so I got an ol' CHB-50 for $30 at a garage sale today (and a old tube tester for $20). The guitar said he planned to convert it for guitar use but never did. It seems maybe he didn't do everything he intended but an 1/4'' 8 ohm output jack was added on the rear and the amp came with a 1/4'' adapter to use the Mic input.
The amp works, I tested the tubes and they all test fine - though the power tubes are the original Bogen.
I don't have any intentions (at least right now) of stripping it down to nothing and building a new amp from scratch. For now, I'd like to just get it sounding good for guitar to use in my bedroom.
It doesn't appear like too many components have been changed...
That is a nice clean chassis should work quite well. I would imagine those large tubular caps will go bad if not already. I should find one of these to play with.
Hi, thanks. Yes I saw that thread but it didn't give much in terms of advice on mods to the CHB-50 circuit, just debate/advice on how to use the iron for other projects and whether it is worth it at all to convert.
Hi, thanks. Yes I saw that thread but it didn't give much in terms of advice on mods to the CHB-50 circuit, just debate/advice on how to use the iron for other projects and whether it is worth it at all to convert.
Hey beedoola, I couldn't tell from your op what exactly you were trying to do, other than trying to get it sound good with a guitar and you didn't want to strip it down and start over ..I thought that thread would point you in the right direction at least. That being said, if you're up to replacing the filter caps and make sure it's properly grounded, plug up a guitar and see how it sounds to you. I started out building amps by playing around with a CHB30. It sounded ok pretty much as is. It wouldn't take much tweaking to get this sounding decent. My 2 cents
"- Yeah, can we have everything louder than everything else? Right!"- Ian Gillan
Shouldn't take much more than checking the caps and resistors. I had a Bogen as my first PA amp in 1966. But at home I just used a patch cable to run my guitar with it. It was a bad mo-fo.
If I remember correctly, Terry Kath of the band CHICAGO used a Bogen for his guitar amp, and featured it in a song on their first album.
would changing V1 to 12AX7 allow for more gain? I read that the 6eu7 is pretty much a 12ax7 but they can't be swapped. I have lots of 12ax7s lying around.
Any rewiring info? And what is the purpose of the 6C4 tube?
beedoola wrote:would changing V1 to 12AX7 allow for more gain? I read that the 6eu7 is pretty much a 12ax7 but they can't be swapped. I have lots of 12ax7s lying around.
Any rewiring info? And what is the purpose of the 6C4 tube?
6EU7 is the same as 12AX7 with a different pinout. So you will have the same gain. There is little harm in rewiring if you want to tube roll.
The 6C4 is a cathodyne (a/k/a concertina or split load) phase splitter (or inverter). You need it there to feed the signal to the power stage.
I used to have 2 of these
I think the biggest change I made were the jacks and changing V1A setup to 100K anode resistor and a 1.5K/22uf combination at cathode.
May be due to the phase splitter in that amp - not sure- but if driven hard these amps sound glorious
Markusv wrote:I used to have 2 of these
I think the biggest change I made were the jacks and changing V1A setup to 100K anode resistor and a 1.5K/22uf combination at cathode.
May be due to the phase splitter in that amp - not sure- but if driven hard these amps sound glorious
Markus V
M Fowler wrote:Could add 470R/5w screen resistors and 1k5 grid resistors to the 6L6GC's.
The rest of the amp should function for guitar as is. Could add a 33k to 68k grid blocker between input jack and V1 at the tube socket.
whats the purpose of both of these? Can you point to them on the schematic? I'm aware of the screen and grids for the 6l6s
For my suggestion, the one half of the 6EU7at the input:
Typically /traditionally there is a 100K resistor connected to the plate of the tube. Then there is a parallel 1.5K resistor/22uf capacitor between cathode and ground.
It will drive the following stage a bit harder for better breakup etc
Please look at typical Fender schematics like say a Bassman or a Deluxe Reverb etc for comparison.
The suggested 33K or 68K grid stopper on the 6EU7 grid is to block unwanted frequencies like radio stations and the like
Markus
Disclaimer- I'm no tech wizard so my explanation may be clumsy
Thanks, as I mentioned, I'm aware of those, I was referring to those bolded in the comments I quoted: the grid resistor and the anode resistor and the resistor/cap combo at the cathode.
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