bogen cha33

[mark enger]

I picked up a cha33 amp at a resale shop seems like a easy conversion for a fender anyone did anything real interesting with one of these, anyone know ot specks? its full of those old waxy yellow caps it would have too bee a gut and rebuild its working but very noisy mark

[gldtp99]

Since nobody else is jumping in here-----i have a CHA33 that came to me cheap---found the OT blown-----i gutted this one and replaced the orig PT with a Twin Reverb-type PT--- i used one of the custom wound Heyboer OT's i have (4k primary--4/8/16 ohm secondary--- 100 watt Fender Twin/Showman sized OT)--added choke--- gutted everything and built a Brownface Fender-type single channel preamp with 350k/70k tapped treble pot--- based on this Brownface schematic: http://www.el34world.com/charts/Schemat ... _schem.pdf
Lar/Mar PPIMV and running two JJ KT88's as outputs. Fixed bias.
Some friends were at my shop yesterday and one was running his Strat w/pedals through this one--- liked it very much. I've done many old PA conversions in many different ways.
Pick almost any 6l6x2 Fender circuit and go for it, just remember that you've got limited space to mount pots--- so plan accordingly---- i've put together several heads (old PA's and scratch builds) based on the Fender 5E5 Tweed circuit, single channel and altered to use all 12ax7's in preamp ----- people love these things----simple circuit to build, too---cathode biased is simpler and can save space---good for @30 watts......................gldtp99

Fender 5E5 schematic: http://www.el34world.com/charts/Schemat ... RO_5E5.pdf

[Markusv]

Gutted a challenger 50 and built a Komet 50-ish clone
Absolutely rips
The iron in those amps is beefy

Another (exactly the same amp) I just tweaked the 2nd stage and added a bypass cap IIRC
Also tweaked the tone stack and added a bright cap

Guy bought it off me and was thrilled. Very Bassman-ish tones IMO
Really like the sound of the 6EU7 triodes. Not sure if your amp has those
Oh Yes.- Replace the dynamite stick Power Supply caps if it has them

Markus

[mark enger]

Ive built a bunch of 5e5 type amps and they always work out great, guys love getting there hands on them, last one i sold to a rock a billy cat and he loved it he was amazed that each input had its own flavor, said he could gig with no pedals , this one has a 6av6 not 6eu7 and 2 12ax7 ive done a few se amps true ptp from sockets to pots this seems like a great chance to try a ptp pp sounds like fun thanks mark

[bandade]

Someone wanted me to look at a CHA 33 to see what was needed to convert it to a tweed style amp. The amp looks like someone buried it in the ground since the 50's but it fired up when plugged in (even has a set of RCA black plates that are showing very good on the tester). Volume was going in and out until one of the 5y3gt's red plated and blew after 5 minutes or so. The can caps were very hot but the transformers were cool to the touch.

I'm am wanting to replace the electrolytics which include a couple of 16uf and 5uf can caps that I can't find and a 16uf electrolytic; what readily available values to you recommend? The can caps need to be replaced with 500V.

I'm also replacing pots, jacks and adding switches but would like to preserve the iron.

Any other suggestions are welcome. Thanks

[Cliff Schecht]

4.7uF for the 5uF cap and 22uF for the 16uF caps.

Funny enough, I literally just finished gutting out a Bogen CH33 including having to drill out those fucking rivets (my hand hurts now) which is not an easy or fun process. Didn't tear up the chassis too bad. I'm building a 4x6V6 Rocket in this chassis, probably with tremolo.


My suggestion.. Gut it and build something useful in there. I've never been too impressed with either the build quality or the stock circuits in these PA heads. You can try to get it going as is but you may find it has issues in other places (bad caps and resistors galore) and these amps are tough to work on sometimes. Also in mine (even though it was in good shape) there were a few sockets that I considered questionable and the power transformer wiring sort of scared me as well from ever even firing mine on.

Another problem with these is the PT is usually too high of voltage (i.e. the HV AC windings are 400-0-400V range) while the OT is too small for 6L6's. I'm going to use the iron out of this amp in something else but I probably wouldn't use an OT this small for any of my 50W Fender builds.

[Firestorm]

4.7uF for the 5uF cap and 22uF for the 16uF.

You can still buy 16uFs, but they meter at 20-22uF anyway so unless you need them to fit a faithful restoration of something like a Vibrolux, who cares. Plus, as Cliff said, just gut it and build something really cool, in which case stock cap values don't matter.