Hi all,, Hopefully not too off topic, but would modding out the 6AV6 to accept a 12AX7, leave me w/the same gain factors of 100?, and might there be any appreciative sound difference? It's a Bogen CHA-10 single ended amp currently w/a 6AV6 mic preamp tube, a 6AU6 for an unused phono section, 1-6L6 & an EZ81 rectifier, headed to the bench to be RnR guitar worthy. So, 6AV6 to 12AX7, same gain>overdrive, same sound?
A waste of energy? Thanks!! Be well all!
A waste of energy? Thanks!! Be well all!
The "same" triode goes into both the 6AV6 and 12AX7. 😉 Of course, manufacturing differences can be present.
Be advised that this "board" is HIFI oriented. Instruments and amps is where guitar stuff belongs. I will notify the moderators.
Be advised that this "board" is HIFI oriented. Instruments and amps is where guitar stuff belongs. I will notify the moderators.
> Bogen CHA-10 ....w/a 6AV6 mic preamp tube, a 6AU6 for an unused phono section, 1-6L6....
No. The 6AU6 is the driver for the 6L6. This much will accept a hi-level ceramic phono needle. For MIC it adds a half-12AX7 (the 6AV6).
The "phono" input sensitivity is about 200mV, will accept your hottest pedals cleanly. The "MIC" input sensitivity is like 5mV, a "hot" headbanger input.
In such SE amps the driver is not a large part of "flavor".
In this low-low-low-price amp the mike stage is run gridleak bias. Fender did that in the early 1950s. Hot pickups forced him to cathode bias, but there are still fans of gridleak inputs. If your axe and style just smoosh this input, steal bias plan and values from any Fender 12AX7 input stage.
I see NO reason to modify this amp. Convert to 3-pin wall power, fix what's broke, find a GOOD speaker, play it.
No. The 6AU6 is the driver for the 6L6. This much will accept a hi-level ceramic phono needle. For MIC it adds a half-12AX7 (the 6AV6).
The "phono" input sensitivity is about 200mV, will accept your hottest pedals cleanly. The "MIC" input sensitivity is like 5mV, a "hot" headbanger input.
In such SE amps the driver is not a large part of "flavor".
In this low-low-low-price amp the mike stage is run gridleak bias. Fender did that in the early 1950s. Hot pickups forced him to cathode bias, but there are still fans of gridleak inputs. If your axe and style just smoosh this input, steal bias plan and values from any Fender 12AX7 input stage.
I see NO reason to modify this amp. Convert to 3-pin wall power, fix what's broke, find a GOOD speaker, play it.
Attachments
Greetings,
I pretty much completely reconfigured one of those a couple years ago after rescuing it from a dumpster. Rebuilt the power supply, AC entry stuff (fuse, grounded line cord, switch), installed 1/4" input and output jacks, etc.. I changed out the 6AV6 for a second 6AU6 and configured the circuit for high gain. Cathode bias on both 6AU6. Put one pot between the two s/s pentodes and another before the 6L6. Messed with the multi pole "tone" control a bit as well. So, it doesn't much resemble the original.
I really like the result and use it a lot, but if you want clean or even semi clean tones, you may not. I can mail you a copy of what I did if you're interested in trying it out. Like I said, it's a dirty amp and not for everyone.
Regards, Jim
I pretty much completely reconfigured one of those a couple years ago after rescuing it from a dumpster. Rebuilt the power supply, AC entry stuff (fuse, grounded line cord, switch), installed 1/4" input and output jacks, etc.. I changed out the 6AV6 for a second 6AU6 and configured the circuit for high gain. Cathode bias on both 6AU6. Put one pot between the two s/s pentodes and another before the 6L6. Messed with the multi pole "tone" control a bit as well. So, it doesn't much resemble the original.
I really like the result and use it a lot, but if you want clean or even semi clean tones, you may not. I can mail you a copy of what I did if you're interested in trying it out. Like I said, it's a dirty amp and not for everyone.
Regards, Jim
Hi Jim,,, thanks, & absolutely send me the laundry list of the mods performed. I didn't realize the 6au6 was a preamp tube, but that the AV6 was.... Sounds like you used the Phono control as a master of sorts, or just a blend of a different flavor o/d to mix w/the main volume?
I want to rock this thing!! I've got plenty of clean lying around. I don't have the amp yet, but should have it next week. Thanks so much for reaching out ,, you're just what the doctor ordered!! Hopefully it gives off a good distortion as opposed to a fuzzy, mushy drive?
Be well ~
Kenny
I want to rock this thing!! I've got plenty of clean lying around. I don't have the amp yet, but should have it next week. Thanks so much for reaching out ,, you're just what the doctor ordered!! Hopefully it gives off a good distortion as opposed to a fuzzy, mushy drive?
Be well ~
Kenny
Greetings,
Hi Kenny! Go here:
analogbros.com - /pictures/Bogen/
The top image is a schematic I drew. It was somewhat preliminary or certainly not final. It should get you into the ball park or at least provide a starting point for you to work from. I used what I had laying around parts wise, no component values are particularly vital.
There are a couple obvious differences between the schematic and the amp as built: for some reason I drew solid state diodes for the rectifier while in the amp I used the EZ-81. Next, it does not show the screen grid resistor for the 6L6/5881; that is a 1K, 3W. The "tone" control circuit is not shown in it's final state; I was messing around with different values and it seems I did not document the final version.
Yes, the first pot attenuates between the two 6AU6 "pre-amp" tubes and the second is like a "master" as it comes between the last preamp stage and the power amp. There are a good variety of dirty tones at different positions.
I would suggest to start with the AC input; grounded line cord, fuse, etc. I installed a new 2 pole switch, so I could eventually use the factory on/off for another function (tone disable). I removed the mic input jack from the front and made a little adapter plate to mount a 1/4" input in its place. I hard wired the output TX secondary to 8R and directly connected that to another 1/4" jack where the phono input RCA was, so there was no need for the jumper on the selector socket. Take a good look at the power supply. I'm pretty sure when I got my amp the caps were shot, but I probably would have replaced them anyway. The multi-section LCR cap isn't ideal in regards to grounding, but saved space and worked out by allowing for additional nodes relative to the stock P/S. I elevated the filament via a resistive center tap to about 40VDC; that helps with hum. Moving all the ac mains wires to the rear panel also helps.
There is no reason to exactly clone what I did; you may actually hate it! Take a shot at it and see how you can improve on what I did and make it your own. If I come across the final schematic, I'll post it and update here. I'm glad to answer any questions. Best of luck with your project!
Regards, Jim
Hi Kenny! Go here:
analogbros.com - /pictures/Bogen/
The top image is a schematic I drew. It was somewhat preliminary or certainly not final. It should get you into the ball park or at least provide a starting point for you to work from. I used what I had laying around parts wise, no component values are particularly vital.
There are a couple obvious differences between the schematic and the amp as built: for some reason I drew solid state diodes for the rectifier while in the amp I used the EZ-81. Next, it does not show the screen grid resistor for the 6L6/5881; that is a 1K, 3W. The "tone" control circuit is not shown in it's final state; I was messing around with different values and it seems I did not document the final version.
Yes, the first pot attenuates between the two 6AU6 "pre-amp" tubes and the second is like a "master" as it comes between the last preamp stage and the power amp. There are a good variety of dirty tones at different positions.
I would suggest to start with the AC input; grounded line cord, fuse, etc. I installed a new 2 pole switch, so I could eventually use the factory on/off for another function (tone disable). I removed the mic input jack from the front and made a little adapter plate to mount a 1/4" input in its place. I hard wired the output TX secondary to 8R and directly connected that to another 1/4" jack where the phono input RCA was, so there was no need for the jumper on the selector socket. Take a good look at the power supply. I'm pretty sure when I got my amp the caps were shot, but I probably would have replaced them anyway. The multi-section LCR cap isn't ideal in regards to grounding, but saved space and worked out by allowing for additional nodes relative to the stock P/S. I elevated the filament via a resistive center tap to about 40VDC; that helps with hum. Moving all the ac mains wires to the rear panel also helps.
There is no reason to exactly clone what I did; you may actually hate it! Take a shot at it and see how you can improve on what I did and make it your own. If I come across the final schematic, I'll post it and update here. I'm glad to answer any questions. Best of luck with your project!
Regards, Jim