5E3 cathode bias resistor value

[chuckulaa]

Hey guys,

I have been putting this post around in different places on the internet.

I have bought the kit to build a 5E3 from weber. I'm waiting on the kit.

I am going to deviate slightly from the stock 5E3. I have a nice pair of matched NOS 6V6 tubes I picked up off eBay (I can't remember the brand right now. Maybe sylvania?)

I think I would like the sound of the hot biased cathode resistor, but I want to protect and preserve my power tubes. With the standby switch provided by weber, I would hope I could use the same power tubes for ~20 years.

I am planing on using more than 250 ohms for the 6V6 cathode bias power resistors. I am considering a 300-390 ohm cathode bias resistor. I was just hoping to get some of you to chime in about what cathode bias resistor value YOU are using, and any experience you have had with adjusting this resistor value.

Again, my intention is to keep the 6V6 power tubes alive for as long as possible, while not changing the tone of the amp too much.

[Firestorm]

If you want to save the tubes, keep the plate voltage low. Hard with a kit. Higher than stock cathode resistor helps a little, but the tubes will draw as much current as they can to produce signal into the load. Too cold won't sound great either.

[Phil_S]

In addition to what Firestorm says...
This is a cathode biased amp and the tubes will mostly do what they want to do. The stock R is 250r or 270r. You might want to change that for tonal reasons but it wont actually do much for tube life. This circuit runs very close to Class A (please, lets not launch off into discussion fo class of operation), which means it's going to be harder on the tubes than other push pull amps. You might consider a bigger dropping resistor between the plate and screen nodes to reduce screen voltage, but that might change the character of the amp -- I don't know, but expect something.

If you are going to build the 5E3, I suggest you will need to choose between tone and tube life. What's the point of having the amp if you don't have the tone? Tubes are meant to get used up and replaced. We all get used to that idea sooner or later. Or maybe you really want some other circuit, like a Princeton?

[martin manning]

Good advice, Phil. If you're going to build a Deluxe, then build a Deluxe. Depends on the power transformer, but a "real" 5Y3 will drop more voltage than some current production rectifiers. The right voltages are part of the tone too.

[chuckulaa]

Thanks for the advise guys. I guess I will go with something close to the classic 250 ohms. Maybe putting in a 300 ohm resistor will let me sleep better at night.

I'm excited to build this amp. I bought it because weber had a discount last august (10% off.)

[Phil_S]

Thanks for the kind words, Martin.

BTW, I don't believe the standby switch does diddly for tube life. I've eliminated them from my thinking and my building. Read here http://www.valvewizard.co.uk/standby.html

[tubeswell]

A stock 5E3 sounds optimum with a plate voltage of around 350 and a 250R cathode resistor on the output stage. The 6V6s should last for years if you run them in that configuration

[Blackburn]

I agree with everyone. Invest in some good old American made NOS tubes and don't worry about tube life.

[Tillydog]

FWIW: It's a lot easier to troubleshoot (should you have teething problems) if you build the kit 'stock' first, get it working, and THEN start modding.

0.02p

[Blackburn]

FWIW: It's a lot easier to troubleshoot (should you have teething problems) if you build the kit 'stock' first, get it working, and THEN start modding.

0.02p

Except for the first two coupling caps, right? Or do you guys like em with those .1s? I always use .02s in place of those.

[tubeswell]

FWIW: It's a lot easier to troubleshoot (should you have teething problems) if you build the kit 'stock' first, get it working, and THEN start modding.

0.02p

Except for the first two coupling caps, right? Or do you guys like em with those .1s? I always use .02s in place of those.

Yep. Me too.

[pdf64]

My view is that the intense vibration from being in very close proximity to the speaker is a significant factor in premature tube failure in combos. May well be the most significant factor as it affects pre-amp and power tubes.
The best thing is to use combos as a head - remove or disregard the internal speaker and use an external cab.
Pete

[rp]

I think the choice of CR value in the original Fenders, this includes the Champs, had to do with the lower wall voltage at the time and the USA tubes that were then available. The fact that BF/SF Deluxes cranked for years from the 70s onward with 125V at the wall and like 430V on the plates said it all about the quality of the old 6V6s.

Tone-wise Tubeswell is right on, though IME you could go up to 370V and still sound sweet, after that I can hear it, both champ and 5E3. With like 385V it doesn't sound bad just harder, less swirl, I actually, think darker though it should be more linear. Friend has a SF champ that had like 420V with a 250R, I think I put a 350 on it went through 20 ANOS pulls I had to find one that didn't red plate, it sounds good in his hands.

I also hear the CR when it gets to far from spec so I wouldn't go beyond 370R, i.e using 1K in a 5F1 to bring it inline isn't the solution. If you are finding that you are forced to use too high a CR and/or can't get the voltages down you need to get a different PT. I went as far as having heyboer custom make me one to hit the sweetspot that Tubewell notes too. It's well worth worth the $100 to get a 5E3 or 5F1 sounding right. Use the old PT for an other project.