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 How About Another Variation? - MikeT 05:01:41 05/19/04 (0)
 I believe the 420 ohm should go to ground. - VoltSecond 23:46:54 05/18/04 (1)
 Should it? - Bas Horneman 01:01:06 05/19/04 (0)

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 How About Another Variation? - MikeT 05:01:41 05/19/04 (0)
 I believe the 420 ohm should go to ground. - VoltSecond 23:46:54 05/18/04 (1)
 Should it? - Bas Horneman 01:01:06 05/19/04 (0)
 Re: Like so Mike? Parafeed compact 2A3 - direct 14:06:02 05/16/04 (0)
 Re: Like so Mike? Parafeed compact 2A3 - Kuei Yang Wang 10:27:12 05/16/04 (6)
 I have some 5842's and 6c45...but am afraid - Bas Horneman 13:28:42 05/16/04 (1)
 Re: I have some 5842's and 6c45...but am afraid - keto 17:17:20 05/16/04 (0)
 Re: Like so Mike? Parafeed compact 2A3 - mqracing 13:05:25 05/16/04 (3)
 "three magic building blocks" - keto 20:14:21 05/18/04 (2)
 Re: "three magic building blocks" - pistoljoe 05:02:38 05/19/04 (1)
 the Harry F. Olson book... - keto 17:07:49 05/19/04 (0)
 Re: Like so Mike? Parafeed compact 2A3 - mqracing 10:16:43 05/16/04 (21)
 No need for speed...take your time Mike - Bas Horneman 16:35:54 05/16/04 (0)
 Will the Robin Hood PF transformer with Nickel be suitable - Bas Horneman 14:22:28 05/16/04 (2)
 Re: Will the Robin Hood PF transformer with Nickel be suitable - MQracing 15:42:32 05/16/04 (1)
 O yes ofcourse the RH series is SE..(nt) - Bas Horneman 16:18:15 05/16/04 (0)
 Parafeed 2 - Bas Horneman 13:49:34 05/16/04 (16)
 Way Too Much Iron on that Chassis - Ejam 17:05:42 05/17/04 (13)
 Re: Way Too Much Iron on that Chassis - Sector-7G 05:47:35 05/21/04 (2)
 make that 8 pcs. Forgot the bias TX... - Sector-7G 17:48:32 05/21/04 (1)
 Re: make that 8 pcs. Forgot the bias TX... - fatbottle 05:14:32 05/22/04 (0)
 It can be done. - Jeff Lessard 19:25:59 05/17/04 (0)
 Way Too Much Iron on that Chassis - mqracing 17:30:31 05/17/04 (8)
 Mikey If We Are Talking Concepts... - Ejam 00:38:02 05/18/04 (7)
 Like this? - Bas Horneman 10:45:26 05/18/04 (6)
 Perfect Bas - Ejam 17:12:26 05/18/04 (1)
 You are welcome... - Bas Horneman 02:57:56 05/19/04 (0)
 Very Nice - MQracing 13:39:31 05/18/04 (3)
 Re: Very Nice - Bas Horneman 15:11:53 05/18/04 (2)
 how much are the svet 310's? - MQracing 09:32:09 05/22/04 (1)
 Around 45$ - Bas Horneman 01:05:31 05/24/04 (0)
 Hey!!! - Jeff Lessard 18:49:03 05/16/04 (0)
 PS..I'll love the schematic drawing...and seeing responses... - Bas Horneman 13:51:35 05/16/04 (0)

And thanks for drawing the schematic. If I could...

1) could you draw in a ground on the ct of the OT as you've done for the 173's ct?

2) make the value of the plate chokes 50H (then we could source the 003's)

3) would be neat to have option of grid choke in front of ECC99.... plus my hunch is that a gc in this position acts like a source (a sponge) for RF coming in at this juncture....

4) say a plate choke on top of the ECC99 (maybe 100H value)

5) I would be tempted to put the ccs in the tail of the cathodes of the 2A3's... and really tie them down.... but... likely I am missing some of the finer points of electronics!!!

just some additional ideas and thanks for taking the time to draw them out for me. Many thanks.

Mike

It may seem counter-intuitive, but one parallel feed capacitors will do fine. Using two only quadruples cost (2 Capacitors with double the capacitance required) and makes the sound worse.

If Mike could make a PP Parallel Feed Output with a the "centertap" brought out as two wires you could place the Cap there. Otherwise one in one leg will do fine.

Otherwise I second the recommendation of an anode and grid choke for the ECC99 (or even a better driver valve), simply adjust the input valves cathode resistor for the correct bias.

Sayonara

A late welcome and thanks for your post.

Where to put the dc blocking caps and what value to use could/would put us into a long thread and require more time from me than I can devote to the subject at this particular point in time.

The points I make below are subjective comments of my own... and should not be taken as gospel or, necessarily, propel us into a long thread. This said;

Allow me to point out that... even two caps of 5 to 6 mics in value is far less "capacitor" than the 40 to 80 mic caps that folks use in series feed arrangements to try to mimic or mirror ONE of the benefits of parallel feed. So... even if we count cap size (in microfarads) as a basis of quality then two 5 mic caps should "win" out the day... I think you might agree to this.

another quick point.... re: an illness known as capacitor-i-tis. Many DIY practioners will go out of their way to minimize the capacitor's value... beleiving it to moreso "removes" or make "invisable" the presence of the dreaded capacitor.... but.... ironically.... Mr. Murphy makes the effect just exactly the opposite.... the smaller the dc blocking cap value (all other things being equal) the moreso it's presence (electrically) is pushed further up into the audio range... if you really want to get the resonance point of the L and C down below the audio range.... and push it down even further.... then use more C not less.... more "c" makes the C moreso "disappear" electrically not less C.

I hope you C what I am saying :=)

Mike

P.S. as an aside... I don't buy into the capacitors are evil or resistors are evil or any such notion. I just always figure I have three things in my electronic tool/trick box to work with... capacitance, inductance and resistance... and getting a circuit to work well and sound great means using each of these three magic building blocks when and where they will work the best... none are inherently good or bad, evil or meritorious.... each can be used poorly or well.

---thanks for taking the time to draw them out for me.
My pleasure...I made the choke 30H ...saw that the exo3 was 30...

---I would be tempted to put the ccs in the tail of the cathodes
---of the 2A3's... and really tie them down.... but... likely I am
---missing some of the finer points of electronics!!!
So still the 120mA CCS and a negative rail? (I miss even the basic points of electronics) ;-)

Cheers,
Bas

Cheers,
Bas

One more observation: why mix SE/PP here? Why not use 6H30 to build cascodes differential setting driving stage with CS at the long tail below cathode instead of on top of plate? I rather put phase split transformer in front of the whole thing, this way, the input can be floated to both RCA and XLR inputs.

Cheers,
Bas

The Robin Hood PF has a UL tap at 43%. So you cannnot get PP behaviour from this primary winding.

We have in the design que some Brooklyns that would serve as our entry level series of PP output transformers. One of the Brooklyn's is a 20 watt 5K guy (B21). Unfortunately, the B21 won't be available with nickel lams as our supplier does not have the stamping dies for this lam size.

If ya want a nickel five K PP critter... you should be looking at the Peerless S-240's.

thanks,

Mike

Should only have this whole 2A3 compact finished in ooooo say a year from now ;-)

Forgive me for being a bit of a stick in the mud but now we are up to seven pieces of iron on the chassis! Too much of a good thing I think. All those magnetic fields interacting makes for one serious headache when mounting the iron on your chassis. I recall Lynn went down this path with his Amity and Aurora amps only to simplify his iron count later. Myself, I have found that it is a major pain to minimise interaction when there is more than four pieces of iron on a reasonable sized chassis. After all we have already used our three dimensions to minimise interaction. Oh, just a thought, bear in mind the poor bastard who has to lift this thing up!

Regards

Ejam

Enjoyed your post! Made me smile. First, keep it mind that this was/is just a concept... wanted to see it laid out...

second.... is that there could be considerable flexibility... build on two chassis (power supply on one... audio on the other)....

also... would be relatively simple to separate out the signal tranneys from the "support" tranneys... and not all of them are very large in size or weigh a ton each... so you could put some on top of the chassis and some below deck. And there would be naturally some "distribution" by function.... plate choke for voltage amp at different end of chassis than plate chokes for output stage....

and the neat thing about this circuit is that it loans itself to many different approaches.... as Bas has already shown you could use CCS in place of at least several pieces of iron....

and then... you could get rid of the tranney phase splitter and go "ultra compact" per Yeo's club offerings.

re: weight... doing this off the top of my head... but the 100 henry plate chokes probably weigh about 2 to 2.5 pounds each (only need one)... the EXO-003's probably weigh about 3 or 3.25 pounds each...
the 173 about 2.25 pounds.... output trans (depends on how overboard ya go) anywhere from say 3 pounds to say 7 pounds each... I think I am up to 18 pounds of iron.... not counting the power trans or power supply filter chokes... not too, too scary so far...

none-the-less, I enjoyed reading your comments.

Mike

As for the weight... Well, that would be a pair of amps you won't move often.

Was looking at Bas's and Keto's EXO-173 PP 2A3 amp and was thinking that a pentode driver instead of a triode driver might be worth a go. High transconductance pentodes run at high current make really nice drivers. Sorry no drawing package but if you want Bas you can draw this up for Version 3. Really appreciate it.

Take a 6688 pentode and using the data Pete Millet posted on his website: B+ 300V, Vpk = 130V, Vg2 = 150V, Ip = 21mA, Ig2 = 5mA and Rcathode = 50 ohms and Rplate = 8k (I used 8k2) operate it as the driver.

Use a DN2540 current source as use the load for a shunt regulator consisting of two VR150 in series. Set the current source at 41mA (21mA for the 6688 and 20mA for the VR tubes). Might have to heatsink your current source. The shunt regulator delivers 300V. Hook this up to the 8k2 plate load resistor. Taking the voltage from the first VR150 tube for your screen voltage of 150V. Cathode resistor is 51 ohm, no bypass. Input resistor 50k pot.

Using the EXO-173 phase splitter topology, that is single ended driver with EXO phase splitting for push pull 2A3 output stage. You will have to raise the B+ for the output stage a tad so as to get sufficient voltage drop across the current source, say 30V. As a suggestion operate the 2A3 at Vpk = 275V, Ip = 60mA and Vgk = -50V. Along with the transformer voltage drop this should give you about 330 - 335V, hence the required voltage drop for the current source. Now you can use a current source for the 2A3 but I like KYW suggestion of tying a 430 ohm resistor back to the 6688 cathode. In this case, adjust the 6688 cathode resistor to 9R1 (a 20R trimmer would be nice to dial it in) I know that it has been mentioned but ultrapathing the output stage with a 20uF oil cap between the B+ and the junction of the 2A3 cathodes works really well. So there you have a pentode driver. I can see the hairs standing up on some of the punter,s necks! I will let you guys in on a little secret, the 6688 is a great tube and produces a simple and very enjoyable PP amp. Listening to it now....fresh off the bench.

Regards

PS. forgot the power supply, 6DM4 damper diodes to an LC filter (5H-470uF). AC filaments.

PPS. iron count 4 and holding......

.

Now... if only you could substitute a WE310A for the 6688. I have a lot of 310A's :=)

neat stuff guys!

Mike

Regards,
Bas

Thanks for your great schematic.

Regards

Ejam

. . .Oh!. . .Remember: Modifying things voids their warrantee.

I'll try it and see, which I prefer.

Regards,
Bas

Joe

That's seven. I run speakers that are comfortable over 100dB 1W-1m and have to stick my head in them to tell the amps are 'ON', and there better hadn't be too much background noise or I'll have to look at the filamnets/switches.
I wouldn't mind adding a second grid choke either...
regards,
Douglas

...FB

Let me dig up the 310A's and see just how many I have...

I wonder how close the svet's would come....

sometimes with rarer original tubes... what I do is have like two sets of china... everyday stuff and the stuff you keep for company...

it's how I've treated my WE300B's... my "ears" are treated to modern not-so-costly versions and I save the good stuff for "company"....

so.... that's why I wonder about the quality and price of the Russian 310A's....

btw.... I was wrong when I said I had your 173PPS ready to ship... I do have some completed.... but the ones finished are built on M4 and you wanted nickel... so I stacked them the other day and will get them into the oven next week sometime.... apologies...

cheers,

MSL

Cheers,
Bas