Bogen Challenger CH18 new project

[Cliff Schecht]

IIRC the 6.3V filament winding was also center tapped..

[rdjones]

[img742]http://music-electronics-forum.com/atta ... 8-ch18.jpg[/img]

Except for the loctal based 7Z4

[xtian]

I have two schematics, both reasonably true to what's on hand. The wiring to the recto is simple, and not at fault.

Cliff is probably right, that the 60-year old caps are causing havoc.

I agree, I don't really want the exiting circuit for a guitar amp, so I guess I'll strip it down!

[rdjones]

I agree, I don't really want the exiting circuit for a guitar amp, so I guess I'll strip it down!

[Cliff Schecht]

I think you'll find that the chassis is very roomy after being stripped down.

A lot of the components in these amps are flat out dangerous to use (wax caps and dead CC resistors) and I usually have no qualms about gutting out these kind of things and putting in something that is actually usable (and well built). I would never rely on one of these stock, even after removing all of the crap components, because of how cheap they were back then. I don't know about the other models but I think the CH18 is a lower end model. I agree with what was said above about Bogen probably recycling the PT from a 6L6 design. The output transformer is barely acceptable for 6V6's IMO, I prefer something beefier.

[xtian]

Man, second frowny face in two days.

I put the GE 6V6GTs from the Challenger in my Egnater Tweaker and played for about 15 minutes yesterday. They sounded great!

I went to play again today, and after about 5 minutes, one started to burn up. Poo.

[rdjones]

"My grandfather's axe" or more correctly "Ship of Theseus"

Decades from now all the surviving Strombergs, Bell/Pacemakers, and Bogens will be mere shells housing generic 5E3's with transformers too large to get "the sound".
Wasn't a part of the Tweed Fender sound found to be that the output transformers were undersized ?

I fully agree that antiquated components that pose any sort hazard should be updated, but what kind of risk is there in carbon comp resistors ?
Aren't these supposed to be prized as being "vintage correct" in the very Fenders that are being cloned ?

Don't get the wrong idea here guys, I just have a different philosophy. It's all well intentioned.
I'm just showing my age and that I'm more into restoration than transformation.

rd

[ampdan]

I'm with you RD. I do minor tweaks to these (grounded ac, filter caps etc) for a local harp guy, and the sound he gets could not be any more authentic for "Chicago Blues". I hate seeing stuff like this butchered.

[Getchellamps]

New to the fourm, joined for other reasons...but I saw that this thread was recent so I thought I'd chime in with some advice on this amp.

1) The PT is WAY too big for 6v6's, it puts out 400-0-400vac.
2) The OT is plenty for a 12-15 watt PP 6v6 guitar amplifier with your typical 100-10k response, but I used it in another amp...not this one.

I tried hard to get the PT down in the sane range for 6v6's to operate, but it just would not happen. With the stock supply it puts out almost 500v on the plates of the poor 6v6's and runs them at almost 18w dissipation!! I even tried the zener in the CT trick, which brought it down to about 490v. I eventually ended up trying a bucking transformer, but it drew the heaters down too much...this amp just plain had a nasty high voltage PT to begin with.

I ended up gutting mine, stripping it, drilling out the sockets, painting it, cleaning/desoldering and re-using the old sockets, using all stainless hardware, new JJ and Orange Drop caps, a mixture of metal film resistors and carbon comps, and wiring up a 5B6 bassman circuit with blackface Bass/Treble controls that you can lift out of the circuit via a toggle switch for a gain boost. I also did a Star ground system on it instead of the original scatter ground- each stage now has its own isolated star ground point at ground for the Rk for each tube, which in turn routes to the main star ground.


The PT has enough juice to run 6L6's and 6L6G's still fit under the hood, however, I had to use a 5V4 rectifier as *most* 5U4's will NOT fit under the hood in the stock location. You can NOT use a 5Y3 if you go this route, it WILL arc over bad at these voltages and currents. 5AR4 might work okay, but B+ will be higher... I ended up with 480v on the plates of the 6L6G's and it runs class A at idle at about 18 watts on the plates....pushing it yes, cranked up it draws about 30 watts from each plate during momentary bursts when she goes in to AB territory.

The output transformer came from a Baldwin organ amp, which was later swiped to put back in the organ amp and I put in a later model Baldwin open bobbin OT made by woodward schumacher (eia code 606, same as fender OT's.)

The amp will shake the walls with clean power through a 4x12, and will keep up with any 50 watt head cranked. Has nice tweedy/early marshall style distortion, but a very fendery clean jangly tone with the tone controls active.

[img:720:540]http://a3.sphotos.ak.fbcdn.net/hphotos- ... 6491_n.jpg[/img]

Controls from left to right are: Input jack with boost switch below it, Volume, Bass, Treble, and Power.

[img:720:540]http://a7.sphotos.ak.fbcdn.net/hphotos- ... 7194_n.jpg[/img]

[img:720:540]http://a4.sphotos.ak.fbcdn.net/hphotos- ... 2401_n.jpg[/img]

[img:720:540]http://a8.sphotos.ak.fbcdn.net/hphotos- ... 9098_n.jpg[/img]

Enjoy![/i]

[Getchellamps]

double post

[xtian]

Thanks for the detailed post!

I'm already thinking about tossing everything but the chassis and the pots. More work (and expense) than I bargained for...but again, only paid $60.