Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: cpk313 on June 01, 2020, 01:31:21 pm
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I have been planning for a couple years now to build a 15w Matchless clone. Originally it was going to have their Spitfire circuit on one channel (single 12ax7, one tone pot) and the the Nighthawk on the other (EF86). I was also going to have reverb and a buffered loop. I decided that I was biting off way more then I should for a first build so I bought two Ceriatone kits and built both successfully and the sound really great. One is a Princeton clone with tremolo and the other is a 2203/2204 type but with two 6v6's instead of 6l6's.
My first question is that I see a few different amps, both Matchless and clones of them that build a 2 channel amp with one channel having two 12ax7 preamp tubes with a treble and bass pots and the second being an EF86 channel but none like I was going to build. Why is that? Am I planning on making an amp that inherently won't work well? Like a significant gain mis-match between the channels? If I need to build it like a 15w version of a Matchless DC30 that is fine, I just don't want to start the next step of finalizing a layout and drilling the chassis only the have made a fatal error.
Second is I have put aside putting a buffered loop in the amp. I put one in the 6v6 Marshell clone and I never use it. It work fine but I ended up just running every thing in the front. But I am still thinking about reverb. With a 2 channel amp do you typically have the reverb on both channels or just one because of phase issues between the two channels. The guy I got the buffered loop from initially looked at what I was going to do and thought I was doing a 15w DC clone and said that I was going to run into issues running the loop on both channels because they are out of phase with each other. But having a single 12ax7 preamp tube and the EF86 they weren't.
Third question is I have 2 output transformers, a Stancor A3800 that has short leads and a new Edcor. The Stancor has a primary impendence of 5k and I am 95% sure I have the leads correct. They were very faded when I got it and I took the bells off to get to an area on the leads that still had some original color so I think I have them right but I am not even sure if the transformer is good or not. It is supposed to be but it was an Ebay buy so you never know. The Edcor is new and it is their 25w PP output transformer and it has a 4k primary impedance which I order special because my understanding is that is what Matchless uses. Impedence not brand. So I am also a little torn between which I should use. I would rather not buy another transformer. I think the Edcor is rated 25w 20Hz to 20kHz so I could actually probably make a 4 EL84 amp but I don't think my power transformer has enough juice to do that as it is rated at 150mA (it's a Hammond 270FX).
Any guidance would be appreciated. Thanks
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I think that the matchless stuff can best be described as improved versions of the vox circuits. They follow established topologies. Id look at what Sluckey did on his DualLite project for an idea how to accomplish what youre after, and search the forum for posts on dual lite builds. https://sluckeyamps.com/dual_lite/dual_lite.htm (https://sluckeyamps.com/dual_lite/dual_lite.htm)
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Thanks, I will check it out!
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I think the Edcor is rated 25w
I built 2 with Q-EL84's never got past yawn for heat, sound however was very good