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Are 6L6 Metal tubes plug and play
Are 6L6 Metal tubes plug and play
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Old 4th August 2019, 07:00 PM   #1
Duke58 is offline Duke58  United States
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Default Are 6L6 Metal tubes plug and play

The data sheet show that metal 6L6 have slightly different pin connections. Looks like pin 1 is different between metal 6L6 tubes versus the glass 6L6 tubes if I'm looking at this correctly.

My question is- can I use these metal 6L6 tubes anywhere a glass 6L6 tube is used? If you can't tell, I've only been into vacuum tube amplifiers for a couple years and am not an EE/audio tech.

Thanks!
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Old 4th August 2019, 07:10 PM   #2
lavane is offline lavane  United States
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Pin 1 is a ground for The metal envelope on the tube. You will want to ground pin 1 on the tube socket. A charge can build up on the metal tube of its not grounded.
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Old 4th August 2019, 07:14 PM   #3
HarryY is offline HarryY  United States
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As I recall Pin one is tied to the metal shield of the 6L6 (the Can).
and the 6L6 is also not rated as high as the "Standard" 6L6GC.

6L6 Data Sheet - 6L6GC Data Sheet

So in the end I would say it depends on the amp.
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Old 4th August 2019, 08:08 PM   #4
pcan is offline pcan  Italy
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Are 6L6 Metal tubes plug and play
Conclusions from my (short) metal tube substitution experiments:

1. some amplifiers have output tube sockets with pin 1 and 8 wired togheter, to be compabilbe with EL34. It is not a issue with 6L6 unless you accidentally make a contact from the envelope to ground, because the envelope will be at cathode potential.

2. output metal tubes become hot, very hot. Instant blistering burn if you touch them. If the transformer is near, it becomes hot too.

3. NOS metal tubes - tubes that really haven't never been used - royally stinks for the first few hours of operation. Burn-in with open windows is suggested.

4. Pin 1 on rectifier socket is often used as tie point for B+. This connection must be severed before using a metal envelope rectifier.
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Old 4th August 2019, 08:30 PM   #5
Tubelab_com is offline Tubelab_com  United States
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The metal 6L6 is electrically similar to the 6L6G, 6L6GA, and 6L6GB. They all have 19 watt plates. The 6L6GC has a larger 30 watt plate. Using the metal 6L6 in an amp designed for the 6L6GC is not a good idea unless you can turn down the current or lower the voltage.

The metal tube can be used in applications intended for the 19 watt tubes IF pin 1 is not used for anything. I found an old Stromberg Carlson amp that used pin one as a tie point for the screen resistor.
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Old 4th August 2019, 10:01 PM   #6
Duke58 is offline Duke58  United States
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Thanks all for your replies!

Mr. Tubelab- I recently bought a Tubelab SSE amp, which I am expecting to be delivered here next week. This amplifier currently has 5881 tubes installed, 12AT7 tube and a 5AR4 rectifier tube. According to your website, this amp also works with different rectifier tubes, such as 5U4, 5AR4 and 5R4, as well as a lot of different output tubes. Is that if and only if a 3mA power transformer is installed?

Being a somewhat new tube amp enthusiast, I'm a little confused about interchangeability of these different tubes. I did see the computer simulations on your website. Those B+ voltages listed correspond to different rectifier tubes, correct? Which tube gave the 374 volts used with the 6V6 tube?

I'm glad that you have extended your 5 year mission.
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Old 5th August 2019, 11:27 AM   #7
emk2 is offline emk2
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An Inside Story About Metal Tubes

An Inside Story About Metal Tubes, October 1935 Radio-Craft - RF Cafe
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Old 5th August 2019, 01:37 PM   #8
Tubelab_com is offline Tubelab_com  United States
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Quote:
I recently bought a Tubelab SSE
First off, fire it up as delivered and make sure it works right. It's also wise to listen to it for several weeks to become familiar with it's sound before messing with it. The SSE is a popular amp and there are some easy tube swaps, but some serious cautions before just sticking anything that someone told you would work into the amp.

The SSE is a builder's amp and there are many different build options and tube / transformer combinations. Find out what transformers are in the amp now and what value resistors were used for the cathode bias parts (R17 and R27). These are usually rectangular white ceramic resistors and the largest resistors in the amp. If the cathode resistors are 560 ohms or higher and the power transformer is large enough, an EL34, 6550, KT88 or 6L6GC can be plugged into the amp. I would NOT recommend a metal 6L6 in this amp without knowing a bit more about how it was built.

The usual rectifier tube in an SSE is the 5AR4. Nearly all SSE's were built with them. Other tubes can be used usually a 5U4 and sometimes a 5R4, but they DO require a 3 amp rating on the power transformer's 5 volt winding.

Remember that there can be over 450 volts in this amp which can make you DEAD if you are not careful! It's wise to learn more about the common tubes used in this amp and which ones can work on which voltages before digging into it.

Check out the Tubelab forum on this site and read about the mods others have done to their SSE's:

https://www.diyaudio.com/forums/tubelab/

There are people of varying skill levels from rookie to "I'll try anything and I don't care if I blow it up, I can fix it."

After you have it working and can tell us a bit more about how it was built, and maybe post a picture there.

Quote:
Those B+ voltages listed correspond to different rectifier tubes, correct? Which tube gave the 374 volts used with the 6V6 tube?
Those charts were intended to help people choose a TRANSFORMER set for their particular tube, and extend beyond the normal range of use for most tubes. Many standard 6V6 tubes will NOT live long on 374 volts. Some of the newer Russian tubes called 6V6's will, so that's why there are numbers listed for them.

Like the metal 6L6, I wouldn't stick ANY 6V6 tube into you SSE, which probably runs well over 400 volts. Myself and others have built SSE's specifically for the 6V6, but a smaller transformer set was used to get about 340 volts of B+ voltage.

As a general rule the 5AR4 tube gives the most B+ voltage and the 5U4 and 5R4's are used when a builder needs to lose a few volts (10 to 20). Big changes in the B+ voltage require a different power transformer which can be a major expense.
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Old 5th August 2019, 01:52 PM   #9
Duke58 is offline Duke58  United States
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Thank you for bearing with my rookie questions, and for all you do for this hobby!
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Old 18th September 2020, 05:58 AM   #10
Cucaracho is offline Cucaracho
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Quote:
Originally Posted by Tubelab_com View Post
First off, fire it up as delivered and make sure it works right. It's also wise to listen to it for several weeks to become familiar with it's sound before messing with it. The SSE is a popular amp and there are some easy tube swaps, but some serious cautions before just sticking anything that someone told you would work into the amp.

The SSE is a builder's amp and there are many different build options and tube / transformer combinations. Find out what transformers are in the amp now and what value resistors were used for the cathode bias parts (R17 and R27). These are usually rectangular white ceramic resistors and the largest resistors in the amp. If the cathode resistors are 560 ohms or higher and the power transformer is large enough, an EL34, 6550, KT88 or 6L6GC can be plugged into the amp. I would NOT recommend a metal 6L6 in this amp without knowing a bit more about how it was built.

The usual rectifier tube in an SSE is the 5AR4. Nearly all SSE's were built with them. Other tubes can be used usually a 5U4 and sometimes a 5R4, but they DO require a 3 amp rating on the power transformer's 5 volt winding.

Remember that there can be over 450 volts in this amp which can make you DEAD if you are not careful! It's wise to learn more about the common tubes used in this amp and which ones can work on which voltages before digging into it.

Check out the Tubelab forum on this site and read about the mods others have done to their SSE's:

https://www.diyaudio.com/forums/tubelab/

There are people of varying skill levels from rookie to "I'll try anything and I don't care if I blow it up, I can fix it."

After you have it working and can tell us a bit more about how it was built, and maybe post a picture there.



Those charts were intended to help people choose a TRANSFORMER set for their particular tube, and extend beyond the normal range of use for most tubes. Many standard 6V6 tubes will NOT live long on 374 volts. Some of the newer Russian tubes called 6V6's will, so that's why there are numbers listed for them.

Like the metal 6L6, I wouldn't stick ANY 6V6 tube into you SSE, which probably runs well over 400 volts. Myself and others have built SSE's specifically for the 6V6, but a smaller transformer set was used to get about 340 volts of B+ voltage. Quote: My experience with 6V6 tubes, either single or as push-pull, were powered by a 5Y3 rectifier tube...

As a general rule the 5AR4 tube gives the most B+ voltage and the 5U4 and 5R4's are used when a builder needs to lose a few volts (10 to 20). Big changes in the B+ voltage require a different power transformer which can be a major expense.
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