Anyone done something like this? Is it worth it? I haven't done the math to fill in the component values but I'm wondering if I should have two inputs (like a mic/inst). I want one to be a drive, one to be clean, and each have their own respective tone stacks, which is the trick I'm trying to figure out. Controlling the clean and driven channels with a separate set of controls. I can't seem to find a schemo after searching for quite a while (not familiar with many amps). So I figured okay, give it up already and just draw it up yourself. Started as a Gibson EH185 then went from there and admittedly its still way early in the thought process on this one. If anyone has any specific amp suggestions to look at I'm all ears. Also, any good tone stacks to use after a pentode?
Another possibility,
Drive Channel: Triode input to pentode to TS to PI
Normal Channel: Pentode to TS to PI (other side?)
--removed-- got a new idea...
Pentode --> Tone Stack
Moderators: pompeiisneaks, Colossal
Pentode --> Tone Stack
Last edited by surfsup on Tue Jan 31, 2012 2:22 pm, edited 1 time in total.
Re: Pentode --> Tone Stack
okay here's what I have for a generalize schemo so far:
[img
688]http://chicagocadcam.com/EH185/pentode_input.JPG[/img]
This gives me the two options on a switch/relay:
1) Clean/Normal: triode to pentode to TS with "clean" MV
2) OD/Gain: triode to pentode to TS to "OD-level" to pentode to TS with OD MV
I'm not planning to get 150 gain out of each pentode so I think this will work okay. I think since I'm switching AC it will be relatively quiet. Should I lead with pentode input or stick with the triode that will give me a gain of about 20 which will raise the noise floor going into the pentode stage? I figure I can get some compression from the signal being higher out of the triode to give a little pick attack, as well.
[img
688]http://chicagocadcam.com/EH185/pentode_input.JPG[/img]
This gives me the two options on a switch/relay:
1) Clean/Normal: triode to pentode to TS with "clean" MV
2) OD/Gain: triode to pentode to TS to "OD-level" to pentode to TS with OD MV
I'm not planning to get 150 gain out of each pentode so I think this will work okay. I think since I'm switching AC it will be relatively quiet. Should I lead with pentode input or stick with the triode that will give me a gain of about 20 which will raise the noise floor going into the pentode stage? I figure I can get some compression from the signal being higher out of the triode to give a little pick attack, as well.
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Luthierwnc
- Posts: 998
- Joined: Sat Feb 18, 2006 10:59 am
- Location: Asheville, NC
Re: Pentode --> Tone Stack
IIRC you need a much higher impedance tone stack for a sharp-cutoff pentode front-end. That's why you see Baxandalls or just a rotary switch coupler bank.
I've done some pentode stuff and like it but you need some sort of buffer in there to lower the impedance if you are going to run a TMB stack. Google an amp called a Route 6V6 for a 6SJ7 idea. 10thTX and I have done some recent musing about how to use a 5879 to drive a 5F6-A/Beano type rig here:
http://ampgarage.com/forum/viewtopic.ph ... 879#190245
Good luck, Skip
I've done some pentode stuff and like it but you need some sort of buffer in there to lower the impedance if you are going to run a TMB stack. Google an amp called a Route 6V6 for a 6SJ7 idea. 10thTX and I have done some recent musing about how to use a 5879 to drive a 5F6-A/Beano type rig here:
http://ampgarage.com/forum/viewtopic.ph ... 879#190245
Good luck, Skip
Re: Pentode --> Tone Stack
I figured that, which is why I"m putting in a mosfet follower between the pentode and TS.
If I put a cathode follower there, with a lower output impedance, doesn't that "artificially" increase the input impedance of the following stage, in this case the TS?
If I put a cathode follower there, with a lower output impedance, doesn't that "artificially" increase the input impedance of the following stage, in this case the TS?
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pinkphiloyd
- Posts: 136
- Joined: Mon Jun 13, 2011 1:01 pm
Re: Pentode --> Tone Stack
FWIW a few months ago I built a Spitfire but replaced the paralleled 12ax7 input with an EF86 and it worked just fine. Sounded great.
Re: Pentode --> Tone Stack
you could put the volume before the tone
a simple pentode pre- volume- half of a dual triode- tone stack and volume
and then another pentode driving the other half of the dual triode as a split load invertor.
I bet you could shrink in down using a couple 7199 , 6an8 or similar.
theres several hagstrom with bandaxal, and a univox with a 6au6 that simply has the volume first
a simple pentode pre- volume- half of a dual triode- tone stack and volume
and then another pentode driving the other half of the dual triode as a split load invertor.
I bet you could shrink in down using a couple 7199 , 6an8 or similar.
theres several hagstrom with bandaxal, and a univox with a 6au6 that simply has the volume first
there is a right way to mic a musical saw
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Luthierwnc
- Posts: 998
- Joined: Sat Feb 18, 2006 10:59 am
- Location: Asheville, NC
Re: Pentode --> Tone Stack
9pins has something.
If you Google around you'll find some ideas on using a dual pentode/triode tube like a 6GH8A where you can gain it up and run a cathode follower buffer out of the same socket. Noise on tubes like that can be all over -- particularly if this is a combo. Shock-mount it somehow. These tubes are cheap so get a couple/three different brands. Also get an assortment of plate/screen/K resistors so you can play with the gain structure. They may already be in the parts bin but the coupling cap between the pentode and the triode matters a lot. Myself, I'd probably put the volume pot between the two stages or at least a 1m trimmer wired as a divider so you don't overwhelm the triode.
The one I'm doodling on is just a 5879 sent for modest gain to a volume pot to a 5F6-A gain stage/cathode follower and TMB stack -- really a Beano with a sharp-cutoff driver. For laughs I might put another pentode with a rotary coupler switch on the bottom of the inverter since the phasing would be right. Great place to put reverb too so they are fighting it out on the page. sh
If you Google around you'll find some ideas on using a dual pentode/triode tube like a 6GH8A where you can gain it up and run a cathode follower buffer out of the same socket. Noise on tubes like that can be all over -- particularly if this is a combo. Shock-mount it somehow. These tubes are cheap so get a couple/three different brands. Also get an assortment of plate/screen/K resistors so you can play with the gain structure. They may already be in the parts bin but the coupling cap between the pentode and the triode matters a lot. Myself, I'd probably put the volume pot between the two stages or at least a 1m trimmer wired as a divider so you don't overwhelm the triode.
The one I'm doodling on is just a 5879 sent for modest gain to a volume pot to a 5F6-A gain stage/cathode follower and TMB stack -- really a Beano with a sharp-cutoff driver. For laughs I might put another pentode with a rotary coupler switch on the bottom of the inverter since the phasing would be right. Great place to put reverb too so they are fighting it out on the page. sh
Re: Pentode --> Tone Stack
Hi surfsup, the source follower should work just dandy. Use IRF820 or similar high-voltage type.
He who dies with the most tubes... wins
Re: Pentode --> Tone Stack
I plan to stick with the existing tube complement since i have them. I will also stay with triode to pentode to hopefully get pentode tone on cleans...
Tubeswell. Thx yea i used the irf 820 on another amp and it worked great. I'm going to work up the schemo a bit more and update it soon
Tubeswell. Thx yea i used the irf 820 on another amp and it worked great. I'm going to work up the schemo a bit more and update it soon