P.I. PLATE LOAD RESISTORS

[ViperDoc]

I see on the layouts that 2W carbon comp seem to be the choice for [edit: P.I.] plate load resistors. I bought a handful of 2W CC resistors a while back and in testing them for value, they are absolute chaos. They may sound good, but when a 100K tests at 126K and I like higher plate voltages, I'd like something that sounds great but won't drift so much. I tested some 82Ks and they were everywhere. These resistors are likely ancient. What do you all prefer to use? Thanks.

[JMPGuitars]

When I use CC resistors it's on the PI plates (12AX7), not EL84s. EL84 plates are connected directly to the OT.

For the PI, I get new production 1W or .5W. Either are fine there as long as they're rated for the voltage.

It's not that big of a deal though, if you can't find good CCs for the PI plates, then use good MF instead.

[geoff 1965]

that's the same reason i did'nt use CC's on the phase plates,tolerance! i bought several 100K's and got from 83 to 120K in variation and thats new ones. i use the Takman CF's which have a 1% tolerance,you buy 100K and that's what you get.

[ViperDoc]

WOW, I am mistaken. I AM referring to the PI plate resistors, not the EL84s, since...er...there are none.

I've used 1W carbon film on several builds. You say MF is better?

[dbharris]

I ordered some 2W CCs recently (maybe from Mouser?) for my PI plates. 5 each of 100K and 82K, new production and all over the place for measured values. I just picked the value of each that was closest. Figured a little imbalance just adds character

[Bieworm]

Just for comfort I use MF, CF or MO all over. Those CC might measure good during the build but will likely drift over time.. there are already enough variables of faillure elsewhere

[TriodeLuvr]

I ordered some 2W CCs recently (maybe from Mouser?) for my PI plates. 5 each of 100K and 82K, new production and all over the place for measured values. I just picked the value of each that was closest. Figured a little imbalance just adds character

I would expect new CCs to all be OK to use. Were they actually out of tolerance? The standard 20% window is pretty big. Even 5% seems sloppy after working with 1% parts in solid state equipment. Actually, I'm more surprised Mouser was selling real carbon comps. The market is flooded with fakes that are actually spiral wound. Gave me hell 20 years ago in a piece of high power RF gear.

Jack

[ViperDoc]

I believe my 2W CCs came from Antique Electronic Supply. My 100Ks measure from 80K to 130K. I stopped after about 10 DMM tests, I just don't that kind of time. Measuring every component is a labor of love for the purist, and I admire that commitment--but that's not for this guy.

I just pulled the trigger on some 5% 3W Vishay MFs to get above 500V. I'm building a Superlite TMB with a slightly reworked layout. Chances are, it won't work properly and I'll give it a "proper introduction".

[JMPGuitars]

I believe my 2W CCs came from Antique Electronic Supply. My 100Ks measure from 80K to 130K. I stopped after about 10 DMM tests, I just don't that kind of time. Measuring every component is a labor of love for the purist, and I admire that commitment--but that's not for this guy.

I just pulled the trigger on some 5% 3W Vishay MFs to get above 500V. I'm building a Superlite TMB with a slightly reworked layout. Chances are, it won't work properly and I'll give it a "proper introduction".

That's overkill. 1W CMF resistors are rated for 500V, which is more than double what you should be seeing at the PI plates.

[ViperDoc]

I believe my 2W CCs came from Antique Electronic Supply. My 100Ks measure from 80K to 130K. I stopped after about 10 DMM tests, I just don't that kind of time. Measuring every component is a labor of love for the purist, and I admire that commitment--but that's not for this guy.

I just pulled the trigger on some 5% 3W Vishay MFs to get above 500V. I'm building a Superlite TMB with a slightly reworked layout. Chances are, it won't work properly and I'll give it a "proper introduction".

That's overkill. 1W CMF resistors are rated for 500V, which is more than double what you should be seeing at the PI plates.

I thought so too, but I couldn't find any alternatives in stock. The chassis will melt before those resistors, most likely.

[crgfrench]

I measure each component and document the values in each amplifier. Each amp has its own notebook documenting the build. OCD I guess?

[Bieworm]

I measure each component and document the values in each amplifier. Each amp has its own notebook documenting the build. OCD I guess?

Whatever keeps your boat floating, Craig!! Good practice I'd rather call it..

[JMPGuitars]

I measure each component and document the values in each amplifier. Each amp has its own notebook documenting the build. OCD I guess?

I also measure everything, but I don't document it. Most components are 1%, so that would be redundant. The CC PI resistors obviously are not that close, but I guess I'm less OCD?

[dbharris]

I ordered some 2W CCs recently (maybe from Mouser?) for my PI plates. 5 each of 100K and 82K, new production and all over the place for measured values. I just picked the value of each that was closest. Figured a little imbalance just adds character

I would expect new CCs to all be OK to use. Were they actually out of tolerance? The standard 20% window is pretty big. Even 5% seems sloppy after working with 1% parts in solid state equipment. Actually, I'm more surprised Mouser was selling real carbon comps. The market is flooded with fakes that are actually spiral wound. Gave me hell 20 years ago in a piece of high power RF gear.

Jack

Within tolerance but closer to the outer limits than the center.

ViperDoc, glad you are getting it straightened out.

-Dan