#1
Few questions for any technical minded amp techs/owners.

I have been using JJ 6L6GCs in my red bear mk 60 for awhile now, and while i think they sound pretty good, id like to try something different when they are finished. The american modern sounding nature of 6L6s isn't really what im looking for, especially with this already trebly amp.

I've been directed toward such things as KT66s, 6550s, 7027s, and stuff like that. but how easy is it to mod an amp from 5881/6L6 specs to EL34 specs?

The plate voltages in my amp are 488v. The bias pot only has a 10k range, and I have read that someone with the 100 watt version of this amp can only send 16.5 watts to each tube. mine is the 50/60 watt version. Does this mean i can send 33 watts to each tube or is it also only 16.5?

Could the bias pot adjustment be the reason why my amp sounds a little quiet? I can literally run the amp with the master on 10 and the preamp on 8 and it is loud as hell but not deafening.
Quote by shakin'cakes
First of all, I enjoy deathcore for it's complexity and it's the only genre heavy enough for me



Quote by Highway60Bob
I want an amp good for playing hippie tunes. I want it to be an actual amp, not a tube amp.
#2
anybody?
Quote by shakin'cakes
First of all, I enjoy deathcore for it's complexity and it's the only genre heavy enough for me



Quote by Highway60Bob
I want an amp good for playing hippie tunes. I want it to be an actual amp, not a tube amp.
#3
Quote by pmeg568c
The bias pot only has a 10k range,
The value of the pot is meaningless. What's important is the range of voltages the bias supply can deliver to the grids of the output tubes.

Quote by pmeg568c
I have read that someone with the 100 watt version of this amp can only send 16.5 watts to each tube. mine is the 50/60 watt version. Does this mean i can send 33 watts to each tube or is it also only 16.5?
This appears to be conjecture build on misunderstanding or utter nonsense. Link please, to what you read.


Setting up a 6L6 amp to be able to use EL34s is relatively easy for a tech.
But you don't sound like a tech.
I recommend having a tech do this for you.
Less chance of you hurting yourself or your amp.
Meadows
Quote by Jackal58
I release my inner liberal every morning when I take a shit.
Quote by SK8RDUDE411
I wont be like those jerks who dedicate their beliefs to logic and reaosn.
#4
i read that here:
http://www.ringomedia.net/spetel.html

The amp has a bias trimmer installed internally and interestingly the maximum idle plate dissipation I could set it to was about 16.5 Watts per tube. Seems there is no way to bias the tubes too hot without mods. The bias range I get from the trimmer is very small (it's only a 10k trimmer). I suppose this would be easy to change but I left it for now.

Since i posted this i have figured out how to mod from a 6L6 to EL34, but im trying to figure out if it will be ok on my transformer. People have told me to check the temp of the transformer after the mod but i want to see if i can know BEFORE i go about doing it. anyone know how i can find it out?
Quote by shakin'cakes
First of all, I enjoy deathcore for it's complexity and it's the only genre heavy enough for me



Quote by Highway60Bob
I want an amp good for playing hippie tunes. I want it to be an actual amp, not a tube amp.
#5
Quote by pmeg568c
i read that here:
http://www.ringomedia.net/spetel.html

The amp has a bias trimmer installed internally and interestingly the maximum idle plate dissipation I could set it to was about 16.5 Watts per tube. Seems there is no way to bias the tubes too hot without mods.
Your're joking, right? The amp that guy was talking about was 2 generations before yours, if it even WAS built by the same people. That's only a vague assumption by the writer.
Quote by The Guy You Linked to
I have owned a russian made, "Spetel" branded tube amp for the past 10 years or so that was sold to me as being a prototype of a Petersburg amp.



Quote by pmeg568c
The bias range I get from the trimmer is very small (it's only a 10k trimmer). I suppose this would be easy to change but I left it for now.
Chances are the resistance value of the bias pot won't matter one bit. Get a schematic and analyze the circuit.


Quote by pmeg568c
Since i posted this i have figured out how to mod from a 6L6 to EL34, but im trying to figure out if it will be ok on my transformer. People have told me to check the temp of the transformer after the mod but i want to see if i can know BEFORE i go about doing it. anyone know how i can find it out?
You are totally dangerous. Stay out of the guts of your amp.
Temperature is a secondary check, done well after the bias has been properly adjusted.

You need to measure the current in the output tubes and adjust the bias voltage to achieve the current from your calculations.
Meadows
Quote by Jackal58
I release my inner liberal every morning when I take a shit.
Quote by SK8RDUDE411
I wont be like those jerks who dedicate their beliefs to logic and reaosn.
#6
dude, why do you have to be such a dick? First of all. The guts of that amp look COMPLETELY identical to the guts of my amp minus 2 power tubes, and using my EARS, the bias trimmer does not make much of a difference.

It sure makes sense that the resistance value of a pot would affect the range, are you serious? A 250K pot in a guitar means their is a smaller range of "tone" you can get from it. I would assume a similar parallel especially after reading it AND hearing it.

I have already done a bunch of mods on my amp so don't tell me to not do anything with it. I honestly know that it is unsafe but my friend and i have worked on 100 watt tube amps a bunch of times and never discharged the caps, and I have never once even gotten close to a shock. I changed the slope resistor and rewired the preamp tube sockets. It obviously isn't as dangerous as everyone says.

you aren't answering my question anyway. I am going to need to modify the bias trimmer in order to use any other type of tube. there is even a good chance I am running the 6L6s cold.

Im asking if there is anyway to tell if a transformer can handle the extra filament tap from an EL34 without there being any spec sheets about it.
Quote by shakin'cakes
First of all, I enjoy deathcore for it's complexity and it's the only genre heavy enough for me



Quote by Highway60Bob
I want an amp good for playing hippie tunes. I want it to be an actual amp, not a tube amp.
#7
Quote by pmeg568c
dude, why do you have to be such a dick? First of all. The guts of that amp look COMPLETELY identical to the guts of my amp minus 2 power tubes, and using my EARS, the bias trimmer does not make much of a difference.

It sure makes sense that the resistance value of a pot would affect the range, are you serious? A 250K pot in a guitar means their is a smaller range of "tone" you can get from it. I would assume a similar parallel especially after reading it AND hearing it.

I have already done a bunch of mods on my amp so don't tell me to not do anything with it. I honestly know that it is unsafe but my friend and i have worked on 100 watt tube amps a bunch of times and never discharged the caps, and I have never once even gotten close to a shock. I changed the slope resistor and rewired the preamp tube sockets. It obviously isn't as dangerous as everyone says.

you aren't answering my question anyway. I am going to need to modify the bias trimmer in order to use any other type of tube. there is even a good chance I am running the 6L6s cold.

Im asking if there is anyway to tell if a transformer can handle the extra filament tap from an EL34 without there being any spec sheets about it.



He's not being a dick. Short and blunt, but not a dick. SYK is probably one of the most knowledgable people on this forum when it comes to tube amps. He knows what he's talking about. He's telling you not to touch the guts of your amp because you don't seem like someone that knows what he's doing. Whether that's true or not, we have no idea. All we have to go on is what you've shown us so far, which isn't much, and the default position with people giving advice on tube amps is the safest possible approach.

It IS as dangerous as everyone says, you've just been lucky enough to not touch the wrong thing or wire it up the wrong way...yet. The fact that you admit to intentionally not discharging the caps is enough for everyone on this forum to refuse to give you any further advice. As I said earlier, here at UG we practice and promote the safest approach based on your perceived level of experience. It's not going to change just because you don't like it. SYK has given you the advice you need, you just don't understand it.

Do you even know how much current your tubes are getting? Seems to me that if you knew what you were doing, you would already know if your tubes were cold or not.
Guitar:
Dean Vendetta 3 - Dave Mustaine Livewires

Amplifier
Carvin X100B - Bias Mod - Tungsol 12AX7's - JJ KT77's

I have built the most badass 212 that puts all others to shame
#8
i haven't yet measured the current running through the tubes. It isn't really necessary at this point. I don't really have the time to do that since i use my amp every day now for band practice. Thats not what i am asking.

I will not have a problem modding the power section to use EL34s. All I want to know is if my transformer can handle it. This guys obviously knows what he is talking about but measuring the current running through my current tubes has nothing to do with what I am asking.

What im looking for is people with experience in this matter. If the amp has insanely high plate voltages does that mean it should be able to handle the extra filament tap of EL34s safely? This is all i want to know. Don't tell me anything else. What calculations? I didn't mention any calculations. It seems like he just wants to tell me things i already know and just didnt mention to show how smart he is rather than focus on my question.
Quote by shakin'cakes
First of all, I enjoy deathcore for it's complexity and it's the only genre heavy enough for me



Quote by Highway60Bob
I want an amp good for playing hippie tunes. I want it to be an actual amp, not a tube amp.
#9
Quote by pmeg568c
dude, why do you have to be such a dick?
If me telling you the truth about you being dangerous makes me a "dick", so be it. I make no apologies for that.


Quote by pmeg568c
First of all. The guts of that amp look COMPLETELY identical to the guts of my amp minus 2 power tubes, and using my EARS, the bias trimmer does not make much of a difference.
You can tell every last wiring detail and component value from looking at a few pictures? I think not.

You're using your EARS to tell what's going on with bias?
What do your instruments tell you?
It's DANGEROUS to adjust bias without measuring the current.
Ears alone will allow you to adjust into regions of operation that could cause catastrophic failure.


Quote by pmeg568c
It sure makes sense that the resistance value of a pot would affect the range, are you serious? A 250K pot in a guitar means their is a smaller range of "tone" you can get from it. I would assume a similar parallel especially after reading it AND hearing it.
You are wrong to make that assumption.

Apples and oranges. You can't compare the two. The resistance of a volume pot in a guitar affects the tone because resistance works with the series inductance of the pickup to form a low-pass filter. This has nothing to do with the way a bias control works.

As I stated previously, you SHOULD be consulting the schematic for this amp to understand how your bias control works and and you SHOULD making voltage and current measurements when adjusting it.

Quote by pmeg568c
I have already done a bunch of mods on my amp so don't tell me to not do anything with it. I honestly know that it is unsafe but my friend and i have worked on 100 watt tube amps a bunch of times and never discharged the caps, and I have never once even gotten close to a shock. I changed the slope resistor and rewired the preamp tube sockets. It obviously isn't as dangerous as everyone says.
Glad to hear you got lucky so far. The way you're approaching this is DANGEROUS. I hope only your amp suffers when you make your first huge mistake. From the sounds of it, that's right around the corner. The only surprise here is that you haven't caused a catastrophic failure already.

Did you notice that until I came along, no one else was replying to your thread?
That's because without a schematic and voltage/current measurements any discussion of how to properly adjust the bias in your amp is frivolous. No self-respecting tech would try to advise you on this without the proper context. Apparently others don't want to hurt your feelings by telling you this. I'm more concerned with your safety and that of your amp than your feelings. Call me a dick if you feel you must, but that's just the way it is.




Quote by pmeg568c
i haven't yet measured the current running through the tubes. It isn't really necessary at this point. I don't really have the time to do that since i use my amp every day now for band practice.
It is. Trust me, it is.
Meadows
Quote by Jackal58
I release my inner liberal every morning when I take a shit.
Quote by SK8RDUDE411
I wont be like those jerks who dedicate their beliefs to logic and reaosn.
#10
Dude, I don't need to know how to adjust the bias or check how hot the tubes are running for gods sake. I know how to do this. It is NOT necessary at this point. Once i find out if my amp can handle EL34s, I will do this, and make sure the bias pot has the correct range, which i already know it doesn't. Stop telling me things i already know. If you really want to see a schematic of the amp here it is. It isn't going to help answer the question of if my amp can handle EL34s


Quote by shakin'cakes
First of all, I enjoy deathcore for it's complexity and it's the only genre heavy enough for me



Quote by Highway60Bob
I want an amp good for playing hippie tunes. I want it to be an actual amp, not a tube amp.
Last edited by pmeg568c at Jul 30, 2009,
#11
sorry about the large pictures. the schematics are sloppy and impossible to read anyway. The other one that i didn't post is even harder to read.
Quote by shakin'cakes
First of all, I enjoy deathcore for it's complexity and it's the only genre heavy enough for me



Quote by Highway60Bob
I want an amp good for playing hippie tunes. I want it to be an actual amp, not a tube amp.
#12
also, using my ears to adjust bias can cause catastrophic failure? I would say that is the best way to do it. Im pretty sure numbers don't speak as loud as what sounds good to you as long as the bias isn't insanely high or insanely low. If blowing power tubes is catastrophic too you maybe you are too safe.
Quote by shakin'cakes
First of all, I enjoy deathcore for it's complexity and it's the only genre heavy enough for me



Quote by Highway60Bob
I want an amp good for playing hippie tunes. I want it to be an actual amp, not a tube amp.
#13
SYK is a dick. But he's rarely wrong.
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#14
has hasn't been wrong with anything he has said, he just isn't answering my question and trying to spread his knowledge to me when i already said i understand what the deal is.

besides i know a ton of techs that have said and done completely idiotic things. There is no such thing as an unbiased perfect amp tech who knows everything.
Quote by shakin'cakes
First of all, I enjoy deathcore for it's complexity and it's the only genre heavy enough for me



Quote by Highway60Bob
I want an amp good for playing hippie tunes. I want it to be an actual amp, not a tube amp.
#15
Quote by pmeg568c
Dude, I don't need to know how to adjust the bias or check how hot the tubes are running for gods sake. I know how to do this. It is NOT necessary at this point.
It certainly IS necessary. Without knowing where your tubes are currently biased, you can't be certain you aren't damaging your amp's health. You're depending on luck. DANGEROUS.

Quote by pmeg568c
Once i find out if my amp can handle EL34s, I will do this, and make sure the bias pot has the correct range, which i already know it doesn't. Stop telling me things i already know. If you really want to see a schematic of the amp here it is. It isn't going to help answer the question of if my amp can handle EL34s
WRONG. It answers everything.

In the schematic you hotlinked, the bias pot is part of a shunt network.
But lucky for you, it has been "idiot-proofed".
You can go to the nearly full negative voltage, but are limited to how much lower the negative voltage can be. Changing the value of that pot will not allow you to decrease the low end of the range. That occurs when the the pot is adjusted to zero resistance.

You CAN adjust other values in that circuit to allow you lower negative voltage and run you tube hotter. I won't explain how. You are too dangerous. You don't understand the importance of knowing where your tubes are operating.

I you want to know if your amp can use EL34s just compare the specs on the tube data sheets. This will tell you if you need a higher or lower negative bias on the EL34s. If the bias needs to be more negative, you can determine what the max negative voltage possible in that circuit is (by the measurement you should have ALREADY made) and compare that with the point on the graphs for plate current.

Quote by pmeg568c
also, using my ears to adjust bias can cause catastrophic failure?
YES.

Quote by pmeg568c
Im pretty sure numbers don't speak as loud as what sounds good to you as long as the bias isn't insanely high or insanely low.
There will be a wide range of what sounds "good". That range extends all the way into areas that are unhealthy for your amp.

Quote by pmeg568c
If blowing power tubes is catastrophic too you maybe you are too safe.
You're doing a great job of proving my accusation about how dangerous you are. Destroying your output tubes unnecessarily would be stupid. But that's not the only thing that can fail. Your OT and PT would be at risk as well.


Try READING and understanding the many tutorials about adjusting bias that are available all over the net. WHEN you're ready for a sensible discussion, I might choose to give you more details. But you are a long way from there, atm. Hence I bid you good day, sir.


Good luck
Meadows
Quote by Jackal58
I release my inner liberal every morning when I take a shit.
Quote by SK8RDUDE411
I wont be like those jerks who dedicate their beliefs to logic and reaosn.
#16
Problem you have is your asking us if the trans can handle it and well we have no way of knowing. Not many here are gonna know the transformer specs for obscure russian made amps. If you had a part # or had the specs for the trans be a different story. Looking at the pics in your link there wasnt a single marking on any of the transformers. After reading the story in your link the guy was simply lucky that what he did or a tech did worked without anything blowing up. I guess your just gonna have to let us all know how it works out.
#17
Quote by SomeoneYouKnew
It certainly IS necessary. Without knowing where your tubes are currently biased, you can't be certain you aren't damaging your amp's health. You're depending on luck. DANGEROUS.

WRONG. It answers everything.

In the schematic you hotlinked, the bias pot is part of a shunt network.
But lucky for you, it has been "idiot-proofed".
You can go to the nearly full negative voltage, but are limited to how much lower the negative voltage can be. Changing the value of that pot will not allow you to decrease the low end of the range. That occurs when the the pot is adjusted to zero resistance.

You CAN adjust other values in that circuit to allow you lower negative voltage and run you tube hotter. I won't explain how. You are too dangerous. You don't understand the importance of knowing where your tubes are operating.

I you want to know if your amp can use EL34s just compare the specs on the tube data sheets. This will tell you if you need a higher or lower negative bias on the EL34s. If the bias needs to be more negative, you can determine what the max negative voltage possible in that circuit is (by the measurement you should have ALREADY made) and compare that with the point on the graphs for plate current.

YES.

There will be a wide range of what sounds "good". That range extends all the way into areas that are unhealthy for your amp.

You're doing a great job of proving my accusation about how dangerous you are. Destroying your output tubes unnecessarily would be stupid. But that's not the only thing that can fail. Your OT and PT would be at risk as well.


Try READING and understanding the many tutorials about adjusting bias that are available all over the net. WHEN you're ready for a sensible discussion, I might choose to give you more details. But you are a long way from there, atm. Hence I bid you good day, sir.


Good luck


You are just like every other tech. when they don't know something they just spout off a bunch of random facts to confuse people.

1. My tubes have been biased where they are for at least 3 months. If they were biased to hot, something would have easily gone wrong by now.

2. Explain shunt network to me?

3. So you are basically saying i can bias the tubes very hot and but very cold? If you think im such an idiot you should use normal everyday terms. I don't know exactly what you mean when you throw around words like negative voltage. I also never said that i thought i just needed to change the value of the pot. all i said was that something about the system would have to be modified, and although i didn't elaborate, it has something to do with resistors i have read.

4. Like i said before, i understand the importance of how hot tubes are run. They are not being run very hot right now. Like i said a million times, I will have to do some changes to the bias circuit. I don't need your help with that, so you dont have to tell me if you think im an idiot. Your knowledge can be found elsewhere from way more qualified people.

5. Why don't we talk milliamps. These are the measurements i am familiar with. From what i've researched, my 6L6s are supposed to be run at 44~ mA each at 488v, that's 70% plate dissipation. Is this bias pot capable of letting that much current through?

6. You still haven't answered my question. My amp can handle the plate voltages of EL34s. The tube sockets can be modded to accecpt them. The only step that is left is if the transformer can handle it. BUT EL34s draw a 1.5-1.6A heater current while 6L6s only draw about a .9, so i need to find out if my transformer can handle this. I know the different biasing that needs to be done when tubes are changed over. The only reason i haven't done it yet is because i do not know this fact

I am not looking for a discussion about biasing. I am looking for a discussion about how i can tell if my transformer can handle the extra filament tap which you have been unable to explain to me. Again, if I am as dumb as you think I am, you should be explaining this in simple terms, but from what i have read you have not answered my question.
Quote by shakin'cakes
First of all, I enjoy deathcore for it's complexity and it's the only genre heavy enough for me



Quote by Highway60Bob
I want an amp good for playing hippie tunes. I want it to be an actual amp, not a tube amp.
#18
Quote by Tackleberry
Problem you have is your asking us if the trans can handle it and well we have no way of knowing. Not many here are gonna know the transformer specs for obscure russian made amps. If you had a part # or had the specs for the trans be a different story. Looking at the pics in your link there wasnt a single marking on any of the transformers. After reading the story in your link the guy was simply lucky that what he did or a tech did worked without anything blowing up. I guess your just gonna have to let us all know how it works out.


I already said there was no information or spec sheets on this transformer. I was simply asking if there was another way to check this. There very well may not be. It just seems like it would be very possible to measure how much heat a transformer can safely put out.
Quote by shakin'cakes
First of all, I enjoy deathcore for it's complexity and it's the only genre heavy enough for me



Quote by Highway60Bob
I want an amp good for playing hippie tunes. I want it to be an actual amp, not a tube amp.
#19
Unfortunately, unless you can find the part # of the transformer and find specs on it, the only way to know if you can run 6l6s is to try it.
My gut says that your amp could handle it, but there's no way of knowing without the specs.

As a side note, if you want a more british voicing you can use JJ 6v6s; they can handle 500V on the plates so all you need is a rebias to run them in a 6l6 amp. The wattage will drop, of course, but there's no mod required and they sound much more british than a 6l6, especially if you mod a few other parts of your amp.
#20
thanks! Thats all i was wondering. I think I actually will try 6v6s first. I feel like that may leave me not loud enough though since there are only 2 power tubes. I have to compete with a very loud drummer and an ampeg with 7027s and a boost. (ps im trying to run EL34s instead of 6L6s not the other way around. Would i just have to lower the bias basically? (Yes i know i will have to measure it)
Quote by shakin'cakes
First of all, I enjoy deathcore for it's complexity and it's the only genre heavy enough for me



Quote by Highway60Bob
I want an amp good for playing hippie tunes. I want it to be an actual amp, not a tube amp.
#21
If your having trouble with volume w 2 6l6 then 2 6v6 will make it worse. It sounds like you need a bigger amp. And there may be some piece of test equipment out there to torture test a transformer but thats gonna be something a manufacturer would have. All the stuff we deal w hammond, weber etc all have readily available specs so know what will do what.

Something I have done is put an EQ in the FX loop of an amp and cranked its volume which increased the amps overall volume quite a bit. Just a thought.
#22
haha im not having a problem with volume really. its just a problem of where i cut. My other guitarist's sound is very rounded and mid-oriented and my sound is a huge wall, but the mids are not as pronouced, hence why i want EL34s. Unless there is an easier solution for a tube with a large mid hump.
Quote by shakin'cakes
First of all, I enjoy deathcore for it's complexity and it's the only genre heavy enough for me



Quote by Highway60Bob
I want an amp good for playing hippie tunes. I want it to be an actual amp, not a tube amp.
#23
you could solve all your problems by purchasing a tube screamer and stepping on it when you need to cut through...
Fender MIM Stratocaster
Ibanez TS-9 Tube Screamer
Fulltone OCD
Dallas-Arbiter Wah Baby
Home-Built Germanium Fuzz Face
MXR Carbon Copy Analog Delay
2 Fender Blues Juniors
#24
...yea like i haven't already tried that hahah. Im talking about modding an amp here. you really think i don't use pedals?
Quote by shakin'cakes
First of all, I enjoy deathcore for it's complexity and it's the only genre heavy enough for me



Quote by Highway60Bob
I want an amp good for playing hippie tunes. I want it to be an actual amp, not a tube amp.
#25
Well after reading your recent post and first one you probably arent going to want EL34s. You say its already almost to trebly, the EL34s will make that worse. You might do better with a good EQ like 1 of the 10 band MXRs or even a rack unit.