Bogen CHB50--first project?

[andrewt]

I found a Bogen CHB50 PA amplifier on craigslist (asking $60, I can probably talk him down a little). Is this simple enough to be a first project?

I have no experience working on amps (other than a little work on my Hammond/Leslie), and a little electronics knowledge. I'd probably just use it unmodified at first until I get an idea of what I want to do with it. I was looking at amp kits but this is a lot cheaper. I already have a cabinet I can use.

[martin manning]

That'll be great; go for it! Here's a good schematic: http://makearadio.com/schematics/index.php

[Structo]

Assuming it is operational, that will be a great amp to get and experiment with.

With the 1M grid leak on the Mic1 input, it should work for guitar.

Remember to always have a speaker load connected to the output anytime you power the amp with tubes.

Here is one in action. Not sure if it has been modded.

http://www.youtube.com/watch?v=Qe4zW0zrYcM


Manual and schematic.
http://makearadio.com/schematics/index.php


[img1643]http://makearadio.com/schematics/images ... hb50-6.jpg[/img]

[andrewt]

Sweet! Thanks guys. I talked to the guy on the phone; he's going to test it and let me know if it works. From the prices I've seen, it looks like I'll do well if I can get it for $50 or less.

What if it doesn't work? Is this amp pretty simple to diagnose, and would it still be worth it?

Also, I have the Guitar Amplifier Handbook by Dave Hunter on my Christmas list. Is there any other suggested reading that explains amp theory without requiring a strong electronics background? (Most of the links in the sticky are dead...)

[Gibsonman63]

Learning a little electronics is unavoidable in this hobby. You need to at least know how to read a schematic, identify componants, trace the signal path through the amplifier and have an understanding of lead dress, but any level of understanding brings more possiblitites.

The Dave Funk book is a good to start with because it starts with the basics, but apparently hard to find because it is out of print. Randall Aiken has some great stuff online. It is fairly technical, but he does a good job of explaining things. Merlin Blencow is also very technical and detailed.

I am about three years into to this and I am still re-reading things to try to understand more.

Make something cool with the Bogen and have fun.

[andrewt]

Learning a little electronics is unavoidable in this hobby. You need to at least know how to read a schematic, identify componants, trace the signal path through the amplifier and have an understanding of lead dress, but any level of understanding brings more possiblitites.

The Dave Funk book is a good to start with because it starts with the basics, but apparently hard to find because it is out of print. Randall Aiken has some great stuff online. It is fairly technical, but he does a good job of explaining things. Merlin Blencow is also very technical and detailed.

I am about three years into to this and I am still re-reading things to try to understand more.

Make something cool with the Bogen and have fun.

Thanks. I didn't mean that I don't want to learn about electronics; I guess what I was asking was if there is something that explains the electronics along the way.

I know the basics of schematics (this amp will motivate me to finally learn the rest) and I can identify components, but I need to learn how to trace the signal (I believe the Hunter book covers this) and I don't know much about lead dress.

But I don't mind looking up any topic I come across that I don't understand (wikipedia is my friend!)

[xtian]

Make sure to review the thread Reading Material on Steroids!

https://tubeamparchive.com/viewtopic.php?t=9023

[Cliff Schecht]

To be honest, I don't think these Bogen amps are good first projects. They are built using some "old school" techniques that I would not encourage builders to learn with. Also stripping down the chassis and building them from scratch is quite a bear as well; they are made of steel that is very tough to drill and all of the sockets are riveted in. Did I mention the sockets they use are a non-standard size so you can't swap in new sockets?

Another thing with these amps is the PT's are always VERY hot, like putting 500-550V on 6V6/6L6 plates. If you aren't familiar with working with such high voltages or the techniques that can be used to reduce this voltage, then you may be setting yourself up for a lot of headaches that you aren't prepared to handle.

I recently converted a Bogen CHA33 to a Trainwreck Rocket and while I was very happy with the end results, it was a lot of work to get that amp where it is (as far as preparing the chassis and planning the build). And I didn't use the stock iron from the Bogen, I set that aside for something else and used a PT that happened to directly drop in and had much lower voltages (like 275-0-275 instead of 400-0-400).

I would recommend getting a kit or putting together something yourself for your first build. It's unfortunate but most first time builders will make mistakes. Working with a well known amplifier design in a familiar kit format will set you up to be much less likely to fail, and you have us to help guide you along the way. I'd set the Bogen aside for your second or third project, after you are familiar with what it takes to get a tube amp up and working.

[martin manning]

Some good points, Cliff. The Schematic shows a voltage doubler supply with 445V on the plates, so typical guitar amp voltage here.

How is the current owner going to test it, I wonder? I don't think it's a good idea to just plug the thing in and power it up at full voltage. Odds are that the power supply caps will need to be replaced anyway, though, and that will require another $50 investment. The good news is that you'll need the whole power supply for a guitar amp conversion.

[andrewt]

Hmm... what about this Filmosound amplifier? http://detroit.craigslist.org/okl/msg/3481971043.html

A kit would be nice; I'm just seeing if I can save a little money...

[xtian]

I did a Filmosound. Cute package. But cute also means small, cramped, and PITA. Not recommended as a beginner project. You want something with LOTS of free space in the chassis.

https://tubeamparchive.com/viewtopic.php?t=16996

Here's another Filmosound project going on:

http://www.thegearpage.net/board/showth ... ?t=1168594

[andrewt]

Another question for you guys about the Bogen CHB 50--looks like it's still for sale and the price dropped to $30. He said he turned it on and the tubes lit up--looks like it might be worth it just for the tubes at this point.

Anyway, I've been reading up--I got Dave Hunter's book and read that, and I got Tom Mitchell's How to Service Your Own Tube Amp from the library, which is very helpful on the general electronics side, as well as the reading sticky on this forum. I'm slowing understanding different parts of amps and how they work, but I haven't gotten to transformers yet

Are the trannies on the Bogen suitable for a Blackface style build? I'm looking for a vintage Fender to get blackface-style cleans and I was thinking about gutting the Bogen and just using the chassis, iron, and tube sockets to build some sort of blackface amp.

[xtian]

Yup, at $30, that's cheap iron!

[andrewt]

Yeah, it's a great deal. Can anyone tell me if those transformers will work in some sort of 2x6L6 Fender build?

What specifications would I need to know to determine this?

[xtian]

Just look at the schematic. Are you using the same or fewer tubes? Or to be more accurate, sum the current draw of the tubes in the original amp. If you use that much current or less, you're safe.