My 36W Project

Double-Bubble! Place for discussing the 36W version...

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Bieworm
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Re: My 36W Project

Post by Bieworm »

Jack, that's what you get with adding a gain stage. Did you attenuate the signal before cascading? You might wanna play with some values there with a/the voltage divider ...
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Re: My 36W Project

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Bieworm wrote: ↑
Mon 02/22/21 3:12 pm
Jack, that's what you get with adding a gain stage. Did you attenuate the signal before cascading? You might wanna play with some values there with a/the voltage divider ...
I built the entire preamp section identical to the Marshall 2104. I did add a voltage divider just ahead of the PI, but it's only marginally helpful. The problem is that there's a huge difference in signal amplitude between the Low and High inputs (approximately 60X). If the PI is attenuated enough to make the High input work well at the MV pot, then the Low input doesn't have enough gain. On the other hand, High gain can't be reduced at the cascade stage without changing the tone of the amp. The additional gain is responsible for allowing the player to crunch the preamp.

I should add that I do have a solution for this, because there's an effects loop between the preamp and the PI that wasn't present in the original design. I can install a send-return patch cable, then use the Send Level pot to reduce MV sensitivity (that won't change the preamp tone). I just want to be sure this sensitive behavior of the MV pot doesn't point to a wiring error or bad component somewhere. That's why I asked whether it's normal for the MV series.

Thanks!
Jack
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Re: My 36W Project

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No new pics yet, but there's progress. It's funny what you learn about amplifier construction when you do something like this for the first time. The amplifier chassis wouldn't fit into the Peavey combo cabinet all the way because the HV cage that I made hit the speaker. The chassis stopped about 1/4" back from where it needs to be. So, I scrapped the cage and made a new one that adds about 1/2" of clearance. Probably can't remove the speaker once the chassis is bolted in, but that might have been true of the original design, too.

Also, I found out yesterday that amplifier mounting straps are readily available in various lengths from Antique Electronic Supply and probably others. I had assumed this would be an OEM-only item, so I never looked. And of course, none of them will fit the 6-1/2" spacing I used for the cage nuts. Doh! So, I spent a few hours today milling two aluminum straps. Now I have to finish the metal and anodize them, much more work that I would have undertaken had I known.

I might have to build a few more amps and sell them just to get my educational investment back... :)

Jack
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Re: My 36W Project

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Here are the final pics of the amplifier chassis. The chassis and Hammond speaker have both been mounted in the donated combo cabinet now. I'll post pics of that as soon as I finish the new nameplate. (It's not a Peavey anymore!) :)

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Re: My 36W Project

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Finally! Here are pics of the amp in the free cabinet. Need to fix a few Tolex blemishes, but it's basically finished at this point. Kyoto Audio is the brand I use for my own creations.

Jack

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Re: My 36W Project

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Also, I want to sincerely thank all of you on these forums who provided comments and advice as I went through the design and build of this amp. It paid off in the end!

Jack
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Re: My 36W Project

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My 36W amp has now been requisitioned by my daughter, who started playing last year. She's thrilled by the tone and the classic British sound. In exchange, she has given me the little Acoustic G10 practice amp we bought for $20. The case is in perfect condition, so I think it will make a good foundation for a future low power tube combo. Not planning any frills in this one, no reverb or FX loop, just lots of high energy gain and a good speaker. Oh, and maybe tremolo. There are so many choices for the output stage, I don't even know where to start. Will probably restrict it to a single-ended design, but even so there are dozens of candidates for the output stage. 6BL7, 6V6 pentode/triode, 6AQ5, 6CL6, 5763, 5686, etc., etc. I'll start a new thread for this when the work starts. :)

Jack
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Re: My 36W Project

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Wow..wait a little.. Maybe this 1 watter I'm building turns out great, and a good option for low power amp build for you.
Lucky you! I have 3 Kids and none of them play music. They only nag when I'm playing πŸ˜‰
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Re: My 36W Project

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Bieworm wrote: ↑
Mon 06/07/21 10:39 am
Wow..wait a little.. Maybe this 1 watter I'm building turns out great, and a good option for low power amp build for you.
Lucky you! I have 3 Kids and none of them play music. They only nag when I'm playing πŸ˜‰
I'm sure your 1W WILL turn out great! I need to do this one on my own though, a one-off mongrel instead of a copy. Also, I have all the basic building blocks on hand for a single ended design - OPTs, power xfmrs, 6X4/6X5 rectifiers, etc. For low power push-pull, I would have to buy at least the OPT. I'm thinking along the lines of two or three high-gain stages driving a James tone stack with a 2W to 4W output stage. Tubes are likely to be types not usually seen in guitar amps. My biggest expense for a project like this will be the chassis and a new speaker. Almost everything else is on the shelf.

Jack
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