New Rectifier Tubes Pulling massive current.

[Jazz P Bass]

-30 to -14 Vdc bias?

Yowsah!
-30 is hot even for an EL34.
-14 will bake a potato.

[g1]

But at -50v, with the Tung Sol, the power tubes will be super cold probably single digit plate current... and the new JJ5u4GB will be in range.

Like JM said, don't speculate, test!
I'm not sure what you are extrapolating from, but it does not seem valid.

[Intergalactic Tourister]

Trying to make them "work" with only -14 to -30V bias (absolutely ludicrous values) is like, say, trying to deform the head to fit a wrong sized hat.

So in a nutshell: use a good rectifier, set bias to Factory suggested value (they "should" know) , measure idle current, which should be about perfect, and slightly tweak to adjust to desired value ... which will be very close anyway.

I hear you on that LOL. I thought it was odd for someone to bias using the old Tung Sol (if that is the case). But I'll rebias to take new rectifier tubes.

Thanks

[Intergalactic Tourister]

Your Bias range needs to be more like -40V to -55V for 6L6GC's. With good rectifier tube installed, with bias anywhere in the range you stated here (-30V to -14V), they WOULD be pulling that much plate current. You need to adjust the bias circuit to increase the negative voltage swing.

Agreed. And thanks. I'm glad I happened to be using my bias meter when I decided to do a simple rectifier swap. The amp ran on the cold side @ -30v with the old Tung Sol 5u4GB, apparently.

[The Dude]

Agreed. And thanks. I'm glad I happened to be using my bias meter when I decided to do a simple rectifier swap. The amp ran on the cold side @ -30v with the old Tung Sol 5u4GB, apparently.

FWIW: "Cold" only compared to -14v. I'm betting it's still really hot. What is your actual bias current? That's what you need to be concerned about.

[Intergalactic Tourister]

Like JM said, don't speculate, test!
I'm not sure what you are extrapolating from, but it does not seem valid.

Will definitely find out. I don't have test equipment to test the rect tube so yes a guesstimation is not really valid. Just curious what you think might happen when rebiased @ -50v and I plug in the Tung Sol?

[The Dude]

Will definitely find out. I don't have test equipment to test the rect tube so yes a guesstimation is not really valid. Just curious what you think might happen when rebiased @ -50v and I plug in the Tung Sol?

You're going at it backwards. Install the tubes and then check and adjust bias current. The voltage is just a reference number. What's important is bias current. The same voltage will result in different bias for different sets of tubes.

[Intergalactic Tourister]

You're going at it backwards. Install the tubes and then check and adjust bias current. The voltage is just a reference number. What's important is bias current. The same voltage will result in different bias for different sets of tubes.

I'll be using the new JJ5u4GB when biasing. I was asking what would happen, after rebias, if I took out the JJ5u4GB and simply installed the Tung Sol. But yes, the bias current needs to decrease drastically for the JJ5u4GB.

[g1]

I think, like others have suggested, that the old rectifier can not supply the current with the bias set so hot.
Once you cool the bias, it will probably hold up and give you similar readings at idle, but maybe not at full cranked volume.
And when you tested it in the other amp, was that just at idle? I'd be interested in what happens at high volume in the other amp, whether the sound suffers with the tung-sol compared to your new rectifiers.

[Intergalactic Tourister]

FWIW: "Cold" only compared to -14v. I'm betting it's still really hot. What is your actual bias current? That's what you need to be concerned about.

It is 48ma with the new JJ6L6... was somewhere in the 30s with the other 6L6s that were in it.

[Intergalactic Tourister]

I think, like others have suggested, that the old rectifier can not supply the current with the bias set so hot.
Once you cool the bias, it will probably hold up and give you similar readings at idle, but maybe not at full cranked volume.
And when you tested it in the other amp, was that just at idle? I'd be interested in what happens at high volume in the other amp, whether the sound suffers with the tung-sol compared to your new rectifiers.

Ah, ok. That makes sense. I understood your explanation the best.

Yes, the other amp was at idle as well. But yeah, this is a first that I've had to deal with such discrepancies in rect tubes... so I'm wondering too. My other amps have solid state rect.

[Chuck H]

Let's look at this another way... The old rectifier tube works with a particular amp. Your particular amp. The amp that has a very limited and low available bias voltage. and ALL the new rectifier tubes are contrary, but behave similarly.?. Maybe the problem is the bias range on the amp and the old rectifier tube rather than the new, and consistent rectifier tubes. The thing that would throw off that suspicion for a novice is the amps bias range. That is, the amp works with with old rectifier and it's assumed that the amp worked when new, of course. Ergo, something is wrong with the new products relative to the old ones. But not necessarily. The giveaway is that the bias range on the amp is plainly not suitable!!! Drifted resistors? Maybe bad electrolytic caps? Maybe the circuit has been modified at some point? Doesn't matter now. The -V for the bias needs to be higher. That the new rectifier tubes are causing a problem with the present conditions may only be indicative that the present conditions are ALSO wrong.?.

[Enzo]

You want a scientific test? The transformer wires come to pins 4 and 6 of the rectifier. My own theory is one side may not be working. SO if we disconnect the wire from pin 4 and test the system, then reconnect 4 and disconnect pin 6 wire, and test, we will find really different numbers, possible one of them won;t work at all.

[J M Fahey]

Will definitely find out. I don't have test equipment to test the rect tube so yes a guesstimation is not really valid. Just curious what you think might happen when rebiased @ -50v and I plug in the Tung Sol?

Who cares? Itīs a DEAD tube.
Why would you want to calibrate your amplifier with a broken part?

Just use the modern, working parts, calibrate following the standard procedure everybody uses and call it a day.

[nevetslab]

I don't know what your plate voltage is with the 6L6GC's installed, but assume it's high 400's or around 500V, since you had 530V without any power tubes installed.. 48mA @ 500V is like 24W dissipation. Too hot for 6L6GC's. 35mA @ 500V plate would be around 17.5W dissipation, and more than adequate. I assume your bias meter can measure both plate (cathode) current and plate voltage.

Is this a custom build amp, or a commercially built amp? I recall the statement 'Fender-like' in the opening thread. You also have the option of using some 1N4008 rectifier diodes in place of the rectifier tube. Your plate voltage would be higher than with either a 5U4GB or 5AR4, but it would take the rectifier tubes out of the variables.