Tube Chassis Layout

[Phil_S]

I admire your willingness to dive in. However, I want to suggest it is not the best approach. This is my opinion about attempting a more complex amp on the first build. Others may not agree.

The lack of experience can be problematic in executing the build to assure it is done well. There are many unwritten "rules" about construction and there is technique to be learned. With respect to technique, there are manual skills that you will need to acquire and master. Yes, making a proper workmanlike solder is not so difficult when you just lay out two things to join. It can be considerably more challenging when you are working inside a chassis where things can get in the way. There are issues of lead dress -- this is the knowing where to place wires in relation to one another to avoid cross talk or introducing hum -- and once you know where the wires should be placed, it can be a whole new adventure getting them to stay put. There are other deceptively simple things like this, for example, how to most effectively hold an manipulate parts with a pliers. So, it is my view that you build the Champ like amp to ramp up your skills and sharpen your eye. That will help to insure the success of a more complex build.

The most expensive thing you can do, both time and money, is build the more complex amp and find, while you connected every component correctly, your work just isn't up to what it should be and the amp exhibits problems or just doesn't sound right. Then you find your only real avenue is to tear out a bunch of stuff and do it again. I think that building a less complex amp for practice is worthwhile.

And so, you end up with two amps. What's wrong with that?

[JJH0906]

The attached is a diagram from a book by Merlin Blencowe, aka the Valve Wizard. I selected this circuit because I believe the theory behind it is that it is an active effects loop and if a cable is plugged into the Send jack, then it allows for the mix of the dry and wet signal. If not, it appears to bypass the Send/Return jacks and just passes the signal to the anti-log pot, which because the signal is not being mixed, there's "zero" potential on the signal and it all just goes to the Output section.

Pretty much everything I've read says the same thing about having ambient effects in a loop and not on the front end. That's basically the reason I wanted to go this route, to allow for some flexibility of having the effects introduced into the signal, or not.

Also, I should note that my work experience is in electricity and electronics. I was modifying amateur radios when I was a teenager, went to a technical college in industrial electronics and now work with machine automation so many of the concepts I've been exposed to with amp building aren't foreign, although admittedly somewhat 'new'. I just got tired of coming across amps that didn't have everything I wanted or were outrageously priced and I decided to mix my passion for music and electronics and hell, why not build an amp?

Just wanted to post this for clarification.

[pompeiisneaks]

I have used Ceriatone Layouts as a guide to build some of my amps. They have pictorial layouts for most of their amps. I have always had good results following their layouts.

Mike

as an FYI many of the ceriatone amps were directly cribbed from the amps here . I.e. you're saying their layouts look good but they're not really 'their layouts' they're HAD's ( or whoever built the one they used for other amps they sell.) As far as I know basically next to nothing is 'original' with ceriatone, they're all clones of existing designs.

~Phil

[JJH0906]

Hey, whatever works, works!

[pdf64]

The attached is a diagram from a book by Merlin Blencowe, aka the Valve Wizard. I selected this circuit because I believe the theory behind it is that it is an active effects loop and if a cable is plugged into the Send jack, then it allows for the mix of the dry and wet signal. If not, it appears to bypass the Send/Return jacks and just passes the signal to the anti-log pot, which because the signal is not being mixed, there's "zero" potential on the signal and it all just goes to the Output section.

Pretty much everything I've read says the same thing about having ambient effects in a loop and not on the front end. That's basically the reason I wanted to go this route, to allow for some flexibility of having the effects introduced into the signal, or not...

Alas, I bought in early, and only have the 1st edition of Merlin's preamp book, but I don't recognise that fx loop?
He tends not to use a pot on the send output for level control, so your drawing seems unusual in that.
I suspect that a log/antilog wet / dry balance pot may be a bit drastic, something of a hair trigger to set, and a linear type may work out better.
I've never tried a parallel loop, but can't help thinking that unless using fx units that can be set fully wet, the benefit may be minimal?

Whilst I'm fully on board with an fx loop in the case of an overdrive preamp, for a low gain, sparkling clean pedal platform, I just don't perceive what the benefits are? Rather the additional circuitry / signal processing seems more likely to degrade the signal to noise ratio, especially if the design / implementation are not of the highest order.

Regarding the choke, it's much bigger and beefier than is necessary for most designs, and so will be needlessly be taking up excessive, valuable space on the chassis.
Most designs don’t pass the full HT current through the choke, rather it only handles current for the screen grid and subsequent HT nodes. For regular pentode push pull output stages, compared to that, there’s no real advantage in using a bigger choke that can handle the full HT current.

[Phil_S]

...I was modifying amateur radios when I was a teenager, went to a technical college in industrial electronics and now work with machine automation...

There was no way to know without you telling us. Though well intended, with this context, what I said wasn't appropriate for you. Apologies offered.

[JJH0906]

No worries... I am not used to forum boards and probably should have given my background in my first post. Whoops!

Everyone has some great ideas so I'm just trying to digest what's being offered to see how it can apply to what I'd like to put together. I am sure I'll be kicking myself later on but so it goes!

[JJH0906]

Regarding Merlin's book.. I think I have the 2nd Edition? It was published in 2012, so it's not very recent but I think it's a different revision. He unabashedly comments in the introduction about all the things he messed up in the previous edition and have tried to correct it!

I've come across a YouTube video where a gent was running a pedalboard into a Roland JC-120 and demonstrated how the parallel effects loop worked with that particular amplifier. It took a bit to grasp but I thought it was an interesting way to mix the wet/dry signal so I've initially elected to do that, versus a serial loop. It could go bollocks but it wouldn't be too difficult to rearrange the components to just make it a serial loop. I had considered making it switchable but I actually decided NOT to add more complexity to it. I already have enough of a mess going on.

[sluckey]

Could we see a schematic for this project? That would make it possible for us to give some more specific comments.

[JJH0906]

I have not done the forum any favors by not adding the schematic. I mentioned earlier that I have pieces of it from various sources but have not put it all together. I'll see if I can get it all drawn out as a complete drawing over the weekend and post it after that for anyone who's interested to review.

[JJH0906]

As suggested, attached is the draft schematic for the clean amp build. It's done on multiple pages, I may combine them into a single drawing down the road but for now, I chose to eat the elephant one bite at a time!

[pdf64]

It's missing a mixing stage for reverb/dry signal paths. As it is, it's totally wet.
The fx send CF stage needs elevating, as it is, it'll be an early, assymetric clipping stage. Also a signal potential divider at its input may be beneficial, maybe move the send control there.
The 6L6 need grid leaks.

[JJH0906]

Thanks for these observations! I scabbed the circuits from various sources and may have missed some things while transferring them into a CAD program. I will double-check the originals against what you've pointed out.

That's why they call 'em "drafts"!

[pdf64]

Fully bypassing cathodes facilitates improved heater hum rejection.
Heater circuit elevation has several benefits.
What’s the intention of the 2nd stage grid stopper? Such a high value will tend to add hiss. Is it really necessary in a low gain design?

[JJH0906]

Fully bypassing cathodes facilitates improved heater hum rejection.
Heater circuit elevation has several benefits.
What’s the intention of the 2nd stage grid stopper? Such a high value will tend to add hiss. Is it really necessary in a low gain design?

Forgive my ignorance but which circuits are you referring to? I'll have to double check the originals to see if I didn't transfer something correctly. Which obviously I have missed alot! The reverb circuit, as you pointed out, has many missing pieces, not sure how I missed that when getting it into the computer but am working on getting it all added back.