All 7 pin tube amp—Video DemoClips Added 1/27/18

General discussion area for tube amps.

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brewdude
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Re: All 7 pin tube amp

Post by brewdude »

Thanks Mark.
Cameron
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Re: All 7 pin tube amp

Post by Cameron »

brewdude wrote: Sun Sep 10, 2017 4:28 pm
gtomax wrote: Sun Sep 10, 2017 4:09 pm
brewdude wrote: Fri Sep 08, 2017 5:20 pm Thanks gtomax,

Wow, that is a crazy circuit. Thanks for posting.
Is that inductor part of a tone circuit?
Looks like a cathodyne PI followed by a gain stage?

I like the cooler weather this week too.
Yep - Lover used it to cancel the hum of a single coil input. My understanding is that the inductor was wired in reverse to swap polarity of the signal and cancel the AC hum from the guitar input just like the 2nd coil in a humbucker (which he also designed) did. Pretty ingenius, just move the 2nd coil into the amp rather than in the guitar.
Fascinating. I'm having trouble seeing how it functions as you described by looking at the schematic, but I am no electronic genius--in fact I would describe myself as knowing enough to be dangerous.
It doesn't......It's just a tone control. It has nothing to do with pickup hum or any of that.
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martin manning
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Re: All 7 pin tube amp

Post by martin manning »

brewdude wrote: Sun Sep 10, 2017 11:41 pm So, I did a little experiment today... I jumpered the wiper of the gain pot to the wiper of the tone pot, effectively eliminating the tone pot and achieved a significant increase in gain... and I liked it--a whole lot!

I going to need a tone defeat switch--maybe a push/pull pot(?). Then again, maybe I should consider eliminating the tilt tone control altogether, possibly replace it with a simple tweed style tone circuit.
Lots of options out there. Do you have a schematic for what you have?

PS if you are a wine guy, how'd you get your screen name?
brewdude
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Re: All 7 pin tube amp

Post by brewdude »

There is a schematic link attached to the first post--just above the photos.

In my life before wine, I was the brewmaster of a brewpub in Napa. I was given the nickname by one of the restaurant managers who was also working one day a week as my assistant brewer.
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Kagliostro
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Re: All 7 pin tube amp

Post by Kagliostro »

You didn't find easily a Tone Control after a pentode, the reason is that Tone Controls are an heavvy load for the pentode

so you can see only few amps that use it, the Route 66 is one and the Gibson GA-90 is one other

Image

Image

but, as told, they are not so common

Bypassing the tone control you recover the signal lost and drive more the second pentode

may be you can try a RAW control to decrease the insertion of the Tone Control at your taste

Image

K
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martin manning
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Re: All 7 pin tube amp

Post by martin manning »

brewdude wrote: Mon Sep 11, 2017 11:20 am There is a schematic link attached to the first post--just above the photos.

In my life before wine, I was the brewmaster of a brewpub in Napa. I was given the nickname by one of the restaurant managers who was also working one day a week as my assistant brewer.
Ok, thanks. Kagliostro is right, the output impedance is pretty high on pentode stages.

Back in the 90's I was into amateur brewing. I wrote for Brewing Techniques and Zymurgy, and made a point of visiting micros and brewpubs when I got the chance. The closest I got to Napa was Marin Brewing and Buffalo Bill's. Which one were you working for? One I'd recognize?
brewdude
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Re: All 7 pin tube amp

Post by brewdude »

The GA-40 that I based this build on actually uses a similar tilt tone control--my biggest deviation was using a 1M instead of 2M pot. Perhaps the 2M is an essential value.
brewdude
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Re: All 7 pin tube amp

Post by brewdude »

Martin, I was at Downtown Joe's in Napa from '94-'03. I took over from my mentor Brian Hunt who is the owner of Moonlight Brewing Company--and one of my favorite persons ever.
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pompeiisneaks
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Re: All 7 pin tube amp

Post by pompeiisneaks »

All this brewing stuff is interesting, I actually almost became a beer brewer at one point, but realized it would cost like 500k just to get started and got shy :)

On the thread, I've been planning a build that's Vox 'ish and has an EF86 normal channel, but I needed another stage to mix the phase between the channels, (Top boost with cathode follower). so I've decided that since pentodes aren't great for tone stacks, to set a half a 12AX7 after it to drive the tone stack, this should work from what I gather as a nice compromise.

I'll be probably bringing that amp here for comment before I build it, etc,

~Phil
tUber Nerd!
tubeswell
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Re: All 7 pin tube amp

Post by tubeswell »

brewdude wrote: Sun Sep 10, 2017 11:41 pm So, I did a little experiment today... I jumpered the wiper of the gain pot to the wiper of the tone pot, effectively eliminating the tone pot and achieved a significant increase in gain... and I liked it--a whole lot!

I going to need a tone defeat switch--maybe a push/pull pot(?). Then again, maybe I should consider eliminating the tilt tone control altogether, possibly replace it with a simple tweed style tone circuit.
You could also convert the tilt control to a Tweed Princeton (5F2A) tone control - A bit less lossy than a tilt control.

Another option (with all the talk about tone stack lifting) is to use a 1MA pot with a SPST switch (i.e. a Tweed Champ vol pot), that is set so that the switch 'on' position shorts a 1M resistor between the bottom of the tone stack and the ground return. When you want the 'raw' option, you just switch the tone control off.
He who dies with the most tubes... wins
brewdude
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Re: All 7 pin tube amp

Post by brewdude »

pompeiisneaks wrote: Mon Sep 11, 2017 7:31 pm All this brewing stuff is interesting, I actually almost became a beer brewer at one point, but realized it would cost like 500k just to get started and got shy :)

On the thread, I've been planning a build that's Vox 'ish and has an EF86 normal channel, but I needed another stage to mix the phase between the channels, (Top boost with cathode follower). so I've decided that since pentodes aren't great for tone stacks, to set a half a 12AX7 after it to drive the tone stack, this should work from what I gather as a nice compromise.

I'll be probably bringing that amp here for comment before I build it, etc,

~Phil
Back when I left the brewery (because I was unhappy working for the owner), I had considered trying to open my own, but could never have raised the money on my own and was uncomfortable asking people I liked to invest so much capitol in a, what was likely a risky business adventure... I really loved the brewing industry--it was a ton of fun. However, spending ones days/evenings in a bar, literally drinking beer for a living, is not good for raising a young family or one health. Did I mention how fun it was--I miss it.

I chose to go the other way on a previous build, in that, I used a 12AX7 as the input, feeding a TB tone stack then a 6SJ7 pentode. I have been happy with this amp. It's my go to amp.
brewdude
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Re: All 7 pin tube amp

Post by brewdude »

tubeswell, I think the 5F2A tone is probably the one I was referring to as the tweed tone control.

I have purchased a 2M pot and may try to wire up a complete new set of gain and tone controls with the addition of a switch and change out the entire unit, but I will probably try switching it to a tweed tone first... If/when I have some free time. The switching pot is a good idea.
brewdude
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Re: All 7 pin tube amp

Post by brewdude »

I have made a few adjustments since the schematic was last updated:
Gain—1M A.
Tone—2M B, with two .001uF caps and a bypass switch.
PA Cathode—110R (to bias with plate dissipation at ~97%).
Added .1uF cap at the input (to eliminate guitar volume pot

I think the gain is better now and the switch adds quite a boost.
It’s a bit livelier biased hotter too.
It’s a fun amp.
darefugee
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Re: All 7 pin tube amp

Post by darefugee »

I love that ground bus. If I may ask, what kind of square stock is that and how did you twist it?
Thanks,

Roger
brewdude
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Re: All 7 pin tube amp

Post by brewdude »

Thanks.
I can’t recall where I bought the square ground bus wire—might have been AES(?).
It’s tinned copper and pretty thick.
I fixed one end of the wire In the chuck of a hand held drill, and the other in a vice, then slowly ran the drill until I achieved the desired twist.
This made the section very straight and relatively stiff.
Then I bent it and trimmed it to fit my circuit board.
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