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'6K6, 6F6, 6Y6, and 6W6 =)'
Author:Jon Anderson (registered user: 1491 posts )
Date: Sat, Mar 25th, 2006 @ 11:53 ( . )

So, along with an assortment of 6V6's that I bought off ebay last fall, I also had an assortment of 6k6GT's, 6F6GT, 6Y6GT, and 1 (i think) 6W6. So last night I started plugging them into my October.

The first thing I tried was the 6K6GT's. They had a higher max plate voltage than regular 6K6's (350, I think). My B+ on the plates is ~ 395V.

So I played them for a good 30 minutes or so. They were pretty dark sounding. With everything dimed, it had this kind middly sound that reminded me alot of the Firefly clips I've heard. Definitely different from the 6V6 sound. So, I decided to try some of the other tubes.

That's when I noticed I had actually plugged in 1 6F6, and one 6K6. Whoops. =) (They _are_ old tubes, and the markings can be tough to read sometimes!)

I dug up another 6K6GT, and plugged it in, and biased everything up. (I biased them as low as I could, which was still ~ 9.6W).

Definitely a nicer sound. Very close to the 6V6, but just a little more scooped, I think.

After playing that a bit, I ran out of time for experimenting, so I plugged my 6V6's back in for comparison. They seemed a little bit louder, but it's tough to judge that sometimes. I'm going to try measuring the actual output wattage today with a dummy load.

Now, to try the other tubes!

Jon

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'6K6, 6F6, 6Y6, and 6W6 =)'
Author:MarkBul (guest: search)
Date: Sat, Mar 25th, 2006 @ 12:03 ( . )

The 6Y6 pulls more heater current than the 6V6. It has a bigger cathode to take heavier use.

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'6K6, 6F6, 6Y6, and 6W6 =)'
Author:Jon Anderson (registered user: 1491 posts )
Date: Sat, Mar 25th, 2006 @ 13:37 ( . )

I should have plenty of heater current. The Hammond 270HX gives you about 6A. If the 12ax7's are pulling .3 a piece, that gives me 5A to work with for the power tubes.

Jon

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'6K6, 6F6, 6Y6, and 6W6 =)'
Author:Jon Anderson (registered user: 1491 posts )
Date: Mon, Mar 27th, 2006 @ 10:40 ( . )

Well, maybe I spoke too soon!

I tried out the 6Y6GT's, and played them a few minutes, and blew a fuse on my B+.

Not sure why yet. As far as I can tell from the tube docs, they should be drawing the same plate current as a 6V6. Maybe I had a bad tube.

Anyway, so I haven't tried them again yet.

Jon

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'6K6, 6F6, 6Y6, and 6W6 =)'
Author:wolf papa (registered user: 440 posts )
Date: Mon, Mar 27th, 2006 @ 12:00 ( . )

The 6Y6 specs that I've seen are only for a single tube - Duncan's Tube guide shows @ 60 ma of current. I haven't seen any specs for 6Y6 used in P-P circuits, but I'm guessing that at 200 volts, you may be getting 90-110 ma. Definitely need to check the bias..... And max voltage for the 6Y6 is shown as 200, quite a bit less than the 6V6. Then there's the load resistance, roughly half that of a 6V6.

The 6V6 single tube is shown with 30-45 ma of current, and in P-P @ 70 ma.

I've tried several of the lower-powered octals in my Octal Fatness, the 6Y6 was my favorite. To be fair, though, the bias resistor was right for the 6Y6, and less than optimal for the others, including 6W6, 6V6, 6K6, and 6F6. I'll be tearing it down to install a tone stack, and an adjustable cathode bias........

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'6K6, 6F6, 6Y6, and 6W6 =)'
Author:Jon Anderson (registered user: 1491 posts )
Date: Mon, Mar 27th, 2006 @ 12:35 ( . )

On 03/27/2006 @ 12:00, wolf papa wrote :
The 6Y6 specs that I've seen are only for a single tube - Duncan's Tube guide shows @ 60 ma of current. I haven't seen any specs for 6Y6 used in P-P circuits, but I'm guessing that at 200 volts, you may be getting 90-110 ma. Definitely need to check the bias..... And max voltage for the 6Y6 is shown as 200, quite a bit less than the 6V6. Then there's the load resistance, roughly half that of a 6V6.

The tubes I was tryign were GT's, which I'm assuming is similar to the G which has a max voltage of 350V, atleast according to:
[link]

(The PP numbers are for 2 tubes, right?)

Of all the old tubes, that's actually the closest to spec I've tried, since my plates are 395V.

I didn't even get around to biasing them. I turned the bias pots all the way down, installed them, fired it up and played a few chords to make sure I was getting sound, set the guitar down to grab my DMM and the fuse blew.

I think I might need to extend my bias range if I'm going to keep trying these old tubes.

Jon

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'6K6, 6F6, 6Y6, and 6W6 =)'
Author:wolf papa (registered user: 440 posts )
Date: Mon, Mar 27th, 2006 @ 13:13 ( . )

That one reference at NJ7P is the only time I've seen that high a voltage listed for ANY of the 6Y6 family.

The Sylvania and GE data sheets (.pdf files from the Frank Philipse Home Page links at Duncan's [link] also show 200 volts max as a class A amp, so my guess was that the higher voltage was only for a class C amplifier/oscillator circuit. So for an audio amp, with almost 400 volts at the plate, I'd think you'd need to bias it pretty cold to stay within the max dissipation............

But if it sounds good, it IS good ;)

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'correction .....'
Author:wolf papa (registered user: 440 posts )
Date: Tue, Mar 28th, 2006 @ 15:41 ( . )

....... here's a RCA data sheet (from 1944) showing 300 volts max for a 6G6-G, pentode mode or triode mode.

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'correction .....'
Author:ZoeNIain (registered user: 4522 posts )
Date: Tue, Mar 28th, 2006 @ 15:46 ( . )

The one I have shows 300v as well, but another I saw showed 250. The beauty of these little buggers is the low heater draw and low current requirements, anyway, so I suppose massive voltage handling isn't much of an issue.

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'6K6, 6F6, 6Y6, and 6W6 =)'
Author:Jon Anderson (registered user: 1491 posts )
Date: Mon, Mar 27th, 2006 @ 11:12 ( . )

Got a change to measure the output with both the 6K6 and the 6V6 in as power tubes.

I don't have a scope, so here's what I did.
Generated a 3 minute 440hz tone and burned it on to a CD, and fed the CD headphone output into the amp input, and tried to adjust the volume of the CD player so is was similar to when I was really pounding on a guitar. Then, I hooked my DMM accross the leads of an 8ohm dummy load, and measured VAC.

I was having a hard time telling when it was starting to clip by ear, so I just kinda swept through all the volume ranges, and recorded what I got. Afterwards, I played a bit at what I thought was the maximum clean sound I could get, and the volumes were very close to what I found, so I think it worked pretty well.

(Tone controls were at 5, and the presence was at 10)

National Union 6V6GTs:
With the 6V6's, 12.0V seemed to be the corner at which the volumes responsiveness tailed off. This was with the MV almost dimed, and V1 and V2 at about 5. After this point, diming everything only took it up to about 12.9V. So that gives me about 18 watts before clipping, 20watts afterward. I think that seems pretty close.

Silvania 6K6GTs:
With the 6K6's, 7.3 seemed to be the turning point. The volumes were at very close to the same as the 6V6's. After that, diming it only took it up to about 7.9, which gives about 6 to 6.5watts.

Funny how your ears/mind work. Prior to measuring, I was sure the 6K6's were only a little bit less loud than the 6V6's. But now it seems I can hear a world of difference.

I installed my 6F6's, but didn't do any testing with them yet. They don't match (One's a big bottle 6F6G, and the other is a small bottle 6F6GT), but they seemed to be closer to the 6V6 in volume, but a little darker.

Jon

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