Possible Vibro Champ Reverb Project...

mjr428

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So I'm looking for a project that my son and I can work on together. He has no interest in music or guitar stuff at all, but is showing an interest in learning about electronics in general (he's 13). I thought that an old tube amp has a relatively simple circuit and that it would be a good project to learn from and I would get a tube amp in the process! I don't know how realistic it would be (I have some basic understanding how to solder etc.) but I would like to give it a go. Now the catch is that I don't really have the funds to just go buy a kit, so I was thinking about the possibility about salvaging the components from old equipment. I have a couple old solid state amps (I can build a new cabinet) but I don't know what would really be feasible as far as harvesting parts. I'm assuming it would probably be best to buy new capacitors, resistors etc... I have an old reverb tank, some speakers, wood for a cabinet. Maybe a possible chassis... I guess what I would need is a power transformer, tube sockets etc... Any suggestions where to find these things for very little cost? Is there anything in an old solid state amp that I could repurpose for a tube amp? I would like to build a vibro champ reverb if at all possible, but I would be happy with just a champ circuit if it makes it easier... I know there is a ton of info on this forum and trust y'alls knowledge... any thoughts would be much appreciated, and thanks in advance!
 

Snfoilhat

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That sounds like a plan for a great experience. Finding and repurposing old electronics can be a great source of materials and can be a richer learning experience than building a kit, because you have to figure out what the thing you’ve brought home from the junk shop is, what parts it is made of, and to what extent it still works or is incomplete or damaged. Then the extra creative work of fitting what you have to a reasonably close music instrument amp circuit to aim for.

Challenges: in some locations, anything with a tube is trash and people are happy to see it go; in others, there’s so much activity among flippers and modders and everyone else prowling the thrift store or online that there’s little savings unless you’re lucky. The low hanging fruit gets picked fast.

Then there’s how suitable/easy it is to convert something. A tube organ reverb driver is a classic example of an easy conversion. Or an old public address. Some ancient AM radio might be way harder. A tube reel-to-reel somewhere in between. It’s possible to overspend your budget (less than the cost of the kit) if your old junk turns out to be inflated price or inappropriate for conversion. Just takes a little study and planning. Good luck!
 

Phrygian77

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Cabinet, transformers, speaker(s), tubes, and chassis are or can be the most expensive parts, followed by caps, pots, and jacks (and other small parts) depending on what you opt for.

You can save some money using a toroidal Antek power transformer. A generic champ size output transformer is fairly cheap. Alpha pots are cheap too.

Here's a complete conversation of an old SS amp that I did.

 
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mjr428

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Stopped by a local thrift store/junk shop and came across this old radio

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I don't know if it works at all but looking for opinions on whether or not this would be worth purchasing for the right price to use for parts (mainly for the PT and possibly the chassis, tube etc.) Again, I'm a noob but I learn quick. Any thoughts?
 

printer2

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It comes down to how often suitable ones come around in your area and how soon you want it. That has a power transformer, tube sockets, the output transformer is not the biggest but would be alright. Possibly volume control and tone control if it has one. Had a suitable radio here a few weeks back where the guy finally sold it for $20. I do not feel (in my market) this one would go for $40. Supply and demand though.
 

mjr428

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It comes down to how often suitable ones come around in your area and how soon you want it. That has a power transformer, tube sockets, the output transformer is not the biggest but would be alright. Possibly volume control and tone control if it has one. Had a suitable radio here a few weeks back where the guy finally sold it for $20. I do not feel (in my market) this one would go for $40. Supply and demand though.
This one is selling for $49... I don't want to pay that much. I'm thinking about offering $20. I'm not looking for a high powered amp, so thinking that PT would be big enough...
 

Mongo Park

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When I look at an old radio I think the most likely part to wart is the power transformer and the output transformer as well bu they are usually to small for my liking. And my buy price is based on the power transformer only. If anything else is usable bonus. Next in line that might still work is a power tube, most preamp radio tubes are not simple to make into a guitar amp as a beginner. Course a 6V6 would be a straight up usable tube. Maybe some terminal strips.
That is how I look at something like what you have in the photo.
Point to point would also be the least expensive
 

printer2

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The tube lineup can vary, 5Y3 , 6V6 , 6SA7 , 6SK7 , 6SQ7 or a 6K6 in place of a 6V6. It has a transformer so it does not run right off the line. An American Five radio, has the heater string would be in series and the line rectified to make the HV. 12SA7GT, 12SK7GT, 12SQ7GT, 50L6GT, and 35Z5GT

So the radio does look promising but I would pay $20-35 if I were looking for one. The output transformer is the most important element for me, if it has a power transformer it will be good enough to make a 5W amp at least.

Somehow I was editing the post and somehow I had the wrong thing posted, fixed it.
 
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Robnik33

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May I suggest you start out with a pedal project? A great way to get comfortable with soldering and building skills.

See this thread I just responded to:

 

mjr428

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May I suggest you start out with a pedal project? A great way to get comfortable with soldering and building skills.

See this thread I just responded to:

Thanks, I am considering this too... I'm thinking about building a fuzz face, because it looks very simple and I want a fuzz
 

mjr428

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So I ended up buying this radio for a sum of $20. I'm not sure what I'm going to do with it, but I'm hoping to use the power transformer, output transformer and possibly the chassis... and anything else that might be useful. Here are some more pics...

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Any other useful parts from this? Maybe some resistors etc...? I'm not sure about the tubes. They're all 8 pin tube sockets... Looks like there's a 6v6 in there as well...
 

printer2

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Nothing wrong with 8-pin sockets. What tubes came with it? Use a drill bit that is a little bigger than the rivet used to hold them in and drill the rivet. The first time you do it you will muck it up, try the terminal strips also. The volume and tone controls might be ok. Do you have the model number on it somewhere? I would not trust any of the resistors, they are cheap enough to buy.
 
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mjr428

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Nothing wrong with 8-pin sockets. What tubes came with it? Use a drill bit that is a little bigger than the rivet used to hold them in and drill the rivet. The first time you do it you will muck it up, try the terminal strips also. The volume and tone controls might be ok. Do you have the model number on it somewhere? I would not trust any of the resistors, they are cheap enough to buy.
Looks like a couple 6SK7 and 6v6 but it was kinda hard to read. I couldn't see the labels on the other ones
 

printer2

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Looks like a couple 6SK7 and 6v6 but it was kinda hard to read. I couldn't see the labels on the other ones
The five tube lineup could be 6SA7 6SK7 6SQ7 6K6 5Y3. The 6SQ7 is like half a 12AX7, so you are half way to having a Champ. If you can get another one you would be there. They are cheaper than a 6SL7, which has two triodes in it. The 6SA7 and 6SK7 are pretty much radio frequency tubes. One day I should try connecting the extra grids together to make a weird triode and see if there is enough gain to use the 6SQ7 and 6V6 in making an amp. I recall talk about it but not if someone did it. I think the amplification factor would be about 15, so a 6SA7 into a 6SK7, 15 x 15 = 225. Maybe a little hotter than wanted but easy enough to get rid of some gain. Darn, I have to go out and pick some weeds. Maybe later.

 

printer2

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What do people think? The triode strapped pentodes should have a gain of 15. I originally thought to just run two of them in series to make up for another 100X gain stage but then thought, what else would work? I salvaged some sockets and I with do a quickie circuit. Why? Just curious. Any other ideas welcome

nAfMQFW.png


Not to hijack the thread, was going to start a new one but with mjr428's blessing maybe we can put it here?
 

mjr428

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What do people think? The triode strapped pentodes should have a gain of 15. I originally thought to just run two of them in series to make up for another 100X gain stage but then thought, what else would work? I salvaged some sockets and I with do a quickie circuit. Why? Just curious. Any other ideas welcome

nAfMQFW.png


Not to hijack the thread, was going to start a new one but with mjr428's blessing maybe we can put it here?
Yeah, I have no problem with you hijacking this thread... I have a lot of interest in your experimentation!
 

printer2

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Yeah, I have no problem with you hijacking this thread... I have a lot of interest in your experimentation!
Wish I knew where that darn aluminum chassis is. It was a radio chassis and I stripped it down as it was small and light. But I thought I will not ever use it (had so many holes it was like Swiss Cheese) and thought I put it on my scrap metal pile. Going to look at it one more time. One good thing, I found an amp chassis, completely loaded, guessing about a 30-40W amp by Yamaha using 7868 tubes.
 




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