Hi,
I have a few DIY Fenders Guitar and want to try swapping the output tubes. Basically, I have PT's & OPT's that are well over rated in these amps and have biased them down a bit. PLENTY of filament current also.
A while back A fellow DIYer here mentioned dropping in EL34's in on 1 of these amps, Basically the recommendation was just ground Pin 1 at the socket and re-bias as needed.
Looking at the Pin-outs on the EL34 Vs 6L6, 5881,6L6 ect ,It looks as like pin 1 & 8 are internally connected??.
My Question is:
Is it better to ground pin 1 or better to just jumper it to pin 8?
I am not really looking to increase output levels as much as I am looking to alter tonal character and have found each different tube to offer their own unique qualities,
Gene
I have a few DIY Fenders Guitar and want to try swapping the output tubes. Basically, I have PT's & OPT's that are well over rated in these amps and have biased them down a bit. PLENTY of filament current also.
A while back A fellow DIYer here mentioned dropping in EL34's in on 1 of these amps, Basically the recommendation was just ground Pin 1 at the socket and re-bias as needed.
Looking at the Pin-outs on the EL34 Vs 6L6, 5881,6L6 ect ,It looks as like pin 1 & 8 are internally connected??.
My Question is:
Is it better to ground pin 1 or better to just jumper it to pin 8?
An externally hosted image should be here but it was not working when we last tested it.
I am not really looking to increase output levels as much as I am looking to alter tonal character and have found each different tube to offer their own unique qualities,
Gene
Hello Gene,
It's better to ground pin1 instead of connecting it to pin 8, in case you have a cathode bias amp. In a fixed bias amp, it doesn't matter because you're already connecting pin 8 to ground.
It's better to ground pin1 instead of connecting it to pin 8, in case you have a cathode bias amp. In a fixed bias amp, it doesn't matter because you're already connecting pin 8 to ground.
This is the Schematic used sort of, I only used the output stage, In Front end is Bandmaster. The Feedback is slightly different but basically the same.
Output info
Cathode Biased for sure.
Gene
Output info
Cathode Biased for sure.
Gene
Either will work, though it will affect bias with EL34 (if cathode biased).
Pin 1 on octals was used for the shield on metal tubes (like original 6L6 6F6 and 6V6) and may be connected to the metal base on 6550 - but it's relatively low voltage if you connect it to the cathode on pin 8.
In old Fenders and other amps - WATCH OUT! Fender sometimes used pin 1 as a tie point for a screen resistor. So a metal tube or metal base could have full B+ on it!
Pin 1 on octals was used for the shield on metal tubes (like original 6L6 6F6 and 6V6) and may be connected to the metal base on 6550 - but it's relatively low voltage if you connect it to the cathode on pin 8.
In old Fenders and other amps - WATCH OUT! Fender sometimes used pin 1 as a tie point for a screen resistor. So a metal tube or metal base could have full B+ on it!
Tom Bavis said:
These are DIY Amps based on Fender designs. I NEVER use extra socket pins as terminal strips Ect.
OK,, Sounds like Its not a big deal Either way as far as the connection point.
I will try it later today and report back.
THANKS GUYS!!!!
Gene
I was the guy who said to ground pin 1. I have tried both ways and it didn't make much difference in the sound in MY amp. YMMV. Try both ways.
I had a shocking experience in an old Stromberg Carlson PA amp that I was using for guitar back in high school. I put in metal 6L6's because they were free. I touched one with one hand while holding the guitar with the other hand. After using bad language, I found that one of the four 6L6's used pin 1 as the B+ tie point. I touched that one. From that moment I have always grounded pin 1 on power tubes of this type.
I had a shocking experience in an old Stromberg Carlson PA amp that I was using for guitar back in high school. I put in metal 6L6's because they were free. I touched one with one hand while holding the guitar with the other hand. After using bad language, I found that one of the four 6L6's used pin 1 as the B+ tie point. I touched that one. From that moment I have always grounded pin 1 on power tubes of this type.
i usually put my grid stopper and input on pin 6 because I am a lazy crapper!
kindof an aside here. How about tying the supressor grid on an EL34 to the -v in a fixed bias amp? I tried it once and ended up drawing slightly more current. Are there any drawbacks to that (other than not being able to use tubes that have the supressor internally grounded)?
kindof an aside here. How about tying the supressor grid on an EL34 to the -v in a fixed bias amp? I tried it once and ended up drawing slightly more current. Are there any drawbacks to that (other than not being able to use tubes that have the supressor internally grounded)?
OK, Just a Thought Here,
Since Pins 1 & 8 are internally connected wont it be a problem to just plug N play? I ask because It looks like it will bypass the Cap/ Resistor on pin #8 when I roll back to 6L6's. If I simply jumper the pins together rather than ground it, wouldnt it then be true plug N play?
I know a switch is also an option.
Oh I had not forgoten who mentioned it, Your insight on DIY amps is PRICELESS! and Highly regarded. I just generally dont name drop. 😀
I have 1 amp converted to grounding pin 1, But then I had a second thought because In my eyes it appears I would need to remove the wire to ground.
I have the schematic finished now, And have another bug/issue to address as well.
So, anyway, The Sound
No Re-bias drop in of EL34 is a success. The amp now has a much bolder sound, Not as Muddy on the bottom end (Very Potent Bottom End), Much brighter Highs. Overall ouput is about the same, But It seems to extended the clean sound further up the power range which I like.
Gene
Since Pins 1 & 8 are internally connected wont it be a problem to just plug N play? I ask because It looks like it will bypass the Cap/ Resistor on pin #8 when I roll back to 6L6's. If I simply jumper the pins together rather than ground it, wouldnt it then be true plug N play?
I know a switch is also an option.
Oh I had not forgoten who mentioned it, Your insight on DIY amps is PRICELESS! and Highly regarded. I just generally dont name drop. 😀
I have 1 amp converted to grounding pin 1, But then I had a second thought because In my eyes it appears I would need to remove the wire to ground.
I have the schematic finished now, And have another bug/issue to address as well.
So, anyway, The Sound
No Re-bias drop in of EL34 is a success. The amp now has a much bolder sound, Not as Muddy on the bottom end (Very Potent Bottom End), Much brighter Highs. Overall ouput is about the same, But It seems to extended the clean sound further up the power range which I like.
Gene
OK,
Here is the schematic I used to build these 2 Modified Bandmaster 5E7's
Schematic
The Only real issue I have not figured out is the Bass Control.
It Seems to control the bass level just fine, BUT when reduced it also kills the volume nearly like a Master volume control.
If I can fix this it might be the best sounding amps I have built yet.
Somehow I suspect That 1 leg of the pot should not be grounded, But the originals I see on the web all show grounded.
Both amps do exactly the same thing, So I am fairly sure its not a wiring thing. Everything else performs great.
Gene
Here is the schematic I used to build these 2 Modified Bandmaster 5E7's
Schematic
The Only real issue I have not figured out is the Bass Control.
It Seems to control the bass level just fine, BUT when reduced it also kills the volume nearly like a Master volume control.
If I can fix this it might be the best sounding amps I have built yet.
Somehow I suspect That 1 leg of the pot should not be grounded, But the originals I see on the web all show grounded.
Both amps do exactly the same thing, So I am fairly sure its not a wiring thing. Everything else performs great.
Gene
No need to remove the ground wire. In all of the tubes except the EL-34 pin 1 is not used, so it doesn't matter what is on pin 1. In fact if you look at your tubes you will see that many of them do not even have a pin 1. The RCA black plate 6L6GC that I am looking at right now has no pin 1 or pin 6. The amp will be a plug and play situation whether you connect pin 1 to pin 8 or to ground. It will only make a difference when you use an EL-34.
The possible exception to this comes if you plan to try any of the metal cased output tubes. These (6L6 included) have the metal case connected tp pin 1. This will put the cathode voltage (about 15 to 25 volts) on the tubes metal case if you have pin 1 connected to pin 8. If you are using the Fender hold the tubes in upside down clips they can short the case to ground, thus shorting out the tubes bias.
In a cathode biased amp ground is essentially the v-. Other than the metal tube issue, I see no reason that you can't do this. The Mullard literature shows a G3 voltage of zero wherever G3 is mentioned. Most other power tubes that spec the G3 voltage show a range of -30 to +30 volts. I wouldn't get carried away though. I tried connecting G3 to the plate in triode connection. It made the curves look ugly, and the test circuit sounded lousy.
The possible exception to this comes if you plan to try any of the metal cased output tubes. These (6L6 included) have the metal case connected tp pin 1. This will put the cathode voltage (about 15 to 25 volts) on the tubes metal case if you have pin 1 connected to pin 8. If you are using the Fender hold the tubes in upside down clips they can short the case to ground, thus shorting out the tubes bias.
In a cathode biased amp ground is essentially the v-. Other than the metal tube issue, I see no reason that you can't do this. The Mullard literature shows a G3 voltage of zero wherever G3 is mentioned. Most other power tubes that spec the G3 voltage show a range of -30 to +30 volts. I wouldn't get carried away though. I tried connecting G3 to the plate in triode connection. It made the curves look ugly, and the test circuit sounded lousy.
Both bass and treble controls will cut off output at one end - circuit doesn't look right to me. If you remove the grounds from the two pots you'll have treble boost and treble cut...
You might want to try the tone stack calculator program from duncanamps.com.
You might want to try the tone stack calculator program from duncanamps.com.
Tom Bavis said:
The Control setup shown is standard Fender Bandmaster of 1955-60. I had a 1958 as a young kid, I just dont remember it cutting off like that. But then again that was 46 yrs ago and memories fade I guess.
I think I'll hit a few Sam Ashes & Guitar Center stores to look for an original to try out again. Perhaps it is just normal of the particular series back then.
Duncans tone control thing shows this setup as E-Series, (Older Fender Design)
Is there a way I can add a resistor to the pot to not allow total cut? The symptom only affects the bass control.
Gene
Regarding the general swopping of output tubes, I am going to be odd man out here. I don't like it; especially beams with pentodes.
Trout, you listed some quite different tubes in the first entry. Firstly, the maximum plate dissipation varies greatly, and simply swapping without bias adjustment might mean overloading some types. Bias re-adjustment was mentioned, but simply replacing e.g. a 6L6 with an EL34 as I have seen, would take the latter into class AB mode. The figures are respectively: EL34 = 25W; 6L6GC = 30W; 6550 = 42W; 6V6GT = 14W (only!).
Then there is also the question of gain, where the EL34 and 6550 has almost twice the Gm of 6L6 (I am going to leave out the 6V6). In the Fender this might not mean much, but if there is any substantial NFB one can run into stability problems, especially at the h.f. end because of quite different inter-electrode capacitances. And in UL an EL34 can be a finicky fellow.
But these are more general observations; I might be regarded as nit-picking in the case of the Fender - not intended.
Trout, you listed some quite different tubes in the first entry. Firstly, the maximum plate dissipation varies greatly, and simply swapping without bias adjustment might mean overloading some types. Bias re-adjustment was mentioned, but simply replacing e.g. a 6L6 with an EL34 as I have seen, would take the latter into class AB mode. The figures are respectively: EL34 = 25W; 6L6GC = 30W; 6550 = 42W; 6V6GT = 14W (only!).
Then there is also the question of gain, where the EL34 and 6550 has almost twice the Gm of 6L6 (I am going to leave out the 6V6). In the Fender this might not mean much, but if there is any substantial NFB one can run into stability problems, especially at the h.f. end because of quite different inter-electrode capacitances. And in UL an EL34 can be a finicky fellow.
But these are more general observations; I might be regarded as nit-picking in the case of the Fender - not intended.
In this case the swap thing only applies to running 6L6's Vs EL34's.
I Built the amps output stage to the original Fender Specs. I have run it an hour or two With 6L6's.
I have swapped to the EL34's with no adjustments at all. I agree Its not a perfect trade, But It sounds Excellent with the EL34's.
Bias voltage is not over the top for either tube in this circuit and I am not running either tube to their perspective potentials. The pre-stages provide more than enough overdrive/Distortion/Crunch at max settings to duplicate even the sweetest Hendrix tones or Van Halen Brown sound.
The Mids and Highs are outstanding with once again the EL34 Winning out big time.
The 6L6's give much smoother Jazz type sounds, Mellow and very well rounded tone.
The EL34's are providing a much tighter bottom end and the Presence/Kick sounds great. I had no plans to go further than the EL34's & 6L6's.
Heres the schematic as its running right now.
Updated schematic
I dont experience any excessive heating in either tube so I think though not perfect, I have a very nice best of both worlds amp.
Gene
No thanks Trout for broadening my horisons; I am not a guitar amp expert and it is informative to note what you consider worth your while. As said, my caution was general.
....and as I might be the first person to submit post on Christmas 2005 (it is now exactly 24:00 here) and I believe many are reading this thread, my best wishes to all, of what ever religeous conviction you may or may not be, for a memorable festive season.
Regards
....and as I might be the first person to submit post on Christmas 2005 (it is now exactly 24:00 here) and I believe many are reading this thread, my best wishes to all, of what ever religeous conviction you may or may not be, for a memorable festive season.
Regards
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