actually specifically refences the SVT in TUT 3. Saying the 22R resistors were there to "squeeze every last watt out of a sextet of 6550s" He says the resistors were shunted with diodes. He recommends removing the diodes and replacing with 1k 5w each. Says the amp never sounded so good.
O'Connor is a real champion of high resistance screens so take advice if you wish.