Hurricane Irene Amp

[TomMcNally]

I put this get*set*go together on Friday night, while waiting for
Hurricane Irene to come up the New Jersey coast and cause about
500,000 people to lose power, hundreds of downed trees and
branches, a hundred thousand or so peope evacuated and
general annoyance.

This amp used the Edcor PA-774 clone, XPWR005, and their
GXSE15-8-3.5K outputs, and a Triode C-254 choke.
As always, it sounds great, using new Sovtek 6B4G's.

Those of you eagle eyes will notice the holes for the plastic
"grommets" are cleaner, not deburred with the Dremel,
I picked up a 5/8" Greenlee Chassis Punch.

more stuff at http://tmamps.com

[battradio]

Very Nice as alway Tom .

Do the Sovtek 6B4G's sound much different than the old american 6B4'S .

Alway nicer to have the Greenlees , did you buy the beaing drive for it , i puchased a impack wrench to make it even easyer with them .

[Geek]

I thought it was Irene?

Professionally done. Great work!

[TomMcNally]

Hmmm you're right Gregg ... no sleep in 24 hours !

I've never tried other 6B4G's ... so no opinion there.

The Hammond chassis are pretty thin, so any punch has to
be used s l o w l y to avoid distorting the metal.

... tom

[EWBrown]

Looks great, and best of all, with no ocean storm debris I'll give it "three thumbs up"



FWIW, I use a larger size Unibit as my deburring tool, just keep the RPMs low, and don't apply too much pressure - and I just use a bit of "finger torque" on the Unibits for cleaning up the burrs from the inner surfaces of the front and rear of the chassis, where a drill can't be used.

There are two styles of the Russian 6C4C / 6B4G, the older 1950s vintage "Svetlana" has the twin plate structures as did the vintage US made 6B4Gs (these tubes essentially contain two 45s, internally connected in parallel).

I'd take precautions to not exceed the standard published 6B4G voltage, current and PD ratings with these older versions.

The newer Russian / Sovtek 6B4Gs are the single plate variety, and they sound equally good, and can take a bit more than the "normal" 6B4G voltage, current and PD ratings, as they are of a more robust internal construction There is also a 6A3 version, the exact same tube "guts" , but mounted on a 4 pin base, rather than on an octal base. I've heard of, but never have actually seen the Russian 2A3 copies, 2C4C.

/ed B in NC

[brians7]

That's one good looking amp Tom. Do you think there would be a improvement using a second choke. My speakers are 104db efficient. Thanks Brian

[EWBrown]

I've used the "second choke" technique, just remove the two 180 ohm WW resistors (R17A, R17B) in parallel, and connect a suitable choke across their former location. Here it is, from an early 2008 build:



The second choke (located in the upper left hand corner of the chassis) is connected across the R17 pads, as the choke's leads were too short to reach, I spliced them on to the twisted orange wires.

/ed B in NC

[TerrySmith]

Glad to hear you are OK Tom! Anyone heard from Sal? How many others from the East Coast?

Since I grew up on the Mississippi gulf coast I've seen many Hurricanes, most were mild like Irene except Camille in 1969 and Katrina in 2005. I'm not trying to downplay Irene, but it could have been a LOT worse!

[brians7]

I am also curious about using Edcore GXSE15-6-8k. Would there be any reason not to use this output transformer. I know there would be less power. Thanks Brian

[TomMcNally]

Sorry for the slow reply ... still busy with all the storm aftermath
here in New Jersey. The electric company is slowly fixing outages,
we ran a couple of transmitters on generators for days. I wasn't
affected by any flooding, but lots of areas in the state were.

I've never tried the dual chokes on a get*set*go, but have used two
chokes many times on the EL-34 SE amps, one choke per channel,
mainly in order to use smaller chokes and keep costs down.

An 8K OPT is way too high for a get*set*go, I've used lots of
5K with no problem, but the gurus say you lose a lot of power
with that high an impedance. It might be worth a try if you can
test them without cutting the lead length.

... tom

[EWBrown]

The Edcor GXSE15-6-8k would be a better match for an SE EL84, 6BQ5 or 6GK6, In triode strapped SE mode, they are "happier" with an 8K load than a 5K load, and the Edcor GXSE15-6-8k could be used with 6 ohm or 8 ohm speakers.

4 ohm speakers would also work, thought the THD would begin to creep up a bit (with a 4 ohm load, the primary would reflect 5.33K, which is still OK for an EL84.

With 6B4Gs, the 8K primary would be rather inefficient and power output would be rather low, less than 2 watts, probably closer to 1.5 watts RMS maximum.

/ed B