An old (complex) project being reactivated

[Dave]

Hi guys,


I wanted to share this because someone may find it useful. During the early part of COVID-19 I started a daring project. The purpose of the project may seem dumb to some, but it was a kind of a let's see if it can be done kind of a thing.


I wanted to build a feature-rich amp that has everything that I like already on board in one package. I also wanted to use as many repurposed components as possible because I can't stand it when people shotgun replace components in a vintage amp. So, I wanted to show that a new amp could be build out of repurposed old stuff. Quite a challenging project.


So here was the idea. Two channels; One 5F6A channel and one 6G6-A bass channel (my two favorites). 6G12 harmonic vibrato as well as tremolo. Blackface reverb. Hoffman hot switches in both channels. And have everything possible be tweak-able.


The harmonic vibrato uses two frequency-dependent channels where one channel vibrates set "A" of frequencies and the other channel vibrates set "B" of frequencies and the two alternate. Some say it bends the frequencies and creates a true vibrato. I say it doesn't, but it does give the illusion of true vibrato and can make some pretty spacey sounds. Anyway, with the right capacitors switched in, you can turn off the frequency dependence of the circuit and turn it into a straight, if not complex, tremolo circuit.


I know that sounds like a lot, but it's what I set out to do. It took a ton of tweaking because the vibrato circuit had a huge effect on the tone, so I had to tweak that all out so that the tone of the two original circuits remained almost unaltered while the effects were engaged, but I was able to get it done.


Somewhere along the way, I decided that I wasn't happy with the 6G6-A circuit and I ripped some stuff out. Now I have to put all that back together.


Unfortunately, I had a pencil-drawn working schematic but that got lost (more on that in a moment). I pulled the amp out yesterday and was fooling around with it (The 5F6A side still works just fine) and I find the amp to be absolutely stunning. It is lots of fun to play around with. I gave it so many features that it's like a kid on Christmas morning fooling with all the stuff.


Schematic... Before I get scolded by Sluckey or someone. The project got shelved because I came down, rather suddenly, with cancer. Everything I have got packaged up and shoved into storage by moving people. I moved about 120 miles away to be closer to family and hospital services and I am just now starting to mess around with amps again.


I am about to start working on the 6G6-A side again and get it back up and going. I remember ripping it apart because I was very unhappy with the way I originally had implemented the hot-switch. It sounded terrible and I wanted to redo it. Originally I settled on the hot switch in front of the 6G6-A circuit because I couldn't decide on a place to put it downstream (ideas are welcome).


Anyway. I am posting a few pics so you guys can see what it looks like. It's very very busy in there. I will try to get some sort of schematic going later. I will also try to post some sounds if I can figure out how to do it. Can you record decently on an I-phone?


Dave

[Dave]

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[sluckey]

Glad you know what's going on in there. Unusual filament string. Are you clazy?   

[Dave]

"Are you clazy?"   "Unusual filament string."
Lord, yes.            Experimenting with trying to make better parallels.


Any ideas on where to put the hot-switch in the Bass channel of a 6G6-A?


How can I record decent sound clips with an I-phone?


I know it ain't perty, but there was a reason behind "some?" of it. The whole thing was mostly an experiment, but the tweed side sounds so outstanding that it must be finished.


Dave

[Dave]

Ok... I got the 6G6 channel back up and running. Turns out I had built a 6G6-B circuit instead of the 6G6-A I thought I had built. I had done some weird modifications to it, not sure what I was trying to accomplish. Now I just have to figure out how I want to implement the hot switch.


Dave

[Dave]

Ok, I finished it up. I will answer any questions if anyone is interested in the implementation of anything. I will try to work on a schematic when I get a chance. Instead of going with a "Hotswitch", on the 6G6-B side, I went with a cold clipper stage. I have it on a switch and it comes in between the last two gain stages. I went with 33k on the cathode of the cold clipper stage.


I paid careful attention to keeping both the 5F6-A and the 6G6-B very original sounding. So, now, both of those amps can be run in their stock form through reverb, tremolo, or vibrato. Pretty cool I think.
With the gain switching on, the tweed side gets very Marshall angry and works very well. The Blonde side goes full-out nuts modern-sounding heavy distortion. Luckily, I didn't have to chase down very many noise problems with the implementation of the extra gain. Everything fell into place nicely. Heavy distortion through harmonic vibrato actually sounds pretty cool too.


Very satisfied with the build and the fact that I did it with probably 80% repurposed ancient parts.


I'm posting new gut shots if anyone is interested.


Dave

[Dave]

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[acheld]

Ambitious!

How can I record decent sound clips with an I-phone?

Look for the "Voice Memos" app already on your phone.   It is surprisingly good and very simple.  Or, use Garage Band -- also very good, but more complex.