Author Topic: Help: Glass for Zenith Y96X or Z96X tuner/preamp  (Read 733 times)

SeniorSteve

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Re: Help: Glass for Zenith Y96X or Z96X tuner/preamp
« Reply #15 on: January 07, 2020, 08:05:19 PM »
Lots of questions!  Yes, mine is a MM2670 model and it has the 12 inch woofers.  I replaced them with ones from MCM that had butyl surrounds on them and I think they were under $20.00 each.  I also sealed both sides on the speakers as this cabinet structure easily let me accomplish that.  It was originally open baffle.

Yes that selenium rectifier is still in there (I should replace it, I know).  That is the rectifier for the B+ for the tube front end, around 250 volts. 

You mention germanium transistors, and while the ones I had were working fine, I did replace them with PNP silicon transistors and had to replace the bias chain resistors for the change to silicon.  When I purchased the transistors the outputs were something like under $4.00 each, and I also used them for the drivers in front of the driver transformer.  All of the transistors on the amplifier chassis were changed to silicon, and I didn't need to change any resistors for bias because of the circuit design.  I had a couple of resistors in the tuner chassis for bias on the pre-amp transistors that were noisy, but once that was done, I can turn the volume up full on tape/aux and there isn't any hum or hiss at all.

If you look at the tuner panel on mine the indicator lamps for the tone controls are #1847, but I left them in.  I did replace the illumination lamps with LED lamps from Parts Express, I think the cost was 5 lamps for around $5.00.

My EM84 tuning indicator is still quite bright.

Power output I believe is around 20-25 real watts (320 watts peak IHF or some magic super number).  The set doesn't get super loud, but I am very happy with the sound and design.

Steve

Do you have the schematic for your Zenith? 

turbineoil

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Re: Help: Glass for Zenith Y96X or Z96X tuner/preamp
« Reply #16 on: January 07, 2020, 11:38:35 PM »

Do you have the schematic for your Zenith?

Hi SeniorSteve,

I found a Sam's Photofact Set 989 Folder 8 for chassis 6YT24.  Do I need any other documents?

Sounds like your transistor mod will reduce your total cost of ownership in the future if any sand goes kaput. Germanium replacements are quite pricey by comparison.  Were your original germanium transistors hissy or noisy?  I've heard some actually claim that the old germaniums (while less stable than silicon) have a more euphonic sound.  I haven't been able to compare or form an opinion yet...

SeniorSteve

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Re: Help: Glass for Zenith Y96X or Z96X tuner/preamp
« Reply #17 on: January 08, 2020, 09:28:07 AM »
I repaired my console in 2018, but don't remember if the original germanium transistors were noisy.  I just knew that all of the filters were bad and it had an open speaker coupling cap on the left side when I bought it.  The replacement output and driver transistors had a beefier rating on them.  I still have the original transistors as they are quite expensive and if I need them for another project, great.  I have a better component system, but it's downstairs in the basement.  The Zenith might not be quite as good, but my hearing isn't what it used to be and I'm satisfied with the quality.  I'm looking up some of the part numbers that I used to repair the set, and I'll send them to you.  Mostly I used Digi-Key, they are quite fast.  As far as that "tube" sound with the germanium transistors, I doubt if I could tell the difference.

I see you are looking to get one like Chazglenn3's Zenith.  I hope you find one, they are gorgeous.

turbineoil

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Re: Help: Glass for Zenith Y96X or Z96X tuner/preamp
« Reply #18 on: January 08, 2020, 09:24:25 PM »
I Deoxited the controls. Listening on headphones.

Observations

1. Music is equal in both channels, but there is a constant hum in the right channel, independent of volume.  Hum is on all inputs.  I'm guessing the problem may be in the amp.  Power supply issue? Any ideas?
2. There is a low level static in the left channel. It gets louder when volume is turned up.  I tapped on transistors and Q23 seemed to respond (AF amp Zenith part 121-602). I reseated it a few times and it cleared up momentarily and came back.  I'm thinking I should swap positions of Q23 and Q22 and see if the issue changes channel.  Or I'll see if I have some cold spray to see if that temporarily fixes it indicating the transistor is bad.
3. A resistor fell out of either the amp or preamp.  It appears to be a 1.6k value.  Brown, blue red, silver.  It could also be brown gray red silver.  The Sam's Photofact I got from an eBay seller didn't include list of all the transistors and location numbers.  Makes hunting for the location hard.  Any ideas?
4. The highs are not crisp and pronounced. The bass is a little tubby and boomy.  Are these hallmarks of the capacitors needing to be changed out?
5. The volume pot: at lower levels the balance is skewed a bit to the left, but the image centers when the volume is turned up.  Must be an issue as the carbon pot ages.  Is there a modern part that will allow for a replacement of the volume/balance control.  I guess it's just two variable volume pots ganged together.  Could an ALPS solution work?

chazglenn3

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Re: Help: Glass for Zenith Y96X or Z96X tuner/preamp
« Reply #19 on: January 09, 2020, 08:24:01 AM »
I have the schematics for the 6AT24 which is very similar if not the same. Would you like a copy?
Charles
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SeniorSteve

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Re: Help: Glass for Zenith Y96X or Z96X tuner/preamp
« Reply #20 on: January 09, 2020, 09:11:48 AM »
I looked at the amplifier schematic for Charles's 6AT24 and compared it to what I had in my console which had an 8MT25.  There are some differences such as 2 extra transistors in my chassis.  On Charles's amplifier there are some different voltages for the touch panel that was on his B966 console that wouldn't be needed for the mechanical switch type panel.  The basic power supply is very similar and those capacitors are easily replaced.  If you noticed the clamps on the filter capacitors on the picture of my amp, the reason I did this was they fit the spacing of the fiber insulators, and more importantly I didn't have to find the twist lock capacitors or try to restuff them.  If you restuff, you basically have to remove them and I don't have much luck of removing the capacitors without breaking the tabs.  The main criteria is to get the right physical sized capacitors to fit the clamps.  You end up with capacitors that are generally much larger in capacitance and higher voltage.  I'm good with that in a audio power supply.  I'm happy to assist you with ideas on how to locate the issues if I can get a copy of the schematic.  I wasn't sure if you had one yet.  I'll see if I can find one as well.

Steve

SeniorSteve

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Re: Help: Glass for Zenith Y96X or Z96X tuner/preamp
« Reply #21 on: January 09, 2020, 09:33:00 AM »
I forgot to mention that if you do need a Sam's Photofact schematic, don't go to Sam's for it.  Their resolution is horrible, and you can't blow them up at all without the diagram pixellating.  I use Steve Johnson's website for the schematics when available.

Here's his link   https://stevenjohnson.com/manuals/schematics.htm

SeniorSteve

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Re: Help: Glass for Zenith Y96X or Z96X tuner/preamp
« Reply #22 on: January 11, 2020, 03:31:22 PM »
If you are going to replace the lamps with LED ones, Parts Express has some that worked for me.  I used them for the dial illumination, and they are a little brighter than the original lamps.  If the original lamps had a shade on them that fit the bulb, it won't work.  I even used the LED for the phonograph compartment lamp, but could not use one for the power on indicator at the center of the front because of the shade issue.  I did have one replacement lamp that flickered, and it was defective so I tossed it. I just didn't feel it worth the time and trouble to get a replacement.

turbineoil

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Re: Help: Glass for Zenith Y96X or Z96X tuner/preamp
« Reply #23 on: January 12, 2020, 09:48:28 AM »
I looked at the amplifier schematic for Charles's 6AT24 and compared it to what I had in my console which had an 8MT25.  There are some differences such as 2 extra transistors in my chassis.  On Charles's amplifier there are some different voltages for the touch panel that was on his B966 console that wouldn't be needed for the mechanical switch type panel.  The basic power supply is very similar and those capacitors are easily replaced.  If you noticed the clamps on the filter capacitors on the picture of my amp, the reason I did this was they fit the spacing of the fiber insulators, and more importantly I didn't have to find the twist lock capacitors or try to restuff them.  If you restuff, you basically have to remove them and I don't have much luck of removing the capacitors without breaking the tabs.  The main criteria is to get the right physical sized capacitors to fit the clamps.  You end up with capacitors that are generally much larger in capacitance and higher voltage.  I'm good with that in a audio power supply.  I'm happy to assist you with ideas on how to locate the issues if I can get a copy of the schematic.  I wasn't sure if you had one yet.  I'll see if I can find one as well.

Steve

Hi SeniorSteve

How did you remove the fiber insulators? Did you drill out the rivets or use a punch?

SeniorSteve

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Re: Help: Glass for Zenith Y96X or Z96X tuner/preamp
« Reply #24 on: January 12, 2020, 10:19:32 AM »
I drilled out the rivets, I used a battery drill and went slow.  The clamps I suggested will line up with the mounting screw holes. 

I see on your chassis it looks like all three have broken insulators so on the triple section can I would just get individual caps and use terminal strips underneath.

turbineoil

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Re: Help: Glass for Zenith Y96X or Z96X tuner/preamp
« Reply #25 on: January 12, 2020, 12:58:12 PM »
I drilled out the rivets, I used a battery drill and went slow.  The clamps I suggested will line up with the mounting screw holes. 

I see on your chassis it looks like all three have broken insulators so on the triple section can I would just get individual caps and use terminal strips underneath.

Thanks. Anyone tried a Hayseed Hamfest custom can for triple section cans?

chazglenn3

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Re: Help: Glass for Zenith Y96X or Z96X tuner/preamp
« Reply #26 on: January 31, 2020, 11:08:27 AM »
As a follow up on this thread, I was able to make a deal with the OP and sent him my complete spare tuner/pre-amp.
Charles
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