Phonoland

Greeting all,

I am hoping I can get a little advice to correct an unacceptable (muddy) output on my AY160 with a SHFA4 amp.

I purchased this one about 6 months ago with the intention to resell it in partial/working restoration. This is my third jukebox restoration with the previos two being a AMI model A and AMI model F80 (both complete restorations). The Seeburg has been a challenge but it's now up and running well with this one issue.

When I finally got the machine to play a record I was pleased that I had sound output but was very dissapointed with the sound. I was totally unacceptable with a great deal of distortion. After monkeying with the mechanism, tubes, adjustments, etc. I could not improve on the quality at all. So I decided do go the next step(s). Here is what I've done.

- Bought a capacitor kit and replaced all caps
- Replaced 220k resistors on the 7199 tubes on both channels ( a suggestion from another post)
- Inpected needles under high magnification. They look good with a nice "V" profile.
- Added more spring tension to both sides of tone arms. This mad a slight improvement in sound.
- Check contacts on mechanism as suggested in Troubleshooting Guide along with following other suggestions in the guide.
- Removed, swapped, tapped, massaged all tubes as suggested. No Difference.
- Removed 6EU7 tube on AVC stage as suggested to dissable AVC. No difference.
- Made sound tests using a mono record of the Byrds 'Turn, Turn, Turn" and "Mr. Tamborine Man". Along with well played stereo records. No difference in clarity.

So, after all that (and more) the sound has improved noticably. However, it is still muddy with less distortion but the overall sound is still unacceptable to sell the jukebox as restored.

So I need some suggestions as to what route to take next.

- Replace all or specific tubes (I have no way to text existing tubes)?
- Replace cartricge?
- Replace needles?
- Send amp out to professional for testing/repair?
- Any other suggestion?

I wish to keep the cost at a minimum as there is not enough profit left for this machine. I do this as a hobby so I don't expect to make a living at this but don't want to lose money either.

Your help in this matter is greatly appreciated and I look forward to your responses.

Larry

Hi Larry,
Not being able to hear it has us at a dis-advantage, so anything said is just a guess--
All resistors correct ? Speakers set on highest taps ? Correct (100k) volume control pot installed?
If all above is not it--needles are probably the culprit--and they are made of unobtainium today. I have a few sets of OEM Pickerings that I will sell, if you wish to pay an absolutely ridiculous price--contact me off list-- Ron Rich

Hello Larry,
As Ron said many things can cause distortion in an amplifier. Is the distortion coming from both channels? That is important in finding where it is coming from. Did you check all resistors in the amplifier? If the amplifier has been worked on in the past, your recap may have just copied an earlier wiring mistake. Voltage checks at each tube can find many problems but if you have a signal tracer or oscilloscope you can quickly find out which stage of the amplifier is causing the distortion. Trying out a different cartridge, or first a set of needles would be advisable if distortion is coming from both channels.

Ron, that volume pot is 1meg. I got one of those later amps from Tenth ave. in the late 80's and sure enough, someone had put a scavenged 25K in there. The resulting sound is why I got it for $10 w/some tubes.

To the original poster. You will need a schematic for this sort of work. Voltage checks, known good styli and frankly, a bit of reality as to what you are dealing with in these machines is needed.

Some thoughts:

This statement: "Removed 6EU7 tube on AVC stage as suggested to disable AVC. No difference" -Indicates a possible problem with the AGC section. When the 6EU7 is removed the gain should increase markedly, especially on a loud record and there will normally be noticeable distortion as the amp's gain structure requires the attenuation of an active AGC circuit to pull down the gain from the transistor preamp output to the first tube stage.

Staying in this section, play a loud record and measure the voltage across C143 -a 200mfd electrolytic. This is the AGC time constant. If there is little or no voltage it indicate a problem. Normally a loud record will produce a voltage close tot aht of the squelch voltage that appears there when the mech is scanning/changing.

Next is the problem of "faded" diodes. These old selenium diodes weaken so often that that I routinely replaced them with modern, small signal silicon diodes. You use one each for CR102 (total 2 diodes). But on CR103 and 104 three in series are needed for each existing diode (6 total for Cr 103 and another 6 for CR 104). this is because modern silicon diodes have a much lower internal impedance and will attenuate the signal too much.

Finally, the styli. You didn't mention if they were new or not. From your description they might have come with the phono. This was at best a mediocre pickup and one of it's shortcomings was inadequate damping of stylus cantilever "singing" or resonance. If the styli are old it is likely that the rubber damping band across the cantilever has dried out a bit and may have shrunken so that it doesn't really grip the cantilever effectively and damp the stylus chatter. This may also be why increasing the tracking pressure helped to a degree by forcing the stylus into a slightl;y different position and pressing it tighter to the record. NOT a desirable fix.

You can reduce the noticeability of chatter and "spittiness" by wiring the channels in mono at the input, but that will of course kill stereo.

BTW: You didn't mention if you tried different speakers. If you don't have a 70v transformer handy, just connect them to the same terminals as the existing speakers but use lower wattage taps if they are 8 ohm. the internals are 16 ohm.

Rob/NYC

Rob,
You are correct--1 meg (each section) pots are used on the SHFA-4 and 5 (only) amps. My great, but not too long memory, half-failed again-----
One "other clue"--since pulling the AVC tube makes no difference, I am wondering if the MS ("squelch") contacts, are "making" ?
If they are not, it will surely cause sound problems-- Ron Rich

Hello gang,

Thanks so much for the respnses. I will do some more testing and respond tomorrow to your inquiries.

I have included an attachment to this post to see if it's possible to attach a sound file. Do not bother opening it it is only a audio snippet for testing.

If it works, I will record the output of the jukebox for reference.

Thanks again.

Larry

Ok, I only have a minute...

I found out that this board does not allow audio attachments (oh well). So here is a link to an audio sample of my jukebox. I think it's a reasonable recreation of the quality (or lack of) of the machine at the moment. This is the best sound I could manage without trying any of the suggestions mentioned yet. Tomorrow....tomorrow...

Have a listen and I'd love to hear your thoughts. I made it into a .mp3 and it's only 1.26 meg in size.

https://www.dropbox.com/s/9zf76md7n0ouf ... Sample.mp3

Thanks

Larry

Larry,
I can't get it to play--which probably makes no difference, as my ears are no longer any good, and listening to it through my computer's sound system will probably change it anyway--- Ron Rich