6K6GT's and 369HX

[dwinstonwood]

I've been searching this forum for info on 6K6GT's. I see that in the past tubenit and HBP, among others, have posted some good info on successfully using these tubes. And, they look to be currently available and relatively inexpensive.

So, I started looking around Hammond's site for a good PT match for these tubes and found the 369HX:
https://www.hammfg.com/files/parts/pdf/369HX.pdf

It's 225-0-225 @ 150mA. It has a 50V Bias tap, and can supply plenty of heater current. With the high cost and scarcity of 6V6GT's this might be the way forward for future builds for me. Plus, I'd welcome less power. If not mistaken, I think two 6K6GT's PP is under 9W.

[PRR]

...If not mistaken, I think two 6K6GT's PP is under 9W. ..

Datasheet says 10.5W. The 6V6 has a similar number. At a less radical load impedance.

All tubes will go "less". Just feed them less voltage. Even your 225VAC is 315V DC which is on the high side for either 6K6 or 6V6 under nominal ratings. "Less" would be under 200V. If you are not playing-out, 150V (120VAC) may be ample, making like 3 Watts in push-pull at popular load impedance.

[bmccowan]

I just built a 6K6 P-P recently. 6SJ7, 6SL7, 2x6K6, 5Y3. I used a 550V CT PT from Musical Power Supplies. I wound up with 275V on the plates of 6K6s. Sounds great for old time blues/jazz. A short thread is here: https://el34world.com/Forum/index.php?topic=28704.msg315991#msg315991  The usual suspects here helped me out with the circuit.

[shooter]

fwiw;
here's the final #'s on my 6K6 PP-selfbiased build (my values are left of the red box)


 the sound is what I expected from a small watt 50's/early 60's, sorta  cleanish rock/jazz (happy electric sound:)

[dwinstonwood]

Thanks PRR. I'm more interested in the apparent availability and affordability of this tube than in an effort to make a quieter amp. I don't have a stockpile of tubes, and so I have to buy tubes for every new project I start. But, a bit less power is good, too.

bmccowan, thanks for the link. I'll read through it tonight. and, "old time blues/jazz" sounds like a worthy pursuit to me.

shooter, a "happy electric sound" is also worthy! 

So, here's my big question: what method did y'all use to get the B+ down in the 275-285-ish range?

Thanks!

[sluckey]

So, here's my big question: what method did y'all use to get the B+ down in the 275-285-ish range?

The best way is to start with a correct PT. Use 200-0-200 with conventional full wave rectifier or 200-0 with full wave bridge.

Maybe this...   https://www.hammfg.com/files/parts/pdf/269EX.pdf

[dwinstonwood]

Thanks sluckey. I did look at that PT, but I wasn't sure if it could supply enough current. That's the only reason I posted the 369HX.

Well, after a closer look, that sheet does say 119mA Max. And, no 5V is fine by me. One less tube to buy. 

And Hawk has the 369EX for $53.10.

[shooter]

fwiw;
here's the build link, many turns, many changes
1482Esq (el34world.com)
here's also the schematic with power-up data and iron values.


the amp is now running 6V6's re-configured as a Mono Audio amp, sounds great.

[bmccowan]

So, here's my big question: what method did y'all use to get the B+ down in the 275-285-ish range?

No real method. My house voltage is 114-117; last house on the line. That transformer is rated 550 at 120V. The NOS 5Y3 rectifier knocked it down the rest of the way. The circuit is a simple mash-up of early Gibson and Valco PP 6V6 amps. I can't play worth a damn so have no sound clips. But if you check out some of Leon C's YouTube clips of old Gibsons, Valcos, and the "Smoothie" - that's the sound. I just wish I could play like him.

[dwinstonwood]

Thanks bmccowan, I'll take a listen to those.

My walls are around 123VAC +/- a couple of volts. I live in a city.

[shooter]

If you look at the schematic I posted, I take the PA tap from "B" not A, so that's one way to knock down B+.

[dwinstonwood]

That was just too simple/obvious a solution for me to catch shooter. 

[dwinstonwood]

So, I'm not good at reading these early datasheets. Is this saying that with a plate voltage of 250 the tubes want to see an OPT primary impedance of 7.6K?

[bmccowan]

OTs always confuse me - here is an article I found helpful. https://www.radioremembered.org/outimp.htm I think Aiken has quite a bit on this subject too.

[PRR]

...datasheets. Is this saying that ....

That's 1-tube SE condition. Weren't you looking at 2-tube push-pull?

It does not help to know the 6K6 is a re-bottomed '42.

[dwinstonwood]

Thanks PRR  I figured I was reading it wrong.
I'm not sure I've come across a current production 12K/15W PP OPT anywhere.10K, maybe.

[shooter]

if you look at reply #3, my target values were in the red box, 12k was the OT recommendation.  I used an EDCOR 10K. for my final

[dwinstonwood]

Weren't you looking at 2-tube push-pull?

Apparently not!  Thanks.

I used an EDCOR 10K. for my final

Thanks shooter.