Ive started building with a 400 volt PT 6L6GC PP amplifier for a guitar and I was thinking about changing the power tubes to EL34 tubes and keeping The 6L6 tube rectifier A 5U4GB ?, My question is this; Is it going to be enough power for the tube swap ? . And Should I get rid of the rectifier tube ? . My donar is a 1960 Whirlizer 501273 organ Amplifier. 501426 PT and a 500882 OT . And For The Pre Amp section I was going to copy The Original Sunn Model T. I'm building a pretty thick Aluminum chassis for it right now. I have it made already but it still has to be Tig welded together. I'm trying to get a hand sensitive deal going with this thing. Just Looking for a few ideas before I start assembling it and I actually start cutting into the new chassis. I have already tested the transformers and everything looks good with both of them. The negative bias is A little bit weird it's using 1/2 of A 12AX7 tube. It took me a little while looking at it to figure that out. I'm New on here. Hi to everyone !
You need to connect pin 1 ( g3) to pin 8 (k) if you use EL34. pin 1 is unconnected in 6L6 thus you can freely switch to 6L6
again with no changes.
You also might need to adjust bias but i guess that you already plan to have it adjustable.
Good luck !
The question is why switch to EL34s? Why not copy the original Wurlitzer 6L6GC power amp design?
Unless you are skilled at tube design and can make the proper accommodations it is usually unproductive to make changes to the power tubes/output transformer pairing. That goes also for other changes in rectifiers, etc.
Unless you are skilled at tube design and can make the proper accommodations it is usually unproductive to make changes to the power tubes/output transformer pairing. That goes also for other changes in rectifiers, etc.
Using the original Wurlitzer power transformer, or a new replacement?
As was stated already . . .
6L6 filaments 0.9A/tube = 1.8A
EL34 filaments 1.5A/tube = 3A
Depending on all other loads on the filaments and on the B+, the power transformer may run hot.
Original early transformers for the US were rated for 110VAC and 115VAC.
Put those original transformers on my 117VAC to 123VAC Power Mains, and they will run Hot!
If the transformer catches fire, the fire truck does not sound pretty.
Safety First
Prevent the "Surviving Spouse Syndrome"
As was stated already . . .
6L6 filaments 0.9A/tube = 1.8A
EL34 filaments 1.5A/tube = 3A
Depending on all other loads on the filaments and on the B+, the power transformer may run hot.
Original early transformers for the US were rated for 110VAC and 115VAC.
Put those original transformers on my 117VAC to 123VAC Power Mains, and they will run Hot!
If the transformer catches fire, the fire truck does not sound pretty.
Safety First
Prevent the "Surviving Spouse Syndrome"
Update, I couldn't find The PT specs anywhere And I'm thinking that it could have been a custom wind ? So I don't know what ma current the PT Heater winding has , so I'm not going to chance it , And I only have one EL34 and it's A Vintage Telefunken so I think that I am just going to leave it with The 6L6 GC for now . I'm waiting for the Big Cap can clamps, the pots and the input plugs and some solder wick , so other than starting to wire it up there's not much that I can do at this point. I'll start to wire it up when the rain comes in A few You can see that I have some work cut out for me. Here's a few pictures of the project.
Attachments
I can understand the reasons why you want to switch to EL34, because in guitarland it is a standard the 3k4 load for a PP of EL34 at around 460V B+ biasing around 60-70% of the plate dissipation: 90% of the recorded rock guitars had this power amp.
You can supply the heaters with a small dedicated SMPS 6V 10A, in order to reduce the load on the power transformer.
Connecting a 4 Ohm cab to the 8 Ohm output of the output transformer you can reach 3k3 load, if it is 6k6:8.
Or you can even keep it at 6k6, that is in the JTM45 range.
Maybe this thread can be moved to the instrumentation section?
You can supply the heaters with a small dedicated SMPS 6V 10A, in order to reduce the load on the power transformer.
Connecting a 4 Ohm cab to the 8 Ohm output of the output transformer you can reach 3k3 load, if it is 6k6:8.
Or you can even keep it at 6k6, that is in the JTM45 range.
Maybe this thread can be moved to the instrumentation section?
You are still thinking in Hi-Fi world.
In guitarland speakers drops at 5kHz, impedances of the speakers varies from 5 to 100 Ohm on the audio range, you drive speakers in pentode mode without any feedback with DF below 0,3 because you want the speaker to colour the tone, you add volumes between the phase splitter and the output tubes to increase distortion…
It’s a totally different world.
In guitarland speakers drops at 5kHz, impedances of the speakers varies from 5 to 100 Ohm on the audio range, you drive speakers in pentode mode without any feedback with DF below 0,3 because you want the speaker to colour the tone, you add volumes between the phase splitter and the output tubes to increase distortion…
It’s a totally different world.
A driver with 6 Ohms DCR, will have 6 to 10 Ohm impedance below resonance, and also above resonance in the upper bass/lower mid range, before the voice coil inductance takes over and raises the driver impedance.
6 to 10 Ohm impedance will definitely cause the primary DCR and the secondary DCR to lose power (increased insertion loss).
How much is the only question.
Guitar amps and speakers, and Hi Fi amps and speakers, all follow the same pre-Einstein Physics.
I can not answer for their performance when they are going Warp Speed.
Just my opinions and my experience.
"Einstein was working on the "Unified Field Theory" but "Relatively" speaking, he never got it all together".
6 to 10 Ohm impedance will definitely cause the primary DCR and the secondary DCR to lose power (increased insertion loss).
How much is the only question.
Guitar amps and speakers, and Hi Fi amps and speakers, all follow the same pre-Einstein Physics.
I can not answer for their performance when they are going Warp Speed.
Just my opinions and my experience.
"Einstein was working on the "Unified Field Theory" but "Relatively" speaking, he never got it all together".
Again, you are thinking in Hi-Fi world.
Guitar cabs are often open, and this is the typical impedance plot of a guitar speaker and cabinet as well:
https://www.tonestack.net/articles/...lestion-seventy-80-impedance-free-air-log.png
This impedance variation is used in guitar amps by removing feedback close to resonance (to add lows, the control is usually called DEPTH) and on high frequencies (to add brilliance, the control is usually called PRESENCE).
Guitar cabs are often open, and this is the typical impedance plot of a guitar speaker and cabinet as well:
https://www.tonestack.net/articles/...lestion-seventy-80-impedance-free-air-log.png
This impedance variation is used in guitar amps by removing feedback close to resonance (to add lows, the control is usually called DEPTH) and on high frequencies (to add brilliance, the control is usually called PRESENCE).
Zintolo,
Look closely at that Graph:
The vertical Ohms scale is Not Linear
The vertical Ohms scale is Not Logarithmic.
It needs to be Either one Or the other.
But I will estimate the impedance of that open cabinet driver to be about 8 Ohms at 45 Hz and 8 Ohms at 180 Hz;
And 6 Ohms at 20Hz and 300 Hz.
For a lead guitar, 45Hz, 180Hz, and 300Hz are within the guitar's fundamental frequency,
and 180Hz and 300Hz are within the guitar's Harmonic frequencies too.
At those frequencies, the output transformer will experience its largest insertion losses.
I do measure the primary DCR and secondary DCR, and the insertion loss of my Hi Fi amplifier output transformers.
If I was to build a Guitar amplifier, I would do the same for its output transformer.
Pentode & beam power output tubes make up for the high frequency impedance rise of the voice coil (with no output stage negative feedback).
Do you think that the designers of my 1938 Philco AM & Shortwave Radio knew about that trick?
I bet they did.
Have fun with Guitar Amps!
Have fun with Hi Fi Amps!
Look closely at that Graph:
The vertical Ohms scale is Not Linear
The vertical Ohms scale is Not Logarithmic.
It needs to be Either one Or the other.
But I will estimate the impedance of that open cabinet driver to be about 8 Ohms at 45 Hz and 8 Ohms at 180 Hz;
And 6 Ohms at 20Hz and 300 Hz.
For a lead guitar, 45Hz, 180Hz, and 300Hz are within the guitar's fundamental frequency,
and 180Hz and 300Hz are within the guitar's Harmonic frequencies too.
At those frequencies, the output transformer will experience its largest insertion losses.
I do measure the primary DCR and secondary DCR, and the insertion loss of my Hi Fi amplifier output transformers.
If I was to build a Guitar amplifier, I would do the same for its output transformer.
Pentode & beam power output tubes make up for the high frequency impedance rise of the voice coil (with no output stage negative feedback).
Do you think that the designers of my 1938 Philco AM & Shortwave Radio knew about that trick?
I bet they did.
Have fun with Guitar Amps!
Have fun with Hi Fi Amps!
No, they are not. Lowest note on a standard lead guitar is the 82 Hz open E string, where the ninetish Ohm resonance impedance is.
That plot comes from Celestion, one of the biggest speaker builder worldwide. Most of the electric guitars you have heard passed through one of them. They have just enhanced the 0-10 Ohm range (the most useful) and compressed the rest (where you just need to know where the resonance is and that the impedance is increasing). I’ve seen some log plots and some plots where values on the y axis was doubled (instead of being “10 * y” they were 10 * 2^y). It is not technically correct, but the purpose is always to enhance the most important part on the plot.
Yes, because you are a skilled technician and you know how to optimize every parameter.
What I’m saying is that in guitarland everything is done in a certain way since decades, simply because the way the tubes misbehave and are abused has to be the same: imagine a poor quad of EL34 with a B+ from 460 to 520 V B+ with g2 at the same voltage biased at 60 to 70% on a 1k7 loadline, abused way above clipping and way above their plate dissipation on the loadline. Indeed some schematics shows the expected signal shape on different stages of the amp, and most of it are totally clipped as it is expected to be.
I’m sure they did. I’m just saying that guitarland is used to work in a different way rather than Hi-Fi world, because goals are different, but I’m sure it would benefit alot frim skilled people like you understanding its different requirements.
The few things I learned from you all here helped me find new roads to improve what I did before in guitarland. And I’m sure alot more could be done by more skilled people like you.
I just read all of your comments and it is a little bit over my head in some ways. But I get A lot of it . I've been working on it and I have run into a snag with The Cap cans and the negative bias. The new Cap cans are polarized and they have a ground and two terminals each 2x 50uf@500 volts and 2x 32uf@500 volts. Large and small cans. My Old cans are not grounded by a terminal wire but By the outside of the cans. I'm not sure if I can connect the diode type of negative bias set up it came with to the new type of cans because of the cans having the terminal chassis grounds ? The bias set up has a few polarized cans in it also. I don't think that I have gotten the concept of the negative Bias section completely and I will change it if I need to. I've done this before building I remember making My own negative bias but I don't remember exactly what I did last time, it's been awhile since I did it. It looks like everything is chassis grounds in The Original Amplifier and I was not trying to change it but I don't know what I can do with The different cans ? The Old large Cap cans have four terminals each. They were a little bit lower values than the New ones 40 uf and 20 uf At 450 volts. I'm still waiting on some parts but I was trying to get the power section and heater's hooked up. I have the power switch, fuze and rectifier tube wired up and the primary OT to it and the output tubes but pin 2 of the rectifier goes to the diode for the negative bias and with the Cap cans grounding issue being different I stopped right there from trying to hook it up. I have another Cap can A Mallory PFP with four terminals but they are lower voltages 50uf@350,100@350,10@300 20@25 , I didn't use it because it was under 400 volts. I wanted to try to Use 400 volts on the Preamp section through 100K res to the Plates . I guess that I should have planned it out a little bit better than I did. I do still have room on the chassis to mount another cap can of I need to but I would have to put it over By The PT somewhere. I'm just thinking that I can't ground the negative bias Cap can by A terminal to ground with the tube type negative bias. But I'm not really familiar with tube type negative bias. But maybe I could use what they have already done with A different type of Cap can like The Mallory ? . I'm not really crazy about the idea and adding a third Cap can and more power wires but it is what it is and I do have to deal with it somehow. I'm in Way too deep to back out now. I should have gotten a simpler design to work with but I wanted to have the option of the tube rectifier. I didn't realize it was tube negative bias until I tested The PT. I'm thinking that maybe I should get away from The Tube type negative bias for some other kind ? What happens if the half of the tube goes bad and it blows up the two 6L6 GCs ? 12AX7s Are pretty reliable tubes but they do go bad sometimes and usually without any warning.
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