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Speakers for 33W DIY amp

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draven66

Member
I ventured out to the local flea market and pawn shops today looking for a 12" speaker for my bogen cha-33 and found some interesting stuff

a pair of Beckman 10" 50W 8ohm speakers. 20$ never heard of these
one Peerless 831727 speaker. 20$ these look too heavy must be for subs
one "Tesla" six inch unknown speaker 5$
and a pair of vintage EV SP8-B speakers for 50$

I'm leaning towards the vintage EV's ! but they are 20W 16oHm each so how will that make out for a bogen with a 33W output? Has anyone used EV's or a pair of 16 oHm impedance speakers for a cab before?? I think teaming up these two 8" speakers would be a little too much resistance or push for my little bogen.
 
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If you want to use both of them, the 16Ω EV's can be wired in parallel for a resistance of 8Ω's. They won't hurt your amp any, and you are just going to have to listen to them to make a final judgement!
 
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The SP-8B are good and good sounding 16 ohm extended range speakers that would work fairly well with your Bogen PA amp. I suspect one would sound a bit better than two in parallel, but either configuration should be fine. Those drivers would be quite happy on an open baffle (or two OBs), and could also benefit from augmentation with a supertweeter (crossed in very high) and/or a subwoofer (judiciously applied).

Is your interest for hi-fi or musical instrument amp use?

In my hardly humble opinion (and FWIW), larger speakers (e.g., unsuffixed EV SP-12) would be a better option (if the option presented itself). 33 watts would let you get away with even fairly insensitive speakers.

PS I wouldn't hesitate to pay $50 US or CDN for a working pair of SP-8B in good condition (FWIW).

EDIT: Good ol' EV doesn't seem to have the EDS (engineering datasheet) online for the SP-8B... but they do have the poop on the SP-8C and the SP-12B and 15B (in case you didn't know). Peruse: http://archives.telex.com/archives/EV/

Here's the EDS for the SP-8C http://archives.telex.com/archives/EV/Speakers/EDS/SP8C, 12C, 15A EDS.pdf
(I am thinking that the 8B has an AlNiCo magnet, and the 8C, ceramic... but I am not certain about that)
 
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ceramic vs alnico

for vintage speakers wouldn't the ceramics be ideal? whats the overall difference in tone and low freq? This will definetly be for guitar since my Bogen cha-33 is a dual channel mono amp and it does have a phono jack that i could play with to get stereo output but I'll save that for a later project since that might mess around with the bias for my guitar sound. So I guess a 33W amp shouldn't have any trouble with them in parallel at 8Ω 40W ..
this amp runs pretty darn hot on the rec and power tubes so I'm hoping that recapping and a little maintenance will fix that. I don't feel like blowing the 12AX7 or 12AT7's that came with it so I'll go easy on the volume and bass levels.

I'll rush out and grab those speakers as soon as it stops raining!
 
That Bogen amplifier is a mono amp and not stereo. Dual channel in your case just means two inputs like a microphone and AUX. It does not mean two speaker, sound seperation. In order to be stereo, it would need a total of two output transformers, and seperate left & right ampifier capabilities, also known as dual mono - one mono amplifier for the left speaker & one mono amplifier for the right speaker.

Power tubes always run hot, its normal. Redplating is not normal. Also, you cannot blow the 12AX7 tubes by over driving or over volume! You can drive the output transformer into saturation and overdrive the output tubes, but overdrive is what a lot of guitarists are looking for. This is what wears out most output tubes faster in a guitar amplifier rather than a hi-fi audio amplifier.
 
two mono channels

ok so connect them in parallel for 8Ω 40W and the cha-33 should be happy, but you suggest using only one? is it a phase issue? I just thought it would make well as a combo 2x8" setup.

I can see what you are saying because allthough the preamps are seperate channels they get mixed together right. So there's no way of seperating them in the amp / mixer stage without completely rebuilding the amp and ruining its classic setup. I would like to take out those old speaker outputs on the back and replace at least one with an XLR. On the schematic, mic 1 & 2 are seperate before they hit the 6av6 so technically I could put one 12AX7 and one 12AT7 tube to have two different sounds right?
 
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interchangeable

what I meant is the two preamp tube sockets, there's one on mic1 and one on mic2 right. When I received the bogen it had two old 12AT7's in there but I recently picked up two mesa 12AX7 for the extra push on the plate. So I think I can have one 12AT7 on mic1 for a bluesy sound with more headspace (12ax7's break up at about 3 on the volume pot) and one 12ax7 on mic2 for the harder sound.

In this pic you can see the 6av6 all the way to the left, then the two preamp tubes.
Boggy_V_ba.jpg
 
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BTW, thats not mine! mine is still black and has the old battered can caps which I could probably benefit from replacing with some newer Mallorys
 
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