DIY 5e3 - Too Much Head Room?!?!

[Kramer]

So I finished my very first amp build, a 5e3. I took it down to my tech so he could fire it up first there, and he played through it a little, and it sounded great, with lots of that early break up the tweed deluxe is known for, right? Well, he said that one of the 6v6's was red plating slightly, and after countless trips to RadioShack’s all over the place to find a beefier resistor, he just so happens to find a 470 ohm resistor laying around in his shop. He gives it to me, and I take the amp home and replace it. I turn it on, plug in, and turn it up to almost half way volume. No grit what so ever! Now, the stock resistor which he said was causing the red plating was 250 ohm. Is it possible, that just that one resistor could change the character of the entire amplifier that much?? Not that it’s a bad thing, it works perfect and sounds good, but I was really looking forward to that Neil Young tone for all this time. Any suggestions on how to get that early break up back? Perhaps try a 350 ohm resistor instead of the 470? I did some research and a lot of 5e3’s have a hot bias like that, so would it be “OK” to go back to that 250 ohm resistor? He said that if I ran it the way it was with the 250 I would be risking burning up 1 or both of the 6v6’s...is he maybe exaggerating a little? I’ll post pictures showing exactly what resistor I replaced. It’s a little messy, but keep in mind it’s my very first build.

Thanks!!

- Kramer

[novosibir]

I for myself don't like it much, when people who step on a new forum the first time can't say 'Hello' or something similar
Maybe because I've learned a different social behaviour in my childhood?

And this even is killing my mood, to give any help or advice

Larry

[Kramer]

Sorry, I was a bit rude coming right in here and asking for help. I wasn’t really thinking about it since I have had a lot on my mind lately, so please let me take the chance now to introduce myself..

Hi, my screen name is Kramer, but my real name is Alex and I live in Pittsburgh, Pennsylvania. I started playing the electric bass several years ago, but have since switched to mainly play just guitar. I like “rock”, but now days that can mean a lot of things. I can’t really name just one genre I play, but some of my favorite bands and players are EVH, Hendrix, Zeppelin, Rush, Aerosmith, Neil Young, AC/DC, Sabbath/Ozzy Osbourne, Guns n Roses, Clapton, Pearl Jam, Stevie Ray Vaughn, Dio, The Who and a lot more. I have had several hobbies over the years, but just recently have I started becoming interested in building my own amps. Surfing the net, I eventually found this place, and since I have become increasingly intrigued by the tone of these amps George has put together. I built the 5e3 first because it is a relatively simple amp to put together and I wanted some experience going into a 50 watt Metro Plexi later this summer, and hopefully a Metro JTM45 before the year is over! Every time I want to hear my dream tone I just go watch the YouTube video demoing a Metro 50 watt Plexi (I’m not kidding).

Also, as a suggestion you should include a dedicated section on the forums where new comers can go to make posts like this and where existing members can welcome them. I used to run forums myself and the need for an Introduce Yourself section became apparent very quickly as more and more people began joining.

- Alex

[woold]

I would put the 250R back in and then try the redplating tube in the other socket. If it redplates there it could well be the tube. Try another matched pair and see if the problem disappears. What tubes are you using?

I personaly like JJ for current manufacture tubes.

Try measuring the bias see:-

http://www.duncanamps.com/technical/lvbias.html" onclick="window.open(this.href);return false;

Hope this helps,

Dave

[Structo]

On 5E3 schematic they show a 250R 5w cathode resistor.
But you have to consider when that amp was designed the wall voltage was 110vac.

Most places in the USA are 120vac these days.

So all the voltages will be higher than what they originally were.
Unless the modern transformer is kept to he same secondary voltage as the original you have to fudge the values a bit.

To measure what the bias is set at simply measure the voltage across the cathode resistor and divide that by the resistor value.

I know this doesn't take into account the screen current but on a deluxe it's close enough.

Say you measure 15vdc on a 250R resistor.
15/250= .060 amps or 60ma. Since there are two power tubes feeding off of one cathode resistor you divide that number by 2.
So each tube is getting 30ma.
You can use the 1 ohm resistor method on each tube but that is kind of overkill on a Deluxe.
You can also bias closer to 100% dissapation on a cathode biased amp.

So if the plate voltage on the 6V6's is 325vdc you're looking at around 80% dissapation.

Which is safe level for the tubes.

One thing that can happen if one tube is drawing more current than the other it can cause problems.

You may simpy have a bad tube and that's why it is redplating.
Swap sockets with the two power tubes.
If the problem follows the tube then you know it's the tube.

If the problem stays at the socket you have other problems.

[Kramer]

Thanks for all the help, I tried the 250 ohm back in and switched the tubes and it worked perfect. To be honest though, I really have no idea what he was talking about red plating..

I swapped the 470 out with the 250, and also switched the 6v6's around. Seemed perfectly fine. Then, I switched the tubes back to the way they were originally...everything seems perfectly normal. It sounded noticeably different when I switched the tubes though, the way they were originally in sounded much louder than when they were switched. This is what they look like now, with the 250 ohm resistor and with the tubes in the original position. Mind I had the amp on for around 20 minutes or so before I took the picture. They were glowing pretty blue, but that’s supposed to be normal right?

[Structo]

Yes some tubes are bluer than others.
Sometimes it can be a symptom of a poor vacuum. Face it, they made tubes much better when everything from radios to TV's were tube powered.