5y3 putting out too much voltage?

[cminor9]

Get this: I have an old 5Y3 that is putting out roughly 420 volts into my 5E3. It is a 5Y3-GT, made by Realistic. It says "made in Germany" on the side.

I switch it out with another old 5Y3GT (from my hammond organ, and it's old...original I think. Says Hammond on the side) and then I get 360V at the first filter cap. Put the realistic in and presto! 420 volts at the first filter cap!

When a 5Y3GT fails (or any recto tube for that matter), would it put out that much more voltage? Am I just losing my mind? Any ideas? This is driving me crazy. I am having a hard time finding a 5Y3 online unless I want a Sovtek, and the tube was working just fine a while ago. Anyone ever seen this before?

[Enzo]

Understand that the rectifier "puts out" what the AC behind it provides. You Might wonder why the old rectifier from the Hammond only puts out 360.

Pull the tube and see what AC resides on pins 4 and 6. Then we will kbnow what to expect once rectified.

[MWJB]

Watford valves have NOS 5Y3, I'm sure that plenty of others do too. Don't buy a Sovtek.

With 360v after the rectifier and the the Hammond 5Y3 you should be expecting to see in the region of 320VAC at pins 4&6 of the rectifier.

The voltages quoted for the Realistic look more in line for a GZ34? This will be putting over 50mA on each tube plate, take it out.

Can you see any physical differences in the glass envelopes?

"and the tube was working just fine a while ago" are you saying that the voltage on pin 8 of the Realistic has jumped up by 60vdc???

[fyl]

Get this: I have an old 5Y3 that is putting out roughly 420 volts into my 5E3. It is a 5Y3-GT, made by Realistic. It says "made in Germany" on the side.

It's not a 5Y3 but a Russian 5C4M (5Ц4M), an indirectly heated recto quite close to a 5V4-GT/GZ32 with a voltage drop of app. 20V @ 125mA vs. 50V for a 5Y-3GT.

The "Made in Germany" label was used from the '50s to the late '80S on gazillions of tubes manufactured in eastern Germany or conveniently transiting thru the DDR... Tandy and other distributors bought boatloads of these.

[cminor9]

It's not a 5Y3 but a Russian 5C4M (5Ц4M), an indirectly heated recto quite close to a 5V4-GT/GZ32 with a voltage drop of app. 20V @ 125mA vs. 50V for a 5Y-3GT.

The "Made in Germany" label was used from the '50s to the late '80S on gazillions of tubes manufactured in eastern Germany or conveniently transiting thru the DDR... Tandy and other distributors bought boatloads of these.

Interesting...that would certainly explain it. Clearly, with the real 5Y3GT the amp gets the correct voltage because of the correct voltage drop.

I built this 5E3 about a month ago, and couldn't figure out why it had so much headroom and was so loud and had no sag. It wasn't what people described, though it was still very nice. I ran it for a month with the wrong recto, and it seemed to have survived the extra voltage. The JJ tubes can take a pretty high plate voltage, and the caps are fortunately pretty over-rated for a 5E3. I put in a different cathode resistor to bias the tubes a *bit* colder, so I guess that helped too.

I like the amp even better with the real 5Y3, though. But, if a guy DID want more headroom on a 5E3...hmmm

My only question for you is how do you know that, about the tube not really being a 5Y3? I cannot verify what you said. It sounds plausible, and the voltage seems to support that claim. But still...where did you get your info from? Just curious.

[cminor9]

The voltages quoted for the Realistic look more in line for a GZ34? This will be putting over 50mA on each tube plate, take it out.

Can you see any physical differences in the glass envelopes?

"and the tube was working just fine a while ago" are you saying that the voltage on pin 8 of the Realistic has jumped up by 60vdc???

Yeah, I took it out. My fuse was blown on my DMM, so I couldn't check the current coming into the power tubes. But you are correct, lots of juice going into the poor tubes.

The tubes look very similar.

A while ago, I measured the voltages with the old recto. I don't remember what they were before unfortunately, but I *know* nothing was over 400vdc. Since then I have rebuilt the first build into a new chassis (that was my first build). I understand grounding much better now and have shored up the grounding. I suspect maybe the amp wasn't built correctly before and something was preventing it from drawing the full voltage? I really don't know. Too many variables have changed to know for sure. I do know that this tube is putting 420vdc on the first filter cap, and it was under 400 before. I really cannot provide any more insight as to why, other than the fact that this second build is just much cleaner and I probably fixed an unknown mistake somewhere. The amp sounded and still sounds very nice, though, so whatever it was wasn't affecting the tone.

[fyl]

My only question for you is how do you know that, about the tube not really being a 5Y3?

A lil' bit of experience.

Just compare the plate and heater structure with a Sovtek 5Y5GT - same Russki 5Ц4M. And how many pins on the octal base ? 4 or 5 ?

[cminor9]

Just compare the plate and heater structure with a Sovtek 5Y5GT - same Russki 5Ц4M. And how many pins on the octal base ? 4 or 5 ?

On the false 5Y3 there are four pins, and on the real one there are 5. I thought that was just directly/indirectly heated cathodes? What, should a true 5Y3GT have five pins?

[fyl]

On the false 5Y3 there are four pins, and on the real one there are 5.

Most relabeled Russki octal rectos had only 4 pins until quite recently. Enough for electrical operation (2 pins are used for heating, 2 for plates) but not for a proper mechanical interface with the socket.

I thought that was just directly/indirectly heated cathodes?

Heating is one of the main diffs, but plate structure is also very different.

What, should a true 5Y3GT have five pins?

Yup, T-9 bulb and octal G-5T or B5-5T base with pin 1 (not connected), 2 8 (filament), 4 6 (plates).