6l6 champ

[avspecialist]

Hi everyone. I am thinking of building a champ but i would like to use a nos RCA 6l6gc black plate and an 8 ohm speaker, any suggestions on which power and output transformer i should buy.  Can I get one large enough that would be versatile to even go  to a Nos Genelex kt88. thanks in advance, Bob

[shooter]

from the data sheet below, looking like 30W max plate dissipation, 300ish vdc on plate, ~4500ohm primary.
but you can "change" parameters to your liking, maybe;
want early breakup, keep plate volts lower, more clean, raise plate volts.  when you do that you have to rework the bias, current.

swapping in an 88 will probably work, but probably won't buy much without reworking plate volts, tube current. 

look over the datasheet, let your head spin, x-out the push-pull, and triode data, head still spins.

the key values for PT, filament current for ALL tubes used, or potentially used. (these values are on the datasheets)
Tube currents, also on datasheet, but you can sorta cheat, use ohms law, I=E/R, plate 300, primary OT 4500 = ~~~70mA, + 5-ishmA for each 12XXXX , fudge factor, so 100ma min, 150ma probably good

[shooter]

here's one of the better threads on how to build...........worth a read

http://el34world.com/Forum/index.php?topic=19777.0

[DummyLoad]

Hi everyone. I am thinking of building a champ but i would like to use a nos RCA 6l6gc black plate and an 8 ohm speaker, any suggestions on which power and output transformer i should buy.  Can I get one large enough that would be versatile to even go  to a Nos Genelex kt88. thanks in advance, Bob

depends entirely on a number of things: OT power rating, OT primary DC current rating and applied supply voltage. all needed parameters to determine PT and OT selection. how much power? how hot do you want to run 6L6? do you switch to optimize for KT88 or just plug-n-pray? e.g., one hole fits all...


--pete 

[DummyLoad]

see attached - my spin on the 5E1 champ: mostly PS modifications.   
voltages are estimates. should work fine & should be relatively hum free if wired with care. add a switch to C4 or omit C4 altogether if high gain is not desired.

--pete

[jjasilli]

This is what I did to convert an SF VibroChamp to 6L6.

[avspecialist]

Thank you all for your quick replies. I’ll have to read through all the posts and links. I look forward on building this amp and get the parts from Doug, i’ll be back soon as I progress getting the parts together.

[SILVERGUN]

here's one of the better threads on how to build...........worth a read

http://el34world.com/Forum/index.php?topic=19777.0

I thought it was a great example of how NOT to 

My 2 cents:
I still use the 2 SE amps for band use as my main rig.
They are very similar except the 6L6 version is fixed bias and the KT88 is cathode biased. Same iron. I used Hammond 290CX(s), and that is overkill, but the KT88 still manages to get it hot. The 6L6 transformers stay cool.
The 6L6 amp is audible with the drummer but I don't feel as though it projects enough to be usable on stage by itself.
The KT88 amp has much more sting and would work in a pinch by itself.

I use both amps at the same time and it can get plenty loud for "my" stage use.

The biggest tweak you could give it would be with speaker selection. Need more volume, go with higher efficiency. (I did)
Don't care about overall volume?...use a less efficient speaker with some character, like a Greenback

Last but not least:
The OT in Dummyload's schematic is a great, inexpensive choice for a 6L6GC equipped version - Classictone 40-18031

[shooter]

a great example of how NOT to

He gets the best of BOTH

joking aside, once you've built a couple "kits" and want to "design", that thread and others like it should
be mandatory reading
when the lightbulb starts glowing brighter, you're ready for the slide rule and questions

[jjasilli]

What's a slide rule?

[shooter]

https://www.amazon.com/Pickett-Slide-Rule-N-500-ES/dp/B0193FCOM4?SubscriptionId=AKIAILSHYYTFIVPWUY6Q&tag=duckduckgo-d-20&linkCode=xm2&camp=2025&creative=165953&creativeASIN=B0193FCOM4

good price

[PRR]

> What's a slide rule?

A back-scratcher with numbers on it.

Yes, $110 for an aluminum Pickett is a good price. Won't bind-up in damp like my $3 pearwood AcuDesign/Charvoz-Roos.

[DummyLoad]

> What's a slide rule?

A back-scratcher with numbers on it.

Yes, $110 for an aluminum Pickett is a good price. Won't bind-up in damp like my $3 pearwood AcuDesign/Charvoz-Roos.

fly swatter... multi purpose tool.


--pete

[jjasilli]

It looks so thin.  Where do you put the batteries?

[shooter]

my $3 pearwood

I was a poor white boy from the hood, mine was plastic
$99 for a 4function TI was a pipe dream

[DummyLoad]

oilfield trash here. mine was a ti59 with IMCo drill mod.


--pete

[sluckey]

SR-11 was my first. $99. I threw my slip-stick away! Two years later when I went to the FAA Academy in OKC, I traded up for the SR-51. Same price. 

https://www.ebay.com/itm/Texas-Instruments-SR-11-Calculator-Charger-Case-w-new-batteries-working-Clean/292391690869?epid=114744055&hash=item4413e72275:g:yUIAAOSw5VtZxnkO

https://www.ebay.com/itm/Vintage-Texas-Instruments-SR-51-II-Calculator-and-CASE-Very-NIce/292392334315?hash=item4413f0f3eb:g:FzIAAOSwiHpaIe6B

[2deaf]

When I was a freshman at UCLA, they didn't allow calculators because they felt that only the affluent students would be able to afford them.  By the next year, TI became a donor and the ban was lifted.  I continued to use my slide rules throughout my college years even though I also had calculators.   

[PRR]

> I was a poor white boy from the hood, mine was plastic

No, you are dating yourself. Once Sterling over-produced good plastic slipsticks, low-price wood vanished from the market.

> $99 for a 4function TI was a pipe dream

Late in school, Sinclair offered a calculator KIT for significantly under $99. I bit. It worked all but one segment on all the digits. I even knew enough to diagnose. I don't recall if I fixed it. TI's prices were falling so fast I soon had something between the two models Sluckey cites. Did a LOT of work on those. Still a TI guy, 30Xa at hand now, though fussy (for a couple years TI was making the decimal points way too small, and I was repairing older ones to keep going).

[DummyLoad]

> I was a poor white boy from the hood, mine was plastic

No, you are dating yourself. Once Sterling over-produced good plastic slipsticks, low-price wood vanished from the market.

> $99 for a 4function TI was a pipe dream

Late in school, Sinclair offered a calculator KIT for significantly under $99. I bit. It worked all but one segment on all the digits. I even knew enough to diagnose. I don't recall if I fixed it. TI's prices were falling so fast I soon had something between the two models Sluckey cites. Did a LOT of work on those. Still a TI guy, 30Xa at hand now, though fussy (for a couple years TI was making the decimal points way too small, and I was repairing older ones to keep going).

this one?


http://tronixstuff.com/2013/09/27/kit-review-sinclair-cambridge-calculator/


--pete

[kagliostro]

I also had an SR-10 or SR-11 (didn't remember well)


I spent a large part of my (student) summer holidays, working (it was my first payed job) and I invested almost all the pay to buy the calculator at 110.000 Lire that for the time was a high price


Franco

[shooter]

back on topic

I looked up your BB thread for that amp, "guidance" for my Hybrid build, why 56k for the grid leak(?) R's(12 & 13)?  doesn't that overly limit the clean input signals swing?  I'm at 220K
thx

No, you are dating yourself

I was in 9th grade when I got my plastic slide, I lusted after the instructors Pickett, and the rich kids TI's.  I also realized that year girls didn't care which method you used to "solve the equation"

[DummyLoad]

back on topic

I looked up your BB thread for that amp, "guidance" for my Hybrid build, why 56k for the grid leak(?) R's(12 & 13)?  doesn't that overly limit the clean input signals swing?  I'm at 220K
thx

No, you are dating yourself

I was in 9th grade when I got my plastic slide, I lusted after the instructors Pickett, and the rich kids TI's.  I also realized that year girls didn't care which method you used to "solve the equation"

these KT120 are running hot and will become gassy over time - 56K grid leak is for fixed bias. i can get away with 220K in the schematic i presented. probably should change that and do away with the CF. i fixated on the fixed bias plan (pun?) when converting the original schema to auto-bias. brain fart. i'll delete that schematic and reply later: post a redux...

clean signal is not an issue with a cathode follower to drive 28k load. with 220K we can omit CF. it will breakup early for a 40W amp.

--pete

[DummyLoad]

three spins - two in this reply.


--pete

[DummyLoad]

...and the third.


--pete

[shooter]

grid leak is for fixed bias.

ah, thx Pete

[VMS]

Borrowing this thread a little:


I'm weighing OT options for my SE build.
I'm between hammond 125DSE and classictone 40-18031


Could the classictone be used as ultra-linear and what would the percentage be on that 5k tap?


http://www.classictone.net/40-18031.pdf

[shooter]

used as ultra-linear

nice idea, not sure it works, but don't know why

the percentage be

guessing it would be 5000/8000 * 100

[VMS]

guessing it would be 5000/8000 * 100

I was thinking this too but from which end do you take the percentage?
Is it 62,5% or 37,5%

[VMS]

now that i think of it, i guess it can be wired both ways but which is which?

[sluckey]

For that particular transformer you would connect the blue to B+, the brown to the screen, and the red to the plate. If you try this please give us a report.

[jjasilli]

A couple of comments:

I think true UL requires some clever winding technique; not just a simple tap    .  Anyway, for guitar amp, that probably won't matter, and it's a creative way to get a lower screen voltage!  (If it's less than perfect maybe add a screen filter stage which would not be needed with true UL.)

Also, I suspect the "screen tap" voltage will be different in factors of 1.414, not simple division.


Maybe someone with more knowledge or experience could address these points.

[VMS]

Thanks guys.

For that particular transformer you would connect the blue to B+, the brown to the screen, and the red to the plate. If you try this please give us a report.

You are probably right but I'm looking this page:


http://www.r-type.org/articles/art-139.htm


and just by looking the picture there maybe i would connect red to B+, brown to screen and blue to plate   


Picture also shows turns percentages and impedance percentages so which one is usually mentioned in proper UL OT?

[VMS]

Upon further reading:


https://www.ampbooks.com/mobile/amp-technology/ultralinear/


I have come to conclusion that the 5k tap would be in UL terms about 61% tap which is no where near the usual 40% tap. So this would probably not be a good UL OT.

[jjasilli]

Yes, this use of the classictone 40-18031 is not true UL.  From the literature you cite it does seem that it will work, as sluckey says, but with more harmonic distortion than 40% UL along with more power output.  Again, maybe an interesting choice for a guitar amp, unless you really want true UL operation.

[PRR]

> true UL requires some clever winding technique; not just a simple tap

The concept only implies a tap. G2 at B+ end is Pentode, G2 at Plate end is Triode, in-between is in-between.

I dunno about "true". But going UL often implies a wish for a "good" amp, so the OT should be planned and wound for good performance. Going from Kay to Dynaco, those ClassicTone windings are on the high end, even if not as tediously wound as the Dynas. I think the "dual-Z" tap will be good-enough for any purpose in this forum. If we need Fine Wine, there's core-sniffer forums for that.

The tap is 80% one way and 20% the other way. (Turns ratio is not impedance ratio.) 80% is near-enough triode to hardly bother. 20% makes no sense on the Mug2=10 tubes like 6V6 6L6 EL34; they will be practically pentode. It may have some effect with higher Mug2 tubes like EL84.

[VMS]

Thank you. So my math was way off again 
How do you get 20% and 80%


Thank you in advance

[jjasilli]

From Aiken amps (NFB page):  "Note that the tap voltage is not linear with respect to the impedance, it varies linearly with the square root of the impedance. That is, the voltage on the 8 ohm tap is not half the voltage on the 16 ohm tap, rather, the voltage on the 4 ohm tap is half the voltage on the 16 ohm tap.  It helps if you think of the equation for power: P = V^2/R.  If you have 100W into 16 ohms, the voltage is V = sqrt(100*16) = 40V RMS. If you have 100W into 8 ohms, the voltage is V = sqrt(100*8) = 28.28V RMS.  If you have 100W into 4 ohms, the voltage is V = sqrt(100*4) = 20V RMS."


Though Aiken is focused on NFB, it's true for voltage per impedance taps generally.  That's why the 5K tap is not 5/8 of the 8K tap in terms of voltage output. 

[DummyLoad]

it's a champ...why do you care about UL? you loose some output stage gain in UL mode.


--pete

[VMS]

I had this big amp with marshall type power section but it was UL with no nfb loop. So i guess i'm thinking if i could create something similar but with lower power.


I got the 61% using this logic from ampbooks site:

The screen taps in output transformers designed for ultralinear operation are typically set to 43 percent of the primary winding. Since impedance varies as the square of the number of turns, the primary impedance for a power tube screen is 18.5 percent of the primary impedance for the plate.Maximum power is achieved with the taps at 20 percent of the primary winding, which corresponds to 4 percent of the primary impedance.

[jjasilli]

UL SE is a recurring topic lately. 


BTW: Just watched the two Falcon Heavy side boosters land simultaneously at the Cape.

[mresistor]

BTW: Just watched the two Falcon Heavy side boosters land simultaneously at the Cape.

Are you serious? You actually had eyes on that ?     cool 

[jjasilli]

Rockets are cool again!