Eliminate both low inputs?

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carl44
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Eliminate both low inputs?

Post by carl44 »

diagramAk.png
Hi guys, building the tremolo/normal 18 watt and would like to eliminate both low inputs. It looks simple to me but can this be done? Thanks
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Crabman
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Re: Eliminate both low inputs?

Post by Crabman »

Absolutely it can be done. In fact it will your life easier since wiring those dual inputs is a pain.

You just need to decide what value of grid stopper you want to use and solder it right to the grid pin on the tube socket. Use shielded wire for the input and be sure to ground the shielding at the appropriate point on the cliff jack (if that is what you are using).
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carl44
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Re: Eliminate both low inputs?

Post by carl44 »

Crabman wrote:
Sat 10/27/18 2:34 pm
Absolutely it can be done. In fact it will your life easier since wiring those dual inputs is a pain.

You just need to decide what value of grid stopper you want to use and solder it right to the grid pin on the tube socket. Use shielded wire for the input and be sure to ground the shielding at the appropriate point on the cliff jack (if that is what you are using).
Thank you sir. Now I'll scour the posts on grid stoppers. For me this is a great education and I thank all you pro's who take the time passing on the info.
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Re: Eliminate both low inputs?

Post by Crabman »

When considering the original 18W schematics, it would appear that no grid stopper was used on the original 18W normal channel. My opinion on this would be to use a grid stopper since it will help prevent picking up radio signals. If you consider the original schematic, the Hi input on the tremolo channel will see two 68K resistors in parallel when you plug into that jack (if I remember correctly). This will produce a 33K resistance in series with the grid. So to reproduce this you could just use 33K grid stoppers on both the normal and tremolo inputs.

If you need to know why this value of resistor is commonly used we can certainly get into that discussion.
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carl44
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Re: Eliminate both low inputs?

Post by carl44 »

Crabman wrote:
Tue 10/30/18 8:28 pm
When considering the original 18W schematics, it would appear that no grid stopper was used on the original 18W normal channel. My opinion on this would be to use a grid stopper since it will help prevent picking up radio signals. If you consider the original schematic, the Hi input on the tremolo channel will see two 68K resistors in parallel when you plug into that jack (if I remember correctly). This will produce a 33K resistance in series with the grid. So to reproduce this you could just use 33K grid stoppers on both the normal and tremolo inputs.

If you need to know why this value of resistor is commonly used we can certainly get into that discussion.
Here is the diagram from TubeDepot(which I now regret using)of the 2-68k. Please continue how you would do this. Thank you kindly for your time.
diagramC.png
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geoff 1965
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Re: Eliminate both low inputs?

Post by geoff 1965 »

hello Carl,
are you building the tube depot kit? i.e. turret board etc or just showing the layout.
i think you'll need to use a 68K for the tremolo input,dropping to 33K will increase the signal slightly which might cause problems.but you could use 10 to 33K on the normal input and use sheilded cable from both jacks with the resistors on the tube sockets.
HI INPUT.jpg
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Re: Eliminate both low inputs?

Post by carl44 »

geoff 1965 wrote:
Fri 11/02/18 8:43 pm
hello Carl,
are you building the tube depot kit? i.e. turret board etc or just showing the layout.
i think you'll need to use a 68K for the tremolo input,dropping to 33K will increase the signal slightly which might cause problems.but you could use 10 to 33K on the normal input and use sheilded cable from both jacks with the resistors on the tube sockets.
HI INPUT.jpg
Thank you for the diagram. I started using the TubeDepot instructions, layout, diagrams etc. for reference because it was free and seemed the most complete thing out there. The 68k's are on the board but I presume I can remove them, bypass the board and attach directly to the tube with one 68k(shielded cable)?
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Re: Eliminate both low inputs?

Post by geoff 1965 »

okay so if they are already on the board you could go from the input jack to T22 and jump the wire across to T20,or you could remove T20 resistor and replace T22 with a 33K this will equal the 2 68K's in parallel like crabman said.you could use normal wire for this way but if you wire from the jack to the tube like the diagram you'll need sheilded cable with a 33K resistor.
just a couple of notes regarding the tubedepot amp!
1st if you fit the PPIMV don't follow the wiring diagram shown,it's wrong.
2nd is Josh pointed out there is no B+ bleed resistor so you might want to fit one,use a 2W metal film 220K soldered between the first + and - terminals on the can capacitor.
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Re: Eliminate both low inputs?

Post by carl44 »

geoff 1965 wrote:
Sat 11/03/18 8:20 am
okay so if they are already on the board you could go from the input jack to T22 and jump the wire across to T20,or you could remove T20 resistor and replace T22 with a 33K this will equal the 2 68K's in parallel like crabman said.you could use normal wire for this way but if you wire from the jack to the tube like the diagram you'll need sheilded cable with a 33K resistor.
just a couple of notes regarding the tubedepot amp!
1st if you fit the PPIMV don't follow the wiring diagram shown,it's wrong.
2nd is Josh pointed out there is no B+ bleed resistor so you might want to fit one,use a 2W metal film 220K soldered between the first + and - terminals on the can capacitor.
Wow...if there is that much wrong with TubeDepot, I'm thinking maybe I should start over. I've only half the board assembled but if it's faulty I'd rather trash it because this won't be my only build. Thanks for the info.
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geoff 1965
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Re: Eliminate both low inputs?

Post by geoff 1965 »

hello Carl,
there's been a few posts with tubedepot builds with good results! i was just pointing out a couple of issues to take into account.have a browse through the forums downloads,there is a good selection of schematics & layouts to consider if your not happy with the tubedepot.
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Re: Eliminate both low inputs?

Post by JMPGuitars »

carl44 wrote:
Sun 11/04/18 12:53 pm
Wow...if there is that much wrong with TubeDepot, I'm thinking maybe I should start over. I've only half the board assembled but if it's faulty I'd rather trash it because this won't be my only build. Thanks for the info.
The layouts and schematics on this site are the best / most vetted you can work with. Whether you trash the current build is up to you, but for the next build I would switch to something from 18watt.com.
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carl44
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Re: Eliminate both low inputs?

Post by carl44 »


The layouts and schematics on this site are the best / most vetted you can work with. Whether you trash the current build is up to you, but for the next build I would switch to something from 18watt.com.
Tell you what the JMP drawing is the best I've seen. I'm going to take a parts inventory and compare to the Trem amps here and decide.Thanks again guys.
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crgfrench
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Re: Eliminate both low inputs?

Post by crgfrench »

Agree, the JMP diagrams are beautiful and easy to follow!
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geoff 1965
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Re: Eliminate both low inputs?

Post by geoff 1965 »

yep i agree, can't wait to see JMP's "beautiful" layout & schematic of the superlite el34!!
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