Beginner question: Vintage Zenith 49CZ860/1 12" full-range and amplifiers

windupman · « **on:** 11 Apr 2020, 06:33 pm »

Hi everyone,

I'm a beginner to all things audio and I'm trying to put together a simple open-baffle system. It's mostly a learning experience and I'm doing it with my twelve-year-old daughter.

We put together an open-baffle speaker very similar to what Poultrygeist suggested: it's the Zenith 12" drivers from a 1959 mono console. From what I understand, the drivers are similar to the 49CZ852 with a slightly different housing for the magnet. They sounded lovely in the console, playing the radio through the tube amp. The plan is to run them full range.

We put them together with some alinco Eminence 15" woofers which come from an organ. I believe they are from the early seventies. We're working on figuring out the crossover, but I tested it using one of those pre-wired Dayton crossovers from Parts Express.

I tried to test the whole thing using an older Yamaha home theater amp. It sounded terrible, like the speakers weren't getting all of the signal. I tried the Zeniths alone, which was no better. I tried it with the woofers (no crossover) and it was a similar experience. So then I tried some Jensen horns (I think RP-108) which came from a Magnavox console. They produced only the highest frequencies. Everything sounded tinny and generally lousy.

I'm sure I'm doing something wrong. Is it just amp compatibility? Some kind of setting? I'd be willing to buy an amp so that I can make something that sounds good, but I'm not sure what to do. I was thinking about getting a plate amp for the woofers and possibly buying a low-cost tube amp from an acquaintance who rebuilds them for guitar players here in Austin. I'd rather have some clue as to what I'm doing before spending money, though.

Thanks in advance for any advice!
David

FullRangeMan · « **Reply #1 on:** 11 Apr 2020, 08:29 pm »

If I understand well what do you do, STM it sounded bad because you connect the Zenith with a Eminence 15" woofer in serie or parallel without a xover or without a inductor to cut the freq, so as both VC are whole different occurs a mismatch as expected.

windupman · « **Reply #2 on:** 11 Apr 2020, 11:05 pm »

Thanks FullRangeMan.

I was running the Zenith full-range, just by itself. (I also tried it with a high-pass crossover at 500hz and a low-pass 500hz for the Eminence drivers - just as a test). It sounded awful, even with no other speakers. i tested all the different drivers that way, which makes me think it's something with the amp.

windupman · « **Reply #3 on:** 11 Apr 2020, 11:49 pm »

Does anyone recommend a low-cost amp that I could order to try it again? I'd go to friends' homes, but we're under stay-at-home orders. I'm DIYing virtually everything here to keep myself from going nuts.

windupman · « **Reply #4 on:** 2 May 2020, 08:47 pm »

A quick update: I got a small tube amplifier and hooked up the full-range speakers to it. It sounds much better, except one of the drivers is making a popping sound and breaks into a squealing feedback. Does that sound like a loose wire? I'm not sure if I have a good pair of these 61-year-old drivers. Thanks!

windupman · « **Reply #5 on:** 2 May 2020, 09:02 pm »

Actually, it's the amp. I switched the left and right and now the other driver squeals with feedback. What could that be? bad tube?

windupman · « **Reply #6 on:** 2 May 2020, 09:17 pm »

Ah never mind! It seems like it was a preamp tube not quite connected. It sounds great now! I can't wait to hook up the bass drivers (with plate amps)

FullRangeMan · « **Reply #7 on:** 2 May 2020, 10:10 pm »

Good news, keep us posted.

opnly bafld · « **Reply #8 on:** 2 May 2020, 11:08 pm »

Quote from: windupman on 2 May 2020, 08:47 pm

A quick update: I got a small tube amplifier and hooked up the full-range speakers to it. It sounds much better, except one of the drivers is making a popping sound and breaks into a squealing feedback. Does that sound like a loose wire? I'm not sure if I have a good pair of these 61-year-old drivers. Thanks!

What amp did you get?

Bemopti123 · « **Reply #9 on:** 2 May 2020, 11:32 pm »

We need to photos to make this something more than just.... Photo porn please!

planet10 · « **Reply #10 on:** 2 May 2020, 11:42 pm »

Quote from: windupman on 11 Apr 2020, 06:33 pm

I tried to test the whole thing using an older Yamaha home theater amp. It sounded terrible, like the speakers weren't getting all of the signal. I tried the Zeniths alone, which was no better. I tried it with the woofers (no crossover) and it was a similar experience. So then I tried some Jensen horns (I think RP-108) which came from a Magnavox console. They produced only the highest frequencies. Everything sounded tinny and generally lousy.

I'm sure I'm doing something wrong. Is it just amp compatibility?

David,

The amp that was drivng them in the console likely would have had a high output impedance. If that is so, and they sounded good in the console, then the issu eis likely the Yamahas low output impedance.

A band-aid to sde if a higher output impedance amplifer is the right direction is to use very skinny wire (like the 24g solid strands pulled from in-wall Cat5/6 network cable) or even a seres R on th espeaker wire.

dave

FullRangeMan · « **Reply #11 on:** 3 May 2020, 12:02 am »

The high output impedance amp would be 16 ohms?

planet10 · « **Reply #12 on:** 3 May 2020, 12:34 am »

Nothing to do with that. High output impedance, R_out

Most SE amps, such as SETs, SEPs, Pass ACA.

dave

FullRangeMan · « **Reply #13 on:** 3 May 2020, 01:42 am »

But the OPT dont decrease the output impedane to 8 or 16 ohms?

windupman · « **Reply #14 on:** 3 May 2020, 02:58 am »

I may have uploaded the same file twice. It's hard to tell. The internet is overloaded now, which I get.

The amp is a Mingda Meixing MC-84C with JJ tubes. It sounded lovely for a second there and now it's back to the banshee howl. I wonder if something is blocking one of the tube connections. The preamp tubes seem to be the problem.

I'm going to run the old Eminence woofers with Yung plate amps that have built in crossovers. And I'll probably end up hooking up tweeters with a single capacitor first order for the high end. The Zeniths are running full-range.

planet10 · « **Reply #15 on:** 3 May 2020, 03:00 am »

The 8 & 16Ω matching taps are not the same thing. They refer to the speaker nominal impedance, R_out is the amplifier’s output impedance. Damping factor is (a bastardized) version of 1/R_out.

dave

opnly bafld · « **Reply #16 on:** 3 May 2020, 03:02 am »

Did you get the amp used?
If used, did the previous owner tube roll?
Could be tubes or loose sockets.

windupman · « **Reply #17 on:** 3 May 2020, 03:03 am »

Here's the amp. It's a cute amp, point-to-point wired and with good transformers.

windupman · « **Reply #18 on:** 3 May 2020, 03:06 am »

Sorry - yes, I got the amp used. And the owner is extremely responsive, even messaging me now. It has to be something with one of the tube connections because when I switch the tubes it's still a problem on the same channel.

Thanks everyone for your help!

windupman · « **Reply #19 on:** 3 May 2020, 03:07 am »

Speaker impedance is nominally 8 ohm. These are ancient speakers, tho