Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: pullshocks on June 22, 2024, 06:22:15 pm
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I’m a sucker for well-played, professionally recorded amp demo videos, like this one from Shawn Tubbs of the Tone King Imperial Mk II. Tone King Imperial MKII In-Depth Demo Video by Shawn Tubbs - YouTube (https://www.youtube.com/watch?v=FPVeJvWGG3Y)
There is a schematic out there on the internet for an earlier version TK Imperial. I copied the rhythm channel preamp (minus bright cap and minus trem) into my old 6V6 single ended amp platform and found it worked out great. More recently I added the Imperial lead channel, using the excellent Hoffman relay board and relay power supply board.
This is still a work in progress. Right now I have a solid state effects loop and digital reverb unit kludged in, and pretty happy with the results. I may try the 1 tube cap-driven reverb from my other recent thread. But I am uncertain if the power transformer can handle the burden.
I could use some help with possibly adding a master volume on the lead channel. Looking at the Tone King preamp schematic there is a 220K resistor to ground (R29 ) edit: R19 after V2b the 3rd triode Could this be changed to a pot without messing up the channel switching system?
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Adding photo with SS FX loop. Tube socket below loop is not connected at this time.
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I could use some help with possibly adding a master volume on the lead channel. Looking at the Tone King preamp schematic there is a 220K resistor to ground (R29) after the 3rd triode. Could this be changed to a pot without messing up the channel switching system?
Ain't seeing it. But there is a 220K (R19) after the fourth triode and that could be replaced with a pot.
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Thank you Sluckey. I should have double checked my post. Corrections posted.
I did mean R19. And it would have been more specific to say V2b. The lead channel consists of 3 triodes, V1b, v1a, and v2b so that is why I caled it the 3rd triode of the lead channel.
I should note that I did not follow the TK control layout or tube numbering--on my build, the rhythm channel is on the left and uses V1a and v1b. The lead channel uses V1a, V2a and V2b
Anyway, I'll go ahead and try changing R19 to a pot.
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Yeah, that clip, great tone, very good player. :icon_biggrin:
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OK, I've been thinking some more about the lead master volume, am I on the right track?
As always, I appreciate the help
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Time flies....
I wired up the lead master control per Option B in the diagram above. I wasn't ready to drill any holes in the conrtrol panel, so it's on a temporary mount.
So far it seems to do what I wanted it to, and I don't notice any drawbacks.
Next I will be trying the 1-tube capacitor driven reverb from my other thread
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If the choke is rated high enough, you might want to move it to before the power tube.
In push-pull designs the transformer, by nature of being push-pull, self-cancels, so the choke is placed after the transformer/before screens. The benefit is that a smaller choke is needed after the transformer since the transformer itself works to smooth ripple.
In a single ended design, however, you don't have the benefit of the transformer's cancelation. The choke will smooth ripple to screens/preamp/everything down stream, but, it doesn't affect ripple at the power tube.
I don't know, something to consider.
Just make sure choke is rated high enough to handle all current if you decide to reposition.
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A cheap alternative will be to use a Gyrator before the node that feeds the power tube and maintain the choke for G2 and preamp tubes
You can also increase the 20uf e-cap
Franco
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If the choke is rated high enough, you might want to move it to before the power tube.
In push-pull designs the transformer, by nature of being push-pull, self-cancels, so the choke is placed after the transformer/before screens. The benefit is that a smaller choke is needed after the transformer since the transformer itself works to smooth ripple.
In a single ended design, however, you don't have the benefit of the transformer's cancelation. The choke will smooth ripple to screens/preamp/everything down stream, but, it doesn't affect ripple at the power tube.
I don't know, something to consider.
Just make sure choke is rated high enough to handle all current if you decide to reposition.
Thank you.
I don't remember for sure why I did it that way. The AX84 power amp schematic (link in first post) has a "choke filtered power supply option" with the choke positioned as you described. Choke spec from the AX84 schematic is 5H 75ma. The choke I used is the Fender Deluxe Reverb style which I believe is 4H 50ma. So I was probably concerned that it would not be adequate.
I did add the extra power supply node before the power amp plate node, which is supposed to reduce noise.
For whatever combination of reasons, the amp does not have noise issues, so I will probably take the path of least resistance (yuk yuk) and leave it as is.
Another questionable power supply feature of my build is the tube rectifier. I do recall that I wanted to be able to use 5Y3, 5V4 or 5AR4 for different B+. The AX84 schematic called for a 250-0-250 volt PT and the PT I had on hand was 302-0-302 so I was probably worried about B+ being too high with a SS rectifier
And just to beat this into the ground, there is the stand by switch.......
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A cheap alternative will be to use a Gyrator before the node that feeds the power tube and maintain the choke for G2 and preamp tubes
You can also increase the 20uf e-cap
Franco
Thanks Kagliostro, good suggestion. The power supply caps are over 20 years old, when they fail I can use some bigger values in some positions. With the 5Y3, from what I've read, the first cap cannot be increased.
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Correct, with a 5Y3 the value to maintain is around 30uF max
If you have the amp open I suggest to sub those old e-caps
Franco