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 Post subject: Re: Bogen
PostPosted: Feb Sun 25, 2018 8:54 pm 
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glue_ru wrote:
The Bogen CHB35/50/100 aren't so desirable as is for guitar use. I have both a 35 and 100 I'm planning soon on
re-circuiting to a design from Paul P amps and Paul Ruby amps, adding a 2 knob tone control I found that 'tweeks'
the tone from a flat line to curved how you want, distortion of course, but that is what a lot of guitarists seem to want,
or switch it for that as a function. Found some other mods considering substituting in or adding. Looking at high end
amps that people ARE buying, seems they have many knobs and tone features, so adding 1 or 2 should be cool.
I'll share some schematics I've gathered, I've not added my mods into yet, they are sep docs.

One good link: http://ppamps.blogspot.com/2013/01/boge ... rsion.html


One thing you have to consider is that a PA amp is made primarily to amplify voices which isn't as demanding as amplifying the full range of a guitar. So a 35/50/100 watt PA amp is not equivalent to a 35/50/100 watt guitar amp. The physical size of the output transformer in a CHB100 is about the same as a 30 watt guitar amp output transformer.

Once you cut out all the bad electrolytic/paper caps and drifting carbon comp resistors you are basically just left with an empty chassis and two transformers. The CHB chassis uses long D-shaft pots so swapping different value pots can be challenging.

Yeah, you can "convert" an old PA amp into a guitar amp. It ends up being more like building an amp from scratch using some PA amp parts, which may end up being more challenging than starting completely from scratch.


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 Post subject: Re: Bogen
PostPosted: Feb Mon 26, 2018 2:39 am 
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true, and not being a guitar amp to begin with, they don't have the options some new ones do.
but with that being said, many guitarists like these and the sound they produce. but not stock, no desire for that at all.
Some research and a few pm/emails I've found a following for these.
I'm building these 2, a 35 and a 100, and I'll see how they go before taking on any others.

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 Post subject: Re: Bogen
PostPosted: Feb Mon 26, 2018 12:47 pm 
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mrriggs wrote:

One thing you have to consider is that a PA amp is made primarily to amplify voices which isn't as demanding as amplifying the full range of a guitar. So a 35/50/100 watt PA amp is not equivalent to a 35/50/100 watt guitar amp. The physical size of the output transformer in a CHB100 is about the same as a 30 watt guitar amp output transformer.


If the tube Bogens are like their later solid state amps (used a transformer to make the different impedances and 70 volt line) they will have a low frequency response down to 70Hz which ws pretty much all that was needed for voice and general background music service so they wouldn't have put in the extra cost for better transformers to reproduce frequencies the amps were not meant to reproduce in their intended application.

Now if the primary impedance is known one could install a proper output transformer if the amp does not have a dedicated feedback winding.


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 Post subject: Re: Bogen
PostPosted: Feb Mon 26, 2018 1:29 pm 
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the same can be said for any vintage amplifier. replacement of old capacitors and resistors, tubes, pots or what ever is necessary. that is the nature of the hobby. I had the best sounding single ended 6L6 Bogen intercom amp. everyone loved it without any mods except for an additional volume control and jacks it sounded great with guitar or harmonica. played it all the time until it blew the power transformer. never did find a replacement transformer for it :cry:


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 Post subject: Re: Bogen
PostPosted: Mar Thu 01, 2018 7:32 pm 
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I see a lot of tube amps being sold for pretty high prices that are not actually suitable for music listening. PA amps and organ amps (Hammond, Leslie) have no need for the wide frequency response found in hi-fi amps, and it costs much less to build them with the smaller output transformers. Distortion is generally quite reasonable, but they are not hi-fi amps.

Bogen did indeed make some fine consumer goods, with a few caveats. They generally performed very well.

Most of the 50's-60's era consumer equipment had at least two versions. It seemed they had an initial build, and if that sold well, a redesigned version was then produced. It wasn't always a cheaper version, but sometimes it was. Unfortunately, the SAMS was almost always of the original, rarer version, so SAMS are often not as much help as they ordinarily would be.

The DB130 mono amp/preamp is a good example. It was produced from early 1955 through about 1960, and went through 3 major revisions. It was a big seller, and is fairly common. The original version was somewhat stripped down, with a solid brass faceplate. Output tube screen balancing and dual rectifier tubes were added to the next version, accompanied by an anodized aluminum faceplate. Finally the db130A went back to a single rectifier with a completely redesigned chassis and front panel, but retained screen balancing. The circuit is largely otherwise the same. By then, however, stereo systems were becoming popular, and sales of all mono equipment was likewise faltering badly.

The R775 mono tuner/preamp was another great set that has been widely overlooked. With 17 tubes it was a no holds barred attempt at a top line set, but being released in 1957 was too late for it to see another version. Anyone spending that kind of money on a system was moving to stereo.

Not sure of the exact release date of the first DB130, however my understanding is SAMS can take up to a year to be published after a sets release. The original manual I have does not list a date, but the manuals for the 2nd version and the DB-130A do, as the schematics seem to be straight copies of the original engineering drawings, retaining full title blocks. While not production dates, I would assume the actual release dates would be within 3 to 6 months of the completion of the schematics.

For the 2nd version, the schematic date is 9-23-55. For the DB-130A, 7-21-58.

Unfortunately, I know of no remaining documentation about the serial and series numbers on Bogen consumer goods. It's really too bad, as Bogen is just as much a part of hi-fi history as Fisher, Harman Kardon, HH Scott, McIntosh, et al..

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 Post subject: Re: Bogen
PostPosted: Mar Thu 01, 2018 7:56 pm 
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early Fender amps had grossly under rated output transformers. probably never even considered frequency range. may have pulled transformers straight out of old radio parts as small as they are. filter capacitors less than 10uF. but they seemed to be the preferred amp of choice for just about everyone. who doesnt want to be like fender. tons of copies. Im sure you could do a lot more with later versions of Bogen PA amps if you mess with it enough. its a hobby not a competition


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 Post subject: Re: Bogen
PostPosted: Mar Thu 01, 2018 8:21 pm 
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tubeAMP wrote:
early Fender amps had grossly under rated output transformers. probably never even considered frequency range.


Perhaps the early amps didn't really need to produce much bass and as such the smaller transformers would have been well suited for that task.


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 Post subject: Re: Bogen
PostPosted: Mar Thu 01, 2018 11:11 pm 
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Tube Radio wrote:
tubeAMP wrote:
early Fender amps had grossly under rated output transformers. probably never even considered frequency range.


Perhaps the early amps didn't really need to produce much bass and as such the smaller transformers would have been well suited for that task.


I've read that the early Fender amps had small output transformers because there weren't any high power guitar speakers at the time. Some models had larger transformers when initially released then were soon downsized in reaction to the warranty repairs. As speakers improved, the output transformers got larger.


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 Post subject: Re: Bogen
PostPosted: Mar Fri 02, 2018 2:22 am 
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tubeAMP wrote:
...Im sure you could do a lot more with later versions of Bogen PA amps if you mess with it enough...

http://www.montagar.com/~patj/bogenspecs.htm

It would take some tweaking and judicious tube matching, and the more tubes in paralell the more distortion is presented, but there certainly is potential.

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 Post subject: Re: Bogen
PostPosted: Mar Tue 06, 2018 2:00 am 
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Still hoping for help with my Bogen R660 tuner. Mono tuner has two outputs...rca jacks side by side, and unlabeled. Is the signal out different in each...does anyone use this tuner? Also have a 60 cycle hum in my speaker which is annoying. Might need cleaner contacts or cleaner power. Any help greatly appreciated. Love my db130 amp...brass face version.


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 Post subject: Re: Bogen
PostPosted: Mar Tue 06, 2018 2:40 am 
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I exchanged some emails with Fab, The Fabulus Fab in Canada who has a CHB35a converted, which is the link to the conversion posted earlier, here is a quote from an email from fab:
----------
I had brought mine to a good tech I know, and I had also found the conversion schematics for him. I could send you copies of the schematics with pleasure. The way the amp is now, it is very loud, very quick on the master volume dial, this is one little flaw I find. The amp sounds great, but difficult to use at lower volumes. The tone is in the Plexi category, but with it's own flavor (also due to tubes). My tech changed the 6EU7 pre-amp to to a 12AX7. It now has 2x 12ax7, one 6x4 (i think it's a rectifier or phase inverter, nit sure) and the power tubes stayed the same, 7868. For me, it is really a ''one of a kind'' amp, it also has a very immediate attack that I can't describe well but that makes it special.
-------

which this is it pretty much, http://ppamps.blogspot.com/2013/01/boge ... rsion.html
talkative guys there if you have questions for them.
I found a 2 knob tone circuit I want to add for more distortion effects, not sure if I'm concerned about low volumes, most guitars players aren't

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 Post subject: Re: Bogen
PostPosted: Mar Tue 06, 2018 4:29 pm 
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Steven C wrote:
Still hoping for help with my Bogen R660 tuner. Mono tuner has two outputs...rca jacks side by side, and unlabeled. Is the signal out different in each...does anyone use this tuner? Also have a 60 cycle hum in my speaker which is annoying. Might need cleaner contacts or cleaner power. Any help greatly appreciated. Love my db130 amp...brass face version.

Which version R660 do you have? There is a version with the tuner cap entirely enclosed in a metal box, and an earlier one called the open cage version with the tuner cap box open on two sides. They each use a slightly different tube lineup.

Both versions have the same output connections, which is two RCA outputs just directly wired together. In this way you could have the tuner wired to two different systems, if needed.

Is the hum coming from the amp or the tuner? In either case, you will need to replace the power supply filter caps to get rid of the hum, and should change the coupling caps as well. Be careful you do not disturb any of the RF wiring in the tuner, or it will need realignment.

Recapping db130s is difficult because there is very little room in the slimline chassis. You will have to cut open the big silver cap can and restuff it with new caps. You will also have to change out the selenium rectifier with a 1N4007 diode and a 2K ohm series resistor. Clean the controls and switches with Deoxit.

I could email you high resolution pics of the manuals, including schematic. I want to scan these at some point, but I haven't yet.

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 Post subject: Re: Bogen
PostPosted: Mar Tue 06, 2018 4:42 pm 
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glue_ru wrote:
I exchanged some emails with Fab...

Low volume distortion is possibly an output tube imbalance. At higher volumes it can be less noticeable.

6X4 is a rectifier.

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 Post subject: Re: Bogen
PostPosted: Mar Wed 07, 2018 12:54 am 
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Hi..Thanks for the help. Hum is in the tuner...is all original and dirty when I got it but it cleaned up nicely and has a metal cover too. I have the enclosed version of the R660...with no printing on the cover enclosing the tuning mechanism. My db130 had been serviced and is clean and very loud. I have the Sam's sheet for the tuner...maybe get a quote from a local guy to go through it. Pulls in many station that sound fine in mono....except for that hum. Good to know either output is fine to use. Thanks again!


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 Post subject: Re: Bogen
PostPosted: Mar Wed 07, 2018 1:47 am 
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Sol wrote:
glue_ru wrote:
I exchanged some emails with Fab...

Low volume distortion is possibly an output tube imbalance. At higher volumes it can be less noticeable.

6X4 is a rectifier.


what would be a better choice?

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 Post subject: Re: Bogen
PostPosted: Mar Wed 07, 2018 3:34 pm 
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glue_ru wrote:
what would be a better choice?

Not sure if I understand your question. And just to be clear, I'm not really that knowledgeable about amps. Was just making some general observations.

I looked up the schematic online, and I see the amp uses a 6C4 phase inverter, so 6X4 was probably just a typo.

The amp does not have provision for output tube balancing, so you will need to ensure you have a properly balanced 7868 output pair. Of course other things could also cause the problem related, but that is where I would start.

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 Post subject: Re: Bogen
PostPosted: Mar Wed 21, 2018 9:02 pm 
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So the hum in my Bogen r660 tuner is either the rectifier 6X4 tube or the filter capacitor I should assume from what I've read here and elsewhere. I should try the tube first? Usually the caps are bad in the 50's tube tuners I thought. Would love to use the tuner with the Bogen amp


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 Post subject: Re: Bogen
PostPosted: Mar Wed 21, 2018 11:15 pm 
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The filter caps and the paper coupling caps should be replaced. If the tuner works at all the 6X4 isn't shorted.

Also, don't forget a new lamp for the meter. ;)

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 Post subject: Re: Bogen
PostPosted: Mar Thu 22, 2018 12:10 am 
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replace the caps without question, you'll know they are bad when they make a thud hitting the trash can, as some say here.
No need for expensive "audio" grade, yellow ones will work fine, contact Sal or Just Radios for what you need. > > > >

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 Post subject: Re: Bogen
PostPosted: Mar Thu 22, 2018 12:22 am 
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glue_ru wrote:
replace the caps without question, you'll know they are bad when they make a thud hitting the trash can, as some say here.
No need for expensive "audio" grade, yellow ones will work fine, contact Sal or Just Radios for what you need. > > > >

Excellent advice.

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