20 Watt OR120

[yossarian83]

I was recently reading about a lot of guys using the new high voltage 6V6GT's (JJ and Tung-Sol) in old high wattage Marshalls in order to crank em without killing their ears. Supposedly the plate voltage handling is 475 on the Tung Sol's, since my OR120 was running 470 with 4 EL34's I decided to get a pair and try them out.
I received my matched pair from Doug's tubes this afternoon, moved the impedance switch to the 4 ohm setting and installed them in my head. Lo and behold my plate voltage jumped to 490

I was initially worried but decided to give it a go anyway. Once I biased them up (17 ma per) I found I was able to crank em much much higher than I could with the quad of GT EL34M's that were in it.
They sound good, somewhat rounder and less middy than the GT's but differences between power tubes tend to be pretty subtle, it's all OR120! Currently there's no red plating and I'll keep you guys up to date if these fail but for now, after playing through the amp on 10 for the past hour, this mod is a win!

[drbob1]

You might want to drop the wall voltage slightly with a Variac or the transformer issues we talked about earlier-would put you back to 470…

[Jondog]

Or maybe a large Zener Diode like this : https://taweber.powweb.com/store/vdump.htm

[yossarian83]

Thanks for the advice but the transformer has already been modded for 125 input voltage. As I said, with the EL34 quad installed the voltages are right in line with the schematic. If I were to drop the voltages any further I'd risk altering the heaters and other internal voltages which could be bad news. I think the 6V6 simply pull less current (far less bias current for sure) leading to the greater plate voltage.

The voltages are sagging while playing which certainly helps although I haven't checked to see how much. So long as Tung Sol's estimates err on the side of caution, these should be fine.

Regardless, I've been playing through it all day and while it's still very loud, it's much more manageable than it was and sounds great. The voice of the amp just blossoms once you get it 3/4 of the way up. I'm happy with it as is and honestly, if any tubes last 6 months to a year with this kind of blasting, I'll be very satisfied. Time will tell.

[Jondog]

The Zener drops the B+ voltage. Not the input voltage.

[yossarian83]

The Zener drops the B+ voltage. Not the input voltage.

Those look interesting, it's be nice if it were switchable as I may decide to return the EL34's at some point. It could be a viable option but I'm not convinced it's necessary. If the 6V6's go frizzle fry in the next few days I may change my mind.

[Jondog]

The Zener drops the B+ voltage. Not the input voltage.

Those look interesting, it's be nice if it were switchable as I may decide to return the EL34's at some point. It could be a viable option but I'm not convinced it's necessary. If the 6V6's go frizzle fry in the next few days I may change my mind.

Install a bypass switch

[yossarian83]

That's an option but weber hasn't had them in stock for years. I guess I could get one from elsewhere but I'll wait to see if it's even an issue.
I don't put much faith in published voltage ratings for tubes seeing as I've
used EL34's with a max plate and screen grid well below what my amp was running without issue.

[OrangePaul]

Awesome, thanks for the heads up.

So does this particular version basically make them a straight 'drop in' alternative for most EL34 amps aside from re-biasing obviously..

[bclaire]

I wonder if it would be easier to get a DIVO and run them through that? I'm not sure if the DIVO can do 6V6's but if it can, that might be the better way to go.

[yossarian83]

Awesome, thanks for the heads up.

So does this particular version basically make them a straight 'drop in' alternative for most EL34 amps aside from re-biasing obviously..

Yeah Paul, that's right. The only other mod I've done is to the PT primary tap (125 vac input using the taps between 115 and 220) in order to get the voltages down where they should be.


Billy, I don't think it's be easier, the DIVO is a pretty elaborate mod whereas 6V6's are drop in replacements, the only mod I'd suggest would be for people in the states to change their PT primary taps, which is very simple. I'm sure the DIVO works just fine but it changes the dynamics of the output stage in ways that I don't necessarily want (makes it perfectly symmetrical). If these tubes fail in a month or two of regular playing, I'll consider it a no-go but even if I have to replace them twice as often as EL34's (or every 6 months) they're about half the price so it's still a good choice for someone wanting power amp saturation at lower volumes without having to compromise tone or buy a whole other amp.

[bclaire]

Gotcha... keep us in the loop as to how it works. If it works, I'll be kicking myself that I got rid of my two Superleads.

[OrangePaul]

So are you running it with a 16 ohm speaker load with amp set to 4 ohms?

Half down to compensate going from EL34's and half down again to compensate running 2 tubes in place of 4?

Yeah definitely keep us updated.. It's great you've volunteered to be our guinea pig like this

[yossarian83]

So are you running it with a 16 ohm speaker load with amp set to 4 ohms?

Half down to compensate going from EL34's and half down again to compensate running 2 tubes in place of 4?

Yeah definitely keep us updated.. It's great you've volunteered to be our guinea pig like this

No prob, man.

Just a quick update, I noticed a small amount of red plating biased around 90% (of 12 watts ) so I brought em down to 60% and they're behaving like they should.

After I fixed this issue I decided to break out my dummy load and check the output, with all controls at 5, the FAC at 3rd click from the left, and volume/gain completely maxed out I'm getting 35 watts. Quite a drop from the 180 watts I was getting from the quad of EL34M's.

[a.hun]

Just a quick update, I noticed a small amount of red plating biased around 90% (of 12 watts ) so I brought em down to 60% and they're behaving like they should.

After I fixed this issue I decided to break out my dummy load and check the output, with all controls at 5, the FAC at 3rd click from the left, and volume/gain completely maxed out I'm getting 35 watts. Quite a drop from the 180 watts I was getting from the quad of EL34M's.

Yeah that'll be a bit more useable anyway!

Have you tried biasing even cooler than 60%? Some even prefer biasing to below the point where crossover distortion begins, saying that it is an intrinsic part of the OR sound!
http://forum.orangeamps.com/viewtopic.php?t=5560" onclick="window.open(this.href);return false;

At any rate I think it is a great idea to let your ears decide these things. Be interested how cool you could get away with with yours, and since you are measuring power output how (little) that was affected too.


Andy.