Help Me Diagnose a Tube Issue

[prspastor]

Okay, here is my followup and my work.

1) I re-touched up every pin on the output tube sockets with my soldering iron. No luck.

2) I took off the diodes - no luck.

3) I did the hammer test... it did not reveal any popping/issues.

4) I traced back and re-touched all of the main B+ solder points to insure a good connection. No luck.

5) I did move around some wires in the pre amp and power amp section. This didn't seem to help at all either.

6) I did check for grounds with my multi-meter. Every ground looks good - less than .01 ohm for all the points I checked except...

7) I did a resistance measurement across the high voltage secondary of the PT (300v secondaries). I got about 40 ohms. I checked from one side of the high voltage secondary to the center tap ground and got about 18 ohms. Does this sound right? Is my ground for the HV secondaries bad and needs to be re-done?

Here is a short video of the crackly distortion. Getting frustrated....

http://www.youtube.com/watch?v=sMzD1Y605kM

[rooster]

OK, ha, that is bad! Where is the volume at for this test? In fact, why don't you show me where your knobs are set, that would help.

[passfan]

Just out of curiosity here , and I may be barking up the wrong tree , but I noticed that you ran two separate lines to ground from pins 1 and pins 8. Where the published layout shows one line from ground through pin 8 to pin 1 which would put the cathode and grid 3 of the output tube on the same reference so to speak as there is no internal connection in the tube. By using a one ohm resistor , how ever minute, this could have these pins on a slightly different reference point to each other. Could it be fine at low current draw and not at higher draws. To add further weight to this theory the 6V6 has the internal connection tied to pin 8 and a dead pin at pin 1 and thus would be unaffected. It would be relatively simple to omit the white jumper at pin 1 and tie pin 8 to pin 1 sending them both through the one ohm resistor to test this theory. You could also run a pair of 6L6GC's which also have the internal connection as well if you have them although in my experience the power resistor feeding the main bias diode would need to be changed (a pain).

[prspastor]

Hi Rooster,
Yes, it is bad. My knobs were:

Volume: 10:00
Treble, Mid, Bass were at noon
Presence was completely off.

Passfan,
I have been concerned about my arrangement of pin 1 and pin 8 from the moment I wired up the power tube sockets as I was not following the layout and going out on my own. I figured ground was ground but I've showed my lack of knowledge in this case. I'll tie 1 into 8 and see what happens. If this fixes my problem, I'm in your debt.

Thank you all.
John

[martin manning]

I don't believe the supressor grid being a volt or so below the cathode is anything to worry about. My money is on two bad sets of TS EL34's. If the Winged C's sound good I don't think the problem is in your amp.

[passfan]

I don't believe the supressor grid being a volt or so below the cathode is anything to worry about. My money is on two bad sets of TS EL34's. If the Winged C's sound good I don't think the problem is in your amp.

I would tend to agree with you as well , but I'm down to grasping here. Are we still at the point of the winged C's working fine and the problem being the Tung Sol's or are all EL 34's giving problems ? I don't really like Tung Sol's anyway I much prefer TAD's.

[prspastor]

Hi Everyone,

Well, the credit must go to Passfan. I tied 1 into 8 and then to ground through the 1 ohm resistor and the amp sounds great now. No crackles anymore. In fact, the amp sounds incredible. Thank you so much Passfan and to everyone who has spoken up to help - you've saved me countless hours of trouble shooting.

I suppose that the Tung-Sols are more sensitive to having the suppressor a volt or two below the cathode than the =C=. Are the Tung-Sols my favorite, no. I plan on getting some =C= in the future.

This does explain why the 6v6 worked fine. I must say that I like the EL 34s better though - the breakup and overdrive sounds better to my ears with the 34s.

I'll try and post some recordings here soon so everyone can hear the end result with EL-34s.

Thanks again to everyone. Good call Passfan!
John

[martin manning]

Glad you got it sorted, John. I still don't believe that the 1-ohm makes any difference... we're talking about ~300mA through 1 ohm, 1/3 of a volt, max. Is it possible that one of those solder joints on pin 1 was bad and you fixed that when you rewired?

[prspastor]

Hi Martin,
That very well could have been what the issue was. I did re-touch all of the solder joints on the pin lugs yesterday, although I did not re-touch the ground lug that 1 and 8 go to.

John

[martin manning]

Looking at your picture of your power tube sockets closely I see the joints do not have much solder on them and the wires are not wrapped around the solder lugs (best practice), so I think a poor connection on one of those is a good possibility. And of course that would not bother a 6V6 with it's internal connection. I use magnification when I solder to make sure my joints are fully flowed.

[passfan]

And I still tend to agree with Martin. Crackling is a sure sign of a bad solder joint when stressed under load. I felt that those looked a little iffy but you stated you reflowed everything so I let it be. I really was grasping at straws and have never run into any suppresor grid problems like that before so it had to be a solder joint. Glad she's up and running again.