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Bozak 305?

kkalchthaler

kkalchthaler

New Member
Hello! My name is Kris and I inherited this beautiful speaker. I unfortunately am not well versed in vintage audio and am wondering if the group can help me figure out what I have. Appreciate your help. Be safe, stay healthy.
 

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Thank you! I will do some research on Electro-Voice. Excited to learn more and put to good use. Lucky to have the original manuals for the Bogen AM/FM and Amplifier. There was a Bozak Speaker System catalog in the file, but nothing about a specific model/specifications. (love that family was organized - at least pointed me in the right direction)
 
scn0006.jpeg Its a Bozak 302 in a larger home made design to look like a 305. But it only has one woofer, a mid and there should be two tweeters in front of the woofer. A 305 has 2 woofers each with two tweeters in front. It will use the old paper coned mid and tweeters which don't hold up well at all. There are some very informative groups out there that can inform about your speakers in very minute detail if you wish. As you have only one and its custom, I doubt you will ever find a mate if thats what you want to do. You should replace the caps in the crossover at a minimum.
 
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That definitely helps piece together some information for me. Along with the Bozak catalog I have, there was a newspaper article from 2004 about Gary Dodd (Dodd Audio - Garland, Texas). Wondering if he custom built the speaker. https://www.audiocircle.com/index.php?topic=7637.0

Appreciate the responses!
 

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twiiii said:
As you have only one and its custom, I doubt you will ever find a mate if that's what you want to do.
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Kris,

Welcome aboard and congrats! on what looks to be very well kept equipment & speaker, note I said speaker. Seeing as the amp is a Mono unit (1 channel) as opposed to Stereo (2 Channel) that's why there is only 1 speaker which was how they were sold back in the day (1950's)

[QUOTE="kkalchthaler, post: 13813387, member: 324824"Lucky to have the original manuals for the Bogen AM/FM and Amplifier. [/QUOTE]

A common response here, not knowing when the last time the amp was used, would be do not plug it in to see if it works. If it has been sitting idle for years, decades the sudden jolt of voltage could do the unit harm.

If you care to learn more about the amp & tuner start a thread over in the "Tube Audio" subforum here at AK (see link below). The tube experts will gladly walk you through suggestions on what & what not to do seeing as those units look pristine.

https://www.audiokarma.org/forums/index.php?forums/tube-audio.14/

The amp looks to be a DB130? if so here's some info you might find interesting

https://www.radiomuseum.org/r/bogen_db130db_13.html

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B-302, Not B-305

The standard B-305 configuration is dual woofer, quad tweeter (two tweeters over each woofer), single midrange, in a 16 Ω configuration. I own one of these. I do not believe your speaker is a B-302 in a B-305 cabinet.

This appears to be a standard B-302 configuration, sideways turned with a stand. The exact dimensions could clarify the situation. As I noted, I own a B-305 and because it has two woofers side-by-side with a midrange between is physically large, roughly twice the size of the B-302 or any of the other single-woofer Bozak units. That makes it possible to find another unit.

The B-302 is a three-way system. Judging by the shiny dust caps on the tweeters (the two eyes in front of the woofer) you have the older "X" paper cone tweeters. That dates your unit to being manufactured prior to 1961. The paper-cone drivers are not as good as the aluminum cone variety. Based upon the tweeters I speculate that you also have a paper-cone B-209 midrange. That, too, is inferior to the aluminum cone variety. While the paper-cone midrange is inferior to its aluminum-cone descendents, it is still a nice driver.

So you have a nice mono system.

The Bozak has very specific requirements for an internal lining and curtain. Homebrew bozaks are often missing that. But the older Bozaks used a lining which of Kimsul, basically asphalt impregnated paper used as building insulation. The later units used Tufflex (a re-processed cellulose) and then cotton. So pulling the back will be useful to verify what is inside. You will likely want to upgrade the Kimsul to cotton batting. That is detailed in other threads. My B-305 dates to the Korean War (was purchased by a returning Vet) and has the ancient Kimsul and paper-cone drivers.

Again, I believe you have a B-302 which can be verified by examining the internals and the driver impedance. The B-302 is an 8 Ω system and the drivers will be clearly marked.

Here is some copy-pasta of reading material, slightly edited. Don't worry if you don't immediately grasp all of this. It will eventually all make sense.

Upgrading Crossover Points and Capacitors

The crossover should be upgraded as the capacitors are degraded and may have outright failed. The sound will suffer.

This thread has much information about how Bozaks work:

I suggest you use the Tobin modification as the benefits are undisputed. Stock crossover points are not the best sonic choice because of B-199 cone breakup above 400 Hz. Threads explain why.

Summary of Tobin Modification

The Tobin modification:
(1) Downwards moves the crossover points for the midrange and woofer from 800 Hz to 400 Hz (inductor taps)
(2) Balances the hotter B-200Y tweeter to the other drivers (attenuator resistor)
(3) Removes the attenuator (bypass capacitor) at the upper end of the tweeters to increase SPL as tweeter falls off
(4) Un-reverses the reversed-polarity midrange so the polarity matches the other drivers.​

Analysis of the Tobin Midrange Tap Choice

Reducing inductance does not negatively shift crossover point because of impedance compensation:
Analysis of the Tobin Attenuator

Analysis of the Tobin attenuator including why I suggest removing the attenuator (2) and booster (3) in favor of a straight L-pad across the tweeter (not replacing shunt in Tobin's attenuator):

TL/DR: Tobin's attenuator uses a single resistor using standard values instead of exact values, and consquently alters the nominal impedance.

Flower Pot Midrange Cover

My Explanation
https://www.audiokarma.org/forums/i...mods-on-my-bozaks.732688/page-9#post-10917938

Volume Calculation
https://audiokarma.org/forums/index...-hoopla-a-solution.736070/page-2#post-9966880

Biggle's Implementation With Photos
https://www.audiokarma.org/forums/i...aks-and-tell-me-what-to.771019/#post-10554590

Analysis of Tobin Restoration of Midrange Polarity

Here's one of my explanations of why the polarity reversal (Wood Effect) matters:

My Design for a Super-Tweeter

Once you have the straight Tobin mod working, I suggest upgrading to the B-200Y tweeters. That will greatly improve the high-end response.

Then you might consider moving a super-tweeter as a four-way configuration, retaining the B-200Y, to fix the distortion at the high end of the treble, plus the poor frequency reproduction above roughly 10k Hz, I describe how to perform that here by adding a super-tweeter with a band-pass filter, and adding a band-pass to the tweeter (adds an inductor, no other changes).

My Explanation

Steve Smiley's Build

Discussion About Tweeter Choice (Typanium vs. the Morel)
I think that will get you started.
.
 
Do not turn on the amplifier or tuner until the power supply capacitors have been replaced. Running with failed or failing capacitors can damage or destroy the power transformer and rectifier tube, both of which are expensive to replace. The magic phrase for searching is "recapping". Threads in the tube forum will explain this in gory detail.

Never operate a tube amplifier without a speaker or resistor connected as this will rapidly destroy the output transformer and output stage. Again, other threads will explain why.

Both of these are common mistakes perpetrated by many sellers who write nonsense like, "powered up, no further testing" which simply means a pilot light lit without the fuse blowing.
 
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