Cathode Biased EL34s, Transformers?

[johndandry]

Wanting to build a Cathode biased 2x EL34 based amplifier. I am wondering about transformers. I am in love with the Dynaco A470 in My 4xEl84 build, but I'm guessing a 6.6k OT would be better? Maybe a Marshall JTM45 or Express style OT would be best? What about PT, want to use a GZ34, standard TW style good, using the 300-0-300v tap? Thanks!

[niversen]

I built a Rocket variant for a buddy of mine that used 2x cathode biased el34's and i used a classictone 50 watt jcm800 OT. I believe the primary impedance on that one is 3.2k. I've never heard a real Rocket or a clone in real life, but the amp i built sounds badass. And that OT is pretty competitively priced.

[hitchcaster]

matchless chieftian/clubman OT? just an idea

[LeftyStrat]

The Matchless Clubman I believe is 4k, so the A470 would be a good match. The 6.6k on the JTM45 was for KT66's. The JMP50 used 3.4k, but if I'm not mistaken, weren't there some Park amps that used 5k?

Depends on what you have or what you want to spend. The 50 watt Marshall might be cheaper. But the EL34/A470 is still a sweet combo for more Voxish chime.

[johndandry]

Cool. So if I wanted less chime and more brown would I move closer to 6k or down to 3.4k?

[LeftyStrat]

Cool. So if I wanted less chime and more brown would I move closer to 6k or down to 3.4k?

I'd go with a Marshall 50 watt OT. I think the chime of the A470 comes more from the fact it is a hifi transformer giving full range at 35 watts, and suitable for MI amplification up to 70 watts.

You may want to look at some of the Marstran JTM50 transformers (http://marstran.com) if you're going for more of a Marshall vibe.

[selloutrr]

The dynaco A431 would be a great middle 5k with tone of the A470.

[cpollack]

If you like the A470 this seems like an easy one to me. I'd just buy the Dyna MK IV transformer set from Triode Electronics and call it good. All the bases are covered, even your GZ34. HiFi guys have successfully converted the ST70 / MK IV topology to cathode bias for decades.

[Cygnus X1]

On a somewhat related note...what value do you plan on using for your cathode bypass caps?

[gingertube]

Did this for a "Junkbox Trainwreck".

Standard 50W Marshall Output Tranny Raa=3K4
B+=380Volts

Note: the grid mute in place of a standby switch. If you switch a standby switch with cathode biased output tubes (tubes hot) you get a huge current surge untill the cathode bypass cap charges up an blow B+ fuses.

Cheers,
Ian

[mark enger]

I used the classictone 50watt ot for my marshally cathiode biased el34 amp, sounded excellect, guy that has it now emailed me he played amp with out a speaker hooked up i tried the edcore 5.2k trainwrek ot i got from rj didnt sound as good as the classictone but sounded good, also ran a 6.6k old ot from a organ and it sounded good, i used a 1000uf 63v cathiode by pass cap, mark