6l6 for el34
- Thread starter crow55
- Start date
I
ildar
Guest
Not without modification, unless you have a switchable bias amp.
mayfly
Epic Member
- Messages
- 8,734
Also EL34s are rated at a much higher plate voltage than 6L6s (700V as opposed to 450V).
Check the power supply rail before you try it. If it's 450 or lower, you should be ok. Then set the bias current to be at a maximum of 40mA and the tubes will run as they were intended. If you don't have any experience with electronics, you should be aware that there are lethal voltages in there and it's probably best to get this done by an amp tech. If you do have electronics experience, don't forget to probe with one hand. A 700V "lifter" will soil your pants pretty fast
Finally, if you really want to get picky, the output impedance of EL34s is different than 6L6s, which means that to do the job properly you'll need a different output transformer. No one I know as actually gone this far with this mod however ...
Check the power supply rail before you try it. If it's 450 or lower, you should be ok. Then set the bias current to be at a maximum of 40mA and the tubes will run as they were intended. If you don't have any experience with electronics, you should be aware that there are lethal voltages in there and it's probably best to get this done by an amp tech. If you do have electronics experience, don't forget to probe with one hand. A 700V "lifter" will soil your pants pretty fast
Finally, if you really want to get picky, the output impedance of EL34s is different than 6L6s, which means that to do the job properly you'll need a different output transformer. No one I know as actually gone this far with this mod however ...
mayfly
Epic Member
- Messages
- 8,734
mayfly said:Also EL34s are rated at a much higher plate voltage than 6L6s (700V as opposed to 450V).
Check the power supply rail before you try it. If it's 450 or lower, you should be ok. Then set the bias current to be at a maximum of 40mA and the tubes will run as they were intended. If you don't have any experience with electronics, you should be aware that there are lethal voltages in there and it's probably best to get this done by an amp tech. If you do have electronics experience, don't forget to probe with one hand. A 700V "lifter" will soil your pants pretty fast
Finally, if you really want to get picky, the output impedance of EL34s is different than 6L6s, which means that to do the job properly you'll need a different output transformer. No one I know as actually gone this far with this mod however ...
Strike the first bit - I was confused and thought you were going from EL34s to 6L6s, and not the other way around. The rail voltage should be fine.
However, there is another wrinkle - EL34s draw much more heater current than 6L6s. 6L6s draw 900 mA each of heater current, and EL34s draw about 1500 mA. You need to make sure that your power transformer is up to the task of that extra current draw. Bias and output transformer comments still apply.
The 6L6 has its suppressor grid connected to pin 8. On the EL34, the suppressor grid is connected to pin 1.
What this means is a few things.
First, there is the heater current issue.
Second, there is the bias voltage issue.
but...
Third, you need to wire the socket such that pin 1 is connected to pin 8 (cathode, ground).
Problem is, lots of amps use pin 1 as a soldering lug for the grid resistor, connected from pin 1 to pin 5. The wire comes in on pin 1, and the signal goes thru the resistor to pin 5. You'll have to deal with that too. You can't just take the resistor and wire it any old place. This is a case of placement matters, and it MUST be in close axial proximity to the tube base. So you'll have to rig a little shrink wrap and tie the wire to the resistor and put the tail of the resistor up in the air in a way that ti doesn't short against anything, especially pin 3 (plate).
So there ya go.
What this means is a few things.
First, there is the heater current issue.
Second, there is the bias voltage issue.
but...
Third, you need to wire the socket such that pin 1 is connected to pin 8 (cathode, ground).
Problem is, lots of amps use pin 1 as a soldering lug for the grid resistor, connected from pin 1 to pin 5. The wire comes in on pin 1, and the signal goes thru the resistor to pin 5. You'll have to deal with that too. You can't just take the resistor and wire it any old place. This is a case of placement matters, and it MUST be in close axial proximity to the tube base. So you'll have to rig a little shrink wrap and tie the wire to the resistor and put the tail of the resistor up in the air in a way that ti doesn't short against anything, especially pin 3 (plate).
So there ya go.
G
guitlouie
Guest
In that case, refer to -CB-s post. There are amps out there with switchable bias, my Mesa Boogie has it, and changing tubes in that is just as easy as sliding the switch over. If your amp doesn't have a switch for this, and I don't think it does, than it will probably be more trouble than it is worth.
jackthehack
Epic Member
- Messages
- 5,630
crow55 said:
Modding a vintage Bandmaster to take EL34s is not only impractical and stupid, it is also sacrilegious. Plug the Bandmaster into a decent 4x12 cab with your choice of Celestions in it.
Add this pedal for more Marshally sound: http://www.prosoundcommunications.com/english/xotic/effects/bb_preamp/
mayfly
Epic Member
- Messages
- 8,734
crow55 said:
Checking the specs, the power transformer of a bandmaster only is rated for 3.15A of heater current. This will not be nearly enough to power a pair of EL34s and the rest of the preamp tubes.
From what I see, your options are:
1 - Mod the bandmaster, with a new power transformer, output transformer, bias tweaks, and the pin 1 issues that CB brought up. If you do this, you'll not likely end up with something that sounds altogether that great and it won't have any resale value.
2 - get a Marshall or Marshall clone. Wait - aren't you the guy who was asking about Ceritone? Why not just get one of those and sell the bandmaster to pay for it? IMHO, of course.
bpmorton777
Hero Member
- Messages
- 1,651
+1 to what Jack said.
isnt it much easyer to just play it clean and put a pedal in front of it?
just curious, how long have you been playing?
Brian
isnt it much easyer to just play it clean and put a pedal in front of it?
just curious, how long have you been playing?
Brian
Modding the Bandmaster is sort of doable - but I agree with Jack that it borderlines routing your 58Burst Les Paul for a tremolo bridge.
If you're heart is on it....
Get two 470 ohm 5w sand cast resistors.
Get two 1500ohm 2w carbon film resistors
Get some shrink wrap to fit over those two watt resistors.
Be prepared to get some 1 watt carbon film resistors to tweak out the bias.
1. Replace the two existing 470 ohm screen grid resistors with the sand cast ones. Its time.
2. Un- do the wire on pin one of one of the power tubes (do one at a time please). Remove the 1500 ohm resistor thats there and connects with pin 5 on that socket. Slide shrink wrap over the wire you took off, and attach and solder the wire to the new 1500 ohm resistor. Shrink the wrap over the resistor and solder the remaining free end of the resistor to pin 5, leaving about 1/8 inch of lead between the pin and the resistor. Bend the resistor up in the air so it sticks up from the middle of the socket.
Note - if the amp is unstable, you'll have to replace these with larger values, perhaps up to 3k or so.
3. Solder an insulated wire from pin 1 to pin 8 on the same socket.
4. Repeat 2 and 3 for the remaining socket. If you do both sockets at once, and your amp squeals like rat in a Turkish Bordello, don't say I didn't warn you to do ONE AT A TIME.
5. Turn on the amp with 6L6's in it. Bias them as cold as possible. Turn off the amp, put in the EL34's and see how they bias, being prepared to power down quickly if they are running hot even at the coldest setting. If you cant get them to bias up ok, and assuming blackface Fender configuration, take the resistor off the bias pot, and replace it with one that is 1w and a slightly larger value. That is, if the resistor is 11k, change it out with say, an 18k or 21k, and test it again. You MAY be able to find a resistor that lets you bias either 6L6 or EL34, depending on the tubes you use, but dont count on it, and dont try and get fancy and use a larger value pot to compensate either. You want the same pot, to offer good rotational control over the setting. A larger pot would make hair movement a big setting change.
All that assumes blackface layout. If you dont have that, please convert to that first.
All the usual - YOU MIGHT GET KILLED, FRY YOUR GENTIALS INTO BEING THE OPPOSITE GENDER, OR WORSE if you dont know how to work on amps safely.
Repeat - YOU MIGHT GET KILLED, FRY YOUR GENTIALS INTO BEING THE OPPOSITE GENDER, OR WORSE if you dont know how to work on amps safely.
Once more with feeling - YOU MIGHT GET KILLED, FRY YOUR GENTIALS INTO BEING THE OPPOSITE GENDER, OR WORSE if you dont know how to work on amps safely.
If you're heart is on it....
Get two 470 ohm 5w sand cast resistors.
Get two 1500ohm 2w carbon film resistors
Get some shrink wrap to fit over those two watt resistors.
Be prepared to get some 1 watt carbon film resistors to tweak out the bias.
1. Replace the two existing 470 ohm screen grid resistors with the sand cast ones. Its time.
2. Un- do the wire on pin one of one of the power tubes (do one at a time please). Remove the 1500 ohm resistor thats there and connects with pin 5 on that socket. Slide shrink wrap over the wire you took off, and attach and solder the wire to the new 1500 ohm resistor. Shrink the wrap over the resistor and solder the remaining free end of the resistor to pin 5, leaving about 1/8 inch of lead between the pin and the resistor. Bend the resistor up in the air so it sticks up from the middle of the socket.
Note - if the amp is unstable, you'll have to replace these with larger values, perhaps up to 3k or so.
3. Solder an insulated wire from pin 1 to pin 8 on the same socket.
4. Repeat 2 and 3 for the remaining socket. If you do both sockets at once, and your amp squeals like rat in a Turkish Bordello, don't say I didn't warn you to do ONE AT A TIME.
5. Turn on the amp with 6L6's in it. Bias them as cold as possible. Turn off the amp, put in the EL34's and see how they bias, being prepared to power down quickly if they are running hot even at the coldest setting. If you cant get them to bias up ok, and assuming blackface Fender configuration, take the resistor off the bias pot, and replace it with one that is 1w and a slightly larger value. That is, if the resistor is 11k, change it out with say, an 18k or 21k, and test it again. You MAY be able to find a resistor that lets you bias either 6L6 or EL34, depending on the tubes you use, but dont count on it, and dont try and get fancy and use a larger value pot to compensate either. You want the same pot, to offer good rotational control over the setting. A larger pot would make hair movement a big setting change.
All that assumes blackface layout. If you dont have that, please convert to that first.
All the usual - YOU MIGHT GET KILLED, FRY YOUR GENTIALS INTO BEING THE OPPOSITE GENDER, OR WORSE if you dont know how to work on amps safely.
Repeat - YOU MIGHT GET KILLED, FRY YOUR GENTIALS INTO BEING THE OPPOSITE GENDER, OR WORSE if you dont know how to work on amps safely.
Once more with feeling - YOU MIGHT GET KILLED, FRY YOUR GENTIALS INTO BEING THE OPPOSITE GENDER, OR WORSE if you dont know how to work on amps safely.
G
guitlouie
Guest
And that, my friends is why -CB- has steadily become one of my heros since joining this board. Don't do it, but here is how, but don't do it. I love it.
jackthehack
Epic Member
- Messages
- 5,630
I call 1st dibs on the Bandmaster chassis after he fries himself!
NonsenseTele
Epic Member
- Messages
- 8,256
GoDrex said:
:toothy12:
NonsenseTele
Epic Member
- Messages
- 8,256
guitlouie said:
+1
Worse....
When you wake up, after the accident, and wonder... why am I under water, and whats all this glass? Then you realize you're nothing but a part of whats left of your brain and single floating eyeball in a piece of lab apparatus, and all the gals are butt fugly as hell, and you cant even close your eye to not look, cuz you got no eyelids. Yah, bad... worse even....
When you wake up, after the accident, and wonder... why am I under water, and whats all this glass? Then you realize you're nothing but a part of whats left of your brain and single floating eyeball in a piece of lab apparatus, and all the gals are butt fugly as hell, and you cant even close your eye to not look, cuz you got no eyelids. Yah, bad... worse even....
jackthehack
Epic Member
- Messages
- 5,630
Note that the current levels in the table are MILLIAMPS, not the multiple amps you'd get zapped with hitting the wrong wire/terminal in a tube amp.
Onset Current Level (mA) Effect
1 Threshold of sensation
8 Mild sensation
10 Painful
13 Cannot let go
21 Muscular paralysis
30 Severe shock
38 Breathing labored
42 Breathing upset
70 Extreme breathing difficulties
90 Ventricular fibrillation
100 Death
Taking from a web page on homicidal electrocution case study, don't click the link if you're squeamish as there are REALLY gross photos published there. On the other hand, if you think you want to dick around inside a tube amp having no real clue about what you're doing as if it is some trivial exercise, study the pics carefully, that is what the "fry yourself" warnings are about.
Onset Current Level (mA) Effect
1 Threshold of sensation
8 Mild sensation
10 Painful
13 Cannot let go
21 Muscular paralysis
30 Severe shock
38 Breathing labored
42 Breathing upset
70 Extreme breathing difficulties
90 Ventricular fibrillation
100 Death
Taking from a web page on homicidal electrocution case study, don't click the link if you're squeamish as there are REALLY gross photos published there. On the other hand, if you think you want to dick around inside a tube amp having no real clue about what you're doing as if it is some trivial exercise, study the pics carefully, that is what the "fry yourself" warnings are about.
