6080 SE amps? - parafeed or otherwise.

[Joel]

Frank, and anyone else - if you have any schematics or info on single-ended 6080 amps, please post them. I mean specifically designs with output transformers. 😉 Not OTL.

Thanks!

Joel

 

[qwad]

HI A few years agoHI-FI WORLD the uk mag published a DIY designed by mr T PARAVINCI, i HAVEN'T A scanner so if you email me your address I will send you a photocopy of the article😉
CHEERS, TJB

 

[fdegrove]

6080

Hi,

They're not easy to come by but here's one that I actually listened to and liked a lot on a Lowther system... not that I like the Lowthers but that's another issue.

And let's not forget Roberts' SRPP amp, I believe every word he said about these...although I'm not convinced that the 5998As would sound better in this particular app.

Cheers and enjoy,😉

Edit: if the cct isn't readable it's because I had to resize it.
Sorry.

 

[Joel]

Thanks Frank - that was the only one I could find also. I can't quite make out what it says for the transformer primary - 1k ohms?

 

[fdegrove]

6080

Hi,

1K is what I read and that seems a plausible value anyway.

It pretty much amount to the mats anyway, a slightly higher value won't hurt.

The OTL idea is a bit of a waste in your system isn't it?

Cheers,😉

 

[Sch3mat1c]

Check the Svetlana website. They have a PSE amp using their 6AS7G.

Tim

 

[Joel]

Thanks Tim.

The 700V supply in that one scares me though. 😱
I've never crossed the 450V line...

Also, I don't have a 1k primary transformer on hand, but perhaps I can use one with 2.5k just as well? I guess I have to go and draw a load line now... rats.

 

[dave slagle]

Thanks Tim.

Also, I don't have a 1k primary transformer on hand, but perhaps I can use one with 2.5k just as well? I guess I have to go and draw a load line now... rats.

hey joel,

you could also swap taps to get 1K25 on the trannie... just place an 8 ohm speaker on the 16 ohm taps....

its worth a listen,... if you build with the 2K5

i also think i have a bunch of 6080's if you need them... i'm in nyc also.

dave

 

[qwad]

yeah, you could also use the much cheaper and more common 6AS7, TUBE IF YOU WANT, instead of the 6080 or even a 6558 I believe, regards to you and as was suggested try different taps on the output tranny according to steve bench a bout 4,5k should be about right, if my memory serves me well regards to all😉 TJB

 

[Sch3mat1c]

If nothing else, then we can design one. I've been thinking of a 20-25W PP amp using a few of the dudes.
Should be no problem at say, 200V using a FW rectifier, then supplying the driver circuitry with 400V from a doubler.

Tim

 

[Joel]

Thanks Dave and Qwad. I have enough 6080's to last a lifetime, thanks to a very nice canadian fellow on eBay.

4.5k huh? Well, I have a set of 125BSE output transformers, which can be wired for a 5k primary - although this brings up a whole other topic which is how can the 125 series primary impedance change at all when all the connection adjustments are made to the secondary?
Anyway, obviously I'd have to use parafeed for the BSE, since it accepts only 45mA of DC. And how about a 10H@200mA choke in the plate circuit? See how everything starts to tie together nicely? 😉

 

[Sch3mat1c]

Simple, it's a transformer. Impedance seen at the primary is just a multiplication of that at the secondary (less losses). The ratio is equal to the voltage (or turns) ratio squared, for instance a 5k:8 ohm transformer has an impedance ratio of 625 and a turns ratio of 25, say 1500:60 turns.
So if you increase the load on the secondary (e.g. 4 ohm load on 8 ohm tap), the primary also appears lower.

Tim

 

[dave slagle]

Simple, it's a transformer.
So if you increase the load on the secondary (e.g. 4 ohm load on 8 ohm tap), the primary also appears lower.
Tim

just to add to this without getting into the depths of design, there are smart ways and dumb ways to do this.

there are a few other numbers attached to the impedance, mainly the inductance and the power handling and dc current, so make sure they fit in with the proposed swap.

lets take a 3K trannie designed for a 300B tube, we can assume the inductance is adequate for a 700 ohm Rp and an 8W output at 70ma or so.

now if we place a 16 ohm load on the 8 ohm tap, we will reflect back 6K rather than 3K but the other values will not chnage or be compromised.

now swap a 50 for the 300B, our Rp has doubled, but the inductance is still set for a 300B, so even if we reflect back 6K the inductance is set for 3K and problems might arise, but you won't know until you try it, expect the bass might get a bit lighter

going the other direction and (more than)halving the Rp as is the case with the 6080, and swapping taps the other way (8 ohm on the 16 ohm taps) our inductance stays the same, but our Rp has gone down, now the reflected load nears an appropriate load, and the extra inductance will only help us, of course thei comes at the cost of other compromises, but just trying it nets quicker and more accurate results than any amount of debate.

dave

 

[fdegrove]

THE PENTHODE MAN.

Hi,

Tim,

Obviously you're used to calculate for a penthode output.

For a triode output stage however an Ri x 2 should work well enough.

So, when we have a tube such as the 6080 with an Ri of 280 R per section a OPT of 600R primary should work fine into an 8R secondary.

Chances are that such an OPT will have better bandwidth at the frequency extremes too, if that's of importance.

All,

Let's not loose sight of Robert Morin's circuit either, it's simple and at least you have the creator's feedback on its' performance too.

Ciao, 😉

 

[dave slagle]

Re: THE PENTHODE MAN.

Hi,

For a triode output stage however an Ri x 2 should work well enough.

Chances are that such an OPT will have better bandwidth at the frequency extremes too, if that's of importance.
Ciao, 😉

also remember anywhere from 2-6X or more rp is acceptable when you use triodes... when considereing midband, where the music is the inductance doens't play as large a role...

and not only will the 600R have better bandwidth, chances are it will be more linear too due to the larger arigap needed to handle the extra DC... only problem is, a DHT sure sounds a lot better than the 6080 :-(


dave

 

[fdegrove]

Jokes Aside.

Hi,

LOL.

only problem is, a DHT sure sounds a lot better than the 6080 :-(

Not to my ears, a 6080 is pretty much like a DC heated 2A3.
There's a lot of family resemble here, both historically and sonically.

Cheers,😉

 

[dave slagle]

Re: Jokes Aside.

Hi,
Not to my ears, a 6080 is pretty much like a DC heated 2A3.
There's a lot of family resemble here, both historically and sonically.
Cheers,😉

luckily we all have out own tastes and opinions... now drive a 6080 with a DC heated 2A3 and you might get 2A3 sound, but at this point the 6080 / trannie combo act as a buffer rahter than an output stage, just go OTL and use a zero autoformer for the total best. (assuming that logic holds)

i chased the low Z tubes for a long time, they are so seductive from a trannie pov, but still a well designed AC heated chinese 2A3 through a good quality output has always sounded better to me.... so much for theory!

do note, that doesn;t mean i have given up on PP, and the low Rp tubes, just that i have yet to better the SE 2A3 with them, but i am still trying.

dave

 

[Joel]

Dave - of course handling all that DC in the core is a problem, etc. That's why it seems obvious to me that a tube like the 6080 is perfect for a parafeed circuit. With an Rp of 280 ohms, even a choke as small as 10H presents a hefty load. And the choke has a DCR of only 63 ohms...

 

[Joel]

power transformer

Oh, and also... I have the power transformer from a junked Fisher 400 receiver - it ran four 7868's in push pull. Is anyone of the opinion that this couldn't handle the current draw of both halves of a 6080 in class A?

I'm thinking it might get pretty toasty.

 

[siu sin man tho]

ji joel.

I had a question.
Sorry for the non-sense questions.
I still not understanding the different between se output & parafeed se output.

thanks

Thomas