new build - Cascode Micro

[wrongtube]

Thinking about my next build – I found an old gutted record player cabinet and thought it might be fun to make a "living room" amp. It's got a hole cut for an 8" speaker, which I will proceed to rip out of a solid-state practice amp

Been interested in the Micro designs on Robinette's page, where you get 1 or 2 watts out of a 12AU7 wired push-pull into a Fender-style reverb transformer… and since I'm also curious about the "cascode" sound, I thought I'd try marrying the Micro power section onto a cascode preamp section.

Here's a first draft of my schematic – anything I should look out for?

Cascode_Micro_v1-0.pdf

Some questions in particular: I'd like to include a Vox-style Cut control, but I'm not sure if that will work with the Trainwreck Type-3 master volume. On the B+ rail, I've just pencilled in my dropping resistors and noted the voltages I'd like to achieve. Was planning on tweaking once I've got it fired up and can take measurements ... but let me know if the values look way off! Also, not certain what the "ideal" B+ voltage is for a cascode design. Any recommendations?

Thanks all

[jabguit]

My $0.02 -

Since a cascode is essentially a dual-triode turned pentode, why not consider a pentode/triode noval tube such as a 6GH8A? Easy to find and cheap and the pentode could give what you're hoping for tonewise plus you get a triode that could be switched for extra gain.
Just a though.

cheers,

[wrongtube]

Hey Jack, that's an interesting idea. Have you seen any schematics that use 6GH8A tubes? Curious how one would go about designing around the two stages. Is the triode stage similar in gain to an AY or AT stage?

I suppose the other block for me is I'm up in Canada, and while those tubes are pretty cheap on Tube Depot, shipping quickly makes it unaffordable unless I'm buying a whole lot of stuff. And I've already got most/all of the components I need for this build...

Eirinn

[didit]

Hello --

I suppose the other block for me is I'm up in Canada, [...]

Look for some here https://pacifictv.ca/main.htm#N6F or here https://www.thetubestore.com/6gh8.

I find John at Pacific TV to be quite helpful. Canada Post will be reasonable if you aren't in rush. The 6GH8 is not the only option, but it's a decent one. Get more than one so that replacing a tired or microphonic one doesn't become a hunt.

Best ..

[wrongtube]

Wow, that Pacific TV site is a gold mine. Thanks for sharing. The 6GH8 sounds like a strong option -- I'll have to do a bit more design research and will be sure to come back with more questions!

Eirinn

[didit]

Note well --

John runs a small shop, essentially on his own, where the inventory and his web catalogue are somewhat out of sync. That said, he's knowledgeable and helpful, and tests tubes before shipping.

Best ..

[chris.lounsbury]

www.thetubestore.com

...is located in Hamilton, Ontario. Has 6GH8 in stock - note the prices are listed in US dollars, though the place itself is in Canada.