Challenger CH30 ??

[brokennarsil]

Hello everyone, I'd like to start by saying that I am a complete noob at the amp building game. I have an old Challenger CH30 and upon tearing it apart, the idea struck me to perhaps make a guitar amp out of it. Upon searching the net, I discovered that this is a rather common practice restoring old PA amps and such. My question is, since I know next to nothing about the guts of this beast, is there any conversion schematics out there for me to look at for this amp? I've looked everywhere and can't seem to find any.

On the other hand, would it be possible to gut the thing and use the tubes, transformers, etc. that are in it and just build a new amp from scratch? I believe the tubes are 6SC7, 6SL7, 5U4G, and 6L6G. Not sure on much else. Thanks.

[balcorn80]

pa conversion

I just finished a complete rebuild of an old pa amp myself. I don't know that I would call it a conversion or a rebuild... I gutted my whole pa amp and used the tube sockets and transformers to build a 5e3 Deluxe. My amp was built to use 6v6 tubes and a 5y3 rectifier with a 6sc7 and a 6sj7 tubes in the pre amp, but I wired my board to use 6sl7 tubes. Works well. Now i have a Deluxe-type amp in a head unit. And you can get circuit board kits for a large variety of amp types, so you should be able to build somethign around your Bogen. I would tend to go towards a complete build, using only the shell and heavy iron, but that's just me....

[thehoj]

I also just did a pa rebuild to guitar amp. It was a bogen challenger chb-35a.

In the end the conversion I did up until the phase inverter was very much a copy of the fender bassman 5e6a circuitry. I did also add adjustable bias control.

Rather than gut the unit and build something from scratch using only the Transformers and chassis, I rewired it bit by bit still in a point to point manner. This allowed me to experiment with different values as I went and see how they affected sound.
In the end just about every single component has been replaced with the exception of chassis (obviously), transformers, tube sockets, and the original power tubes.

It was great from a learning point of view, but if I was doing it all again (at this point in time) I would definitely be stripping it right down and doing my wiring from scratch.
I've heard it time and time again and never believed it until I did this rebuild, but I now believe it would honestly be simpler to figure out what you want to build that will work with the chassis and transformers that you've got, and then strip your chassis and build that from scratch.

I'm not saying I regret doing the modification the way I did, but it was definitely more time consuming than stripping it down and building something from scratch would be.

I took my amp from
http://schematicheaven.com/hifiamps/bogen_chb35a.pdf

to
http://vwtweaked.ca/images/Bogen%20BassFlex.jpg

I'd love to find another old pa amp of some sort, and do a complete strip and rebuild.

[brokennarsil]

Well thanks for the ideas guys. I'll probably strip everything out anyway (this thing is pretty dirty). My only holdup is knowing if I can use what I have. I'd like to spend as little money as possible, so I don't really want to go buy a handful of new tubes if I can help it. The small stuff I'm going to replace anyway (resistors, caps, wiring etc.) Does anybody know if I can use the included tubes and transformers and just reconfigure the setup?

[thehoj]

Well thanks for the ideas guys. I'll probably strip everything out anyway (this thing is pretty dirty). My only holdup is knowing if I can use what I have. I'd like to spend as little money as possible, so I don't really want to go buy a handful of new tubes if I can help it. The small stuff I'm going to replace anyway (resistors, caps, wiring etc.) Does anybody know if I can use the included tubes and transformers and just reconfigure the setup?

This might not be the best advice, but with my amp when I first got it, after I took a quick look at the components to look for anything obviously wrong, I just powered it up and used it as it was meant to be used.
Turned out that everything worked, and so I went ahead with re-wiring and replacing everything other than the tubes and transformers.

[brokennarsil]

That's really not a bad idea, and I'll do just that if it comes to it. I've just been dazzled by the prospect of conversion so much. I really want to see what kind of sound the thing is capable of. If I'm not mistaken, won't it be very clean if I just use it as is?

[brokennarsil]

So I just finished gutting everything in the chassis and cleaning it all up. This thing is so ancient. The mic and speaker jacks I've never seen anything like. I'm not sure if they still make that kinda stuff. So I'll be updating those regardless of what else I do.

I also found out that someone has done work on this thing before. The smaller transformer looks like a replacement (the thing doesn't even line up with the original hole) and the 5U4G tube has been replaced (noticed a nasty black mark on the metal where something had gone up in smoke!)

I believe at this point I'm going to try looking about for schematics and ideas for what to do, if I don't just put everything back together how it should be. Does anyone know of some sites where I might find some basic overviews on how to wire up amps?

[GuitarRock04]

Transformers

I have a CH30 as well that I disassembled long ago, and am now getting around to trying to create a guitar amp out of it. Over time, I've completely lost track of which pin is what for both the power and output transformers. They both have numbered tabs. Does anyone have a schematic for this amp that calls out transformer lug numbers? Or would you be willing to post a high res pic of the inside of your amp so that I can trace everything out and get a good idea? Or possibly even describe what each transformer pin is connected to?

Any help would be greatly appreciated.

[brokennarsil]

I have a CH30 as well that I disassembled long ago, and am now getting around to trying to create a guitar amp out of it. Over time, I've completely lost track of which pin is what for both the power and output transformers. They both have numbered tabs. Does anyone have a schematic for this amp that calls out transformer lug numbers? Or would you be willing to post a high res pic of the inside of your amp so that I can trace everything out and get a good idea? Or possibly even describe what each transformer pin is connected to?

Any help would be greatly appreciated.

Jeez, mine's already gutted or I would have taken that pic for you. I hope someone answers your question because I would like to know myself! btw, do you know what voltage ratings these transformers are?

[brokennarsil]

I was looking at the PT just now and it has nothing but a number on the side. The number is T365-1. Is this just a production number, or perhaps a model?

[GuitarRock04]

Yes that number is the transformer model number. The OT is T-279-1. On the bottom of the PT there are 10 lugs, numbered 1 through 10, and the OT has lugs 1 through 8. By measuring continuity and resistance between pins, I believe I have the power tranny sorted out, but it would be nice to double check. If I'm not mistake the PT, at 123v on the primary, gives 5v, 6.3v, and a little over 600v AC on the secondaries. It's mainly the OT that doesn't make any sense. It could be that I have an open winding or something, but would like to check before I cave and just purchase a replacement...

theused.com - Vintage Audios

Above has almost everything except this particular pa from bogen...

[brokennarsil]

thanks for that info. yeah, the ch30 seems to be a very hard-to-find topic on the net (just my luck that I'm trying to learn about building amps with such a difficult pos)

what i'm confused about is (and this is probably due to my general ignorance with amp theory) where does what go in relation to the transformer posts? I mean, how can I tell where to stick which wires to get me started?

[GuitarRock04]

Well, that's what I'm trying to find...

It would have been wise for the both of us to better document the original before tearing it apart.

And if you're new at this, please be careful. Voltages inside these amps can kill you. Even when everything is unplugged and switched off, power supply caps can still contain enough juice to do you serious harm.

You can somewhat decipher transformers by measuring the resistance between pins. If you clip one of your DMM leads to pin 1, for example, and measure resistance to all the other leads, you can find the other pins for than winding. If pin 1 is the primary, any other lead that exhibits continuity will be part of that winding. Secondaries will show infinite resistance to the primary, and the other secondary windings.

On the primary, you will have two 120v leads, and possibly a center tap. On the secondary, you will have a High Voltage winding and probably a center tap, as well as 6.3v and 5v windings. The resistance between your hi v windings will be highest, with the center tap being half that resistance. The primary will have less resistance, 6.3v significantly less, and 5v will be lowest resistance. Once your relatively sure, you can actually apply mains voltage to the primary and measure actual voltage output on the secondaries.

Google it, and you can find further detail on identifying transformer windings.

[brokennarsil]

thanks alot, guitarrock. yeah, I always make sure to be careful working with any kind of electricity. I have a background in automotive electrical systems and such, but sadly that only requires the basics of electrical theory. electronics, or more specific amps, are a good deal more complex.

and i totally agree that we should have documented the thing better before tearing it apart. I only did it a few days ago, and was halfway through the process when it hit me that I should have at least taken a picture. but you live and learn!

and thanks for the tips on the transformer. I suppose that will be my next step in learning about the amps. I've already crammed a ton of info into my head in a few days of trying to learn this...still waiting for it all to 'click'.

I wish you the best of luck with your amp, and if you have any breakthroughs, feel free to share

[GuitarRock04]

Power Transformer Woes

I do believe I have all of the transformers sorted out now. One of the OT pins got somehow disconnected from the winding, and it was a simple repair. Don't ask me how that happened. I will post my findings when I get a chance.

In the meantime, I feel like I'm missing something obvious, but I'm having trouble grasping the following and would like some help from someone more knowledgeable than I.

The high voltage secondary winding is way higher voltage than I remember. With 116v at the wall, I'm getting approximately 830v AC across the entire secondary. That's totally and completely unusable for my application. But between either of those leads and the CT, I get a very usable 412v AC. Now I haven't changed the tube complement from original, so this transformer was intended for a circuit at least similar to what I've built, but as far I know, I can't simply use half of the secondary (where I would get an appropriate voltage) because that CT needs to be referenced to ground. Right? This transformer has to be able to do what I need somehow, I'm just missing something obvious here...

Any input is greatly appreciated.