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Swap EL34 with 6L6 or 6V6

tgenc

Member
2016-03-31 9:53 am
hello there,
I have looked at internet but doesn't find the clear answer.
I have an amplifier which se 6SL7 as preamp and EL34 as power vacuum tubes. So my question is, can I change (just swap without any modification) EL34 to 6V6, 6L6 or KT66 ?

Thanks for reading
Tanzer
 

tgenc

Member
2016-03-31 9:53 am
No. You would need to change a few things, such as bias.

This question comes up every few months. Try searching.

hi DF,
i made too many searches but it's the same result as always. somebody says yes, some of them says no. so I want to make a clear subject for everybody who want to made the swap.

could you please give a little information which changes I should do? I would like to make a dwaring a step by step guide


thanks
Tanzer
 

tgenc

Member
2016-03-31 9:53 am
Please show your schematic and you propably get full instructions of what to modify.

6V6 has much smaller power rating than 6L6 and KT66.
I would therefore ignore it as an alternative to EL34.

hi arto,
I have the information, the only problem is -voltage anode should not be greater than 350 volts for 6V6.


Of coruse i am not an expert, this is why i am asking
 
Without changing anything except the tube, the EL34 amp will not plug and play nicely with the other three tubes you listed. The major reason is that the EL34 has a different pinout than the other 3.

EL34 pinout:
8ep.gif


Other 3 pinout:
7ac.gif


The difference between the two pinouts is how pin 1 connects to the tube. With the EL34, pin 1 connects to G3, the suppressor grid. With the other 3, pin 1 either has no connection, or connects to the envelope (metal can or shield). Depending on the actual circuitry in your amplifier, the other 3 tubes may or may not function the same as an EL34 in the same socket.

If you are willing to re-bias or otherwise modify your amplifier, 2 of the other 3 tubes will probably survive in it: the 6L6 and the KT66. I wouldn't use a 6V6 in place of an EL34, because it might not survive very long. Two better choices would be KT77 or 6CA7. Even if you swap out EL34 for EL34 tubes, re-biasing is highly recommended as cheap insurance against nasty, deadly side effects of imbalance or overload.
 
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hello there,
I have looked at internet but doesn't find the clear answer.
I have an amplifier which se 6SL7 as preamp and EL34 as power vacuum tubes. So my question is, can I change (just swap without any modification) EL34 to 6V6, 6L6 or KT66 ?

Thanks for reading
Tanzer
No, not if you want to keep the amp's performance.
If you don't care about sound quality and/or tube lifespan, feel free to use them.

( personally i don't see why )
 

DAK808

Member
2012-05-27 7:34 pm
Without changing anything except the tube, the EL34 amp will not plug and play nicely with the other three tubes you listed. The major reason is that the EL34 has a different pinout than the other 3.

EL34 pinout:
8ep.gif


Other 3 pinout:
7ac.gif


"If you are willing to re-bias or otherwise modify your amplifier, 2 of the other 3 tubes will probably survive in it: the 6L6 and the KT66. I wouldn't use a 6V6 in place of an EL34, because it might not survive very long. Two better choices would be KT77 or 6CA7. Even if you swap out EL34 for EL34 tubes, re-biasing is highly recommended as cheap insurance against nasty, deadly side effects of imbalance or overload.

"The difference between the two pinouts is how pin 1 connects to the tube. With the EL34, pin 1 connects to G3, the suppressor grid. With the other 3, pin 1 either has no connection, or connects to the envelope (metal can or shield). Depending on the actual circuitry in your amplifier, the other 3 tubes may or may not function the same as an EL34 in the same socket."

This is not an issue since pin 1 is NC not connected in 6L6 of 6V6 types. Therefore, these tubes are "usable" in his single ended amp. The other of operating conditions need to be addressed for best performance.



I have a SE amp that can use both 6V6, 6L6 and EL34 types. The solution is to have a vacuum tube rectifier plus a method to switch the bias current on the different power tubes to comply with its requirements. The rectifier's forward voltage drop is different for various rectifiers. 5R4, 5Y3, and 5U4, etc, have the most voltage drop. 5AR4, 5V4 or a SS replacement have the least. The difference can be about 40vdc between the low drop vs. the high loss. Obviously, one uses the high loss 5Y3 or 5R4 for the 6V6 and the 5AR4 for the EL34 and 6L6.
The second part of it is to parallel the proper resistor to the 6V6 bias resistor along with a switch. The switched resistor will be used with the EL34 tube which requires more current for proper operation.
In my personal amps I use an LM317 voltage regulator as a CCS on the power tube to set the bias. I switch the voltage adjusting resistor for 6v6 vs 6l6 tubes and also change the rectifier for the different power tube. easy peasy, cheers,808
 
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Yes, I know about the pin 1 and 8 deal. With MOST (not EVERY) EL34 amps, pins 1 and 8 are connected at the bottom of the socket. But what happens if you insert a metal envelope 6V6 or 6L6? The can gets connected to the cathode, which may or may not be at ground potential (cathode bias). This configuration could lead to a nasty surprise if you touched the can while music was playing (or idling).

Still haven't heard back from the OP on anything specific. My answer still stands: You shouldn't just unplug the amp, swap to different tube types, plug back in, and play. Luck is not on your side. Not knowing how the particular amp is biased, it is not possible to recommend a specific change.
 
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tgenc said:
i made too many searches but it's the same result as always. somebody says yes, some of them says no. so I want to make a clear subject for everybody who want to made the swap.
When a question gets various answers (some of them right; some of them wrong) it is unlikely that asking the question again will provide clarification. Basically, you need to consider the existing answers and decide for yourself which you believe. You decide by looking at the technical content of the answers, not the perceived status of the person. Having done this, you will probably still not be in a position to provide clear guidance to others; they will just have to regard your findings as yet another answer to the question which they will have to consider themselves.
 

tgenc

Member
2016-03-31 9:53 am
When a question gets various answers (some of them right; some of them wrong) it is unlikely that asking the question again will provide clarification. Basically, you need to consider the existing answers and decide for yourself which you believe. You decide by looking at the technical content of the answers, not the perceived status of the person. Having done this, you will probably still not be in a position to provide clear guidance to others; they will just have to regard your findings as yet another answer to the question which they will have to consider themselves.

Hi DF,
thank you for your unnecessary answer instead of solution ;)
 

dotneck335

Member
2012-12-11 10:10 pm
"When the Yellow Jackets® converters are installed in larger amplifiers intended for 6L6s or EL34 output tubes, the high plate and screen voltages are reduced as well as current limited to protect the EL84 (or 6V6)and to drop output power. The distortion is smoother and more even and the output is both substantially reduced and more compressed due to the Class-A nature of the Yellow Jackets® converters"
https://www.yellowjacketstc.com/more-information
 
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tgenc said:
Hi DF,
thank you for your unnecessary answer instead of solution
I wasn't offering an answer, but wisdom. I already gave you my answer in my first post in this thread.

It is unfortunate that octal output pentodes tend to have similar pinouts, because this leads people to ask if they can swap them around. Useful for emergency repairs; less useful for normal purposes.
 
Hi, tgenc
I previously asked similar question when I bought a SE PCB using 6SL7 and KT88.
I end up using EL34 - but I have to change the cathode bias resistor & capacitor.
The vendor suggested changing the resistor/capacitor value supplying B+ to reduce the B+ voltage for 6L6.
So in short, it depends on the schematic design and it is not a straight swap of compatible pin valves. I don't think you will have any real clarification as it all depends on the schematic design.
If you really want to try out different valve for learning purpose and do not know how to calculate the components value, I suggest you google the schematic of each type in choosing the value for trial and error.
 

DAK808

Member
2012-05-27 7:34 pm
hello there,
I have looked at internet but doesn't find the clear answer.
I have an amplifier which se 6SL7 as preamp and EL34 as power vacuum tubes. So my question is, can I change (just swap without any modification) EL34 to 6V6, 6L6 or KT66 ?

Thanks for reading
Tanzer

To address your question directly, the tubes you mention are "pin combatible" in your amp. You can install a 6v6 with no problem except the tube may last only a short time before burning itself up and possibly taking out other components, like an output transformer, when it expires. Afterall, it is your amp and you can do what you want. So, 6v6, not recommended without modifications to power supply and biasing circuit.
The other tubes are more compatible since they have similar specifications to the EL34. Specs are close for the EL34 and KT66. Filament is 1.5 to 1.3. Anode and G2 voltages are about the same in both types. For pentode mode plate dissipation is about 12 watts for each type. If you want to use the 6l6 you should use a 6l6gc version since it handles higher voltages. The KT66 especially original ones may be the best sounding tube in your amp. cheers, 808
 
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