Voice of Music model 869 new to me--and I am new to tubes

[Looking4help]

I won a VM model 869 at an estate auction a few years ago for $2. It is in good shape. it came with schematics for its pre-amp (VM#20026) and its amp (#20053), and its original bill of sale ($360.00 on March 17, 1964).

right after I got it, I fixed the record player with a little bit of work and parts from Gary Stork at V-M Audio Enthusiasts.

Now I want to use it more regularly, but sound is only coming out of the right side. I tried trading the speaker wires between A and B, and then sound only came out of the left side, so it looks like I have a problem in the preamp or in the amp, not in the speakers.

Are these things difficult to fix? I do not know where to begin. Is there a procedure to follow, or do I just take it to a shop?

Thanks!

 

[primosounds]

Well the fact that you are asking about how to fix it does not inspire confidence in your experience with tubed equipment. The fact that you paid only a few bucks means you are way ahead of the game and if you are serious about reviving the equipment then getting someone to refurbish it for you will bring your costs to about what one would pay for an unrestored unit. That being said if you want to start to learn how to work on tube stuff then your initial cost makes mucking it up not a big tragedy, after all it is not a McIntosh. So you decided to give it a go! read on.
If the unit doesn't show any signs of stress while it is on like tubes glowing bright orange/red or smoke coming from inside or underneath the chassis or a strong acrid smell of something burning. then try and wiggle the tubes in the offending channel and notice if you get any sound even if it is not the music that is playing. Sometimes the tubes are not making good contact in their sockets and wiggling them will make it work. If that brings it back then you should probably clean and retension the tube sockets. Also you should have all your tubes tested if they have not been. Another problem area is the switch for the tape monitor. Switches go bad especially 60 year old ones. Sometimes only 1 channel will be affected.
I am guessing that your VM unit is a console? It will be hard to test it without removing the amp and preamp. I would work on the amp first since it is the simpler piece. Try and post some pics so we can have an idea of what you are dealing with. Also a schematic is a must have if you plan to work on it. cheers.

 

[larryderouin]

The preamp is on the top of the console, meaning that the Amp is on the bottom, so there should be RCA Cables between the tuner and preamp, and the preamp and the AMP. Make sure these are clean, tight, and in the correct RCA JACK. Wiggle each tube like primo said (a little DeOxit on the pins will help). If the cables have proprietary plugs, pull them and make sure they get a little DeOxit on the pins and plug them back in. DO ONE AT A TIME so you don't get cornfused. It's probably something simple at this stage as you have a left channel.

For everyones edification, the Model year 1964 VOM 869 Console. I definately want one of these!

 

[Sam08861]

The above advice is spot on in my novice experience.

I have a voice of music 915, which is pretty similar. One common area to check is the speaker balance pot, so deox/work that a bit as a very first step to see if that helps. Also, the RCA jacks going from the record player can also work themselves loose. Be sure to unplug before spraying the balance pots, and let dry before plugging back in. You might have to get to the left and right halves from inside the preamp. Also, you should find pasted inside the cabinet after taking the back panel off, the schematic and also the wiring/tube diagram pasted on the floor of the unit. Gary may have these also, if you don't see them.

Also, be sure to unplug before taking the back off, and still be careful, since there are several large filter capacitors that can hold a strong charge that can kill you.

After ruling out the balance pot... To troubleshoot, inside there are RCA cables going from turntable and tuner ( separately) to the preamp (the one with tone controls). Then, There's then RCA cables from the pre amp to the amp. Finally these usually have speaker outs from the amp to the speakers in cable form in plugs that have two pins (one larger than the other to ensure polarity) that can also be swapped.

Make sure these are ale secure first then give it a try. After checking these connections, you can trace to which component the issue is by process of elimination. Put another music source that has rca line level outs to the aux and see if it's still left side only. There will be labeled inputs on the preamp. If it acts the same as the record player, then you can rule that out. Be sure to move the selector switch to the appropriate input. You can also try your reel to reel as a source if you have media and that as an option. Btw reel to reel playback on these units is absolutely sublime, but I'm using an external Ampex 1455 while yours has the option in the cabinet. Nice!

Because everything in these units have a left and right you can switch the a/b cables starting at the source, then preamp then amp, then the speakers to see if it switches sides. The same can be done with tubes, as they are almost are all specific to one side or the other.

Btw you may have to wipe the bottom of the unit with a towel as there may be a fine layer of dust. I thought my floor of the unit was MDF but a wipe with a very slightly damp the towel revealed the solid cherry cabinet and the schematics.

If you can post pictures of the inside and the schematics the folks on this board can help you troubleshoot further if the above doesn't help. You can search my posts to see the guts of my unit and my rehab with lots of pictures. Was my first unit I ever worked on before getting a bunch of other stuff. Link...
http://audiokarma.org/forums/index.php?threads/new-guy-just-got-a-voice-of-music-model-915.698210/

As you can read I was a complete dummy and learned a lot along the way and am now an incomplete dummy.

Best of luck and I'm sure the good folks on this board can help you sort this out.

 

[Looking4help]

The above advice is spot on in my novice experience.

I have a voice of music 915, which is pretty similar. One common area to check is the speaker balance pot, so deox/work that a bit as a very first step to see if that helps. Also, the RCA jacks going from the record player can also work themselves loose. Be sure to unplug before spraying the balance pots, and let dry before plugging back in. You might have to get to the left and right halves from inside the preamp. Also, you should find pasted inside the cabinet after taking the back panel off, the schematic and also the wiring/tube diagram pasted on the floor of the unit. Gary may have these also, if you don't see them.

Also, be sure to unplug before taking the back off, and still be careful, since there are several large filter capacitors that can hold a strong charge that can kill you.

After ruling out the balance pot... To troubleshoot, inside there are RCA cables going from turntable and tuner ( separately) to the preamp (the one with tone controls). Then, There's then RCA cables from the pre amp to the amp. Finally these usually have speaker outs from the amp to the speakers in cable form in plugs that have two pins (one larger than the other to ensure polarity) that can also be swapped.

Make sure these are ale secure first then give it a try. After checking these connections, you can trace to which component the issue is by process of elimination. Put another music source that has rca line level outs to the aux and see if it's still left side only. There will be labeled inputs on the preamp. If it acts the same as the record player, then you can rule that out. Be sure to move the selector switch to the appropriate input. You can also try your reel to reel as a source if you have media and that as an option. Btw reel to reel playback on these units is absolutely sublime, but I'm using an external Ampex 1455 while yours has the option in the cabinet. Nice!

Because everything in these units have a left and right you can switch the a/b cables starting at the source, then preamp then amp, then the speakers to see if it switches sides. The same can be done with tubes, as they are almost are all specific to one side or the other.

Btw you may have to wipe the bottom of the unit with a towel as there may be a fine layer of dust. I thought my floor of the unit was MDF but a wipe with a very slightly damp the towel revealed the solid cherry cabinet and the schematics.

If you can post pictures of the inside and the schematics the folks on this board can help you troubleshoot further if the above doesn't help. You can search my posts to see the guts of my unit and my rehab with lots of pictures. Was my first unit I ever worked on before getting a bunch of other stuff. Link...
http://audiokarma.org/forums/index.php?threads/new-guy-just-got-a-voice-of-music-model-915.698210/

As you can read I was a complete dummy and learned a lot along the way and am now an incomplete dummy.

Best of luck and I'm sure the good folks on this board can help you sort this out.

Thanks for your replies!

Being able to follow a thread with a complete restoration on it is a real gift.

Mine looks a good deal cleaner than yours was, but my amp is mounted on the side of the cabinet, so it collects less dust.

I am especially grateful for the picture of the underside of the amp.

I do not have the tape deck. That must have been an option that the original purchaser did not want.

We already had the back off. We pulled the radio out to get to the pre-amp.

We had already found that sound came out only from one side, whether we ran the radio, the record player, or the auxiliary. So that seems to point to the pre-amp or the amp.

I wiggled the tubes on the amplifier. I removed the RCA patch cords between the pre-amp and the amp, and replaced them with a new RCA patch cable. We turned on the record player, but sound came out only from the left side.

I at the pre-amp, I switched the left and right wires to the amp and we put the record player back on. Now we get sound only from the right side. That seems like good news. The Amp works, but the pre-amp is sending a signal on only one side.

I tried turning the balance back and forth. The side that worked got quieter or louder, but the dead side stayed dead.

Could you name some likely starting points to check in the pre-amp? Thanks!

 

[Looking4help]

The strategy of trading things between left and right to isolate the problem worked.

I pulled the tubes from the pre-amp and traded their places. That shifted the music from right to left. Then I pulled them and traded them back, and that shifted the music from left to right. So it looks like I have one bad tube.

Not bad for a 53 year old hifi!

Thanks again!

 

[Omegaman]

I have the exact same VoM console

http://audiokarma.org/forums/index....del-869-console-with-tape-deck-option.728754/

It could be something simple

Your best bet is to find a qualified technician

But if you remove the pre-amp and amp and clean and De-Oxit things you might find the problem and fix it

 

[danrclem]

I'll have to say that you definitely got your $2.00 worth. Switch one tube at a time from each side and you should be able to find the bad one.

 

[Looking4help]

It looks like my problem is one of the two 12AX7 tubes in the pre-amp. I ordered a new one.

On my pre-amp, both of the 12AX7 tubes have metal shields around them. Why do they have those?

Thanks!

 

[larryderouin]

RF shielding. Any RF gets shunted to the chassis ground and kept away from the tubes that could amplify it.

 

[Sam08861]

Glad you found the issue so quickly. If it's not to late to change your order, and you ordered a new tube, you might consider changing the order to 2 tubes so that they are matched, if that's an option.

Not sure if it makes a difference, but then your old one would could be a spare to keep you going in case one of the new ones goes bad in the future.

Sam

 

[Looking4help]

The tube arrived today. My son and I pulled the radio out again, pulled one of the tubes from the pre-amp and installed the new, Russian made 12AX7 in its place and replaced the shield around the tube. Man from La Mancha on the turntable, only one side made sound. Pulled the other tube and put back the one we had pulled from the other side. "To Dream the Impossible Dream" came up in stereo. We put the radio back in and fired it up, and it worked too.

After looking at Omegaman's thread on his VM869, and Sam 08861's thread on his VM915, I can see that I am not done yet. I can tell by hearing it too, there is something not quite right yet.

Thanks again for documenting your work so well. Those threads will be very valuable going forward!

I will have to take some pictures that I can post, too.

Have a good day,
Chris

 

[Sam08861]

Hi Chris,

Have you checked out the voltages per the schematic yet?

Typically on units these old, the capacitors can dry up and not be effective in doing what they're supposed to. Some folks replace them as a matter of course (others like to double check before changing). The voltages should measured close to the schematic markings at the various points. Anything that's off usually indicates something off with the preceding components. While I'm a relative newbie, I'm willing to bet that replacing the electrolytics and double checking all the tubes are in good condition will get you very very close to sorted. Re-read the cautions given to me in my thread, get yourself a properly insulated voltmeter/probes and 'grabbers' and be extra careful and ensure, plenty of time, a good comfortable, quiet and well lit working space with NO distractions when working with such high voltage. A bit daunting at first, but that's a good thing to keep you safe and learn.

If you can detail the symptoms of what's not right and post the results of the voltage checks, as specifically as you can, the good folks here will continue to help you troubleshoot as well.

 

[Looking4help]

Hi Chris,

Have you checked out the voltages per the schematic yet?

Typically on units these old, the capacitors can dry up and not be effective in doing what they're supposed to. Some folks replace them as a matter of course (others like to double check before changing). The voltages should measured close to the schematic markings at the various points. Anything that's off usually indicates something off with the preceding components. While I'm a relative newbie, I'm willing to bet that replacing the electrolytics and double checking all the tubes are in good condition will get you very very close to sorted. Re-read the cautions given to me in my thread, get yourself a properly insulated voltmeter/probes and 'grabbers' and be extra careful and ensure, plenty of time, a good comfortable, quiet and well lit working space with NO distractions when working with such high voltage. A bit daunting at first, but that's a good thing to keep you safe and learn.

If you can detail the symptoms of what's not right and post the results of the voltage checks, as specifically as you can, the good folks here will continue to help you troubleshoot as well.

Thanks, Sam08861.

Yes, I read the cautions on your project thread. As at owwm.org, experienced people are very generous with their time when dangers unforeseen to newbies come into question. That is a nice thing. There is no substitute for an experienced friend when it comes to hidden dangers.

My cousin talked me into changing the tweeter crossover caps. That got me started. My son and I finished that task the other day. Both were rated at 2 uF, but one measured 3 and the other measured 3.8 on the capacitance meter I got last week. I replaced them with Solen polypropylene caps.

Looking at your thread and Omegaman's thread, I see that there are quite a few more capacitors that will need replacement.

On the big multi-part electrolytic caps, I want to find out what is the best way to replace them. For the big 60/40/20/20 cap in the middle of the amp, you constructed a replacement from collection of smaller caps. Omegaman installed a 40/40/20/20 on top and added a 20 underneath to match the original value. I want to get a clear strategy on the best way to deal with that before I mess with it. I also want to learn more about working on "the high voltage side" before I touch anything underneath the amp.

I am not in any hurry on this, but it will be nice to make additional improvements to the old thing as I go along.

My more pressing stereo project at the moment is to recap my Infinity Quantum 3s. Recapping the tweeters and fixing the tube on the VM served as a low stakes warmup for the Infinity project.

Thanks again and have a good day,
Chris

 

[Sam08861]

Sounds like you're on your way.

One option I didn't know about for the can caps was a website called hayseed hamfest that can make up a custom can for you pretty reasonably. If I had to do it over again, I would use them for the sake of convenience and fit. Omegamans strategy would also be a great timesaver, getting a can from antique electronics supply or other place and augmenting underneath.

Btw those Infinitys look to be pretty cool speakers.