Bias versus tube brand in the 5E3

[mbratch]

I've read a few different posts and articles regarding the bias in the original 5E3 design, and that it tends to be on the hot side for most 6V6s. So I thought I'd measure mine. My 5E3 has stock values in the circuit components (with little variation anyway - a 270 ohm power tube cathode resistor instead of 250 ohm).

I have 3 different 5Y3GT tubes that I tried:

• Ken Rad (USA)
• Sovtek (new - USSR)
• Tung-Sol (USA)

I have 3 different pairs of 6V6s that I tried against each of these 5Y3 tubes:

• JJ (new)
• Tung-Sol (new - USSR)
• Phillips (vintage)

Here's what I measured for plate power (at idle):

• With Sovtek 5Y3, JJs ran about 17.8 watts (plate voltages around 403V)
• With Sovtek 5Y3, the other 6V6s ran about 17.2-17.5 watts (plate voltages around 408V)
• With the non-Sovtek 5Y3s, JJs ran about 14.0-14.4 watts (plate voltages around 363V)
• With the non-Sovtek 5Y3s, the other 6V6s ran about 13.8-14.0 watts (plate voltages around 365V)

So what's up with this new Sovtek 5Y3? Do they all run "hotter" than other brands? Or do NOS 5Y3's generally run "cooler" than new 5Y3's (the Sovtek is the only new 5Y3 I have to check)? Or does it just simply vary tube to tube and you have to check each time?

Seems like in any case, these tubes are being pushed pretty hard. Should I be trying to find a way to bring down the plate voltage?

[stingray_65]

sovtec 5Y3 recto's are NOT 5Y3's even though they are printed that way.

they will likley not harm your amp, but they will give you a much different B+ voltage (higher) and thus create a different biasing no matter what power tubes you use.

ANY rectifier tube. and for that matter any tube, can sometimes have comparitveley HUGE differences. most are in the +or- 20% range

one of the things a lot of thermonic hobbiest love to do is what is called "tube rolling"

that is to say just pulling your tubes and putting in others and the difference is AMAZING!

you'll quickly hear differences, even swapping your 6v6's from V3 to V4 can do that.

remember too that back in the day when these amps were new they would just go to the corner store and buy a new tube and chuck it in.

the school of thought about " matching" tubes is a hifi thing and important to them as they are looking for the most neutral sound possible.

guitar amps are creating the sound and giving its own flavor.

I've gotten fantastic tones from the 5E3 by seriously mis matching my power tubes

by accident i had even had a 6K6 and a 6v6 in V3&4 and it had a very Marshall esque quality about it. I don't know the ramifications of continuous operation that way, but damn it was awsome

12A_7's can be dropped in V1&2 so try a few 12AU7 or AT7's or 7025's

even half worn out tubes can sound great.

plug em in and run em the 5E3 is rugged and will happily take the abuse


Ray

[mbratch]

Thanks Ray!

At 17watts idle power I was more concerned about the tubes than the amp. I wasn't even sure if the JJ's would handle it over a long time of use.

I had to discard my EH 12AY7 due to it being noisy. And since I had no spare, I put a 12AU7 in V1 just to get by. With that tube the 5E3 has as much volume/gain on tap as my BFPR, so it's a reasonable substitute. I also tried a 12AT7 in V1 but it was a little too gainy for me.

On the power tube front, I'll probably settle into various combinations but not a Sovtek 5Y3. That thing scares me!

But you're right: seems you can put all sorts of stuff in this amp and it just sounds sweet, in a different way.