40's Epiphone to 40's Gibson EH150

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I've been building a lot lately, but mostly hacking stuff into test beds, restoring things, and trying to remember to practice playing! I'm posting about the Gibson EH150 circuit because I think it is worthy of more attention than it gets.

Here I have my 40's Epi Electar Zephyr amp, that I bought 2 years ago, that was to do duty for my trad. jazz gigs. Django used one of these amps over here, so I was a bit obsessed. It blew up right after I bought it (sight unseen on ebay) and spent a lot of time and money in the shop. It never was quite right and it sat in the corner. It was at that point I decided I was gonna learn how to fix stuff.

I pulled it out a couple months ago, played it for 5 min, was reminded how crappy it sounded, then the FC speaker blew. I figured my time had come to fulfill my destiny, so I cracked it open and spent a couple days restoring it, and converting it to a PM speaker. I was thrilled when I got it running, but over the past few weeks I realized I still just wasn't happy with the sound. To my ears the FC or PM didn't sound that different, just both kinda lacking.

I did trace out the amp as I had it, and it turns out it's quite different than any other Electar schematic I've seen. Note the fixed bias via "back biasing" arrangement. I still don't have an opinion as to when it was modified for fixed bias, or if it even was originally, as most all of these amps are cathode biased, yet back biasing is an old, early form of getting negative voltage, that I've never seen, or even seen discussed practically.

Jump to a couple days ago the cosmetics of the front of the cab met the headstock of a guitar in a bizarro twist. No malice involved but it's a long story. I'll leave it at that.

Yesterday, I stood at a crossroads, looking at an amp whose sound I wasn't diggin, and whose cabinet was a mess. So, I clipped out the board, and put one of the EH150 circuits in. I only put in the instrument channel, as this was to be a "jazz" amp, but I've built the whole shebang in the past, and the "mic" channel is basically one of the first unintentional overdrive circuits. Warm, sweet, aggressive octals. TRY IT! It's wonderful.

I spent some time today salvaging the cab, so now I've got a Gibson amp in an Epi cabinet and chassis, with mojotone grill cloth, original large hot PT and smaller OT. I kept the tone control like it is with the Epi, as doing it like the EH150 would've meant another sheilded run to the control panel, which is at the top of the cab. I was gonna put the tone on the back of the chassis, but the back panel covers it up, and is just too pretty. I felt bad enough gutting this thing.

For the EH150 circuit, I subbed a 150r10W for the field coil, and am running the 6L6GCs at 450V, with 300r cathode. A bit cold, but it suits me just fine. I have to work it a bit harder to get hot. I did include 470r screens but no grid stoppers

My awesome Fender special design speaker got crunched in the mayhem, but I fixed it with some toilet paper and some nail polish. I'm currently looking for another speaker for this amp, but that's what I used in the clip. This amp isn't finished quite yet!

https://soundcloud.com/jeremyslemenda/eh150sweetsue

Amp was just cracked, loud and clean, but gets dirty even with the "clean channel", whether you turn it up, or dig in. Guitar is 40's Epi Zenith with Dearmond pickup.

There are only a few, but good threads, concerning specifics of this amp, as David Root, Colossal, and Mark have built them . It's amps like this that make me wonder why reinvent the wheel. Just learn from those that made it roll in the first place. Of course those 6SQ7s can be noisy as fuck, same with the 6N7s.

..and on an acoustic note, here's some stuff that inspired amplification, once it became necessary: https://www.youtube.com/watch?v=uhcrRuTsPFI

I hope to see more EH150 builds! -J

[billc]

very cool! I have an ancient prewar PA amp I'll be building along those lines as the tube lineup is similar and I'm a big fan of Charlie Christian so an EH series inspired build seems ideal...BTW a Cannabis Rex speaker might be worth a try, I used one in a Gibson BR-6F I rebuilt that was completely trashed, like it a lot and it has the vintage jazz tone I want.

[img864]https://lh4.googleusercontent.com/-viza ... 121644.jpg[/img]

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Awesome! Dig those long chickenheads! If it's gonna be a jazz amp I'd suggest ditching the "mic" channel, if you do one of the EHs.
However Josh Homme has been using a'39 EH150 for some time now, I'm assuming in OD mode. Quite the versatile amp.

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Oh and thanks for the C Rex recommendation. I'll give that a shot