Bogen to D conversion

[ampgeek]

Greetings!

First post here. Really digging the sound clips (and sage advice)from all of the contributors here. VERY well done! Thanks for sharing.

I have an engineering background (chem) and have built a handful of amps (2X scratch, 2X kit and 2X conversion) so..I would probably be considered an advance beginner. I have access to a full up metal/machine shop so fabrication limitations are minimal.

I am contemplating next year's project and I find some mint Bogen CHB-35 iron in my "stash" just crying to be used. I have done some nice Marshall'esq type amps with the same iron (fixed bias, 7868 power tubes in p/p topology) and was very satisfied with the results.

Any thoughts how effective this iron would be in a D type circuit? I lean more toward the liquidy, overdriven D tone (Santana'ish?) so I think that I am looking at an HRM configuration. Not trying to nail any given tone in particular though.

This will be a total scratch build so there are no constraints other than I would like to use the Bogen iron if possible.

TIA!

Happy Holidays,
Dave O.

[Luthierwnc]

I would be be leery of the OT. Many moons ago I built a guitar amp out of a CHB-50. It came out pretty well but the output iron was a two-bolt open-structure job. These amps need a lot of transformer core to keep the bottom end tight. You don't want much break-up at all in the power section. IIRC, the chassis is also very shallow so there isn't room to do any double-decker boards.

Just an opinion but I'd use those components for something that includes power tube saturation as part of the sound.

Skip

[Bob-I]

I agree with Luthier. I had a great Deluxe clone which I converted to a Dumble and never liked the sound. It was suggested that the OT was not beefy enough so I installed a Bassman xformer even though I was using 6V6's. Amazing difference, it's now my favorite amp.

Bottom line, don't skimp on iron, these amps need it.

[ampgeek]

Whew...potential catastrophie avoided.

Yep..I was a little concerned about "premature" power section distortion but believed that the 7868's were close enough to EL34's in the critical characteristics to make them a reasonable substitute (with the proper tweaking of course). Maybe they still are with a "better"/more traditional OT?

However, I hadn't given enough thought to how significant the OT was to the overall D tone. I stopped short at just knowing that it matched the 7868's.


Ok...back to the drawing board!

Thanks much for your thoughts,
Dave O.

[Luthierwnc]

The tubes might be OK. The issue in my mind is the frequency capability of the trannie. I went to school when they were still using those things to make announcements -- don't remember the fidelity being too good.

Within the limits of your budget, make your first as close to the concensus build recommendations as you can. After some research, you'll usually find that the more experienced builders use heavy iron. While I'm running up your bill, make sure the power transformer can take a decent load without too much sag.

Good luck, Skip

[ampgeek]

Thanks Skip!

No worries on the budget. I only do a couple of projects a year and usually end up selling them to associate musicians for at least the cost of the parts I have in them. I am more of an experimentalist/hobbyist than anything. Just trying to learn something new and spread around "good tone" in the process whever I can!

While the original concept for this project was to open up bench space by using pieces I have lying around, I certainly don't want to jeopardize the higher goal of attaining a characteristic D tone for the cost of the iron.

I hear ya on the apparent lack of fidelity from the old Bogen iron. However, I was pleasantly surprised at how good it sounds in Marshall'esq type builds with decent speakers (almost exclusively Weber Alnicos for my limited build experiences). Sure....a very different circuit/tone goal than the D's but still worthy of at least initial consideration.

Thanks again,
Dave O.