330-0-55-330 PT with 6V6 pp pairs

[pjd3]

Hello,

There are two ways I can go with this. My current build will use 6V6 PP pairs with a PT using Diode rectification which mathematically results in approximately (330 x 1.4 minus minus a few volts for the OT coil dcr) = 460 vdc B+.

Do you think the JJ's 6V6's are up for this? Note: this amp will be played at a low-medium level, pedal platform, fairly clean and not ever pushed.

I will check the DCR of the choke, I think its fairly high, 140 ohms or so but I will check. It's been claimed that the JJ's will handle up to 500V plate volts but try not to exceed 450 on the screens.

Do you think I'll be OK going with this or are there any caveats to watch out for? I was going to make a couple of B+MOSFET reducers but, I'd really like to avoid that extra complication if I safely can.

Thank you very much for your input.
Best,
Phil D - PJD3

[Roe]

might work. are the voltages unloaded voltages or are the unloaded voltages even higher?!

[dorrisant]

This JJ6V6S will hold. No sweat. I frequently run them at around 480-490... Long term, relatively abused, gig worthy.

[pjd3]

Hi Roe, thanks,

I believe I was seeing around 670 ac unloaded across the HT coil. I had all PT secondaries heat shrunk for the headphone test and was curious to see the HT coil end differential.

Thanks,

Phil D

[pjd3]

Thats good news dorrisant.

Sure hope that will be the case for my up-and-coming amp. I'm using a pair of JJ's now, but they are seeing about 440 on the plates. Been running fine and steady for over a year now of steady gigging.

Thanks man,

Phil D

[dorrisant]

I tried tracking down the original post for this info... No dice. The Wayback Machine tells us that the original link directs you a place no longer freely accessible. Here it is as a quote.

"What follows is a review of the JJ 6V6S by Lord Valve. I am unable to find the original source, but I found it so interesting that I decided to include it here. Judge for yourself.

"I just got finished doing the matching on my first batch of JJ 6V6s. Just for fun, I decided to see if I could kill the last tube in the batch. A good batch, BTW - only 2 croaked out of 150 during the 48-hour stabilization burn. And something odd - *all* of the 148 tubes that survived the burn fell between 13 and 21 mA during matching. I've never seen a batch of *any* power tube fall into a range that narrow. Somebody's doing something right at JJ. This is a BEEFY-looking tube - it's built in the same bottle as the JJ GZ-34, which makes it larger than any non-Cokebottle 6V6 I've seen before. The plates are also considerably larger than other 6V6s. Meaty!
Anyway...I decided to see how much current I could pull through the last tube before it red-plated. My test voltages for 6V6s are 425 plate, 425 screen, -40 G1. This particular tube read 15.6 mA at those voltages. I increased the current to 30 mA. No sweat. 40 mA. No signs of distress at 17 watts static, which is beyond ratings for this tube. 50 mA - no problemo. Still no red, not even a stripe. At 21.25 watts, we're well into 6L6 territory. (BTW, I let the tube cook for around 10 minutes at each level.) 60 mA - 25.5 watts static, passing max EL34 ratings now. No stripe. Jeeze...cue X-files music? SEVENTY mA. Beyond max spec for a 6L6GC...and *finally* a narrow red stripe on either side of the plate. I let it sit for ten minutes - whacked it with a nutdriver handle a few times. Happy as a clam. OK, I cranked the bias down as far as it would go...81.4 mA through the tube. The red stripes got wider, but nothing else changed. I let it sit ten minutes, then shut it down and let it cool off. After a half hour, I powered it back up and took readings from it at my standard test voltages. How' bout dat...15.7 mA, within 1/10th mA of the original reading. Aside from the fact that part of the logo burned off, the tube showed no signs of misuse.
I have no idea how these tubes sound yet, but I do know *one* thing: they are *damn* hard to kill. I sent two quads to Doug Roccaforte today; we'll see what he has to say about 'em. And if Jim Kelley is reading this, give me a call. *Your* amps are the most notorious 6V6 killers on the planet, and I think I may have something for ya. Interested in your take on the tone."
-Lord Valve"

https://ampgarage.com/forum/viewtopic.p ... 978#p21978

My personal experience is that I've built a Kelly clone that gets played regularly for several years now on the set of JJs i put in it, day one.

I have at least 4 JJ6V6S based ODSs out there that get gigged or used as a studio main-rig. Youngest of that batch is 4 years old and all are on the original JJs.

These are, off hand, 5 examples that I have personally witnessed running at voltage and current that would exceed the datasheet max of most 6V6s. The 4 ODSs mentioned above are all idling at about 36 watts. So those are biased hotter than the max on their specific datasheet... and still running... after at least 4 years or more. I have built even more running these tubes at similar voltage and dissipation. As a side note... all of these amps exceed the datasheet max of 450 volts on the screens.

So, if you want to find the limit of these tubes, this is a good start. Maybe we should continue that with a different topic though.

[pjd3]

Thank you for that dorrisant.

After looking at all of this I'm going forward with letting the 460vdc or so sit on the plates. Maybe set close to 70% emissions. By what I'm garnering from all of this information is I'll probably be fine with this. And of course I'll make sure the screens aren't getting too loaded. One thing I may have on my side is that this amp won't ever be pushed very hard. Its basically a pedal platform where I get all my overdrive from pedals, and the types of places I play call for a low to medium volume. Everyone is miced. (I'll need two mics once this is up and running).

I'm feeling pretty good about this now. Now, the JJ's will hopefully share my "feelings". I mean, tubes are people too, right? Sure.

The reason I wanted to keep away from using the B+Mosfet reducer was not to introduce any grounding/loop complications that I wouldn't be able to alleviate. Usually, when I think of the B+Mosfet reducer I think of using the chassis as a heat sink which could also be used as a return path for the Mosfet. I know there are ways to insulate the Mosfet electrically if need but, It would also entail finding a good spot for it, and real estate isn't quite at a premium with this (two 20 watt plexis in a Twin reverb chassis). I installed a B+Mosfet reducer in a Fender style amp, just 20 volts or so, to ease up the V on an expensive pair of WGB6L6's. Worked great. Used the chassis as heat sink and ground return, located it right near the base of a power ground also connected to the chassis.

OK, so forward march. Just installed the AC cord hole, power switch hole, fuse hole and standby (trickle switch) on right channel last night. It was a challenge to get all of that cropped reasonably to one of the chassis. Fun stuff.

Thank you for all of your very useful information. it really does help my decision-making processes and to move this amp forward. I've got my heart set on making this a good performer.

Best,
Phil D.