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Dirty-South Blues Harp forum: wail on! > 12au7 as Power Tube
12au7 as Power Tube
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11 posts
Dec 08, 2021
4:44 PM
I have the opportunity to purchase a new Supro Delta King 8 at dealer cost. The amp generates 1 watt through a 12au7 tube with a 12ax7 in the preamp. Amp is a little fizzy until I run it through my pedal rig which consists of a Harp Attack, Octave and Break however with the 12ax7, the feedback demon is definitely ready and waiting to rear it's ugly head. I used it at a jam the other night and while its a little nasally/boxy as most combos using an 8" speaker would be, I was pretty happy with the tone and volume which was surprisingly loud for it's published 1 watt output.

I have replaced the preamp tubes in my 68 Champ and VHT Special 6 with 5751's which I'm very happy with. Logic tells me switching out the 12ax7 for 5751 in the Supro will provide the same results and give me a bit more volume before feedback as it does with my 6V6 based amps however I have no experience with an amp using a 12au7 for the power section.

Appreciate any/all info provided. Cheers!
992 posts
Dec 12, 2021
8:46 AM
I would try a 5751 or a 12AT7 in the preamp section. Replace all tubes if there cheap Chinese tubes with some quality brands. It's a low cost amp made in China so my guess is the tubes are low cost/quality?
13 posts
Dec 14, 2021
10:34 AM
Harpaholic - Thank you! I ordered a JJ 5751 and will install it upon receipt. The tubes are mounted sideways on the chassis so they are facing toward the speaker. That said, I'll have to drop the chassis to install the new preamp tube and inspect the 12AU7. Safe to say the factory installed tubes are not the best quality at this point. I really put her through her paces last weekend and can already hear the stock speaker breaking in nicely though I'll probably end up replacing it as well. Maybe I can even get a 10" in there.

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