JJ 6V6's and output transformer.

[Alan0354]

That can well be true, maybe the JJ like lower primary resistance. I did not try that!!!! I am too busy, when I have time, I am going to use the 8 ohm tape to make the primary 4K and see whether I can get some more power out of the JJ.

[Chuck H]

That can well be true, maybe the JJ like lower primary resistance. I did not try that!!!! I am too busy, when I have time, I am going to use the 8 ohm tape to make the primary 4K and see whether I can get some more power out of the JJ.

DO report

[Rhodesplyr]

I'll take the small loss of power with JJ 6V6's over the short and sparky life of EH or (fake) TungSol russki's or chinese firecrackers. The difference between 17.5 and 22 watts, same as 1.75 and 2.2 watts. Not much to worry about.

I agree. I was simply trying to verify for Alan that getting slightly lower output from JJ 6V6s is to be expected and that it's not due to defective tubes.

[wozt]

Many thanks, been away for a few days in a wonderful isolated cottage in Wales. Lots of info for me to use. I am not wanting a FDR clone, just a 6v6 power section really. I haven't yet settled on my pre amp.

[Joe L]

Many thanks, been away for a few days in a wonderful isolated cottage in Wales. Lots of info for me to use. I am not wanting a FDR clone, just a 6v6 power section really. I haven't yet settled on my pre amp.

I did a comparison between identical FDRs, one with a MC DR transformer and another with a Heyboer DR and everyone present chose the Heyboer.

[Chuck H]

I am not wanting a FDR clone, just a 6v6 power section really.

I did a comparison between identical FDRs, one with a MC DR transformer and another with a Heyboer DR and everyone present chose the Heyboer.

Since wozt isn't necessarily after a Fender clone (and since we're whipping them out), I built three identical amps with two different trannies (EL84's, not 6V6's, but still in a similar power range). One with the off the shelf Hammond mentioned above, not one of their "guitar" models, and two with custom Heyboers. Everyone likes the Hammond amp a little better. IMHO they're similar enough that it's not worth getting your panties in a bunch. We've seen similar comparisons done here at other times too. I think one of the Marshall forums did one that included something like five identical recorded tracks, each with a different OT! MM, Heyboer, Hammond, Weber and I can't remember the fifth. In the end, with five different ones to choose from there were a lot of opinions on which was best. Proof positive that tastes vary. You honestly could have cut and spliced the tracks with four of them without really noticing if you weren't listening for it. The other was just enough thinner sounding to have stuck out, but still not profoundly different. I think any good OT is going to be good. wozt seems more concerned with the operating parameters anyway. Which, as we discussed already, is also not worth getting your panties bunched up. As long as one is using a primary Z within the suitable range and the OT is of good quality I'll even say that the PT could have a greater effect on the overall sound and feel based on what operating voltages one would choose. Certainly you'll hear more difference between speakers than OT's. Do choose a good OT. I'm not saying quality doesn't matter. Why build at all if we're not chasing that extra five percent of rich and tasty goodness that costs so much more than mass produced amps do? So do get a product of known quality and reputation. But I don't think it needs to be considered or fretted about beyond that.

[J M Fahey]

I did a comparison between identical FDRs, one with a MC DR transformer and another with a Heyboer DR and everyone present chose the Heyboer.

Interesting.

Did you use a plug in connector, say a Molex or similar, to plug in/out both transformers for comparison?

Or you soldered them in/out in the same open chassis?

How would you describe the difference?

Thanks.

[Chuck H]

Interesting.

Did you use a plug in connector, say a Molex or similar, to plug in/out both transformers for comparison?

Or you soldered them in/out in the same open chassis?

How would you describe the difference?

Thanks.

I interpret that the OT's were in two different amps. Different, by definition, is not identical. And of course there will be some tolerance difference in components, small variations in lead dress, etc. But how far does it need to go, really? I had three amps of the same model to play with. The two with the Heyboers sounded the same and the one with the Hammond sounded a tad better. Good enough for me.

[mcgruff]

As you increase impedance screen grid dissipation increases, plate dissipation will decrease though.

Do you think this is why Matchless used a 4k primary in the dual EL84 Spitfire & Lightning, ie to fine-tune the balance between screen and plate? I guess lower screen dissipation would add more headroom.

[Gingertube]

The lower power achieved with JJ would seem to me to be related to Vsat. The voltage you can swing across each half primary is equal to the B+ less the saturation voltage left across the tube when the signal swings peak positive on the grid such that Vg1k goes to 0V.
6V6, EL84 typically have a Vsat of 40V. 6L6 is typically 50 to 60V, so the comment that the JJ 6V6 is more like a 6L6 would seem correct.
Cheers,
Ian

[jazbo8]

I am not familiar with the JJ 6V6S, so I had to look up its datasheet, and it turned out that it is not quite the same as the 6V6GT, perhaps that would explain the lower output power, i.e., perhaps the "S" stands for smaller...

Plate characteristic compared against the 6V6GT:

[pdf64]

jazbo8, where did you find that JJ 6V6S info?

They only seem to publish curves for triode arrangement http://www.jjtubes.eu/image/data/powertubes/6V6.pdf

Over at TAG, Martin Manning has been using the uTracer to good effect, see The Amp Garage :: View topic - u-Tracer (Micro Curve Tracer) for his JJ 6V6S work.

Regarding a 6k6 p-p load for 6V6GTA, when plugging some guestimate loaded voltages into nickb's interactive data sheet Interactive Valve Data Sheets it does seem to result in the plate dissipation being rather over the 14W limiting value.

Winding the p-p load down to 3k3 (to simulate 4 ohm on the secondary from the use of an extension cab) pushes the plate dissipation to an horrendous level, even with the plate and screen voltages sagged lower still!

8k p-p for 6V6GTA seems about optimal for max power output at a reasonable plate dissipation.

As mentioned, the 10k p-p load on the JJ info is for a lowish VB+ of 250V, but also in class A1.
Plugging the JJ conditions into the interactive data sheet indicates a power output of 8.5W, rather than 10W.

[jazbo8]

jazb08, where did you find that JJ 6V6S info?

Using the triode curves provided by JJ, I was able to build a SPICE model which was then used to plot the pentode curves.

Over at TAG, Martin Manning has been using the uTracer to good effect for his JJ 6V6S work.

I'd forgotten about Martin's great thread, glad to see that the actual traced curves correspond pretty close to the one I made from the SPICE model. So it does suggest that when using the JJ 6V6S, the bias and the load need to be adjusted accordingly.

[wozt]

Posted this suggestion before ...
I've beern using these with push pull 6V6 with stunning results.
It is a medium quality HIFI tranny which makes it ideal for a guitar amp. I've also used these with 6GW8 (ECL86) with equally good results.
86PP output transformer.
Even used them with switchable Ultralinear in a 6V6 Guitar Amp.
Cheers,
Ian

Some happy browsing to do on that website, nice one.
What push pull schematic you following?

[PeanutNore]

I am thrilled with the discovery of this mableaudio site, though unfortunately it seems pretty hard to find power transformers with 115 or 120 volt primaries. Still, $18 for a push pull EL84/6V6 OT is a pretty awesome price.