Hey folks, I'm new here so wanted to first introduce myself and let everyone in on a project concerning a Bogen CHB 100 I got once I decided I wanted to build an amp. With my interest in schematic reading I thought it wouldn't be too terribly difficult but now I think it might be otherwise. I've been reading up alot on amp layout and design; I didn't realize how rusty I am with this stuff. Since this is my first build, I'm keeping it simple and doing as little heavy lifting as I can and doing some copy-and-paste engineering. I've come across this build along with schematic and audio clip which is very nice and something I'm looking to replicate, except for the fact it's for a Bogen CHB 35a.
http://www.guitarscanada.com/amps-cabs/ ... -into.html
Here is the schematic presented in the link and then the schematic for the CHB 100.
http://vwtweaked.ca/images/Bogen%20Bass ... 8feb10.jpg
http://uglyampking.brinkster.net/Images/CHB100.jpg
Seeing as the 100 just uses two more 7868's, can I essentially just compensate for the extra tubes in the circuit? I know there's alot more work on my end, such as switching out the 6EU7 for a 12AX7 and looking at voltages across the circuit (at quick glance I can already see there's 420v across the 7868's in the 100 and 430 across the BassFlex circuit), but I just wanted to ensure I'm on the right path or at least headed in the right direction.
First Project, Bogen CHB 100
Moderators: pompeiisneaks, Colossal
Re: First Project, Bogen CHB 100
Welcome to the amp garage.
Are you planning on using point to point wiring on the new version?
That can be a bit tricky if you haven't done it before.
I wouldn't sweat a 10v difference.
The 7868 has a max plate voltage of 550v and the screens are rated at 440v.
Not familiar with that tube.
It seems you could also use EL84 power tubes with simple rewiring.
Strange they don't use screen resistors.
I wonder what the cap and resistor is for coming off the center tap of the OT?
Much smarter guys than I will be along shortly to give you better advice.
Are you planning on using point to point wiring on the new version?
That can be a bit tricky if you haven't done it before.
I wouldn't sweat a 10v difference.
The 7868 has a max plate voltage of 550v and the screens are rated at 440v.
Not familiar with that tube.
It seems you could also use EL84 power tubes with simple rewiring.
Strange they don't use screen resistors.
I wonder what the cap and resistor is for coming off the center tap of the OT?
Much smarter guys than I will be along shortly to give you better advice.
Tom
Don't let that smoke out!
Don't let that smoke out!
Re: First Project, Bogen CHB 100
CHB100 has a Voltage Doubler type power supply---- the first stage is not too much different than many Marshall 100 watters--- different rectifier.
I've re-done many CHB series Bogens----- 10's, 20's, 35's, 50's, and i have a CHB100 sitting in storage that i'll do something with one day.
In the past couple of months i've sold (locally) a CHB35A with a Marshall 1987-based preamp and cathode biased 6L6GC's, a CHB35A with a hotter 1987-based preamp and fixed bias 7868's, and a CHB50 with a Marshall 1986-based preamp and fixed bias EL34's.
One can build almost any 2 or 3 tube preamp into these things--- the voltages published in those Bogen schematics are general guides and might not accurately reflect what you might find in your particular amp.
Orig RCA or Sylvania 7868's are not super easy or cheap to find in matched quads--- EH makes a 7868 that is ok--- but why not just convert to the much more common 6L6GC and you'll have a greater choice in output tubes-----change the output tube sockets and 6L6GC's will work fine under 7868 conditions (usually 6.6k primary Z for two tubes).
Many people around here are buying these rebuilt old PA heads from me lately----i've sold several others besides the CHB-series Bogens described above----- rebuilding an early 40's Knight head now---- was orig a 14 watt 6v6x2----- i've gutted everything and i'm using 50 watt BF Fender iron (Classic Tone) and cathode biased 6L6GCx2 for @35-40 watts----found some NOS 5U4GB's in my stash and one Sylvania looks like the one for this amp-----going with either a 5E5-based preamp or maybe use a version of the Paraphase PI similar to the 5D3, not sure yet.
Also have a couple of old Stromberg-Carlson heads that will be rebuilt after this Knight----also have an early 50's Knight 93 that's promised, after rebuild, to a local studio.
This old PA head rebuilding is all well and good, and i'm happy that people like the amps i rebuild--- but i've had most people play the Hiwatt DR504 clone (my personal one that's in my shop for demos), several modern hi-gain prototypes, a nice Marshall 1987 clone i've built, many rebuilt Fender BF's--- and they love these amps--- but when they hear how much i have to sell them for (and i'm not at the top of the price heap, by any means) they want cheaper amps---so i pull out a Bogen CHB series, Challenger, Newcomb, Knight, etc and they like the tones of whatever old classic circuit i've built into the things..............and they buy them---- so i'll build up more of the darned things if that's what they want--- i've got a bunch of different old PA heads stored away.
I'd much rather build more nice looking amps from scratch but i seemingly can't sell the ones i have now, even though they love the amps------- people don't have much extra $$$ to spend------- Rant Over..........................gldtp99
PS--- sorry for the rant------ i used many old PA heads as learning platforms and they are great for that---i went this route instead of building kit amps and i bought a lot of old PA heads back when they were cheaper on e-bay---i though i had moved away from them---i even went through a period where i'd pull the good iron from PA heads and scratch build many 30-50 watt heads on new chassis and locally built head cabs---maybe i'll do some more of these with several 60's and 70's Knight 32-35 watters i have underfoot------- people like 5F6A/JTM45-ish and 6l6GC 5e3 (aka 5E5) circuits, and Marshall 1987-ish circuits even when they have no idea what they're playing--- even if they've never played any of the orig amps.
And I've seen people's eyes light up when they play a Hiwatt DR504 (one of my clones) for the first time---and then their eyes dull when they find out what they cost----except one guy who actually bought another DR504 clone i did---i have parts onhand for more Hiwatt builds (chassis, head cabs, turret boards, etc) but i don't want to build up any just to look at them.
I've re-done many CHB series Bogens----- 10's, 20's, 35's, 50's, and i have a CHB100 sitting in storage that i'll do something with one day.
In the past couple of months i've sold (locally) a CHB35A with a Marshall 1987-based preamp and cathode biased 6L6GC's, a CHB35A with a hotter 1987-based preamp and fixed bias 7868's, and a CHB50 with a Marshall 1986-based preamp and fixed bias EL34's.
One can build almost any 2 or 3 tube preamp into these things--- the voltages published in those Bogen schematics are general guides and might not accurately reflect what you might find in your particular amp.
Orig RCA or Sylvania 7868's are not super easy or cheap to find in matched quads--- EH makes a 7868 that is ok--- but why not just convert to the much more common 6L6GC and you'll have a greater choice in output tubes-----change the output tube sockets and 6L6GC's will work fine under 7868 conditions (usually 6.6k primary Z for two tubes).
Many people around here are buying these rebuilt old PA heads from me lately----i've sold several others besides the CHB-series Bogens described above----- rebuilding an early 40's Knight head now---- was orig a 14 watt 6v6x2----- i've gutted everything and i'm using 50 watt BF Fender iron (Classic Tone) and cathode biased 6L6GCx2 for @35-40 watts----found some NOS 5U4GB's in my stash and one Sylvania looks like the one for this amp-----going with either a 5E5-based preamp or maybe use a version of the Paraphase PI similar to the 5D3, not sure yet.
Also have a couple of old Stromberg-Carlson heads that will be rebuilt after this Knight----also have an early 50's Knight 93 that's promised, after rebuild, to a local studio.
This old PA head rebuilding is all well and good, and i'm happy that people like the amps i rebuild--- but i've had most people play the Hiwatt DR504 clone (my personal one that's in my shop for demos), several modern hi-gain prototypes, a nice Marshall 1987 clone i've built, many rebuilt Fender BF's--- and they love these amps--- but when they hear how much i have to sell them for (and i'm not at the top of the price heap, by any means) they want cheaper amps---so i pull out a Bogen CHB series, Challenger, Newcomb, Knight, etc and they like the tones of whatever old classic circuit i've built into the things..............and they buy them---- so i'll build up more of the darned things if that's what they want--- i've got a bunch of different old PA heads stored away.
I'd much rather build more nice looking amps from scratch but i seemingly can't sell the ones i have now, even though they love the amps------- people don't have much extra $$$ to spend------- Rant Over..........................gldtp99
PS--- sorry for the rant------ i used many old PA heads as learning platforms and they are great for that---i went this route instead of building kit amps and i bought a lot of old PA heads back when they were cheaper on e-bay---i though i had moved away from them---i even went through a period where i'd pull the good iron from PA heads and scratch build many 30-50 watt heads on new chassis and locally built head cabs---maybe i'll do some more of these with several 60's and 70's Knight 32-35 watters i have underfoot------- people like 5F6A/JTM45-ish and 6l6GC 5e3 (aka 5E5) circuits, and Marshall 1987-ish circuits even when they have no idea what they're playing--- even if they've never played any of the orig amps.
And I've seen people's eyes light up when they play a Hiwatt DR504 (one of my clones) for the first time---and then their eyes dull when they find out what they cost----except one guy who actually bought another DR504 clone i did---i have parts onhand for more Hiwatt builds (chassis, head cabs, turret boards, etc) but i don't want to build up any just to look at them.