Just received the ACF 12VAC tube buffer board and part kit from Glassware Audio.
I would really like to use 6CG7's but find myself in over my head as far as making sure I'm using the correct cap and resistor values.
Would greatly appreciate any help with determining recommended values for C1-C3 and R1-R13 for that tube...similar to how they are listed for 6DJ8/12AU7/12BH7/ECC99 in the user guide.
Included photos of the part of the guide that I’m working with.
Thanks a ton for the assistance.
I would really like to use 6CG7's but find myself in over my head as far as making sure I'm using the correct cap and resistor values.
Would greatly appreciate any help with determining recommended values for C1-C3 and R1-R13 for that tube...similar to how they are listed for 6DJ8/12AU7/12BH7/ECC99 in the user guide.
Included photos of the part of the guide that I’m working with.
Thanks a ton for the assistance.
Attachments
6CG7 is a close approximation to 12AU7 and 6SN7 used for decades as horizontal and vertical deflection in tube TV sets decades ago. Mainly their differ in pinning at the base, some has a shield between plates and a bigger plate dissipation. Use the values suggested and if you can, modify they as you want.
The caps will be the same regardless of tube chosen. I believe R8 is related to the mu of the tube. Since the 12AU7 and the 6CG7 have roughly the same mu, use the R8 specified for the 12AU7. I don't see R13 in your photos but assume it is a B+ dropping resistor. Try either the 620 ohm or the 1.5K and see what happens. Likely not super critical. Start with the 1.5K to be on the safe side.
HERE'S A TRICK WITH BROSKIE'S BOARDS: They're thicker than most and a real pain to de-solder and change components. Just tack-solder the components you might need to change out. By this I mean don't insert component leads through the board. Just bend the ends of leads over (~1/4") and solder to the pads on the board.
S.
HERE'S A TRICK WITH BROSKIE'S BOARDS: They're thicker than most and a real pain to de-solder and change components. Just tack-solder the components you might need to change out. By this I mean don't insert component leads through the board. Just bend the ends of leads over (~1/4") and solder to the pads on the board.
S.
Appreciate the responses!
@Steve Morley - Thank you. This is the info I was looking for. Will use the R8 value for 12AU7 and will start with 1.5 K ohm for R13.
Should I pretty much stick to the various resistor values listed in the 12AU7 column? And am I correct in reading that R10 should be jumpered regardless of tube used?
Odd that R11-R13 don’t seem to be in the schematic…but I’m schematic illiterate so the info would be lost on me anyway.
PS - Such a useful tip about the tack soldering since desoldering from PCB’s makes my eye twitch.
@Steve Morley - Thank you. This is the info I was looking for. Will use the R8 value for 12AU7 and will start with 1.5 K ohm for R13.
Should I pretty much stick to the various resistor values listed in the 12AU7 column? And am I correct in reading that R10 should be jumpered regardless of tube used?
Odd that R11-R13 don’t seem to be in the schematic…but I’m schematic illiterate so the info would be lost on me anyway.
PS - Such a useful tip about the tack soldering since desoldering from PCB’s makes my eye twitch.
Re R11-13: I haven't seen all of your manual but if it's like the Aikido 12Vac line stage, the power supply schematic will be on a different page in the manual. There will be jumpers on the board for filament supply to the tubes. Their configuration will depend on if your tubes have 6 volt or 12 volt filaments. If you are planning on 6CG7 tubes, then the jumper(s) will need to be set for 6 volts. Other than R8 and R11 all resistors and caps will be the same regardless of tube chosen. Post a pic of the power supply schematic if there is one. Also, if you are using a 6CG7, get a wall wart with enough current capacity or use a small toroid, Triad (from Mouser perhaps) or Antek. Yes, it looks like R10 is a jumper.
S.
S.
Much appreciated @Steve Morley. Thanks again. Here are photos of the page that speaks to the PS. Looks like I’ll only need to jumper J2 for 6CG7.
I see what you mean about all the cap values being the same but I’m a little confused when you say that all the resistors - apart from R8 and R11 - will have the same value regardless of tube chosen.
When I look back at the photo re “Typical Part Values” in my original post, it seems to show otherwise.
For example the R2 and R6 value for 6DJ8’s is different than the one listed for 12AU7/12BH7/ECC99.
Or the R12 value for 6DJ8/12AU7 is different than the one for 12BH7/ECC99.
Am I overthinking this and should just go ahead use the R1-R13 values for 12AU7 and jumper J2 in the power supply?
I see what you mean about all the cap values being the same but I’m a little confused when you say that all the resistors - apart from R8 and R11 - will have the same value regardless of tube chosen.
When I look back at the photo re “Typical Part Values” in my original post, it seems to show otherwise.
For example the R2 and R6 value for 6DJ8’s is different than the one listed for 12AU7/12BH7/ECC99.
Or the R12 value for 6DJ8/12AU7 is different than the one for 12BH7/ECC99.
Am I overthinking this and should just go ahead use the R1-R13 values for 12AU7 and jumper J2 in the power supply?
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Oops, I goofed. Good catch. You are correct. R2 and R6 are different, depending on tube used. It would likely be best to start with the resistors used for the 12AU7. You might wind up changing R13 for a lower value after your first power-up. You'll just have to try it and see. Notice the line on the parts value page that lists the idle currents. Once you are up and running measure the voltage across R6 and calculate the current. (I=E/R). If it's below 5mA try changing out R13 (1.5K for the 12AU7) for one of the lower values (620 or 470) included in the kit. A lower value will raise the B+ a bit and raise the current a bit too.
J2 is the correct one for 6 volt tubes.
One thing I like to do, wherever possible, is solder components on both sides of the board. I especially like to do this with the tube sockets because of the stress they receive when tubes are inserted and removed.
Sorry for the misdirection on the resistors.
S.
J2 is the correct one for 6 volt tubes.
One thing I like to do, wherever possible, is solder components on both sides of the board. I especially like to do this with the tube sockets because of the stress they receive when tubes are inserted and removed.
Sorry for the misdirection on the resistors.
S.
No sweat at all @Steve Morley. Just grateful for the help. Coincidentally, John Broskie replied to an email I sent last week. I assumed he likely wouldn’t reply given the volume of emails he deals with. John says to use 470 ohm for R11-R13.
So I think I have all the resistor values I need. Does this look right?
R1, 5, 7 - 1M ohm
R2, 6 - 100 ohm
R3, 4 - 300 ohm
R8 - 5.9K ohm
R9 - 100K ohm
R10 - jumper
R11 - 470 ohm
R12 - 470 ohm
R13 - 470 ohm
I did want to circle back re R8. You previously recommended using the R8 value for 12AU7 (5.9k ohm). Does that change at all given Broskie’s response?
So I think I have all the resistor values I need. Does this look right?
R1, 5, 7 - 1M ohm
R2, 6 - 100 ohm
R3, 4 - 300 ohm
R8 - 5.9K ohm
R9 - 100K ohm
R10 - jumper
R11 - 470 ohm
R12 - 470 ohm
R13 - 470 ohm
I did want to circle back re R8. You previously recommended using the R8 value for 12AU7 (5.9k ohm). Does that change at all given Broskie’s response?
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5.9K should be at or near the proper value for R8. This one is related to the mU of the tube. Since the 12AU7 and 6CG7 have roughly the same mU 5.9K is the way to go.
Using 470 ohms for R11, 12 and 13 will result in a higher B+ on (and more current flow through) the tubes. The 6CG7 will easily handle this.
Good luck,
S.
Using 470 ohms for R11, 12 and 13 will result in a higher B+ on (and more current flow through) the tubes. The 6CG7 will easily handle this.
Good luck,
S.