Chorus II � 2a3 or 300B?

[Marvel]

Thanks Erik, I think I can handle that no problem... []

I'll add it to my summer projects list. The choke would be pretty easy to do to.They seem pretty balanced to me, but I know others might come to my house and go, "what the...." I even have bass on my LS with these guys. Must be something wrong.

After wrestling with the space inside an ST-70, these look more spacious than I remembered.

Time to go listen to them now, before I hit the sack.

[Erik Mandaville]

Bruce:

Of course -- please pardon the safety issue commentary. I do things like that all day long, and it just happens! Soldering in live chassis has been mentioned here before, and that's something that scares the hell out of me. Getting zapped is not my idea of fun, and I always want to mention the seriousness of working with active components like this. Problems can happen when we forget to be afraid!

Maybe try those little mods one at a time to see what each does, and you never know, maybe all of them combined make for a really nice sound for you. An equal chance, too, that you won't like any of them. I mention these in part because the first owner of you amp and I were throwing ideas around about the Ultrapath years ago, and were both experimenting with it. He makes an incredibly nice turntable, by the way.

I have a new idea for the Klipsch Heritage crossover autoformer, but I need to check some things out about it first!

Erik

[Erik Mandaville]

Oh: The MQ grid choke will fit fine on either side of the 2A3 socket (underside of chassis), which would be a great spot for it if you decided to adopt one for each amp.

Erik

[Marvel]

Of course -- please pardon the safety issue commentary. I do things like that all day long, and it just happens! Soldering in live chassis has been mentioned here before, and that's something that scares the hell out of me. Getting zapped is not my idea of fun, and I always want to mention the seriousness of working with active components like this. Problems can happen when we forget to be afraid!

No apologies needed. I am comfortable enough soldering and workin on my gear, but always a bit afraid as well.

It is funny that the one thing I sould like to try owuld be the most expensive... putting in the grid chokes. My budget is rather tight right now (whose isn't?), but maybe later in the summer.

I've saved all the info about the mods, so I won't have to ask again. Well, I won't have to ask if I remember where I saved it, anyway.

Bruce

[Cody_Mack]

8 watts > 3.5 watts > 1.8 watts per channel that is!

Yer gittin there. Just another 698.2 watts per channel and you'll be able to play real music. Someday........someday.

So that makes the pCAT only about 675 watts per channel short of being a real amp, capable of playing real music, eh?

[Clipped and Shorn]

"The Chokes are much, much smaller than the parafeed plate load choke or the 15H filter choke in the Moondog,..."

Where in the Moondog circuit do they use the 15H choke? just curious.

C&S

[Marvel]

The choke is in the power supply, between the first two electroytics, coming off the GZ37...

[Erik Mandaville]

"Where in the Moondog circuit do they use the 15H choke? just curious."

Read again the quote you copied regarding its comparison to the grid choke. The information you're looking for is already there. It's really not all that large in terms of value of inductance. In that respect, the grid choke is nearly 5,000 times greater, despite its physically smaller size. You are reading that correctly -- nearly 5,000H.

Erik

[Erik Mandaville]

Bruce:

"The choke is in the power supply, between the first two electroytics, coming off the GZ37..."

It does look that way at a first glance. The filter choke is actually between the 10uf film input to filter cap and the first of the two 100uf electrolytics. In effect, the 10uf bumps up B+ immediately after the rectifier, and from there through the choke and a large voltage dropping resistor. As far as textbook values go for the GZ37, 10uf is actully more than twice the suggested max value for an input to filter capacitor. There are a couple of people I know who have experienced premature rectifier failure as a result. Others with the same amp haven't had any problems at all. One could get by better, IMO, with a smaller value -- such as 1uf - 4uf, and then reduce the value of the large resistor mentioned above to compensate.

What happens is that the big input capacitor yanks up the B+ up too high, and the resistor says 'no' and knocks it back down again. Going the other way around, IME, is possibly more appropriate, mainly in that it's easier on the rectifier. The opinions of others may not see it the same way; I just prefer to stick to the book and extend tube life if possible.

Erik

[Erik Mandaville]

There is much less chance of possible arcing with a 5AR4, which makes a good substitute for the GZ37. It's not quite as nice looking (depending on what's in one's eye as far as beauty goes...), but appropriate. Others use the 5Y3 in 2A3 amps, such as George Wright's. It's a great tube, too, but has a directly heated cathode for an instant high voltage application. I think Sovtek makes an indirectly heated 5Y3, however.

Erik

[Marvel]

"Between" was a poor choice of words. I didn't want to post the schematic... we've been through all that before. [:#]

[Erik Mandaville]

""Between" was a poor choice of words. I didn't want to post the schematic... we've been through all that before."

Well, that's really what it looks like at first. An easy interpretation to make, Bruce. This very thing has come up before about the Moondog.

Erik

[Erik Mandaville]

"Hmmm? Sounds like a good controversy I missed."

I wouldn't say that. It was just a discussion about some common modifications some have made to this particular amplifier. Just a slight alteration of words to reflect accuracy regarding the position of a filter choke, Mark. Seems there is always controversy regarding SET amps on this forum, but this one is okay I think -- at least so far.

Have a good day,

Erik

[Duke Spinner]

I have to give my Opinion ..here ..

the Forte 2 would be a much bettr' match for your Amplification ...[]

[Audio Flynn]

Hmmm? Sounds like a good controversy I missed.

Na just the run of the mill flea power love fest.[]

2A3 I heard maybe 5 times and all times I was unimpressed with detail, attack and bass.

My room is 16 x 24 and I like to "sit on the edge of the orchestra pit" so to speak.

300B I heard do well on RF-7s once.

Of course it is all in the design and implementation just like in push pull. Still want to hear a 2A3 push pull someday...

[Marvel]

Still want to hear a 2A3 push pull someday...

You could travel south of the border and visit Tony. He has one of Jeff's PP 2A3 amps.

The controversy had to do with shring the schematic of the Moondogs. No more, no less.

As for detail, both of my sons love the Moondogs, detail, attack and bass... go figure. I know they aren't just humoring the old man. Maybe....[*-)]

[Audio Flynn]

Still want to hear a 2A3 push pull someday...

You could travel south of the border and visit Tony. He has one of Jeff's PP 2A3 amps.

The controversy had to do with shring the schematic of the Moondogs. No more, no less.

As for detail, both of my sions love the Moondogs, detail, attack and bass... go figure. I know they aren't just humoring the old man. Maybe....

That is why I made the comment on the "implementation". I am fairly certain I have not heard Moondogs. I hear a bunch but you cannot listen to all.

Even the big Moth Audio 2A3 I heard were lacking but they were being played through some monster folded horn furniture pieces with Lowther drivers. Impressive looking system but my Belles sound far better even with the "liability" of needing a crossover network.

Cannot rember where Tony resides.

Maybe between business and the new scuba hobby I will get a chance to get close by on the future.

[Marvel]

Cannot rember where Tony resides.

In sunny San Salvador. Might make a nice vacation. []

[Erik Mandaville]

"Even the big Moth Audio 2A3 I heard were lacking but they were being played through some monster folded horn furniture pieces with Lowther drivers. Impressive looking system but my Belles sound far better even with the "liability" of needing a crossover network."

Excellent point. The Moth in folded horn Lowthers is pretty impressive. I also use PP El-34s on our Klipschorns. But........an argument so weary and beaten to death here. Moondogs are nice 2A3 amps, too. I particularly prefer the absence of coupling capacitors in the Moth, which is just my cup of tea, but that combined with a Loudspeaker that doesn't have the drawbacks of passive inductors and capacitors to split frequencies between multiple drivers can, as you say -- in the right implementation -- make for some very good sounding tunes.

Many people find amps such as the Moth and Moondogs on speakers like Klipschorns, Belles, and Lascalas wonderful. That's why they continue to use them. Some don't. Some think using antique Klipsch Heritage horn speakers is absurd...laughable (I've heard that before). Some don't.

Erik

[Dmannnnn]

My amplifier has the option of being converted into a 2a3 amp. Running 300B now. The 8 watts seems quite ample. I can convert it but before I do I was wondering if people thought that the Chorus II would be fine with 2a3. It is 101db 1watt/1 meter efficient so I seem good there, its impedance curve seems somewhat severe from what I have read. Was wondering if anyone had any experience here or thoughts. I can always go back but if it isn’t going to work I would rather roll some 300B’s than spend the money on new 2a3’s. Thanks!

Did you make the switch? How did it turn out?