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 Post subject: Bogen DB-130 amp 'restoration'...
PostPosted: Sep Fri 14, 2012 3:38 am 
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Hiya!

Recently I came into a Bogen DB-130 amp/preamp - and then another - and then another!

Does anybody know anything about these amps? If so, I want to hear from YOU! :)


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 Post subject: Re: Bogen DB-130 amp 'restoration'...
PostPosted: Sep Fri 14, 2012 3:19 pm 
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yes. you have three of them


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 Post subject: Re: Bogen DB-130 amp 'restoration'...
PostPosted: Sep Fri 14, 2012 3:31 pm 
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Service information for DB130 is in Sams 332-4, DB130A is in 449-7. I have both.

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 Post subject: Re: Bogen DB-130 amp 'restoration'...
PostPosted: Sep Fri 14, 2012 3:45 pm 
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looks like a monoral audio tube amplifier. Bogen makes some rock solid equipment. well engineered. good sound quality


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 Post subject: Re: Bogen DB-130 amp 'restoration'...
PostPosted: Sep Fri 14, 2012 4:14 pm 
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Thanks for the posts guys!

Yes, I had the Sams in my collection. Actually, Bogen made these in no less than three versions. Fortunately these are early ones which match the Sams, though there are some errors in the schematic.

Well, I was hoping someone might have some experience with these, and could point out some common fixes and maybe even a few light improvements, such as replacing the stock 6AK5 output tubes with 6FW5's, a pin-for-pin replacement that slips right in and gives about 20 more watts of peak headroom.

I think it kind of strange because these amps are not all that rare but it seems so few people know of them.

Let me quote the stock specs as released from Bogen:

35 watts continuous, 70 watts peak, up to 100 watts on transients, plus or minus 0.5 db 15 to 30,000 Hz. 0.3% harmonic distortion at full power, less than 1.5% IM distortion at full power. Noise figure -80 db. Active tone controls, active loudness control, active switchable low and high filters. 6 inputs and 7 selectable phono compensation curves.

...and all this from 1956! :o

Surely, I think, someone knows something about refurbishing these amps...? :?


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 Post subject: Re: Bogen DB-130 amp 'restoration'...
PostPosted: Sep Fri 14, 2012 6:13 pm 
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I had to replace all the paper capacitors, they were so leaky that none of the preamp stages worked. The 6FW5 output tubes are a necessary change, as they are rated for 700 volts on the plates. 6AV5 tubes tend to red-plate or flash over in this amplifier.
You will find that the bass response is better than most sub-woofers, great for watching movies on TV. If it has variable damping, that affects bass output a lot.
Don


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 Post subject: Re: Bogen DB-130 amp 'restoration'...
PostPosted: Sep Sun 16, 2012 3:15 pm 
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Great info BikenSwim - thanks so much!

I heard on another forum that at high volume levels the rectifier can red-plate too - have you heard of or seen this? Do you have any experience with rectifier substitution, such as a 5R4 instead of the 5U4?

I am also thinking of implementing the output balancing circuit of the DB-130A into it. Have you heard of anyone doing this?


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 Post subject: Re: Bogen DB-130 amp 'restoration'...
PostPosted: Sep Sun 16, 2012 4:09 pm 
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With today's higher line voltage, it is easy to have the idle current set too high, which would then lead to red-plating. My DB-130 amplifiers have two 5Y3 rectifiers.
EDIT: There are two pots, one to balance idle current and one to set the screen voltage which adjusts the idle current.
By the way, both tubes have to be the same brand or look the same internally, to balance the current.
There is a selenium rectifier for the -55 volts bias, replace that with a silicon diode so you will have full bias voltage, as there is no adjustment for that.


Bogen also used a similar circuit in their LX-60 60 watt full-range public-address amplifiers. Those started out with four 6AV5 tubes and Three 5Y3 tubes. They then changed to Two 5AR4/GZ34 rectifiers and only 8 MFD for the first filter capacitor to prevent flash-over in the rectifiers, for my LX-60. I used Solen Fast Capacitors for the filter caps in the LX-60, as they were rated for 630 volts and fit nicely in capacitor clamps as long as the negative lead was on top for safety. 6FW5 works well there, no red-plating anywhere in full-volume public-address service! It can peel paint off the walls. I bought a bunch of NOS 6FW5 for $3 each, and swapped around to get 4 that would share current properly.
Don


Last edited by BikenSwim on Sep Sun 16, 2012 6:57 pm, edited 1 time in total.

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 Post subject: Re: Bogen DB-130 amp 'restoration'...
PostPosted: Sep Sun 16, 2012 4:26 pm 
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Wow, thanks again BikenSwim. Great name, BTW. :)

Though it might be nice to have the balancing circuit, the 6FW5's are cheap enough to buy a dozen and find a couple balanced pairs, so perhaps would not be worth the trouble to add the circuit.

The single 5U4GB rectifiers in the early model are pretty capable tubes, perhaps I will stick to stock for now and see if any problems develop.

So, you are saying the amount of input capacitance can affect flashover? I would like to add some capacitance to the PS, but perhaps there is a right and a wrong way to do it. Any further suggestions? :)


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 Post subject: Re: Bogen DB-130 amp 'restoration'...
PostPosted: Sep Sun 16, 2012 6:51 pm 
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The 5U4GB is an excellent tube, also shorter height than 5U4GC. I have a H H Scott amplifier where I cannot fit in a taller tube, just a heads-up.
The maximum input filter capacitance is 40 MFD for a 5U4GB to limit the hot-switching current and strain on the transformer. Note that my Bogen shows two 30 MFD 400 volt capacitors in series, which gives an actual capacitance of 15 MFD, well within the tube's rating and enough to work well. Bogen units are well designed.

5AR4 is like a damper tube, must use a smaller input filter capacitor to avoid flashover as it has a much lower internal resistance and voltage drop than a 5U4GB.

Note that 6FW5 and 6AV5 are television horizontal sweep tubes, with large cathodes that can deliver high peak currents. They are very linear too, so they give great audio performance. The guy who had red-plating may have connected 4 ohm speakers to the 8 or 16 ohm tap, causing these powerful tubes to draw too much current at high volume. Also, setting the damping factor pot incorrectly will cause a loud oscillation.
I edited my earlier post above.
Don


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 Post subject: Re: Bogen DB-130 amp 'restoration'...
PostPosted: Sep Mon 17, 2012 12:18 am 
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Folks, when tubes were a dollar or two nobody cared much. Guitar folks used to re tube after every other gig or so leaving the old glass in a box hoping it get credit as duds, and many did. We were all crooks then as now.

So notch them down a peg or two, you'll never know the difference. Ain't no new ones availaible.


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 Post subject: Re: Bogen DB-130 amp 'restoration'...
PostPosted: Sep Mon 17, 2012 1:34 pm 
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+1.

L

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 Post subject: Re: Bogen DB-130 amp 'restoration'...
PostPosted: Sep Mon 17, 2012 3:30 pm 
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Thanks again BikenSwim. :)

Funny thing, in the single rectifier DB-130 the tube is mounted sideways, so the height isn't a factor. Unfortunately, they do not have the lowered mounting of the output tubes, so if I put in anything but GT tubes the cover won't fit on. Perhaps I'll be building wooden cases for these. That makes sense about the PS caps, and the likely reasons a tube might red-plate in these.


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 Post subject: Re: Bogen DB-130 amp 'restoration'...
PostPosted: Sep Mon 17, 2012 3:31 pm 
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Interesting anecdote codefox.

I'll keep it in mind. :)


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 Post subject: Re: Bogen DB-130 amp 'restoration'...
PostPosted: Feb Sat 10, 2018 3:29 am 
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Please help ....hum from my Dual 1019 when connected to my Bogen db130. It is grounded to the chassis. Same hum on both phono inputs. Using a combining box to balance the stereo to mono conversion. Works great on digital media thru aux input. Cartridge is an old Empire 888PE. Any ideas? How do I troubleshoot. Thanks!


Last edited by Steven C on Feb Sat 10, 2018 9:15 am, edited 1 time in total.

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 Post subject: Re: Bogen DB-130 amp 'restoration'...
PostPosted: Feb Sat 10, 2018 3:38 am 
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Attachment:
IMG_20180209_193507_kindlephoto-1919564.jpg
IMG_20180209_193507_kindlephoto-1919564.jpg [ 25.85 KiB | Viewed 2213 times ]
Here is the combiner...better than the Y plug


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 Post subject: Re: Bogen DB-130 amp 'restoration'...
PostPosted: Feb Sat 10, 2018 4:11 pm 
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Have you had the amp completely electronically restored? This should be done first and foremost.

I cannot find your 'Match Master' to check it's specifications, but I assume you are getting hum from the power connection to it.

One thing you might try is pulling the amp power cord, turning it over and plugging it back in, so that the prongs are reversed. There is also a 'Hum Adjust' control on the amp.

Something else to try is eliminating the 'Match Master' altogether.

Ordinarily, to play a stereo cart to a mono amp the cart is 'strapped' for mono.
http://forums.stevehoffman.tv/threads/stereo-cartridge-mono-wiring.181411/

This is known to work better with some carts than others, but you won't know until you try.

Good luck!

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 Post subject: Re: Bogen DB-130 amp 'restoration'...
PostPosted: Feb Sat 10, 2018 6:36 pm 
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Sol wrote:
Let me quote the stock specs as released from Bogen:

35 watts continuous, 70 watts peak, up to 100 watts on transients, plus or minus 0.5 db 15 to 30,000 Hz. 0.3% harmonic distortion at full power, less than 1.5% IM distortion at full power. Noise figure -80 db.


Should you chose to test any of these, you might want to "manage your expectations" a bit, because you may not get what they claim! The "peak" and "transient" power are undefined by any spec I am aware of so disregard that, and the 35 watts may be possible but not at .3 percent distortion. That doesn't mean it's not a good amplifier, just that the claims, in the pre-IHF standards era, may not be entirely congruent with reality.

Brett


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 Post subject: Re: Bogen DB-130 amp 'restoration'...
PostPosted: Feb Sat 10, 2018 6:40 pm 
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Location: Sunnyvale CA
Sol wrote:
Ordinarily, to play a stereo cart to a mono amp the cart is 'strapped' for mono.
http://forums.stevehoffman.tv/threads/stereo-cartridge-mono-wiring.181411/

This is known to work better with some carts than others, but you won't know until you try.


I would suggest trying mixing it to mono after putting it through a stereo phono preamp instead of on the low-voltage side of the system. I think you will find that will prevent the impedance matching problem. But, as you say, sometimes it works better than others.

Brett


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 Post subject: Re: Bogen DB-130 amp 'restoration'...
PostPosted: Feb Sun 11, 2018 2:48 pm 
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Brett_Buck wrote:
Sol wrote:
Let me quote the stock specs as released from Bogen:

35 watts continuous, 70 watts peak, up to 100 watts on transients, plus or minus 0.5 db 15 to 30,000 Hz. 0.3% harmonic distortion at full power, less than 1.5% IM distortion at full power. Noise figure -80 db.


Should you chose to test any of these, you might want to "manage your expectations" a bit, because you may not get what they claim! The "peak" and "transient" power are undefined by any spec I am aware of so disregard that, and the 35 watts may be possible but not at .3 percent distortion. That doesn't mean it's not a good amplifier, just that the claims, in the pre-IHF standards era, may not be entirely congruent with reality.

Brett

Quite possibly true, but for a wide variety of reasons.

Modern testing of another tube amp of the next generation:
https://www.stereophile.com/content/fisher-500-c-vintage-stereo-receiver-reviewing-testing-vintage-audio-components

The limits and variety of the 6AV5 output tube:
http://tubelab.com/articles/tube-testing/6av5-sweep-tube/

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