Good quality 12AX7s in Hybrid A and other stuff.

[skyboltone]

Greetings lads:
I am finally back to my Hybrid A that I started last year and built upside down and inside out. It is requiring a full rewire, tubes, pots the works. Anyway, I got a whole bunch of used and NOS 12AX7s in my tube caddy, including a couple of Sovtek new ones.

Problem is, with the power supply loaded up right I'm getting pre amp voltages all over the lot depending on the tube inserted. One tube will show 208 at pin 1 but 248 at pin 6 on V1. The next will show 204 and 205 or so. Then looking at V2 I might get a balanced 218 or so or another wacko pin 6. Seems like they ought to be the same. Also I have to pull the board tomorrow, I think I've got the 100k and 110k resistors reversed, one of them's on the bottom. I can't balance any tube in V3, even with the trimmer all the way over. The dropping string has a 3.3K, 22K, and 1K. Voltages are within a couple of the scheme except the I have 323 following the 22K instead of 303. With everything so close, I'm reluctant to change to a 25K when it may be tubes. Then again, it might put V1 right on the money at 200.

In any case, here's the question. I want some decent tubes. I can't afford to buy a bunch of Tungsram or Mullards. Whats a decent predicatable and affordable AX7 to put in stock.

Perhaps for another thread but I fryed one of my KT66s. When you mirror image those, the cathode is right, the heaters are right, but the OT primary ends up on NC #6 and you end up putting screen voltage on the control grid with 470 ohms across to the plate. Whoops. They don't do that. One of my pair now sucks bias down to zero when inserted, it was the one that went red. The other seems fine. Hummmmm, buy one or two? Three, yup.

Anybody running 6.6K primary on 6L6GCs? With my OT my choices are to run the 6.6K or switch to 9K and run the speakers at half tap. Netting 4500 ohms. I seem to recall that Fender runs about 4.5K on something with 6L6GCs

It's been a long story on this amp but the Amplates front panel looks good! And I'm having fun ain't I. And it's goin in a Trainwreck style cab too.

Thanks
Dan

[heisthl]

I seem to remember most on this forum liked the EH offerings for 12AX7s, personally I've had better luck with the SovTek WA 12AX7s. They seem really consistent from tube to tube and its not uncommon to be able to interchange them within an amp without having the plate voltages change. I too have a bunch of NOS preamp tubes - I never put them in anything just for the reasons you've described. Worse yet, if you tweak an amp with NOS tubes you're screwed when the NOS needs replaced. IMHO the biggest ripoff today is buying NOS tubes on EBAY.

[dogears]

I have about 50 tubes here. None of mine exhibit the voltage abnormalities you have. Most are within 15V between triodes. Many are less than 10V different.

For me, the Sovtek WA, WB, WC have the worst tone by far. The EH is definately a huge improvement.

You can also try the newer Chinese stuff, ala Ruby or Penta.

The Tung-Sol reissues from New Sensor are OK too, just kind of gainy.

Don't worry about DC balancing the PI. That is meaningless and not recommended. I usually get about 10V lower on the B triode. Set it to about 10K difference between plates and sweep the trimmer and listen for best tone.

The last dropping resistor should be a 2.2K fwiw. You don't need to shoot for 200V on V1. Most Dumbles had less. 190 is perfectly fine. My buddies has less than that.

[skyboltone]

IMHO the biggest ripoff today is buying NOS tubes on EBAY.

Thanks Heisthl. Yeah, I never do that. These came from suppsedly reliable dealers and pulls from an old Concord tape deck I found at a garage sale. There were a dozen in there.

For me, the Sovtek WA, WB, WC have the worst tone by far. The EH is definately a huge improvement.

Thanks Scott. I'll change the last resistor to 2.2K. The problem was much worse until I remembered the 150K end of the line. On SovTeks, of the three I've tried, one ended up doing duty in V1 of my AO-35 bastard, and of the other two one's a complete dud and the other exhibits about 27 volts between plates. Odd that you haven't seen that. Just my luck.

What's the primary impedence of a Bassman OT?

Thanks
Dan

[skeezbo]

If you are looking for Euro-sounding 12AX7s to approach the sound of a Mullard or Tungsram you might try JJs. The frame-grid version is certainly affordable, but I am primarily a hobbyist and haven't used a large enough quantity of anything to judge reliability. I like their sound to sort of sweeten Fenderish preamps.
The Tung- Sols sound good to me, too, maybe more "American" than the JJs, if that makes sense. You should also try the current Chinese pruduction tubes (the Groove Tubes Mullard Reissue sounds good, but less like a real Mullard than the much cheaper JJ). I also like the EH and Sovtek LPS.

Good Luck!
Skeezbo

[yeahyeah]

Well while we're on the subject of tubes.

What power tubes do you prefer/suggest?

[stelligan]

On the 12AX7 subject - I have JJ's in one build and like them. They brought the voltages down a hair below 200 and I liked the sound. Those tubes seemed to suck more voltage than EH's or any other tube I've tried in that amp. I run JJ's in my 50 watter and EH in my D'Lite.
On Power tubes - I've been liking SED 6L6 in two non-HRMs (D'Lite and MusicMan conversion). Sovtek 5881 were cheap and cool in a rock and roll sort of way. Just my observations....YMMV

[Bob-I]

Well while we're on the subject of tubes.

What power tubes do you prefer/suggest?

I kinda liek the JJ KT-77's in my HRM amps. In the little Princeton sized Hybrid I built I'm really liking the Sovtek's. Like stelligan said, kinda cool in a RnR way. I've been using that in a classic rock band playing AC/DC, Pat Benetar and other raunchy type rock. That little amp really smokes and I can crank it without killing, mikes up really well with a single warehouse.com vintage 30.

As for preamp tubes, I like the EH in V2 for their smoothness of overdrive, V1 is a tossup, sometimes I like the Chinese tubes, sometimes I like the EH. I've had no luck with JJ's. The PI I like EH or for a brighter more rock-ish sound I like the 12AX7LPS.

[skyboltone]

Greetings lads:
I am finally back to my Hybrid A that I started last year and built upside down and inside out. It is requiring a full rewire, tubes, pots the works.

Well hell. I just ripped out every wire in there except the newly rewired tube sockets. When I attacked the pot side it began to look like it had been wired by the Aginbite of Inwit and I just couldn't stand that.

Here's to a better job this time! (lifts an old 807 with a strong, hale, and mighty right arm)

(Left hand injured by needlenostrils while attacking said bad wires)

Dan H