Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: alange5 on April 15, 2020, 04:58:33 pm
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Hello all,
A while ago I built a single-channel 6G3 deluxe. I omitted the tremolo, added a larger output transformer, and biased for 6L6's. It sounds very nice, but I'd like to squeeze just a little bit more volume out of it. Played full-tilt through efficient speakers, it doesn't quite keep up with my drummer.
original 6G3 schematic:
[img width= height= alt=6g3-schematic" border="0]https://i.ibb.co/nBbBLXm/6g3-schematic.gif[/img] (https://ibb.co/nBbBLXm)
my schematic:
[img width= height= alt=brown-deluxe-single-channel-schematic" border="0]https://i.ibb.co/PQRMRp4/brown-deluxe-single-channel-schematic.png[/img] (https://ibb.co/PQRMRp4)
my layout:
[img width= height= alt=single-channel-6g3-layout" border="0]https://i.ibb.co/Qj9Fyys/single-channel-6g3-layout.jpg[/img] (https://ibb.co/Qj9Fyys)
A few questions:
Should I be using a 3K resistor on the first cathode since I'm only using one channel?
Is the 220K series resistor after the volume/tone control necessary? (it was originally a mixing resistor for the two channels)
That divider before the phase inverter is dumping a lot of signal. Will increasing the value of the 15K resistor result in more volume, or merely more clipping?
Thanks in advance.
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Is the 220K series
short it out with a gator clip and test
the 15k probably can be jumped also for test, but suspect it was "designed" to NOT overdrive the PI
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my schematic:
(https://i.ibb.co/PQRMRp4/brown-deluxe-single-channel-schematic.png) (https://ibb.co/PQRMRp4)
That divider before the phase inverter is dumping a lot of signal. Will increasing the value of the 15K resistor result in more volume, or merely more clipping?
Getting rid of the split load would definitely increase the signal overall.
Whether it clips the signal depends on how you deal with the headroom in the signal after this gain stage.
You could do some experimentation e.g.
1) change the output ratio of the split load in increments until you notice unwanted clipping, or get rid of it altogether
2) increase the overall voltage on the HT supply rail (going to SS diode rectification, you may need to up-rate the filter cap voltage ratings)
3) Stiffen the HT supply for the screens and PI by increasing filter capacitance (This can improve bandwidth esp in low frequencies)
4) Change the HT rail supply resistors to get higher voltage on the PI supply node. (e.g. swap out the 10k supply resistor for 4k7 or 2k2 - you may want to double or triple the filter capacitance on the PI node to compensate for this)
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a better PS will probably change the tone some, but agree 6L6's like sweating :laugh:
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A few questions:
Should I be using a 3K resistor on the first cathode since I'm only using one channel?No. Stay with 1.5k
Is the 220K series resistor after the volume/tone control necessary? no
That divider before the phase inverter is dumping a lot of signal. Will increasing the value of the 15K resistor result in more volume, or merely more clipping? Just connect the .01µF PI input cap directly to the plate of the previous triode.
If you really want more power you need to use a bigger PT.
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you mention a larger output transformer. no mention of what was done with the power transformer. was the power transformer swapped for one suitable for 40-50W power stage? what's the B+ to the OT CT? what's the impedance of the OT?
your preamp and phase inverter are likely not the issue. you need to move more air.
build a 200W twin head & load a 4x12 cabinet with 4x JBL K120's or EV12Ls - point it at the drummer. :icon_biggrin:
--pete
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point it at the drummer
:l2:
world 3.0 he'll be isolated in his own box, no solder required :icon_biggrin:
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> it doesn't quite keep up with my drummer.
If it did, the drummer would hear you, and easily play louder to compensate.
Don't hope for a longer sword when you really need a cannon.
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I went to remove that 15K resistor in the divider and discovered I had a 1K5 installed. I even had it labeled that way on my layout. Whoops!
I replaced it with a 15K and the amp is now incredibly loud. Way, way louder than it was.
Sorry for the goose chase but thanks for the help.
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LOL!
Having an extra 20dB or so of gain can tend to make things louder :)
Glad to see you found the problem!
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Always a good feeling to find and resolve a problem before you buy an expensive transformer!
I went to remove that 15K resistor in the divider and discovered I had a 1K5 installed.
I did the same thing recently as I had put a resistor in the wrong parts drawer and soldered it in without looking closely at it. But a voltage check quickly revealed the mistake. And with Fender circuits you almost always have voltage recorded on a schematic or layout or both, making a comparison easy.
Don't let the drummer mic his drums!