Bogen CBH 100 , Make good guitar amp ?

Gary Mattis

Gary Mattis

Active Member
The 7 pin I can't read. Was thinking about it as a guitar head with 12AX7 and EL 34 tubes, or can use the 7868 Jukebox/Fisher 400 tubes ? . Is the iron any good and will it drive four 12's pretty good. I built a 6AV5 GA 30 watt Bogen mono for a friend and it sounded great on a two 12 cabinet with a distortion / gain pedal. Anyone know what the 7 pin tube is ? 6EU7 is the first Tube ? . Sold my 100 watt Mig amp a few years ago and was thinking maybe this could replace it. Using a 6L6 40watt right now. Would like more power if I play outside. Even inside you need more power sometimes.
 

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Pretty sure the small tube is a 6C4, a triode.

I would be concerned that EL34 would need more heater current than what is available. I would stay with 7868s. Also the OT is spec’d for that tube. Unless you mean a pair of EL34s instead of four 7868s which could be a possibility.

Iron is good, if not ideal for guitar.
 
The other issue is the driver. A 7868 or 7591 needs a whole lot less drive than an EL34 or 6L6 family tube, so if you convert it and make the needed changes to bias it, you're not likely to get full output power without reworking the driver stage too.

Honestly it probably won't do too bad as-built. Maybe the tone control stuff needs fiddling with to get the right sound but the power amp is probably OK.
 
gadget73 said:
The other issue is the driver. A 7868 or 7591 needs a whole lot less drive than an EL34 or 6L6 family tube, so if you convert it and make the needed changes to bias it, you're not likely to get full output power without reworking the driver stage too.

Honestly it probably won't do too bad as-built. Maybe the tone control stuff needs fiddling with to get the right sound but the power amp is probably OK.
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I will take your advice and try using it with a stock rebuild. Usually you put a 47 or 68 K resistance on the input for guitar , the mic inputs use Cap's instead ? But the mag and aux use resistance. Should I use one of those inputs instead of the mic inputs ? Or just add a resistance before the cap if it is even needed ? . I did some research and a lot of jazz player's use a A Ampeg guitar amp similar with 50 watts, two 7868 tubes. With four they are supposed to be really good for guitar. I would like to have more tone control even under break up , with El 34 and 6L6 that seems to be limited on them, I was hoping these tubes may be better at it and still give me enough power. In tall large rooms and outside it takes a lot of power to cut through the mix. I want my amp to sound better than a store bought amp. My speaker is a Old JCM 600 series 1960 A Marshall lead cab with four 75 watt Celeston speakers , it seems to work really well with just about any tube amp over 40 watts. I know a lot of people use the 30 Celeston but I like the 75 sound better and they are rock solid reliable.
 
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An Ampeg preamp grafted to the Bogen power amp is what I would do.
I have an Ampeg SB12 that is a one-channel amp using a pair of 7868; it's a great amp, more like 30 watts though. Four of them would make 60 watts or so and with your 4x12 should be plenty loud unless the rest of the band is Megadeath.

The preamp circuit in the Ampeg uses a Baxandal tone control that is less lossy that FMV-type controls. There are two schematics out there as that amp was later used with 6L6 power tubes but the preamp remained the same. Let me now if you can't find it (mine is glued to the amp!). That Bogen used the 6EU7 as a magnetic phono preamp and then had the 12AX7 for the Hi-Z mic inputs. You'd scrap all of that and rebuild per a known amp such as the Ampeg.

Four power tubes is a little tricky. Have you ever worked with a Twin or a Showman? If it were mine I would build in bias level adjustments and bias balance, otherwise you would need to find matched tubes which will really set you back.
 
The caps are just there as DC blockers, probably in case someone hooked up an elecret mic or whatever that leaked DC voltage. You can sub a resistor for the cap if you know there isn't any chance of DC voltage coming in to the input jack.

yeah parallel output tubes can be a little bit fussy. They still really should be matched for best performance no matter what you do for bias adjustments.

I'll also agree that 60 watts seems more realistic than 100 just based on voltages and what a typical pair of 7868 can make. 25-30 is the usual, so double that for parallel and you're in the 50-60 range. Pushed a little harder and allowing for higher distortion maybe you can nudge 70 but thats probably it.

If you want more overdrive, you may be able to back down on the feedback. That will allow for more overdrive in the power amp section. The trouble is that phase inverter, that style gets pretty ugly sounding if seriously over-driven.
 
RWood said:
An Ampeg preamp grafted to the Bogen power amp is what I would do.
I have an Ampeg SB12 that is a one-channel amp using a pair of 7868; it's a great amp, more like 30 watts though. Four of them would make 60 watts or so and with your 4x12 should be plenty loud unless the rest of the band is Megadeath.

The preamp circuit in the Ampeg uses a Baxandal tone control that is less lossy that FMV-type controls. There are two schematics out there as that amp was later used with 6L6 power tubes but the preamp remained the same. Let me now if you can't find it (mine is glued to the amp!). That Bogen used the 6EU7 as a magnetic phono preamp and then had the 12AX7 for the Hi-Z mic inputs. You'd scrap all of that and rebuild per a known amp such as the Ampeg.

Four power tubes is a little tricky. Have you ever worked with a Twin or a Showman? If it were mine I would build in bias level adjustments and bias balance, otherwise you would need to find matched tubes which will really set you back.
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I have a Quad of vintage 7868 tubes in a working spare Jukebox amp, I have tubes, amps , jukeboxes and parts. I think I have more vintage 7868 tubes in my tube caddy. Bogen was a pretty smart dude overall , I still use a DB230A with 6AV5 GA tubes in my music recording studio , maybe I should try it like it is before changing it ? . It may be better with 100 watts than just 60 ? , My Mig 100 lead was 120/130 watts with EL34 mullards, had 580 on the plates and neg 80 bias, Vintage Ei pre amp tubes. That's what I am trying to replace with this. I know it will not be that powerful but I would like to get as much power as possible out of this amp. Lowering the power output is not a option for me. I have two 6L6 guitar amps already , a 1952 Silvertone / Dan Electro made with 2 12's and a Homebrew 6L6 RCA amp with 6J5 pre amp. Both are pretty good amps so I'm covered down at lower volumes already. Nothing is as bad as having too small of an amp in a big venue ! , It is all the way up and so is the guitar and you still cannot make it go any louder no matter what you do ! . Happened to me a few months ago. That 30 watt Fender modeling amp sounded so dam flat up loud and still could not cut it with a Strat ! , It was a good thing everyone was drunk and could not tell how bad it sounded. It was embarrassing how flat it sounded up on 10. All I wanted to do was shut that amp off the whole time I was playing it. No headroom is the problem with little amps , a tall sealing and your out of luck ! . I was out of state and could not go home for my other amps, not sure if they would have been enough either ! , Better to have too much power than not enough !
 
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Bogen made great stuff and I have seen a lot of their PA amps on YouTube used as guitar amps but I am wondering if the output transformers are really up to the abuse guitar players like to put on their made-for-guitar amplifiers? :dunno:

I don't play the guitar - just love electronics and music however I do own just one guitar amplifier. It was my dad's. It's a Fender tube FE5 tremolux. If you think I am ever getting rid of that, guess again! :beerchug:
 
This exact model,running into a Traynor YC-810,aka the Big B,was my bass rig most of the way through high school and slightly later.

The preamp was modified for much higher gain,and I included a hefty boost at around 2K. When it was overdriven,it sounded just like John Entwistle on Live At Leeds. Considering that I was playing in a Who cover band at the time,and this album was our stock show,this was a really sweet setup.I was using a really cheesy (plywood body) shortscale Japanese made explorer bass.

Damned loud (I doubt anyone could get away with these levels on stage today!),and despite the power tube plates usually glowing a dull cherry red,this thing was totally stable and bulletproof.

I shudder to think just how much grunt and grind this thing could give a guitar through a 4x12o_O

The ONLY other head I have ever owned that could rival the CHB-100 for tone was a Garnet BTO-400,which was what replaced the Bogen. I wish I still had both of them.....
 
century tek said:
Bogen made great stuff and I have seen a lot of their PA amps on YouTube used as guitar amps but I am wondering if the output transformers are really up to the abuse guitar players like to put on their made-for-guitar amplifiers? :dunno:

I don't play the guitar - just love electronics and music however I do own just one guitar amplifier. It was my dad's. It's a Fender tube FE5 tremolux. If you think I am ever getting rid of that, guess again! :beerchug:
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Not much on Fender amps, have ragged out some silverface champ's in the past ! , Like Migs and Marshall amps. Just don't have the money for them right now ! . Have a 52 Silvertone 6L6 Tube Tremelo Amp by Dan Electro , About the best Tremelo Amp ever made ! , to compare the fender side by side with it would be interesting. Reliability is my problem with old Fenders, the OT's wear out and go flat. You think it is tubes but it is not, the OT has gone flat ! , Before that happens they sound good usually.
 
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arts said:
This exact model,running into a Traynor YC-810,aka the Big B,was my bass rig most of the way through high school and slightly later.

The preamp was modified for much higher gain,and I included a hefty boost at around 2K. When it was overdriven,it sounded just like John Entwistle on Live At Leeds. Considering that I was playing in a Who cover band at the time,and this album was our stock show,this was a really sweet setup.I was using a really cheesy (plywood body) shortscale Japanese made explorer bass.

Damned loud (I doubt anyone could get away with these levels on stage today!),and despite the power tube plates usually glowing a dull cherry red,this thing was totally stable and bulletproof.

I shudder to think just how much grunt and grind this thing could give a guitar through a 4x12o_O

The ONLY other head I have ever owned that could rival the CHB-100 for tone was a Garnet BTO-400,which was what replaced the Bogen. I wish I still had both of them.....
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Great to hear that ! , I noticed that it has a master volume and volume on the wiring diagram. I like good tone also, Someone said that the OT may not be big enough for guitar ? , Not sure size is as important as quality of the OT product. They make them big on guitar amps but is that because they use cheap windings on guitar amps ? , I always wondered about that ? Cheap windings melt easier so you use bigger iron to compensate. Audio amps don't have giant OT's usually. I have plenty of gain pedal access in my pedal suitcase and a Morley wah. If the amp just puts out a good tone and good power I should be ok with it. Got a great sounding Strat and 67 flying V , both have it ! (Pic) that is my 40 watt homemade amp in pic with 6J5/6L6 tubes. One metal 6J5 in it - the glass one's are getting expensive ! , Been thinking about using 6SN7 to replace the 6J5 and tying both sides together , right now I can use 6N7 also the way I wired it up , if I use 6SN7 it could not use the 6N7 also ! , 6J5 glass we're dirt cheap until I built it then they went ski high in price. Have to find another unknown tube now to use ! , Once they are known the price shoots up !.
 

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Well,insofar as the physical size of that transformer goes,it certainly provided a glorious bass tone,so it should be ''adequate'' for guitar,haha!! I'm not sure what the actual specs were for the amplifier,but most PA amps aren't really designed with low end in mind,so that must have been a better than average OPT.

When it comes to output transformer design,there are a lot of variables,not least of which is stack size and especially the type of metal used.

Many companies use a huge stack of laminations because they are using what, by audio standards, would be considered scrap metal,which often tricks people into believing ''wow,now that is a serious transformer!''I hate to say it,but your MIG 100 used a transformer of this type:(

Unfortunately,a large quantity of poorly performing magnetic medium doesn't get you much.Looks impressive and weighs lots,but so do most boat anchors.And it probably won't sound any better. Really good output transformers cost bucks,and use materials such as Radiometal for the laminations,which is a very high-performance steel designed for this purpose.A transformer of this type will oftentimes be smaller than usual,as better performance can be achieved with a smaller stack.Some small transformers can be very deceptive.
 
Here is the schematic Gary.My recommendation would be to re-configure the 6EU7 section (you could always go to a 12AX7 instead,they're the same tube with different pin-outs) as either a Fender or Marshall first stage as your new input,and run that into the Master volume pot. If you are feeling creative,you've got lots of volume controls in there (Mic1,Mic2,Master) to play with. Channel switcher anyone?;)

bogen-chb100b-6.jpg
 
arts said:
I just noticed your attached file; nice setup,I like the ''V''.

Here's my living room rumbler:
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Is that a 15 BW speaker ? Well worn P bass there, I just restored my V , it was pretty rough looking like your P bass before. Changed the Cap's to PIO and added the 4th. Pot for LP tone control. It always had good tone but is even better now. That and a 12 string ES 635 are my main two guitar's. The cheap wooden strat had good sounding electronics and was thin like an original Strat, I hate newer USAs , sometimes you need a strat but not usually, I just have it for when I need to use one. Has a wide thin CD neck with a refret medium high .052 before leveling and re crowns. .045 ish now. Cheap hardware but I super glued everything. It will do for a Strat, have a really nice Tele with a Kaylor Flyer and Special Pick up. I just don't play any of my Fenders much, they sit most of the time. I have a 1960 ES 125 TC also with a P90 pick up. I have a Tele rythum pick up in the neck of the 635 ES and I love it ! That is my clean set up ! The more I play it the more I like it. I have too many guitar's and too many tube amps .
 
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arts said:
The amp is a 1965 Ampeg B18NL,the ''L'' signifying that it was factory equipped with an 18'' JBL.My bass has certainly been around the block a few times; it's a '59.:)
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Nice stuff ! , I played bass 78 to 81; and I had a Fender Music master and a 63 Hoffner , had a Gibson ripper I really liked also but The Hoffner was my favorite bass , gave it to a friend of mine for 100 dollars after he dropped his brand new Guild bass, told him that I wanted it back for the same price if he gets rid of it. Never got it back oh well.
 
Been thinking about using a 12Ax7 instead of the 6EU7 tube, found two NOS 6C4 tubes that test good. Have not found any 6EU7 tubes yet, still have places to look though. Expensive tube in NOS or Vintage Mullards. I have a bunch of the Russian 6NP2 tubes NOS , this looks like a good place to use one ! . Some of the 6N2P's I tested were quite good , others were average sounding like a cheaper 12AX7. I have plenty 12ax7 tubes but sense no one wants the 6N2P tubes why not use one here ? The good ones have a Vintage Ei type of tone to them. Guitar's like that Vintage Ei type of tone. Seems stupid to pay the 6EU7 price when I have so many other tubes. Maybe I should just go 6N2P all the way !. Did a voltage test and OT test and everything tested good. Gonna order the new Cap's for it now.
 
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Decided to use a A 12ax7 to replace the 6eu7 in stage 1 , took about an hour to convert the socket wiring. Not as easy as it looked. I was wondering if I should use a short or long plate in the 6C4 PI? I have both types.
 
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