OK New issue with JJ tubes!

[Bruce / Mission Amps]

Just built up a push pull, cathode biased, tweedish type Fendery amp with 6V6s.
About 370vdc at the plates with a @100ma PT.
350vdc at the screens.
Running a slightly lowish Zed 6K6 OT for this.
JJ6V6s idling right at 12.8 watts each.
The amp seems rather low in power output.... about 9.8 to almost 11 watts output.

10-11 watts in a 5E3 I can see... and would just accept that.

Tried an 8K OT.... same thing around 10.5 watts.
So I stuck in 6 different matched pairs of JJ6V6s with the exact same results.... <10-11 watts max output.

Pulled out an unmatched pair of old but NOS Russian 6P6S / 6V6 and ...bingo... 14.5 watts.
Tried a well used pair of those same tubes..... 13.5 watts.
Tried some new 6V6EHs.... +14 watts again.
Stuck the JJ6V6s back in.... 10 watts.
Put a NOS set of RCA black plates in..... 15.3 watts.

Randomly picked a new pair of JJ6V6s from new stock I had not yet tried.... 10 watts.

Sorry but a 40% increase in power using cheaper tubes is not cutting it for me!

What could possibly be going on here?
Am I just cursed with respect to JJ tubes!?
I think this is getting ridiculous.

[imaradiostar]

This seems peculiar. Subscribed to see what comes of it.

JT

[Tom Phillips]

It would be interesting to vary the dummy load resistance with the JJs installed and determine if the max power peaks at a different value than expected.

[Bruce / Mission Amps]

It would be interesting to vary the dummy load resistance with the JJs installed and determine if the max power peaks at a different value than expected.

Did that... ran 12 ohm power resistors (8 and 4 in series) on the 8 ohm tap and picked up an extra 2.5 watts.
Ran 16 ohms on the 8 ohm tap and got about 9.5-10 watts again.
I'm starting to think all my JJ tubes are bad from CE Distribution.
For fun, I tried two 6K6GTs with the 12 ohm load on the 8 ohm tap and got 8.5 watts.
They actually sounded killer too... ha ha

[Tom Phillips]

... ran 12 ohm power resistors (8 and 4 in series) on the 8 ohm tap and picked up an extra 2.5 watts...

Since they seem to put out more power with a higher impedance plate load it appears that the JJs are not true to the original 6V6 specifications, as are probably many current production tubes. The tubes you are testing do seem farther "off" than I would expect. However, since none of the current manufacturers need to pass standard tests in order to sell a tube as a given part number I guess we shouldn't be surprised.

[imaradiostar]

I don't know if you'll be able to compare but had the JJ tubes made sufficient power in the past?

JT

[Bruce / Mission Amps]

I don't know if you'll be able to compare but had the JJ tubes made sufficient power in the past?

JT

In the past, with my other fixed biased 6V6 amps at around 430vdc-440vdc, I've been able to get as much as 22-24 watts out of a pair of JJ6V6s fairly easily.

Side note:
I'm very surprised to see the cheaper Russian 6P6S, $6.00 tubes put out more power in this amp.
Also mildly disappointing, in some nebulous snobby way, is that the 6P6S tubes sounded every bit as good in this amp as the $22 a pair 6V6EHs.... both probably Reflektor tubes.
I'm thinking the lower B+ voltage has something to do with this....

[imaradiostar]

Thanks for the reply.

The new JJ's are low output- but do they sound bad? I don't mind lower output, especially if they still tolerate the high voltages they're traditionally known for.

Jamie

[wizard333]

I've got a ton of bad JJs from CE in the last few years. For a while I talked them into testing before shipping because I got tired of shipping/rejecting 80 tubes to get 20 good ones. That solved it til they started to refuse testing. Now I don't order from CE, but aren't they the NA distributor for JJ, so anyone who sells them here is getting them from there?

[Steve A.]

JJ started selling EL844's in 2010 which is a lower power version of the EL84. Perhaps they are doing something like that with the 6V6's that you received, Bruce. Possibly an unannounced beta test or maybe someone just screwed up.

So other than the lower wattage did they sound okay? Dr Z thought that the EL844's sounded okay in his cathode biased amps but Bill Machrone thought that they sounded terrible in his fixed bias Blues Jr.

Steve

[Bruce / Mission Amps]

JJ started selling EL844's in 2010 which is a lower power version of the EL84. Perhaps they are doing something like that with the 6V6's that you received, Bruce. Possibly an unannounced beta test or maybe someone just screwed up.

So other than the lower wattage did they sound okay? Dr Z thought that the EL844's sounded okay in his cathode biased amps but Bill Machrone thought that they sounded terrible in his fixed bias Blues Jr.

Steve

Yes, the cathode biased amp sounds fine with the JJs and I don't hear a night and day difference between the JJ6V6 and various other power tubes.
Maybe, the JJs sounds very VERY slightly darker.... really subtle.
I didn't mean to imply I could hear a big difference between 10-11 watts and 14-15 watts through any given speaker.

[nickb]

JJs are not true to the original 6V6 specifications, as are probably many current production tubes.

Probably true, sadly.

JJ do publish a datasheet for their "6V6". If I do a spot check on the datasheets at Vp=250, Vg2=200 Vg1=0 I get about 85mA for both JJ and Tung_sol so they should perform similarly.

Bruce, how about you set up a test with those conditions and measure the plate current on your JJ 6V6? I'd test one myself but I don't think I have any right now (..sounds of rummaging..).

[Tom Phillips]

That quote is overly truncated. I don't know that for a fact.

[loudthud]

Bruce, does the plate current seem low at idle on the JJs? Do you have good strong heater voltage? Does the screen current seem low?

[bob p]

That quote is overly truncated. I don't know that for a fact.

I hate it when that happens. If too much context gets removed then misquoting can make it look like you're saying things that aren't true.

It's probably not a good idea to cut up sentences when quoting. I prefer to leave a complete sentence as the smallest possible non-modifiable unit.