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Hello,
Since this is my first project, I am trying to stick to the schematic pretty strictly (figure that is a good thing, since I am learning as I go). I decided to use a different option on the layout, and that calls out a slightly lower capacitance value in the high voltage supply - 2x200uf @ 500v vs 2x 220uf @ 500v. I assume that this not a problem, and from a post here, it sounds like putting it after the choke would be the optimal spot for it. The 2x220uf is one of the few caps I already have, so I hesitate to exclude it if there is no issue.
Please let me know.
Regards -- Roger
Follow Ups:
Hi Roger,
Are you sure, that 805 tube (860V, 130mA) is a good beginning for first project?
I'm afraid that this schematic is not correct, a little defective.
Original site (translated german to english):
https://translate.google.com/translate?sl=de&tl=en&js=y&prev=_t&hl=hu&ie=UTF-8&u=http%3A%2F%2Fwww.jogis-roehrenbude.de%2FLeserbriefe%2FRKoridon-Amp%2F805-Story.htm&edit-text=
It seems Shishido style amplifier, but Shishido san used TWO (!) series 3k5 output transformers. Most 805 Amp use 6k-7k5 transformer.
If you use single transformer, try 2000-2500V operating voltage version ones. Good 6-7k 50W SE (2kV) output transformer is large, heavy and very expensive.
Do you read it?
http://www.diyaudio.com/forums/tubes-valves/232484-midlife-crisis-my-833c-amp-build.html
I agree, I was expecting a feedback loop in there to kinda force the thing to work.
I would expect pretty disappointing bass fromost speakers out of such an amp.
I gather that 'x' is feedback from the output transformer back into the first stage. Not sure if 'y' into the 805 is also a feedback component and / or part of the hum adjustment for the tube......
Regards -- Roger
Ah, yes, there is some. Well, that will help things.
Hello,
I understand your point about the 805 as a starting project, but circumstances sort of dropped me into it. An abandoned 805 project came available, consisting of all of the correct, NOS Tango iron for the project, which includes the extremely large power transformer and 2 huge output transformers (as called out in the schematic) - also the correct 2 interstage transformers and choke, plus a couple of large caps (shown above). The transformers are beautifully built and finished - my only remote fear is that the iron are Chinese fakes, but they seem correct and way too nice for that, and I am not sure they ever went for the custom Shishido / Tango transformers.
I actually have recently communicated with Ronald, the author of the first article you included. He was very helpful. I gather many of his issues were because he could not source the correct transformers. I will indeed read the second article you provided.
I was trained as an electrical engineer back in the day of discrete components, and spent a fair amount of time at a bench building and testing boards, but that was 20+ years ago and had nothing to do with tubes. I do tend to want to validate things that I come across that are not clear (like the capacitor structure), so hopefully that will help me avoid a lot of blunders. I understand that it is quite complicated and a real undertaking, but I feel pretty comfortable with it and am not in a rush (which helps a lot).
Regards -- Roger
"(like the capacitor structure)"
As you can see this is the classical voltage doubler.
C1 and C2 may be such 2x...uF/500V Cerafine you showed, but C3 and C4 are single capacitors. R1 and R2 are medium wattage (2-3W) balancing resistors for stacked capacitors.
In my practice, single diode in voltage doubler sometimes busted. Over the 300V I use two series 600-1200V (SiC) diodes.
IMHO in SE amplifier last capacitor is more important, so this position I would use Cerafines. Paralleling each 2x100uF, then stacking them.
Partsconnexion ( http://www.partsconnexion.com/capacitor_ele_jensen_radial_sgl.html) sell Jensen 500-550V radial single capacitors. These types good for first stacked capacitors.
If you have a single capacitor that is 2x220uF, you can't use just it in either the first or second stage, as the caps need to be wired in series and these two section caps tend to share a ground.
You need two 220uF/500V caps in series behind the choke, and two 220uF/500V caps in series in front of the choke.
Do also be aware that the filament supply for the 805 in the schematic you posted is drawn, but not labeled.
Thank you very much for your reply. I tried to find a schematic for these, and had absolutely no luck. Also tried to ohm them out, but couldn't figure out an effective method. Given the way they always seemed to be used in circuit applications, I assumed that they were configured in a stacked / series configuration. Looks like that may have been an error.....
If indeed these are parallel rather than series, then it complicates things quite a bit..... Do you know these, and can you please let me know. These and the iron were pretty much what I got from someone's abandoned project, and I was hoping I could use them.
Regards -- Roger
All those caps have a shared ground, so you can't wire the internal halves in series.
You have two 2x100uF/500V caps in that photo. Parallel each cap to make two 200uF/500V caps, then wire each of those in series. No doubt this is what the project's originator intended.
The other cap was probably intended to serve as the 200uF/350V filter cap for the driver.
Thanks very much. Could I also use the 2 x 220 in the bottom portion of the high voltage stage, since there is a common ground there (both sides of the choke) and then stack a parallel 2 x 100 capacitor on either side? I realize there would be a slight capacitance difference, but would that matter??
I am aware of the filament supply. There are 3 variants of the design, and one of the other schematics has all the associated information (missing some watt information on some of the resistors, but I think I can calculate those out close enough). Thanks for asking though. I am trying to pay attention to every little detail since I have not done this before and want to do it right. I know there are not a lot of components associated with the build, but I figure they are all important or things will not come together well or properly.
Regards -- Roger
When you calculate resistor wattage with Ohm's Law, triple what you get and use a resistor of at least that power.
I wouldn't recommend putting two different electrolytic caps in series. We aren't talking about a ton of cash for caps here, just spend $50 and do it the right way.
Hello,
I put together a drawing of what I tried to describe above. I was thinking that one pair of caps has the 440 in between, and the other a resistor divider leg (perhaps not best description), so not strictly in series. Is this what you were concerned about? If so, suggestions on alternatives would be appreciated.
Regards -- Roger
Do this instead.
Hello,
If the dual capacitors are structured as you say, with a common -, then this is impossible. In your diagram the lower 1/2 220 has the - tied to ground, and the upper portion would require the - tied to 440.
Regards --Roger
I might suggest that you are way, way over your head on this project.
The upper capacitor is one can capacitor with the two halves paralleled.
The bottom capacitor is one can capacitor with the two halves paralleled.
You ground the ground of the bottom can capacitor.
You connect the positive side of the bottom capacitor to the negative side of the upper capacitor.
Hello,
That is what is depicted in my schematic, if you look closely. Each upper capacitor (2x100uf) is independent and the - is connected to the + of the capacitor below it. Fortunately the - terminals of both lower capacitors are connected to ground, allowing the use of a common ground dual capacitor.
In your schematic, the two capacitor segments on the right side share a ground ( - terminal) - they are the 2 halves of the 2 x 220uf capacitor. It is not possible to connect the + of one side of that capacitor to the - of the other half, because there is only one - for both capacitor sides and you already have it connected to ground. Maybe the terminology of 1/2 of 2x220 was not clear.....
Regards -- Roger
Ah, I thought the two capacitor symbols wrapped in a shroud represented two capacitors inside one can.
In any case, you have two 2x100uF caps, use each one like a 200uF/500V cap, and stack them for the first stage. For the second stage, purchase another pair of identical capacitors.
Hi,
Thanks for the resistor recommendation - will do.
Sorry if this is a dumb question, and perhaps I am misunderstanding, but what are you suggesting by way of a 200uf 500v cap that is not electrolytic??
Regards -- Roger
"Sorry if this is a dumb question, and perhaps I am misunderstanding, but what are you suggesting by way of a 200uf 500v cap that is not electrolytic??"
I never really said anything about a non-lytic cap. Just buy several 220uF/500V caps that are the same where you need to put them in series.
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