Have you ordered the new OTs for the NEW 5902 yet?
Those are going to be the CXPP-25-MS-4k ($58) ... right?

Will you be ordering the OTs for the 6V6 version at the same time too? Which ones. The CXPP-25-MS-8k ?

I did order the ot's for the 6V6

https://www.edcorusa.com/cxpp25-ms-8k

Have not ordered the 5902 transformers yet. That amp will be built for my Cousin later.
I also want to build the Paraphraser, after the 1019 is finished.

Just listening to some very sweet 5902 amplified songs.

Peter
I am thinking about needing a metal chassis to support those big OT's.
What do you recommend?
They will look Looney with the little 5902's when I build the second amp.
Not so bad with the 6V6s.

So what if they look lonely... ( if you are hell bent on max everything) it's a show of "overkill" for maximum freq range.... but only if you want it bad enough.
I'd be quite happy with the very respectable $27.00 (GXPP10-16-8K) ... with 8-ohm speakers gives 4k reflected impedance.

Correct Professor.
Just wanted to try the best for the 6V6 amp, that I can afford. The GXPP10-16-8Ks will work great for the 5902. I need to ask Cousin about his speaker impedance.

I can get 220uf caps at 450 volt. Do you think 440uf will work in the PS in place of the 470s? Would 520 be better?

I am happy with the sound of the speakers, so will finish them soon.
But even with the 5902 amp I have, the tubes don't look right with the big transformers. No big deal.

Does a big guy like you look "right" next to a tiny lady when she's all-a-glow?
Same thing.

520uf would be fine and 440uf is ok too. Can you get some 520uf @450v easily and reasonably priced.
I don't think you'll need more than 400v but more is safer.

I just bought this lot of 5 for $15.95... = $3.19ea... can't find 'em any cheaper.

Lot of 5 Nippon Chemi-Con 470 uf mfd 450 v vdc Industrial Grade Capacitor.
105 degrees centigrade rated.
http://www.ebay.com/itm/291304235685

They have 3 lots left.

I also just bought a lot of 5 pcs
50 ohm 10watt = $3.71
http://www.ebay.com/itm/171724341009?_t ... EBIDX%3AIT

and I only need three of these 39k 2 watters... ( in parallel=13k)
but the whole lot of 50 was too cheap to pass up...lol :
http://www.ebay.com/itm/290945067350?_t ... EBIDX%3AIT

520s I could get only in a flash style.
I have some 220ufs, 480 volt. But just ordered some 470s at 480 volt.
Now I have everything for the PS.

And there is 15" difference between me and my wife. So you see I am kinda odd.

I got the same cap deal. Not so bad at about 3 bucks each.

I had the 50 ohms and the 120 ohm, used for other stuff.

Great deal on the 39Ks also. I just went for the 8 pack. Let see, Mexico smuggled them from the USA. Sold them to China 20 years ago. They went obsolete, so sell the to us cheap. So they were actually made in the US anyway...
Some very good deals Peter.

Peter
I am going a little hog wild on this amp because I believe it will be superior and want the best.
Also when I retire work, I may have to watch my expanses.
I mean, the 5902 amp is very reasonable with costs but sounds great.
So, using a higher power output tube, a supped up PS, a better OT, and your refined electronics, I expect a very nice amp.
It might be my best amp.
I still need to build the RIAA preamp, and maybe a tone control preamp also, but later.
Thanks for your help. You have a way of a great explanation every time.

Great John:
Well if nothing else... at least you're have fun.. and learning a tad here and there. That's the part I like too.
Learning.. and then putting it to use on the bench to experiment and/or design and build rewarding projects!!!!!!!!

I hear that. I never do something that is not enjoyable.
And I have a lot of fun designing and building electrical-mechanical systems.
The amps I am building are the best. Thanks to you guys.

I started building the four CCSs last night. I had a Ratshack pc-board here that's made for 20 pin ICs with two on the board.


I found that I can get all of the 7 parts for each CCS on one 10- pin half-side of each 20-pin layout.

So now that I laid out one the other 3 will go together quickly.
The 25ma bias current set by the CCS creates 13.5v on the grid. So I set my clamping-Zener at several volts higher than 13.5.
So, I'm using 16.2v for the Zener because that's what I had laying around here.( 10v + 6.2v)
But I'm sure that 17v or even 18v will work ok too.

Peter
Is it ok to use a 24 volt zener? And is it ok to use 4001 diodes? What voltage for the 1000uf cap?
Thanks.

Hi John:
Refer back to that CCS theory I sent to you.

"The zener diode will put the hard breaks on the cathodes climbing too high in voltage due to rectification effects that result from overdriving the triodes. Just pick a zener that will break at some voltage beyond what you ever expect to find a triode biasing to at the desired idle current."
(The example drawing used Triodes not pentodes)

So I think it should be a few volts above the grid bias point.
For this 6V6 / 6AQ5 amp our grid bias is set to 13.5v @ 25ma
So the Zener should be 16v or 17v
(We used a 24v Zener in the 5902 because its bias was at 21v @ 20ma).

The diodes are Ultra Fast type. So they can switch quickly.
The Tube-Cad article recommended using type MUR410G
I chose to use an alternate, fast switching diode which is the UF4007 ... or UF4001 series.
Because it was easier to find and it seems to work fine.

Flip:
What's your thoughts on this question about how two "weak-testing" tubes operate with CCS bias?:
viewtopic.php?f=19&t=274417

It's a minor amusement but too many variables. For one, tube bias varies quite a bit, even when 'new'. What bias was needed then? Don't know. Another factor, it might have high grid leakage.

I had a similar situation, way back when, using my current mirror. If you remember, one side is (semi) normal cathode bias and the other tube is forced to match. Well, it performed normally until I inadvertently swapped tube locations. Turned out one of the 6EM7s had high grid leakage and when in the 'controlled current' side it was 'forced' to match the good tube but when swapped it ran away (plate current), with the good tube forced to follow it. Now, that was a much worse situation but it shows how 'CCS' can 'force' (seemingly) good behavior from an otherwise leaky tube.

If you really want to know whether its in range you need to put it on a normal cathode bias: each with their own bypassed R.

Oh yeah.
.. I did that. Too.
With a 540 ohm resistor in this same PP circuit instead of a CCS they both do the sort-of same thing; instead of a normal -13.5v which a "good/new" tube does.. the weakest one does -12 ( 22.2ma) and the other almost -14 (26ma)