Something new from something old?

[Monkey Boy]

I found an old Bogen Challenger PA Amp (CHA 75) I would like to use its guts to build a guitar amp. I don't know how hard this would be, or if anyone has tried this...but I figured I'd ask for some help form the experts...any experts out there?

Oh yeah...here is some more info as far as I can tell...
4 6AV5GA Tubes (Bogen USA)
2 GZ34 Tubes
1 12AX7
1 6CM7
1 6AN8
1 6AU6

260 Watts 2.5 amps 117VAC ~60

It appears to have three channels, 2 MIC and a Record Player.

[Luthierwnc]

Sure, you can make a pretty good guitar amp from that. Do a life-sized drawing of what you want to put in before you start tearing things out. Pay special attention to the capacity of the output transformer. Chances are you'll use a more conventional octal power tube and you want to be sure the output impedances match your speaker set-up (or vice-versa).

Good luck, Skip

[Monkey Boy]

I am pretty clueless as far as most of this goes. Currently the amp is set up for four different impedance options.

I am not looking to build a high power amp, more a something to use at home. Am I starting off with to much juice?

Thanks.

[Cygnus X1]

2 GZ34's?

Sweet!

[Monkey Boy]

2 GZ34's?

Sweet!

Again, you are talking to captain clueless, so what is so sweet?

I hit up my father in law to help with this, since he is an electical engineer. Only problem being he hasn't touched a tube in ages.

Any ideas or thoughts on how/or what I might do with this thing?

[Cygnus X1]

The GZ34's are rectifier tubes.
Used in most blackface Fender amps like the Princetons, Deluxr Reverbs, and so on.
You only need to use one.

NOS GZ34's are pricey!

[ic-racer]

Depends on what you want to accomplish. If you don't have a tube amp and want one, it will take some work but you might wind up using only the chassis after you have replaced all the parts. None of the 'standard' amps circuits out there use those tubes.

However, the way I would approach something like this is to try and find some unique sound that the other amps I have don't produce. Perhaps there is some magic in that specific combination of tubes and the transformers.

First I would draw out a schematic.
If the amp doesn't work I would start by replacing any tubes or components that are faulty and make it work.
Then I would do any modifications needed to make it safe.
Then I would re-voice it to work with a guitar. Check all the inputs, maybe one is good sounding with a guitar already.
Then I would consider adding gain, unless you want a clean amp.

You did not say if it works or not, but if it works, then just plug a guitar into the inputs and see which sounds best. It may not require much work at all. Back in the 70's I used an un-mofified Bell mono Hi-Fi amp as my guitar amp. I used a distortion box in front of it and it sounded fine.

[Monkey Boy]

Thanks...
Are there readily available schematics on this site or on the web? Especially something that would work with the tubes I have? Again, I am such a noob that they need to come up with another term for me. Maybe pre-noob.

[Structo]

I think since you are new to tube amps perhaps a simple amp kit would be good to start with.
Save the PA amp for a later project until you feel more confident.
Obviously, you are pretty green about electronics, so a good kit with complete instructions would be the ticket.
Like an Allen kit.

[ic-racer]

Thanks...
Are there readily available schematics on this site or on the web? Especially something that would work with the tubes I have? Again, I am such a noob that they need to come up with another term for me. Maybe pre-noob.

Actually I meant to draw out the schematic for the amp you have, as it is before any modifications. Just as a baseline and something to help you get it all sorted out and working. You can post this and people can suggest any changes to make it more 'guitar-like.'

If you try to re-do it to fit some of the many schematics available, you will wind up replacing pretty much all the components except the chassis. Even then getting a better chassis (with the correct holes for the circuit you want to build) will be best.

So, in a nutshell, get it working and plug a guitar in to it to see how it sounds. If it does not sound right, tweaking the tone stack can help get it in line. But we would need to see a schematic of the tone stack you have now to be able to make suggestions. You can just draw this out with pencil and paper.

[sportster4eva]

Here's a great place to obtain data for the tubes in that Bogen.
They seemed to like to use some oddball tubes from time to time in their PA gear.

http://www.nj7p.org/Tube4.php?tube=6av5ga

With that lineup of tubes you could make a 25-30 watt amp.
The 6av5 is somewhat like a 6v6 as far as dissipation ratings, but it draws more than double the filament current, which is no problem for an amp made to use them.
The 12ax7 could be your first two gain stages, and that 6cm7
could be the last gain stage and a concertina phase splitter.
The 6au6 could be a second channel pentode input, but I've heard some people that have used them claim they don't sound that great.

There's plenty of room in that chassis, so you could have some fun with that old beast.

Heck, you could turn it into a double Deluxe! grab yourself a turret or eyelet board for a tweed Deluxe and a schematic and layout.... just a thought...

[Monkey Boy]

Great help thus far. I am learning a lot and getting some great ideas...any more ideas will be appreciated.

[Monkey Boy]

I like the idea of a "Double Deluxe" but I am having trouble finding a schematic. The only company I know of that actually makes one of these is Victoria. Any ideas?