1n4007 spike protection

[daz]

Ok, i think i understand what you're saying in a sort of tongue in cheek way. True, i know next to nothing about this stuff, but never the less, how big a difference would there have to be to make a 100 ohms difference in cathode resistor value normal? With voltages going up or down as much as 20 V i never calculated the need to change the R anywhere remotley near that much. Then again i could have errored because i was using a online calculator and maybe entering something wrong, who knows. Still seems like a lot to me when every schematic i've looked at is 250 ohms.

[Enzo]

To me? I wasn't being funny, tube dissipation is the issue, but just current, and plate voltage - or rather the voltage across the tube itself - is an important factor. 450v on the plate will be very different from 300v on the plate. So when comparing amps with wide variation in cathode resistor value, one must also consider the voltage it is running on.

If all these are roughly on the same voltage, then I guess we'd have to figure out case by case what they are trying to do.

[daz]

Thats what i was saying. Go look at a bunch of 6V6 amps. Maybe you'll find different and i just coincidentally happened upon a number of them using the same cathode R. But i'd say i looked at 10 schematics and all but that weber kit were using 250 ohm R's. So of course it would seem odd to me that this one amp has a cathode R thats a 100 ohms lower. Anyways, i'm using 250 as i was in my former el34 18 watt that i converted to 6v6.

[lowell]

Enzo is exactly right. You're not taking plate voltage into account. You're also not taking the tube manufacturer variable into account. JJ 6L6 tubes have a 30watt max dissipation, at least 5 watts higher than tubes of yesteryear. So you also need to take older designs and older tubes into account. My 4x6V6 amp has a low plate voltage of around 320-340VDC can't remember exact number. This allows for much more plate current than 450VDC on the plates... as Enzo pointed out. You should keep the sound you're after as the deciding factor in cathode resistor and plate voltage. Higher plate voltage and larger cathode resistor will lead to a harder, cleaner, overall brighter sounding amp and vice versa.

[daz]

But i think you're missing the point. I AM taking voltage into account, but my point is that all the amp schematics i looked at with 6v6 can't all possibly have the same plate V, yet they all use 250. So what i'm trying to figure out is why the weber kit uses a 150 and everything else uses a 250, a huge difference. Could it be all the amps i saw are about the same plate V and the weber has vastly more? I suppose, but it doesn't seem likely. Anyways, the point is now moot for me because i've decided to look at the possibility of building a EL34 amp if i can do so w/o any more trouble.

[lowell]

no the weber would have vastly LESS plate voltage if the cathode resistor is smaller. alot of amps have "standard" values, thus the 250ohm on most that you saw. w/ EL34 you can have a large amount of plate current so that'll be nice... assuming the plate voltage is in a stable range.

[Bruce / Mission Amps]

On that weber schematic theres something that confuses me. Every 6V6X2 schematic i've seen thats cathode biased has a 250 ohm cathode R. i would think a 4x6V6 amp would either have two, one per pair, or if theres only one i would think it would be either halved or doubled. But that shows a single 150 ohm. Any insight as to why this is and what i should do?

That is my amp design and it was based on using a specific Weber power transformer, with a specific plate voltage after rectification, .... depending on the actual rectifier or fake rectifier tube used [the solid state copper cap rectifier]... and then delivering that B+ into a specific inexpensive (smallish for the job) Weber output transformer.... that can or can not handle a certain amount of DC idle current with four 6V6 power tubes idling at high or medium high idle current and then while rockin' out, with a bunch of AC audio flowing through the OT.
In truth, I think the 5E3X2 amps (my Mission Amps name for that thing) with those trannys worked better with a 180 to 200 ohm cathode biasing resistor and a NOS 5U4GB. That is totally different then what a little 5E3 with two 6V6s would need with it's lower B+ and a soft 5Y3GT rectifier.
Regardless, you must know what the B+ is at the power tube's plates under idle current load, with respect to what kind of AC current will be riding on the OT when driven hard and be ready to change the cathode biasing resistor, and the screen voltage too.
You can not make these leaps of understanding with out some basic theory and reality info... which is almost always empirically derived...... that means lots of experience in blowing crap up and trying to figure out how to fix it before the customer shows back up.

[daz]

You can not make these leaps of understanding with out some basic theory and reality info... which is almost always empirically derived...... that means lots of experience in blowing crap up and trying to figure out how to fix it before the customer shows back up.

LOL!!! (i literally did)