which 300B project? help please

[cdeveza]

Richard,

You have to realize that the welborne labs kit is not exactly the same as the one presented here. The OPT that welborne lab is using is the model TM3KB, rated at 10watt and the one presented here is using ST3KB rated at 20watt, both from electra-print. The 300B cathode resistor is adjustable where the welborne labs is fixed. I think that the one presented is flexible and capable to be optimized to get more power off the amp. However, I feel that although they will not sound the same, I think both will sound good. You just need to match the welborne amp to a more efficient speaker.

 

[rick57]

Thanks

Alex

I knew the components weren't the same, but didn't know that the zipped parts list would produce a more powerful amp.

I'm building an open baffle active 3 way on based on Linkwitz's Orion; , with a 94 dB PHL midrange covering from 100 Hz to 1200 Hz, that I wanted the tube amp for.

It's to go in a generous but not large room. I sometimes listen loud (100-110 dB??)

Would either have enough power. Your thoughts?

What is the benefit of the cathode resistor being adjustable?

Regards

 

[cdeveza]

The amp presented here were measured (at the randall museum in san fran), and it gave an output power of close to 12 watts, the welborne labs is probably close to 8 watts. With 94db speakers, I would go with the higher wattage.

The benefit of using adjustable resistor on this amp is that you can optimize the operating point of the output tube. The welborne labs can be easily be converted to use adjustable resistor instead of the provided one. You can adjust the bias of the 300B by adjusting the cathode resistor, although its easier said than actually doing it.

Another thing is if I remember right is that the Welborne labs standard package uses Solen caps for the ultrapath, where as we use Oil caps here, which is the same caps offered by welborne on his ultra-upgrade package.

The bottom line I think is with the speaker that you are going to use this amp for, I think, you are going to need more than 8 watts of power, although this amp, the one presented here or welborne, has very high speed that you have a good perception of loudness.

Alex

 

[ashok]

Finally at the end ( for now )....

Gosh this thread is long. Took me quite a while to skim through it just stopping when I thought I could use some info.
Well I couldn't make a decision so I decided to ask. I hope this has not yet been answered.

I have some Sovtek 2A3's . After I try this I will make a 300B amp.

I want to make either :

a. A single tube SE
b. A parallel tube ( 2 x 2A3's) SE or
c. A PP 2A3 amp.

Which one would be best sonically ? Would the PP be far behind the (b) or (a) ?

Can I use a 6SL7 to drive it ? How about a 6SN7. I already have these tubes.
Thanks,
Ashok.

 

[Morse]

Hi Ashok;

Some time ago I built a 2A3 SET driven by 6SL7's - it uses a cathode follower arrangement (no flames please!) and sounds great. The schemo can be found at angela.com in their "how to" section. It's the JE Labs 2001 Edition. While the basic schemo is not mine, the layout and parts selection are, and the result can be seen at: http://home.earthlink.net/~shidenkai/id2.html along with pics of some of my other projects (you'll need to go to the links at the bottom of each page).

FWIW, here are the changes I would make if I had to do it over though. 1. PS Trafo - I used a Hammond 272JX - I would substitute the 372JX. 2. Chassis - I used oak hardwood throughout (the sidewalls are 1-1/2" thick) and would add a layer of 1/2" plywood under the top deck. That's because I had some problems with the stability of the oak due to transformer heating in one spot - the plywood really would have helped. It's fine now, but it took considerable bother to "fix up" that oversight. 3. Volume control - I used the hard to find Alps Black Beauty, and frankly would have been better served with the equally good and easier to find Alps Blue Velvet. The Blue Velvet is also sturdier in terms of the construction of it's solder tabs (that's the Black Beauty's Achilles Heel). Lastly, I used a 5U4G rectifier, rather than the superior GZ37 (5U4G is not a "slow turnon" variety, and it had caused problems with the turnon spike). After some mods (including a standby switch), it's fine - but it would have been easier to allow for that from the first, or just use the proper rectifier.

Hope I didn't put you to sleep!
Good luck on your amp and all the best;
Morse
PS You've made a fine choice in the SovTek 2A3. It's tough as nails and sounds great! It's one of the best buys on the audio scene these days, IMHO.

 

[ashok]

Thanks.

Hi Morse,
Your amp looks very nice ! The wood especially looks quite nice.

Thanks for all the details. That circuit looks good. I also saw one with a SRPP input stage. I found SRPP to perform slightly better audibly in some preamp stages. I wonder if that will be true in this case. In any case the amps have so few components that it is worth while trying them out. I guess voltage gain is also important. The SRPP will have much less gain.
Thanks again.
Ashok.

 

[Morse]

Hi Ashok;

Thanks for the compliments on the chassis work. One other addenda to my post would be that you should use a polyurethane glue (Titebond II "outdoor grade" or "professional" or something like that - read the fine print and you'll find out that the right stuff is a kind of polyurethane), which stands up to high temperatures better. The white glues tend to fall apart after a while of medium to high temp exposure.

>>>...That circuit looks good. I also saw one with a SRPP input stage. I found SRPP to perform slightly better audibly in some preamp stages. I wonder if that will be true in this case. In any case the amps have so few components that it is worth while trying them out...<<<

Frankly the circuits are so simple that you might want to try building both of them on separate, interchangeable, "plates". Then build a single power supply/chassis and try them both out. If you find that one topology sounds MUCH better to you, then you can always use the "surplus" mounting plate/amp circuit as a testbed for different topologies/components. To simplify the swapping out, you could design the chassis to use terminal strips so you wouldn't even need to undo any solder joins.

You could even try a 6SN7 cascade to drive the 2A3. It works for 300B, so why not for the 2A3?

Just an idea. Wish I had the $$ to pursue it these days, myself!

All the best,
Morse

 

[fdegrove]

Hi,

The SRPP will have much less gain.

That depends on what tube you're using, the main advantage of the SRPP as the input/driver stage for a SE amp is that you often have all the gain you require and a low enough Zout from a single stage.

As with everything else it has its drawbacks too so you'll need to decide which corners to cut.

Cheers,

 

[analog_sa]

even try a 6SN7 cascade to drive the 2A3. It works for 300B, so why not for the 2A3?

'works' is open to interpretation. it will certainly make some noises but these kind of drivers are largely responsible for a lot of negative attitude towards the 300B. Now a 2A3 makes a nice 300B or 2A3 driver. A bit more modest but also good is a 6L6 or even a 12B4 or 5687. If you want an amp with power and authority you have to use a powerful driver.

 

[pingfloid]

I also saw one with a SRPP input stage

Hi Ashok,

Where can I find that schematic?

Thanks

Manuel.

 

[siu sin man tho]

2a3 SRPP

hi Pingfiold,

pls see this 6SL7 & 12BH7 SRPP circuit. This is another circuit beside JE labs. I both test them & I use this circuit to build one SE amp two years old. Sounds quite good, my friend go to my home hear the sound & get it away. Paid money to me.
This circuit had a powerful & deep bass but good texture.

pls study & hope can fit for U.

thanks

thomas

 

[pingfloid]

Thank you very much, Thomas.

Regards,

Manuel

 

[ThorstenL]

Konnichiwa,

Where can I find that schematic?

Well, here is a schematic for a 2A3 PSE Amp by Kondo, it also has a SRPP Driver and sounds quite good, if implemented correctly and with the correct parts.

[IMGDEAD]http://www.ys-audio.com/wce/audionote2a3.JPG[/IMGDEAD]

Kondo nowadays also makes a version with build in Preamp, basically an "integrated" Amp alled Neiro-Ongaku, the linestage is close to the M7 shown below.

Sayonara

 

[Marlowe]

Hello Kuei Yang Wang,

I'm interested to build the 5687 preamp.
Is the PSU in the schematic of 5687 preamp for mono?
How much is the voltage at B+?

 

[ThorstenL]

Konnichiwa,

I'm interested to build the 5687 preamp.

Be aware output impedance is very high and cables need to be low capaictance and the permissable load is 100K or higher. This limits usability. The 5687 ise used one valve, one system per channel. Also note that the Silver Leaf output coupling capacitor and the silver wiring plus the KO-On attenuator are crucial to the sound of this preamp.

You can ge a nice Silver/Mica type that will be a nice substitute from www.diyhifisupply.com. Silver wire is from the usual places, attenuator is difficult to find, you could try a PEC Carbon Pot.

Is the PSU in the schematic of 5687 preamp for mono?

No, stereo.

How much is the voltage at B+?

Around 220V IIRC.

Sayonara

 

[Marlowe]

Thank Kuei Yang Wang,

Since the Audio Note silver wire and silver foil paper in oil are very expensive, why the power supply is just composed of conventional parts like white coffin resistors and CRC filter?

P.S.
Is the filament grounding (connected to pin 8 of 5687) also stereo?

 

[ThorstenL]

Konnichiwa,

Since the Audio Note silver wire and silver foil paper in oil are very expensive, why the power supply is just composed of conventional parts like white coffin resistors and CRC filter?

You may have to ask Kondo San that question.

Is the filament grounding (connected to pin 8 of 5687) also stereo?

The heater would be series connection between 4/5 for 12.6V.

Sayonara

 

[Marlowe]

Hello Kuei Yang Wang

The heater would be series connection between 4/5 for 12.6V.

But I still don't know the filament ground (the middle part of the schematic) is for one tube or two?

 

[ThorstenL]

Konnichiwa,

Originally posted by Marlowe But I still don't know the filament ground (the middle part of the schematic) is for one tube or two?

Given that there is only one valve (with two systems) the answer would seem obvious....

One!

Sayonara

 

[Marlowe]

Hello Kuei Yang Wang,

Therefore, That's only one tube (= two systems) for stereo channel?
The two systems in ONE 5687 are independent, not connected in parallel?

Sorry for my stupid questions,
but the schematic indeed made me confusing.